Physiological and Molecular Characterization of Crop Tolerance to Abiotic Stresses

The high phosphorus (P) acquisition ability of crops can reduce their dependence on artificial inorganic phosphate (Pi) supplementation under Pi-limited conditions. Melon (Cucumis melo L.) is vulnerable to Pi deficiency. This study was carried out to explore the morphological and physiological responses of melon to low-Pi stress under a hydroponic system. The results show that low-Pi stress significantly disturbed nutrient homeostasis, reduced P content, and resulted in iron accumulation in melon seedlings and brown iron plaque formation on the root surface. A nutrient pool of P and Fe formed on the roots to forage for more Pi under low-Pi conditions. Severe long-term low-Pi stress promoted primary root elongation and inhibited lateral root growth, which increased the longitudinal absorption zone of the roots. The decrease in P content of the roots upregulated the expression of the acid phosphatase (APase) gene and increased APase activity. The high-affinity phosphate transporter (Pht1) genes were also upregulated significantly. These morphological and physiological responses significantly increased Pi uptake rate and P utilization efficiency at the melon seedling stage. These findings will be useful for screening low-Pi-tolerant varieties and sustaining melon production in P-limited environments. Full article

Mungbean is susceptible to waterlogging stress; therefore, breeding tolerant varieties would provide Australian growers with management options for wet summer season planting. Selection for waterlogging tolerance could be improved using vegetative indices that correlate to yield. Five mungbean genotypes were exposed to waterlogging stress at the pod-filling stage and characterised for various morphological and physiological traits governing seed yield. Waterlogging during pod filling decreased stomatal conductance (g_s) and photosynthetic rate (A_sat) to ~27% and 25% compared to control, respectively, resulting in a decline in effective quantum yield of PSII (ФPSII) and maximum efficiency of PSII of dark-adapted leaves (Fv/Fm) and leaf chlorophyll while increasing excitation pressure (1-qP) significantly. Waterlogging at pod filling reduced leaf count (19%), plant height (23%), leaf dry weight (38%), stem dry weight (33%), pod dry weight (36%), above-ground biomass (34%), root biomass (26%), and 100-seed weight (4%). Seed yield was highly positively correlated with A_sat (0.86), g_s (0.69), chlorophyll content (0.63), and ФPSII (0.59), with a highly negative correlation with 1-qP (−0.87) at 30 days of treatment imposition. A yield penalty of 32% was recorded under waterlogging stress compared to control plants, while the performance of all genotypes was found to be similar in terms of seed yield. Interestingly, genotype AVTMB#3 produced significantly larger seeds under waterlogging stress relative to other genotypes, including the leading Australian mungbean variety, Jade-AU. Based on a robust and significantly strong correlation with seed yield under waterlogging stress, 1-qP and photosynthetic rates (A_sat) are recommended as potential indicators for the screening of mungbean genotypes. Thus, the current study presents a framework for screening waterlogging tolerance, which can provide a reasonable basis for the selection of various genotypes in future mungbean breeding programs. Full article

The effects of short-term 48 h long NaCl-stress and spermidine level modification on polyamines level and antioxidant status in cucumber (Cucumis sativus cv. Dar) leaves were investigated. Seedlings kept in nutrient solutions treated with 50 mM NaCl for 48 h exhibited reduced relative water content and accumulation of free polyamines, especially spermidine. Salinity stress caused an increase in superoxide radicals and hydrogen peroxide generation during the salinity-induced increase in antioxidant enzyme activities. Spermidine application before stress resulted in a marked increase in spermidine and spermine contents in the leaves of salt-stressed cucumber seedlings. Additionally, increased spermidine/spermine level mobilised the antioxidant enzyme’s activity and limited reactive oxygen species content. Polyamine synthesis inhibitor (MGBG) slightly decreased spermidine and spermine levels during salinity and reversed the antioxidant activity mobilisation. These results showed that Spd modifications significantly improved PAs, enhancing salinity stress tolerance by detoxifying ROS. Our findings determined the implication of PAs for improving the salinity tolerance of important vegetable species. Full article

Rice (Oryza sativa L.) is one of the main food crops for human survival, and its yield is often restricted by abiotic stresses. Drought and soil salinity are among the most damaging abiotic stresses affecting today’s agriculture. Given the importance of abscisic acid (ABA) in plant growth and abiotic stress responses, it is very important to identify new genes involved in ABA signal transduction. We screened a drought-inducing gene containing about 158 amino acid residues from the transcriptome library of rice exposed to drought treatment, and we found ABA-related cis-acting elements and multiple drought-stress-related cis-acting elements in its promoter sequence. The results of real-time PCR showed that OsMLP423 was strongly induced by drought and salt stresses. The physiological and biochemical phenotype analysis of transgenic plants confirmed that overexpression of OsMLP423 enhanced the tolerance to drought and salt stresses in rice. The expression of OsMLP423-GFP fusion protein indicated that OsMLP423 was located in both the cell membrane system and nucleus. Compared with the wild type, the overexpressed OsMLP423 showed enhanced sensitivity to ABA. Physiological analyses showed that the overexpression of OsMLP423 may regulate the water loss efficiency and ABA-responsive gene expression of rice plants under drought and salt stresses, and it reduces membrane damage and the accumulation of reactive oxygen species. These results indicate that OsMLP423 is a positive regulator of drought and salinity tolerance in rice, governing the tolerance of rice to abiotic stresses through an ABA-dependent pathway. Therefore, this study provides a new insight into the physiological and molecular mechanisms of OsMLP423-mediated ABA signal transduction participating in drought and salt stresses. Full article

Weather factors and drought could impact the yield of foxtail millet, and varieties with traits that could alleviate the negative effects of deteriorating weather factors in the future should be developed. A total of 25 foxtail millet varieties were evaluated in experiments from 2016 to 2020 under well-watered (WW) and water-stressed (WS) treatments. Future climate change might favor an increased temperature that impedes grain yield, so varieties with characters that are less sensitive to temperature change are preferred. Varieties with a high panicle dry-weight per plant, thousand grain weight, leaf area and water productivity in deep soil layer usually gave better grain production under both water treatments. Under the WW treatment, low grain abortion rate, optimal chlorophyll and canopy temperature and more roots in the upper soil layer could favor a high yield and drought resistance. Under the WS treatment, varieties with a high harvest index, low rate of water loss and more roots in the upper soil layer usually produced a high yield. Full article

Physiological responses of different interspecific Pyrus hybrids and an open pollinated Pyrus communis ‘Williams’ (Pcw) grown under in vitro culture conditions simulating lime induced chlorosis were studied. The hybrids were derived from crosses between the ‘Pyriam’ pear rootstock and four Pyrus species of the Mediterranean region, namely P. amygdaliformis Vill. (Pa), P. amygdaliformis persica Bornme. (Pap), P. communis cordata (Desv.) Hook. (Pcc), and P. elaeagrifolia Pall (Pe), all known for their higher field tolerance to iron-chlorosis than P. communis. Twenty hybrids and one open pollinated Pcw were micropropagated, and plantlets were in vitro characterized for their physiological responses to iron-deficiency conditions. Rooted plantlets were transferred to a culture medium with 2 µM Fe³⁺ DTPA and 10 or 20 mM NaHCO₃. These physiological responses were scored at 1, 3, 7, and 28 days from the start of the in vitro assay. Leaf total chlorophyll content, the capacity of roots to acidify the medium, reduced iron, and exudates of phenolic acids and organic acids were analyzed in each media and time sample. Leaf chlorophyll levels for the clones derived from Pcc were the highest, especially under the highest bicarbonate concentration, followed by those derived from Pap and Pa. The higher chlorophyll content of Pcc clones were related with their higher capacity to acidify the media but not with their iron reduction capacity at the root level. On the other hand, hybrid clones derived from Pe showed a higher Fe³⁺ reduction ability than clones from all the other species during the whole assay but only when the bicarbonate concentration was lower. The exudation of phenolic acids by the roots was higher in Pcw than in the other species, and this response might explain why the total chlorophyll levels in Pcw clones are similar to those of Pe and Pa ones. These results with Pyrus spp. bring more evidence in support of the idea that iron reduction capacity at the root level is not directly related with a higher tolerance to iron deficiency caused by the high pH of calcareous soils. Instead, the ability to acidify the rhizosphere is the trait of choice for the selection of the pear hybrid clones better adapted to lime induced chlorosis. In addition, the in vitro assay to select the Pyrus clones for tolerance to iron chlorosis could be shortened to one week of culture in 10 mM NaHCO₃, measuring the leaf chlorophyll level, acidification of the culture medium, and exudation of phenolic acids as the physiological responses to predict tolerance to lime-induced chlorosis. Full article

Regulated deficit irrigation (RDI) strategies may greatly contribute to save irrigation water, especially in low water availability conditions. The effects of RDI on the growth process, photosynthesis, fruit yield, and some quality traits were assessed for two years on three plum (Prunus salicina Lindl.) cultivars (‘Black Diamond’, ‘Black Gold’ and ‘Black Star’) grown in Midwest Tunisia. The experiment was conducted during two successive seasons (2011–2012). Two water regimes were applied per cultivar during the phase of fruit growth until fruit ripening. Stressed trees receive 50% of the amount of irrigation compared to controls (CI). Several eco-physiological parameters and some pomological criteria were measured, based on the climatic condition (ETo, ETc, and VDP). Results showed that the three cultivars had an aptitude for tolerance for moderate stress with varying degrees of response time to drought stress. Globally, a slight decrease in the gas exchange rate (AN and gs) and the water status (RWC, Ψmin, and Ψos) was registered. Tree yields, size and weight show a slight decrease under water stress. Nevertheless, there was an improvement in the total soluble solid content (SSC) and firmness in same cultivars. Our results proved that the Black Star cultivar was the most tolerant to deficit irrigation, in reason that it maintains a good water status and a high photosynthetic activity. Full article

Chromium toxicity is considered within the most severe and dangerous nutritional disorders, and it can often be observed in crops grown in industrial areas. The present study aims to determine the effects of Cr(VI) toxicity on the growth, nutrition, and physiological performance of grapevines. In a pot hydroponic experiment, own-rooted Merlot and Cabernet Franc grapevine cultivars or cultivars grafted onto 1103P and 101-14 Mgt rootstocks were exposed to 120 μM Cr(VI). Leaf interveinal chlorosis appeared after forty-five days of treatment. Overall leaf chlorosis and brown root coloration after sixty days was reported. A significant effect on the majority of the measured parameters due to the Cr(VI) treatment was observed. Chromium stress increased the total Cr concentrations in all parts of the vines, i.e., leaves, shoots, roots, and trunks. When comparing between the studied plant sections, the roots presented the highest Cr concentrations, ranging from 396 to 868 mg kg⁻¹ d. w., and then, in descending order, the Cr concentrations ranged from 41 to 102 mg kg⁻¹ d. w. in the trunks, from 2.0 to 3.3 mg kg⁻¹ d. w. in the leaves, and from 1.9 to 3.0 mg kg⁻¹ d. w. in the shoots. Between the assessed rootstocks, 1103P was identified to be a better excluder of Cr concentration in the roots and other aerial parts of the vines. Additionally, chromium toxicity negatively affected the concentrations and compartmentalization of the most important nutrients. Leaf chlorophyll (Chl) concentration decreased down to approximately 53% after sixty days of Cr stress. Chromium toxicity significantly reduced the stem water potential (SWP), net CO₂ assimilation rate (A), stomatal conductance (gs), and PSII maximum quantum yield in all the cases of grafted or own-rooted vines. At this stage, chromium stress increased the leaf total phenolic content from 46.14% in Merlot vines to 75.91% in Cabernet Franc vines. Full article

Heat stress (HS) has been considered as a severe threat to crop yields in recent years. Sucrose, as a major product of photosynthesis, plays an important role in plant growth and stress response. Sucrose phosphate synthase (SPS) is a key rate-limiting enzyme in the sucrose synthesis pathway in plants. However, its molecular mechanism and signaling pathway remain unclear. In this study, we identified a novel SPS gene (SlSPS) in tomato and generated over-expression and knock-out of SlSPS gene transgenic tomato plants to investigate its biological functions related to the growth and thermotolerance of tomato. Over-expression of SlSPS gene increased the growth and biomass of transgenic tomato plants, such as fresh weight, dry weight, plant height, fruit weight and root length. In contrast, knock-out of SlSPS gene decreased the growth and biomass of transgenic tomato plants. Under heat stress, the survival rates were positively correlated with the expression level of SlSPS gene in different tomato varieties. Furthermore, SlSPS-overexpressing tomato plants showed higher SPS activity and sucrose content and heat stress resistant phenotypes. By comparison, knock-out tomato plants showed lower SPS activity and sucrose content and susceptible to heat stress. The determination of several reference values of oxidative stress parameters were also consistent with their heat resistance of these transgenic plants. In summary, SlSPS gene could positively mediate the growth and thermotolerance in tomato plants. Full article

The aim of the study was to investigate the morphological, physiological, and biochemical parameters of leaves to evaluate the yield of Solanum tuberosum L. We conducted 3-year experiments with 24 varieties of potatoes, differing in ripeness groups (early ripening, mid-early ripening and mid ripening). Plant height, linear dimensions, number of stomata per unit leaf area as well as content of pigments, proline, membrane lipids and proteins, and the level of lipid per oxidation in the leaves of each variety were investigated. A 3D modeling method showed the yield of early varieties negatively correlated with an increase in temperatures (R = –0.97). The soil moisture content positively correlated with the yield of medium-early varieties (R = 0.97). The soil moisture content and the tuber numbers in mid-season varieties had a negative correlation (R = –0.96). The regulation mechanisms of processes in cells depend on the ripening time of a variety. In order to increase productivity and to improve the potato quality, it is necessary to take into account the peculiarities of the regional climatic conditions and use the varieties of a certain ripening group. Our data refine the understanding of the relationship between the potato above-ground mass and the yield of tubers. Full article

Increasing extreme drought events due to climate change may cause severe damage to blueberry industries, including decreased fruit yield and quality. Previous studies on drought tolerance of blueberries focus mainly on functional changes of leaves, while hydraulic properties of blueberry stems related to drought resistance are poorly reported. Here, both xylem anatomical and functional traits of stems of two southern highbush (SHB) and three rabbiteye blueberry (REB) cultivars were investigated. Compared with REB, SHB showed lower sapwood hydraulic conductivity (K_S) and P₅₀ (xylem water potential with 50% embolism in xylem), suggesting that SHB has less conductive but safer xylem than REB. The hydraulic functional differences between two blueberry xylems were highly related to their significant differences in vessel anatomy. Small vessel diameter and total inner pit aperture area per vessel area (A_PA) limited the hydraulic conductivity of SHB xylem, but high conduit wall reinforcement, wood density, and vessel-grouping index in SHB xylem showed strong mechanical support and safe water transport. Besides, pseudo-tori pit membranes were found in all five cultivars, while the similar thickness of homogenous pit membrane in two blueberry species was not linked to other functional traits, which may be due to its limited measurements. These results reveal a trade-off between the water transport efficiency and safety in the blueberry xylem and clarify the variance of stem drought resistance in different cultivars from a hydraulic perspective. Further studies with such a perspective on other organs of blueberries are required to understand the drought tolerance of a whole plant, which builds a solid foundation for the introduction, cultivation, and management of blueberry industries. Full article

Drought stress severely affects plant growth and development, causing significant yield loss in rice. This study demonstrates the relevance of water use efficiency with deeper rooting along with other root traits and gas exchange parameters. Forty-nine rice genotypes were evaluated in the basket method to examine leaf-level water use efficiency (WUEi) variation and its relation to root traits. Significant variation in WUEi was observed (from 2.29 to 7.39 µmol CO₂ mmol⁻¹ H₂O) under drought stress. Regression analysis revealed that high WUEi was associated with higher biomass accumulation, low transpiration rate, and deep rooting ratio. The ratio of deep rooting was also associated with low internal CO₂ concentration. The association of deep rooting with lower root number and root dry weight suggests that an ideal drought-tolerant genotype with higher water use efficiency should have deeper rooting (>30% RDR) with moderate root number and root dry weight to be sustained under drought for a longer period. The study also revealed that, under drought stress conditions, landraces are more water-use efficient with superior root traits than improved genotypes. Full article

Exposure to ultraviolet-B (UV-B) radiation can lead to oxidative damage in plants, increasing reactive oxygen species (ROS) production. To overcome ROS burst, plants have antioxidant mechanisms related to ROS scavenging which can be improved by elicitation with biological agents or derived molecules (elicitors), as they can trigger a physiological alert state called “priming”. This work describes the effects of lipo-chitooligosaccharides (LCOs) treatment applied to tomato plants under UV-B stress. The LCOs used in the study are produced by three species of the genus Ensifer (formerly Sinorhizobium) (SinCEU-1, SinCEU-2, and SinCEU-3) were assayed on tomato plants under UV-B stress. LCOs were able to significantly increase most of the enzymatic activities related to ROS scavenging while non-enzymatic antioxidants were not modified. This response was associated with a lower oxidative stress, according to malondialdehyde (MDA) levels and the higher antioxidant capacity of the plants. Furthermore, the photosynthetic efficiency of LCOs-treated plants indicated a better physiological state than the control plants. Therefore, although more studies and deepening of certain aspects are necessary, LCOs have shown great potential to protect plants from high UV-B radiation conditions. Full article

Chilling stress is one of the major abiotic stresses which hinder seedling emergence and growth. Herein, we investigated the effects of chilling/low temperature stress on the morphological, physiological, and biochemical attributes of two silage corn genotypes during the seedling establishment phase. The experiment was conducted in a growth chamber, and silage corn seedlings of Yukon-R and A4177G-RIB were grown at optimum temperature up to V3 stage and then subjected to five temperature regimes (25 °C as control, 20 °C, 15 °C, 10 °C, and 5 °C) for 5 days. After the temperature treatment, the morphological, physiological, and biochemical parameters were recorded. Results indicated that temperatures of 15 °C and lower significantly affected seedling growth, photosynthesis system, reactive oxygen species (ROS) accumulation, and antioxidant enzyme activities. Changes in seedlings’ growth parameters were in the order of 25 °C > 20 °C > 15 °C > 10 °C > 5 °C, irrespective of genotypes. The chlorophyll content, photosynthetic rate, and maximal photochemical efficiency of PS-II (F_v/F_m) were drastically decreased under chilling conditions. Moreover, chilling stress induced accumulation of hydrogen peroxide (H₂O₂)and malonaldehyde (MDA) contents. Increased proline content and enzymatic antioxidants, including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxide (APX), were found to alleviate oxidative damage under chilling stress. However, the genotype of Yukon-R exhibited better adaption to chilling stress than A4177G3-RIB. Yukon-R showed significantly higher proline content and enzymatic antioxidant activities than A4177G3-RIB under severe chilling conditions (temperature ≤ 10 °C). Similarly, Yukon-R expressed low temperature-induced ROS accumulation. Furthermore, the interaction effects were found between temperature treatment and genotype on the ROS accumulation, proline content and antioxidant enzyme activities. In summary, the present study indicated that Yukon-R has shown better adaptation and resilience against chilling temperature stress, and therefore could be considered a potential candidate genotype to be grown in the boreal climate. Full article

Heat stress is one of the major abiotic factors that limit the growth, development, and productivity of plants. Both glycine betaine (GB) and β-aminobutyric acid (BABA) have received considerable attention due to their roles in stimulating tolerance to diverse abiotic stresses. In order to understand how GB and BABA biostimulants alleviate heat stress in a cool-weather Chinese cabbage (Brassica rapa L. ssp. pekinensis) plant, we investigated the GB- and BABA-primed heat-stressed plants in terms of their morpho-physiological and biochemical traits. Priming with GB (15 mM) and BABA (0.2 mM) was conducted at the third leaf stage by applying foliar sprays daily for 5 days before 5 days of heat stress (45 °C in 16 h light/35 °C in 8 h dark) on Chinese cabbage seedlings. The results indicate that GB and BABA significantly increased chlorophyll content, and the parameters of both gas exchange and chlorophyll fluorescence, of Chinese cabbage under heat stress. Compared with the unprimed heat-stressed control, the dry weights of GB- and BABA-primed plants were significantly increased by 36.36% and 45.45%, respectively. GB and BABA priming also greatly mitigated membrane damage, as indicated by the reduction in malondialdehyde (MDA) and electrolyte leakage through the elevation of proline content, and increased activity levels of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). Taken together, GB and BABA have great potential to enhance the thermotolerance of Chinese cabbage through higher photosynthesis performance, osmoprotection, and antioxidant enzyme activity. Full article

Grapes are subject to a wide range of climatic conditions during their life cycle, but the use of rootstocks can effectively ameliorate the effects of abiotic stress. However, the tolerance mechanism of different grape rootstock varieties varies under various stresses, and systematic research on this aspect is limited. On the basis of previous research, transcriptome sequencing was performed on three tolerant grape rootstock varieties (3309C, 520A, 1103P) and three intolerant grape rootstock varieties (5BB, 101–14, Beta). In total, 56,478,468 clean reads were obtained. One hundred and ten genes only existed in all combinations during P1 with a downregulated trend, and 178 genes existed only in P1 of tolerant grape rootstock varieties. Salt treatment firstly affected the photosynthesis of leaves, and tolerant varieties weakened or even eliminated this effect through their own mechanisms in the later stage. Tolerant varieties mobilized a large number of MFs during the P2 stage, such as hydrolase activity, carboxypeptidase activity, and dioxygenase activity. Carbon metabolism was significantly enriched in P1, while circadian rhythm and flavonoid biosynthesis were only enriched in tolerant varieties. In the intolerant varieties, photosynthesis-related pathways were always the most significantly enriched. There were large differences in the gene expression of the main signal pathways related to salt stress in different varieties. Salt stress affected the expression of genes related to plant abiotic stress, biotic stress, transcription factors, hormones, and secondary metabolism. Tolerant varieties mobilized more bHLH, WRKY, and MYB transcription factors to respond to salt stress than intolerant varieties. In the tolerant rootstocks, SOS was co-expressed. Among these, SOS1 and SOS2 were upregulated, and the SOS3 and SOS5 components were downregulated. The genes of heat shock proteins and the phenylalanine pathway were upregulated in the tolerant varieties. These findings outline a tolerance mechanism model for rootstocks for coping with osmotic stress, providing important information for improving the resistance of grapes under global climate change. Full article

Plant stress-associated proteins (SAPs) contain A20/AN1 zinc finger domains and are involved in plant response to abiotic stresses. In this study, we aimed to explore the biological function of tea plant CsSAPs. A total of 14 CsSAP genes were identified in the tea plant genome using a reference genome database (Camellia sinensis var. sinensis). The CsSAPs were divided into the following two groups: Group I, containing one AN1 domain and/or one A20 domain; and Group II, containing two AN1 domains and/or two C2H2 domains. The sequence alignments and conserved domains analysis indicated that the CsSAPs were highly structurally conserved in terms of amino acid sequence and protein structure. The CsSAPs showed different transcript levels in spatio-temporal expression and in response to cold and drought stress in tea plants. Furthermore, the expression of CsSAP12 was considerably upregulated under drought stress. The overexpression of CsSAP12 in transgenic tomatoes showed increased tolerance to drought stress compared with the wild type. Altogether, the results showed that CsSAP12 might be involved in drought stress. Thus, CsSAP12 might be a target gene in genetic engineering to improve drought tolerance in tea plants. Full article

Exogenous brassinolide (BR) application is a feasible measure to alleviate abiotic stresses on crop productivity. The effects of BR application at the silking-stage on the accumulation, translocation, and remobilization of dry matter (DM) and nutrients (nitrogen, phosphorus, and potassium) of waxy maize exposed to post-silking high temperature (HT) were studied using Jingkenuo2000 (JKN2000, heat-tolerant) and Yunuo7 (YN7, heat-sensitive) as materials. BR application mitigated the penalty of HT on grain yield. HT reduced the post-silking accumulation and increased the translocation of pre-silking DM and nutrients in YN7. In JKN2000, accumulation and remobilization of DM were unaffected by HT. The contribution rate of DM and nutrients translocation to grain yield were unaffected by HT in JKN2000 and increased in YN7. Under HT, the accumulation, translocation, and remobilization of DM were unaffected by BR application, whereas the nitrogen, phosphorus, and potassium response were dependent on hybrids. The harvest index of DM and nutrients in response to HT and BR were different between the two hybrids. In conclusion, BR application relieved the negative effects of HT mainly caused by the increased post-silking accumulation and remobilization of DM and nitrogen, and the alleviation was more obvious in the heat-tolerant hybrid. Full article

The size and the weight of wheat grains vary across the length of each spike (Triticum aestivum L.). High temperature and water scarcity often reduce the single grain weight, and this reduction also varies across the spike length. Plants tend to cope with high temperature and drought stress through inherent mechanisms such ascanopy cooling through transpiration, which can contribute to yield stability. The effect of canopy cooling on the average grain weight at different positions in spike is still unknown. In this study, we planned to assess the role of canopy temperature, yield-related traits, and spike shape in final grain weight. For two years (2017–2018 and 2018–2019), fifteen diverse genotypes released for cultivation in different environmental conditions were grown in the field. They were examined for canopy temperature, spikelets spike⁻¹, grain number spike⁻¹, grain yield spike⁻¹, and grain weight of the spike’s basal, median, and distal regions. The Pearson correlation coefficient (r) was obtained for all pair-wise combinations of traits under different treatments and spike shapes. The results indicated that cooler canopy is correlated to grain weight in normal spike shape at all three positions within the spike irrespective of stress. The advantage of the cooler canopy in improving grain-filling at basal, median, and distal regions was more conspicuous in the high temperature stress conditions compared to non-stressed and drought conditions. Full article

The sweet-basil (Ocimum basilicum L.) fruit/pericarp produces mucilage that engulfs the fruit and seed within minutes of hydration. Seed mucilage is produced by plant species that have adapted to arid, sandy soils. This study was conducted to determine how basil-seed mucilage improves ecological fitness. A second objective was to find ways to remove mucilage, which may interfere with commercial planting. Basil fruit/seeds were examined using light and environmental scanning electron microscopy. Columnar structures of basil mucilage rapidly unfolded from the pericarp upon initial hydration. Dilute hydrochloric acid removed the mucilage, which decreased the water content four-fold but did not inhibit seed germination in a laboratory test. Nondestructive Fourier-transform mid-infrared (FTIR) spectroscopy confirmed that the mucilage was primarily composed of hemicellulose that anchored the basil seed to resist movement. The fully hydrated seeds approached zero water potential, so the mucilage did not interfere with hydration. The seeds that were planted in growing media with mucilage had from 12 to 28% higher seedling emergence and survival percentages after 10 days than seeds without mucilage. Basil-fruit/seed mucilage provides a reservoir of loosely bound water at high water potential for seed germination and early seedling development, thus improving survivability under low moisture. Full article

Crops around the world are facing a diversity of environmental problems, of which high temperatures are proving to be the most serious threat to crops. Polyamine putrescine (Put) acts as a master growth regulator that contributes to optimal plant growth and development and increased stress tolerance. Here, the current study aimed to elucidate how Put functions in regulating chlorophyll (Chl) metabolism, oxidative stress, and antioxidant defense, as well as to characterize the expression of genes related to heat stress in tomato seedlings under such stress. The results revealed that Put treatment significantly attenuates heat-induced damage by promoting biomass production, increasing photosynthetic efficiency, and inhibiting excessive production of oxidative stress markers. Heat stress markedly decreased the Chl content in the tomato leaf and accelerated the leaf yellowing process. However, Put-treated tomato seedlings showed a higher Chl content, which could be associated with the functions of Put in elevating PBGD activity (Chl biosynthesis enzyme) and suppressing the activity of the Chl catabolic enzyme (Chlase and MDCase). Under high-temperature stress, the expression levels of the gene encoding factors involved in Chl biosynthesis and Chl catabolism were significantly down- and upregulated, respectively, and this trend was reversed in Put-treated heat-stressed seedlings. In addition, exogenous application of Put boosted the activity of antioxidant enzymes, along with the levels of expression of their encoding genes, only in plants that were heat stressed. Furthermore, the expression levels of heat-shock-related genes (HSP90, HSP70, and HsfA1) were elevated in Put-treated, high-temperature-stressed tomato seedlings. Taken together, our results indicate that Put treatment significantly increases the heat tolerance of tomato seedlings, by elevating Chl concentrations and suppressing Chl catabolic enzyme activity, modulating endogenous free PA content, increasing antioxidant defense efficiency, and upregulating the expression of heat-shock-related genes. Full article

Salt stress is a worldwide environmental signal, reducing the growth and yield of crops. To improve crop tolerance to salt, several beneficial microbes are utilized. Here, nitrogen-fixing bacterium Azorhizobium caulinodans and root endophytic fungus Piriformospora indica were used to inoculate tomato (Solanum lycopersicum) under salt stress, and the effects of the co-inoculation were investigated. Results showed that A. caulinodans colonized in the intercellular space in stems and roots of tomato plants, while P. indica colonized in the root cortex. Two weeks following salt treatment, co-inoculated tomato plants grew substantially taller and had larger stem base diameters. Activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and reduced and oxidized ascorbate and glutathione (i.e., AsA, DHA, GSH, and GSSG, respectively) concentrations along with the ratios of AsA/(AsA + DHA) and GSH/(GSH + GSSG) increased in the leaves of co-inoculated plants under salt stress. The co-inoculation significantly increased soluble proteins and AsA in fruits; however, concentrations of soluble sugars and proanthocyanins did not show significant changes, compared with NaCl only treatment. Data suggest that A. caulinodans and P. indica co-inoculation boosted tomato growth and improved the quality of tomato fruits under salt stress. O-inoculation of A. caulinodans and P. indica might be employed to enhance tomato plant salt tolerance. Full article

Winter hardiness is influenced by many environmental factors, and freezing tolerance is among the main ones, rendering the phenotypic selection of winter wheat (Triticum aestivum L.) under field conditions a difficult task due to the irregular occurrence or absence of winter damage in field trials. Plant growth in response to low temperatures during the acclimation period might be used as an indirect approach to assess freezing tolerance. Thirteen winter wheat cultivars were investigated for autumn and spring growth and winter hardiness under field conditions for two growing seasons. Additionally, a precise and non-destructive technique was applied to study leaf growth at a high temporal resolution accompanied by a freezing tolerance test under laboratory and semi-field conditions. The results of the study revealed variations in thermal growth patterns among the 13 winter wheat cultivars. The cultivars with the lower base temperature (T_b) values, in particular ‘Lakaja DS’ and ‘Sedula DS’, grew slower and, thus, had a lower response to temperature increases (Slp_LER-T) than the fast-growing cultivars, such as ‘Simano” and ‘KWS Ferrum’, whose Slp_LER-T values were stronger and whose T_b values were higher. A correlation analysis of the investigated traits showed a clear association between leaf growth parameters and freezing tolerance, indicating a certain level of genetic adaptation to growth cessation under low temperatures, and which confirmed that these are important factors for explaining the freezing tolerance of different cultivars. The evaluated freezing tolerance (LT₃₀) showed a strong negative correlation (r = −0.82 ÷ −0.89, p = 0.01) to winter hardiness scores from the field experiment, supporting the essential contribution of growth rate patterns to winter hardiness. The findings provide novel information for the development of winter-hardy wheat cultivars that are adapted to the future environments. Full article

Metal tolerance proteins (MTP) as divalent cation transporters are essential for plant metal tolerance and homeostasis. However, the characterization and the definitive phylogeny of the MTP gene family in Fagopyrum tartaricum, and their roles in response to metal stress are still unknown. In the present study, MTP genes in Fagopyrum tartaricum were identified, and their phylogenetic relationships, structural characteristics, physicochemical parameters, as well as expression profiles under five metal stresses including Fe, Mn, Cu, Zn, and Cd were also investigated. Phylogenetic relationship analysis showed that 12 Fagopyrum tartaricum MTP genes were classified into three major clusters and seven groups. All FtMTPs had typical structural features of the MTP gene family and were predicted to be located in the cell vacuole. The upstream region of FtMTPs contained abundant cis-acting elements, implying their functions in development progress and stress response. Tissue-specific expression analysis results indicated the regulation of FtMTPs in the growth and development of Fagopyrum tataricum. Besides, the expression of most FtMTP genes could be induced by multiple metals and showed different expression patterns under at least two metal stresses. These findings provide useful information for the research of the metal tolerance mechanism and genetic improvement of Fagopyrum tataricum. Full article

Salt stress is considered as one of the most common abiotic stresses reducing the productivity and fruit quality of crop plants. The present study was carried out to assess the salt tolerance among 15 local squash (Cucurbita maxima Duchesne) landraces. Different salt (NaCl) concentrations of 0, 100, 200 and 300 mM were selected in order to evaluate the response of the study germplasm to salt stress based on 12 agronomic parameters and 3 biochemical traits, proline, malondialdehyde (MDA) and chlorophylls. A varied effect of the salt stress level was observed among the studied landraces based on germination potential, as well as on growth and biochemical parameters at seedling stage. Results showed that all landraces were drastically affected at high stress level with a significant variation in their stress response, indicating the existence of considerable genetic variability. Landraces “746” and “747” were the best performing cultivars across stress levels, whereas “1007”, “1008” and “1009” were the most negatively affected. Based on the tested landrace performance, four landraceswere selected and further evaluated at biochemical level, focusing on the determination of compounds that play a key role in the ability to withstand salt stress. The mean MDA content across landraces was generally increased in stressed plants, as compared to the control treatment; the increase was attributed to a peak in MDA content at specific stress levels. In particular, “746” and “1007” showed the maximum content at 100 mM NaCl, while in landrace “751”, MDA content reached its peak at 300 mM NaCl. In addition, the response of most landraces to salt stress involved an increase in free proline content, with the exception of “746”, with the maximum content being observed either at 200 mM (“748” and “751” landraces) or at 300 mM NaCl, where only “747” expressed the highest content. These findings can be extrapolated into efforts to develop more salt-tolerant squash landraces and exhaust the possibilities of using saline water or soils under changing climate conditions. Full article

Accumulated evidence has revealed the mitigation effects of exogenous melatonin on cold stress in plants. In this study, to investigate the defensive roles of exogenous melatonin in banana under cold stress, we researched the influences of exogenous melatonin on the chlorophyll fluorescence parameters, antioxidant defense indexes and expression levels of cold-responsive genes in cold-stressed ‘Brazil’ banana seedlings. Results showed that 100 μM of exogenous melatonin achieved the best cold-resistance-promoting effect in banana. Exogenous melatonin treatment significantly increased the electron transfer rate, light harvesting efficiency, total antioxidant capacity, catalase and superoxidase activities and proline and soluble sugar contents and significantly reduced the accumulations of malondialdehyde, superoxide anion and hydrogen peroxide in the leaves of cold-stressed banana. In addition, under cold stress, melatonin significantly induced the expression of low-temperature-responsive genes, such as MaChiI1, MaCSD1C, MaWhy1, MaKIN10, MaADA1 and MaHOS1. It was concluded that the application of exogenous melatonin enhanced antioxidant defense and induced the expression of cold-responsive genes, thereby improving the cold resistance of banana. Our study will provide a basis for the application of exogenous melatonin in improving plant cold resistance. Full article

Dehydration-responsive element-binding protein 1 (DREB1)/C-repeat binding factor (CBF) family plays a key role in plant tolerance against different abiotic stresses. In this study, an orthologous gene of the DWARF AND DELAYED FLOWERING (DDF) members in Arabidopsis, SlDDF2, was identified in tomato plants. The SlDDF2 gene expression was analyzed, and a clear induction in response to ABA treatment, cold, salinity, and drought stresses was observed. Furthermore, two transgenic lines (SlDDF2-IOE#6 and SlDDF2-IOE#9) with stress-inducible overexpression of SlDDF2 under Rd29a promoter were generated. Under stress conditions, the gene expression of SlDDF2 was significantly higher in both transgenic lines. The growth performance, as well as physiological parameters, were evaluated in wild-type and transgenic plants. The transgenic lines showed growth retardation phenotypes and had higher chlorophyll content under stress conditions in plants. However, the relative decrease in growth performance (plant height, leaf number, and leaf area) in stressed transgenic lines was lower than that in stressed wild-type plants, compared with nonstressed conditions. The reduction in the relative water content and water loss rate was also lower in the transgenic lines. Compared with wild-type plants, transgenic lines showed enhanced tolerance to different abiotic stresses including water deficit, salinity, and cold. In conclusion, stress-inducible expression of SlDDF2 can be a useful tool to improve tolerance against multiple abiotic stresses in tomato plants. Full article

Salicylic acid (SA) has been shown to ameliorate drought stress. However, physiological and biochemical mechanisms involved in drought stress tolerance induced by SA in plants have not been well understood. Thus, this study aimed to study the role of SA application on enzymatic and non-enzymatic antioxidants, photosynthetic performance, and plant growth in A. chilensis plants subjected to moderate drought stress. One-year-old A. chilensis plants were subjected to 100% and 60% of field capacity. When plants reached moderate drought stress (average of stem water potential of −1.0 MPa, considered as moderate drought stress), a single SA application was performed on plants. Then, physiological and biochemical features were determined at different times during 14 days. Our study showed that SA application increased 13.5% plant growth and recovered 41.9% A_N and 40.7% g_s in drought-stressed plants on day 3 compared to drought-stressed plants without SA application. Interestingly, SOD and APX activities were increased 85% and 60%, respectively, in drought-stressed SA-treated plants on day 3. Likewise, SA improved 30% total phenolic content and 60% antioxidant capacity in drought-stressed A. chilensis plants. Our study provides insight into the SA mechanism to tolerate moderate drought stress in A. chilensis plants. Full article

5-Aminolevulinic acid (ALA) is the precursor of tetrapyrrole synthesis, and hydrogen sulfide (H₂S) is a gas signal molecule. Studies have shown that exogenous ALA and H₂S can alleviate abiotic stress. This study evaluated the roles of ALA and H₂S and their interactions in regulating antioxidant activity in pepper seedlings under chilling stress. Chilling stress significantly inhibited the growth of pepper seedlings and increased the amounts of hydrogen peroxide (H₂O₂), superoxide anion (O₂^•−), and malondialdehyde (MDA). ALA and/or H₂S increased the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Moreover, ALA and/or H₂S enhanced the ascorbate (AsA)-glutathione (GSH) cycle by increasing the contents of AsA and GSH, the ratio of AsA to dehydroascorbic acid and GSH to glutathione disulfide increased, and the activities of ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) also increased. At the transcriptional level, ALA and/or H₂S upregulated the expressions of CaSOD, CaPOD, CaCAT, CaAPX, CaGR, CaDHAR, and CaMDHAR in seedlings under chilling stress. ALA and/or H₂S also reduced the contents of H₂O₂, O₂^•− and MDA, eventually mitigating the inhibitory effects of chilling stress on pepper seedling growth. The combination of ALA and H₂S had a better effect than ALA or H₂S alone. Moreover, ALA and H₂S interact to regulate the oxidative stress response of pepper seedlings under chilling stress. Full article

A pot experiment was conducted to assess the effect of drought stress on growth and secondary compound accumulation of Ocimum species, in a semi-controlled greenhouse during the year 2020. The experiment was performed as a factorial that was based on a randomized complete design with three species of basil namely O. basilicum ‘Genovese’, O. x africanum, and O. americanum, and three levels of water supply (70, 50, and 30% soil water capacity-SWC) that were replicated twice. The results revealed that severe drought conditions (30% SWC) significantly lowered the relative water content and, as a consequence, plants were shorter, narrower in the canopy, and produced smaller leaves which, in turn, resulted in a 50% fresh and dry herb yield loss. Furthermore, severe drought stress negatively affected the essential oil content (except O. x africanum where no change was seen), essential oil yield, and the antioxidant capacity. However, slight enhancements of glandular hair density were observed in the drought treatment than in the control. Regardless of the soil water capacity variation, the major compound of the essential oil and total polyphenol content remained unchanged. Besides drought, morphological and chemical variations were also detected among the Ocimum species. Sweet basil cultivar Genovese produced the maximum biomass (344.7 g/plant) whereas O. x africanum accumulated higher essential oil (2.79%). The major compounds that were identified were linalool in O. basilicum; 1, 8-cineole, and camphor in O. x africanum; and O. americanum had more neral and geranial. In conclusion, a higher water supply is recommended for higher biomass and essential oil yield production in the tested basil species. Full article

Drought is considered as one of the major limiting factors to plant growth and productivity. Drought stress reduces stomatal conductance, affecting water relations and decreasing CO₂ assimilation rate and photosynthesis. Several strategies have been developed to alleviate the negative effects of drought in the agricultural industry. One of these strategies is the use of the mulching technology, which retains water in the soil surface. Knowing that hormones play a key role in plant growth and drought stress responses, we hypothesized that the use of a new ecological mulching technology called hydromulching would improve growth over bare soil under drought stress through changes in the hormonal balance. To test this hypothesis, escarole plants (Cichorium endivia L.) were grown in pots filled with coco fiber, non-covered (bare soil) or covered with polyethylene film (PE) and three types of hydromulches made up with recycled additives: wheat straw (WS), rice hulls (RH), and substrate used for mushroom cultivation (MS). Half of the plants were subjected to drought by reducing the volume of irrigation water to 70% of crop evapotranspiration. Despite drought stress impaired escarole growth-related parameters in all treatments, plants mulched with MS maintained significantly superior growth, due to improved plant water relations and photosynthetic function. This can be explained by an efficient interaction hydromulch/soil/plant in regulating the hormonal balance under water depletion. Indeed, the concentrations of the active cytokinins (CKs), trans-zeatin and isopentenyladenine, were higher in plants grown with MS treatment, associated with shoot growth-enhancing and photosynthetic rate maintenance under stress conditions. The concentrations of the stress-related hormone, abscisic acid (ABA), varied antagonistically to those of the active CKs. In this regard, ABA increased with drought but to a lower extent in MS plants thus regulating stomata opening, which, in crosstalk with the ethylene precursor 1-aminocyclopropane-1-carboxylic acid and salicylic acid, improved plant water relations. The results obtained demonstrate that hydromulching is an efficient and sustainable management strategy to ameliorate the drought effects on escarole plants through fine regulation of the CKs/ABA balance, which will be of utmost interest and applicability in the actual climate change scenario. Full article

In this paper, an auxin-responsive transcription factor, CpARF7, was isolated from the roots of Chinese cherry (Cerasus pseudocerasus Lindl. Cv. “Manao Hong”). CpARF7 is highly homologous to AtARF7 or AtARF19 in Arabidopsis, and PavARF1 or PavARF14 in sweet cherry. However, in the phenotype of transgenic tomatoes, the root morphology changed, the main root elongated, and the lateral root increased. Both drought treatment and low-phosphorus conditions can elongate the roots of transgenic tomatoes. In addition, the drought resistance and low-phosphorus tolerance of the transgenic lines are improved, and the POD, SOD, and CAT activities under drought and low-phosphorus environments are increased. There is an effect on the tomato somatotropin suppressor gene, SlIAAs, in which SlIAA1/14/19/29 are up-regulated and SlIAA2/11/12/16 are down-regulated. These results indicate that CpARF7 plays an essential regulatory role in root formation and abiotic stress response, and deepens the understanding of auxin-responsive genes in root growth and abiotic stress. Full article

Zoysia japonica is a warm-season turfgrass that is extensively used in landscaping, sports fields, and golf courses worldwide. Uncovering the low-temperature response mechanism of Z. japonica can help to accelerate the development of new cold-tolerant cultivars, which could be used to prolong the ornamental and usage duration of turf. A novel Z. japonica biotype, YueNong-9 (YN-9), was collected from northeastern China for this study. Phenotypic measurements, cold-tolerance investigation, and whole-transcriptome surveys were performed on YN-9 and LanYin-3 (LY-3), the most popular Z. japonica cultivar in Southern China. The results indicated the following: YN-9 has longer second and third leaves than LY-3; when exposed to the natural low temperature during winter in Guangzhou, YN-9 accumulated 4.74 times more anthocyanin than LY-3; after cold acclimation and freezing treatment, 83.25 ± 9.55% of YN-9 survived while all LY-3 leaves died, and the dark green color index (DGCI) value of YN-9 was 1.78 times that of LY-3; in YN-9, there was a unique up-regulation of Phenylalanine ammonia-lyase (PAL), Homeobox-leucine Zipper IV (HD-ZIP), and ATP-Binding Cassette transporter B8 (ABCB8) expressions, as well as a unique down-regulation of zinc-regulated transporters and iron-regulated transporter-like proteins (ZIPs) expression, which may promote anthocyanin biosynthesis, transport, and accumulation. In conclusion, YN-9 exhibited enhanced cold tolerance and is thus an excellent candidate for breeding cold-tolerant Z. japonica variety, and its unique low-temperature-induced anthocyanin accumulation and gene responses provide ideas and candidate genes for the study of low-temperature tolerance mechanisms and genetic engineering breeding. Full article

Sweet osmanthus (Osmanthus fragrans) is an evergreen woody plant that emits a floral aroma and is widely used in the landscape and fragrance industries. However, its application and cultivation regions are limited by cold stress. Heat-shock transcription factor (HSF) family members are widely present in plants and participate in, and regulate, the defense processes of plants under various abiotic stress conditions, but now, the role of this family in the responses of O. fragrans to cold stress is still not clear. Here, 46 OfHSF members were identified in the O. fragrans genome and divided into three subfamilies on the basis of a phylogenetic analysis. The promoter regions of most OfHSFs contained many cis-acting elements involved in multiple hormonal and abiotic stresses. RNA-seq data revealed that most of OfHSF genes were differentially expressed in various tissues, and some OfHSF members were induced by cold stress. The qRT-PCR analysis identified four OfHSFs that were induced by both cold and heat stresses, in which OfHSF11 and OfHSF43 had contrary expression trends under cold stress conditions and their expression patterns both showed recovery tendencies after the cold stress. OfHSF11 and OfHSF43 localized to the nuclei and their expression patterns were also induced under multiple abiotic stresses and hormonal treatments, indicating that they play critical roles in responses to multiple stresses. Furthermore, after a cold treatment, transient expression revealed that the malondialdehyde (MDA) content of OfHSF11-transformed tobacco significantly increased, and the expression levels of cold-response regulatory gene NbDREB3, cold response gene NbLEA5 and ROS detoxification gene NbCAT were significantly inhibited, implying that OfHSF11 is a negative regulator of cold responses in O. fragrans. Our study contributes to the further functional characterization of OfHSFs and will be useful in developing improved cold-tolerant cultivars of O. fragrans. Full article

Aspartate is the most critical amino acid in the aspartate metabolic pathway, which is associated with multiple metabolic pathways, such as protein synthesis, nucleotide metabolism, TCA cycle, glycolysis, and hormone biosynthesis. Aspartate also plays an important role in plant resistance to abiotic stress, such as cold stress, drought stress, salt stress or heavy metal stress. This study found that the chlorophyll content and antioxidant active enzyme content (SOD, CAT, POD and APX) of perennial ryegrass treated with 2 mM aspartate were significantly higher than those treated with water under heat stress. The electrolyte leakage rate, MDA content and peroxide levels (O²⁻ and H₂O₂) of perennial ryegrass treated with aspartate were significantly lower than those of perennial ryegrass treated with water, indicating that exogenous aspartate increases the content of chlorophyll, maintain the integrity of cell membrane system, and enhances SOD-CAT antioxidant pathway to eliminate the oxidative damage caused by ROS in perennial ryegrass under heat stress. Furthermore, exogenous aspartate could enhance the TCA cycle, the metabolism of the amino acids related to the TCA cycle, and pyrimidine metabolism to enhance the heat tolerance of perennial ryegrass. Full article

Fluctuating light (FL) is a typical natural light stress that can cause photodamage to photosystem I (PSI). However, the effect of growth light on FL-induced PSI photoinhibition remains controversial. Plants grown under high light enhance photorespiration to sustain photosynthesis, but the contribution of photorespiration to PSI photoprotection under FL is largely unknown. In this study, we examined the photosynthetic performance under FL in tomato (Lycopersicon esculentum) plants grown under high light (HL-plants) and moderate light (ML-plants). After an abrupt increase in illumination, the over-reduction of PSI was lowered in HL-plants, resulting in a lower FL-induced PSI photoinhibition. HL-plants displayed higher capacities for CO₂ fixation and photorespiration than ML-plants. Within the first 60 s after transition from low to high light, PSII electron transport was much higher in HL-plants, but the gross CO₂ assimilation rate showed no significant difference between them. Therefore, upon a sudden increase in illumination, the difference in PSII electron transport between HL- and ML-plants was not attributed to the Calvin–Benson cycle but was caused by the change in photorespiration. These results indicated that the higher photorespiration in HL-plants enhanced the PSI electron sink downstream under FL, which mitigated the over-reduction of PSI and thus alleviated PSI photoinhibition under FL. Taking together, we here for the first time propose that photorespiration acts as a safety valve for PSI photoprotection under FL. Full article

Drought has been recognized as a potential challenge to maize production around the world, particularly in arid and semi-arid regions. The primary focus of the present study was to investigate the metabolic and physiological adjustment mechanisms as well as drought-responsive gene expression patterns in five maize (Zea mays L.) genotypes (G314, G2, G10, G123, and G326) with varying drought-tolerance capacities at the vegetative stage. Twenty-one days-old maize plants from five maize genotypes were submitted to a well-watered (10 days) watering interval as a control, mild water stress (15 day interval), and severe water stress (20 day interval) treatments in a field experiment for two successive seasons (2019 and 2020). For all maize genotypes, the results showed that water stress significantly reduced plant height, leaf area, biomass, and yield characteristics. However, water stress, which was associated with the length of the watering interval, increased the concentrations of glycine betaine, amino acids, proline, phenols, flavonoids, soluble proteins, and soluble sugars, as well as catalase and peroxidase activities. On the transcriptional level, prolonged water stress increased the expression of drought-responsive genes (LOS5, Rad17, NCED1, CAT1, and ZmP5CS1), with G10 and G123 genotypes being the most drought-resistant. Herein, genotypes G10 and G123 were shown in this study to be relatively water stress tolerant due to improved osmoregulatory, antioxidant, and metabolic activities under water stress conditions, as well as the fact that they were endowed with stress-responsive genes. Full article

Exogenous glycine betaine (GB) application has been reported to improve plant tolerance to various abiotic stresses, but its effect on freezing tolerance has not been well studied. We investigated the effect of exogenous GB on freezing tolerance of cabbage (Brassica oleracea L.) leaves. Seedlings fed with 30 mM GB via sub-irrigation showed effectively assimilated GB as evident by higher GB concentration. Exogenous GB did not retard leaf-growth (fresh weight, dry weight, and leaf area) rather slightly promoted it. Temperature controlled freeze-thaw tests proved GB-fed plants were more freeze-tolerant as indicated by lower electrolyte leakage (i.e., indication of less membrane damage) and alleviating oxidative stress (less accumulation of O₂^•− and H₂O₂, as well as of malondialdehyde (MDA)) following a relatively moderate or severe freeze-thaw stress, i.e., −2.5 and −3.5 °C. Improved freezing tolerance induced by exogenous GB application may be associated with accumulation of compatible solute (proline) and antioxidant (glutathione). GB-fed leaves also had higher activity of antioxidant enzymes, catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD). These changes, together, may improve freezing tolerance through membrane protection from freeze-desiccation and alleviation of freeze-induced oxidative stress. Full article

One of the major problems in the fruit production of citrus, including pummelo (Citrus grandis) is controlling flowering induction. Water stress is known to be related to flowering induction via physiological responses related to the flowering gene. However, reports on the mechanisms underlying floral induction by water stress in pummelo are limited. Thus, this study aimed to determine the physiological characteristics and the expression of genes related to flowering induction, CiFT (Citrus Flowering locus T), in pummelo at different levels of water stress. Experiments were conducted under two growing conditions: field and container conditions, each using a 2 × 5 factorial experiment in a randomized complete block. Factor A consisted of two red-flesh pummelo cultivars while factor B consisted of five levels of water stress based on the leaf rolling index. Among the seven characteristics studied, only the data of total nitrogen, CiFT, and flower number were combined for analysis due to their results in a homogeneity test. Although a consistent tendency was not observed for the interaction among environments, genotypes, and water stress levels of all characteristics, ‘KKU-105’ grew more flowers under higher water stress conditions (225 flowers). This result may imply that decreases in total nitrogen (1.48%), stomatal conductance (50.53 m⁻²s⁻¹), chlorophyll fluorescence (0.30 Fv/Fm), and upregulation of CiFT mRNA level (13.95) may induce flowering in the pummelo cultivar ‘KKU-105’. Full article

Plants are frequently exposed to various abiotic stresses, including aluminum, cadmium and salinity stress. Barley (Hordeum vulgare) displays wide genetic diversity in its tolerance to various abiotic stresses. In this study, small RNA and degradome libraries from the roots of a barley cultivar, Golden Promise, treated with aluminum, cadmium and salt or controls were constructed to understand the molecular mechanisms of microRNAs in regulating tolerance to these stresses. A total of 525 microRNAs including 198 known and 327 novel members were identified through high-throughput sequencing. Among these, 31 microRNAs in 17 families were responsive to these stresses, and Gene Ontology (GO) analysis revealed that their targeting genes were mostly highlighted as transcription factors. Furthermore, five (miR166a, miR166a-3p, miR167b-5p, miR172b-3p and miR390), four (MIR159a, miR160a, miR172b-5p and miR393) and three (miR156a, miR156d and miR171a-3p) microRNAs were specifically responsive to aluminum, cadmium and salt stress, respectively. Six miRNAs, i.e., miR156b, miR166a-5p, miR169a, miR171a-5p, miR394 and miR396e, were involved in the responses to the three stresses, with different expression patterns. A model of microRNAs responding to aluminum, cadmium and salt stresses was proposed, which may be helpful in comprehensively understanding the mechanisms of microRNAs in regulating stress tolerance in barley. Full article

Cold stress is a limiting factor to the growth and development of cucumber in the temperate regions; hence, improving the crop’s tolerance to low temperature is highly pertinent. The regulation of low-temperature tolerance with exogenous ABA and CaCl₂ was investigated in the cucumber variety Zhongnong 26. Under low-temperature conditions (day/night 12/12 h at 5 °C), seedlings were sprayed with a single application of ABA, CaCl₂, or a combination of both. Our analysis included a calculated chilling injury index, malondialdehyde (MDA) content, relative electrical conductivity, antioxidant enzyme activities (SOD, CAT, and APX), leaf tissue structure, and expression of cold-related genes by transcriptome sequencing. Compared with the water control treatment, the combined ABA + CaCl₂ treatment significantly improved the superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) of the seedlings by 34.47%, 59.66%, and 118.80%, respectively (p < 0.05), and significantly reduced the chilling injury index, relative electrical conductivity, and MDA content, by 89.47%, 62.17%, and 44.55%, respectively (p < 0.05). Transcriptome analysis showed that compared with the water control treatment, 3442 genes were differentially expressed for the combined treatment, 3921 for the ABA treatment, and 1333 for the CaCl₂ treatment. KEGG enrichment analysis for both the ABA and combined ABA + CaCl₂ treatments (as compared to the water control) showed that it mainly involves genes of the photosynthesis pathway and metabolic pathways. Differentially expressed genes following the CaCl₂ treatment were mainly involved in plant hormone signal transduction, plant–pathogen interaction, MAPK signaling pathway–plant, phenylpropanoid biosynthesis, and circadian rhythm–plant. qRT-PCR analysis and RNA-seq results showed a consistent trend in variation of differential gene expression. Overall, this study demonstrated that although all three treatments provided some protection, the combined treatment of ABA (35 mg/L) with CaCl₂ (500 mg/L) afforded the best results. A combined ABA + CaCl₂ treatment can effectively alleviate cold-stress damage to cucumber seedlings by inducing physiological changes in photosynthesis and metabolism, and provides a theoretical basis and technical support for the application of exogenous ABA and CaCl₂ for low-temperature protection of cucumber seedlings. Full article

Late spring frosts can become one of the limiting factors for the expansion of cultivation area towards a harsher climate for the almond [Prunus amygdalus Batsch syn P. dulcis (Mill.) D.A. Webb] crop as spring frost can damage up to 90% of the harvest. In order to identify key genes favoring cold tolerance in almonds, branches from three late-blooming genotypes: ‘Guara’, ‘Soleta’ and ‘Belona’ were exposed at −4 °C during 24 h in a constant climate chamber. Phenotype analysis showed that ‘Guara’ and ‘Soleta’ had a greater acclimation capacity to cold than ‘Belona’. The qRT-PCR BioMark System technology was used to monitor the relative expression of 30 candidate genes with a potential relation to cold response, which are either involved in the ICE-CBF-COR pathway or the independent CBF pathway, and also genes not yet characterized or with unknown function in almond genome. Differences in the gene expression profiles were found among the three studied genotypes and the three time-points of cold exposure (0, 2 and 24 h). BBX20 and CLO genes behaved as differentiator genes between tolerant and susceptible genotypes in cold stress response in almond pistils. In addition, the differences of expression among the tolerant genotypes suggested the intervention of different mechanisms responding to cold stress in almonds. Full article

The goal of this study was to identify the zoysiagrass rust pathogens and to analyze the differences in rust-resistant and rust-susceptible Zoysia japonica germplasm upon inoculation. Based on the assessment of spore morphology and 18S ribosomal DNA (rDNA) molecular identification, the zoysiagrass rust pathogen was identified as Puccinia zoysiae Diet. The development of mycelium, the rate of spreading, and the timing of spore production were more delayed in the rust-resistant (RR) genotype than the rust-susceptible (RS) genotype. After inoculation, the activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) initially decreased, then increased in both the RR and RS genotypes, but the increased enzyme activities were faster in the RR than in the RS genotype. Rust resistance was positively correlated with antioxidant enzyme activity. The observed changes in CAT, POD and APX activity corresponded to their gene expression levels. The results of this study may be utilized in accurately evaluating the damage of rust disease and rust-resistance in zoysiagrass germplasm aimed at breeding the rust-resistant zoysiagrass varieties and improving disease management of zoysiagrass turf. Full article

Rootstocks from Actinidia valvata are much more tolerant to waterlogging stress than those from Actinidia deliciosa, which are commonly used in kiwifruit production. To date, the tolerance mechanism of A. valvata rootstocks’ adaptation to waterlogging stress has not been well explored. In this study, the responses of KR5 (A. valvata) and ‘Hayward’ (A. deliciosa) to waterlogging stress were compared. Results showed that KR5 plants performed much better than ‘Hayward’ during waterlogging by exhibiting higher net photosynthetic rates in leaves, more rapid formation of adventitious roots at the base of stems, and less severe damage to the main root system. In addition to morphological adaptations, metabolic responses of roots including sufficient sucrose reserves, modulated adjustment of fermentative enzymes, avoidance of excess lactic acid and ethanol accumulation, and promoted accumulation of total amino acids all possibly rendered KR5 plants more tolerant to waterlogging stress compared to ‘Hayward’ plants. Lysine contents of roots under waterlogging stress were increased in ‘Hayward’ and decreased in KR5 compared with their corresponding controls. Overall, our results revealed the morphological and metabolic adaptations of two kiwifruit rootstocks to waterlogging stress, which may be responsible for their genotypic difference in waterlogging tolerance. Full article

The use of anti-hail nets on orchards changes the microclimate underneath the net. This might be of great importance in apple growing regions characterized by high radiation levels and hot and dry climates during the summer season. But, depending on the net colour and on the local climatic conditions, the shade promoted triggers different responses by the trees. Grey and black anti-hail nets were applied in an apple orchard (cv. ‘Golden Delicious’) located in Northeast Portugal. Under the nets a lower concentration of glomalin related-soil proteins was observed, along with an improvement on trees water status, stomatal conductance, net photosynthetic rate, total chlorophylls, N, Mg, Fe and Cu concentrations, as well as an increase in mean fruit weight. The major difference between nets was on the photosynthetic efficiency, being higher on black net in sunny days, while grey net performed better under cloudy conditions. The use of netting systems proved to be effective in improving “Golden Delicious” apple trees performance under a Mediterranean climate, mainly when the radiation reaching the plants surpass the tree saturation point for photosynthesis. Therefore, these findings anticipate solutions for current and forecasted negative effects of climate change. Full article

An efficient regeneration protocol was applied to regenerate shoots on salt stress-tolerant calli lines of aubergine (Solanum melongena). These NaCl-tolerant cell lines were obtained by two different methods. On the one hand, the developed callus tissue was transferred to a medium with a continuous salt content of 40, 80, 120, or 160 mM NaCl. On the other hand, the callus tissue was subjected to a stepwise increasing salinity to 160 mM NaCl every 30 days. With the second method, calli which could be selected were characterized by compact growth, a greenish color, and absence of necrotic zones. When grown on salt-free medium again, NaCl-tolerant calli showed a decline in relative growth rate and water content in comparison to the control line. This was more obvious in the 120 mM NaCl-tolerant callus. Lipid peroxidase activity increased in 40 and 80 mM NaCl-tolerant calli; yet did not increase further in 120 mM-tolerant callus. An increase in ascorbic acid content was observed in 80 and 120 mM NaCl-tolerant calli compared to the 40 mM NaCl-tolerant lines, in which ascorbic acid content was twice that of the control. All NaCl-tolerant lines showed significantly higher superoxide dismutase (SOD) (208–305–370 µmol min⁻¹ mg⁻¹ FW) and catalase (CAT) (136–211–238 µmol min⁻¹ mg⁻¹ FW) activities compared to control plants (231 and 126 µmol min⁻¹ mg⁻¹ FW). Plants were regenerated on the calli lines that could tolerate up to 120 mM NaCl. From the 32 plants tested in vitro, ten plants with a higher number of leaves and root length could be selected for further evaluation in the field. Their high salt tolerance was evident by their more elevated fresh and dry weight, their more increased relative water content, and a higher number and weight of fruits compared to the wild-type parental control. The presented work shows that somaclonal variation can be efficiently used to develop salt-tolerant mutants. Full article

For the dissection and identification of the molecular response mechanisms to salt stress in cannabis, an experiment was conducted surveying the diversity of physiological characteristics. RNA-seq profiling was carried out to identify differential expression genes and pathway which respond to salt stress in different cannabis materials. The result of physiological diversity analyses showed that it is more sensitive to proline contents in K94 than in W20; 6 h was needed to reach the maximum in K94, compared to 12 h in W20. For profiling 0–72 h after treatment, a total of 10,149 differentially expressed genes were identified, and 249 genes exhibited significantly diverse expression levels in K94, which were clustered in plant hormone signal transduction and the MAPK signaling pathway. A total of 371 genes showed significant diversity expression variations in W20, which were clustered in the phenylpropanoid biosynthesis and plant hormone signal transduction pathway. The pathway enrichment by genes which were identified in K94 and W20 showed a similar trend to those clustered in plant hormone signal transduction pathways and MAPK signaling. Otherwise, there were 85 genes which identified overlaps between the two materials, indicating that these may be underlying genes related to salt stress in cannabis. The 86.67% agreement of the RNA-seq and qRT-PCR indicated the accuracy and reliability of the RNA-seq technique. Additionally, the result of physiological diversity was consistent with the predicted RNA-seq-based findings. This research may offer new insights into the molecular networks mediating cannabis to respond to salt stress. Full article

Auxins are plant hormones that affect plant growth, development, and improve a plant’s tolerance to stress. In this study, we found that the application of indole-3-butyric acid (IBA) had diverse effects on the growth of maize (Zea mays L.) roots treated without/with Cd. IBA caused changes in the growth and morphology of the roots under non-stress conditions; hence, we were able to select two concentrations of IBA (10⁻¹¹ M as stimulatory and 10⁻⁷ M as inhibitory). IBA in stimulatory concentration did not affect the concentration of H₂O₂ or the activity of antioxidant enzymes while IBA in inhibitory concentration increased only the concentration of H₂O₂ (40.6%). The application of IBA also affected the concentrations of mineral nutrients. IBA in stimulatory concentration increased the concentration of N, K, Ca, S, and Zn (5.8–14.8%) and in inhibitory concentration decreased concentration of P, K, Ca, S, Fe, Mn, Zn, and Cu (5.5–36.6%). Moreover, IBA in the concentration 10⁻⁹ M had the most positive effects on the plants cultivated with Cd. It decreased the concentration of H₂O₂ (34.3%), the activity of antioxidant enzymes (23.7–36.4%), and increased the concentration of all followed elements, except Mg (5.5–34.1%), when compared to the Cd. Full article

The impacts of low temperature occasionally encountered at higher latitude regions on maize seed germination present significant threats to yield and cultivation. Exploring the association of antioxidant system with low temperature (LT) germination could support the breeding strategies for better responding to LT disturbance. In this study, we have examined the germination rate and growth potential of a set of elite maize inbred accessions under LT and normal temperature (NT) conditions in the field. These accessions were found to have variable germination rate and growth potential when grown at LT, whereas the difference is not significant under NT. Physiological study revealed lower hydrogen peroxide content in LT tolerant accessions when compared with sensitive ones. LT-tolerant and LT-sensitive lines maintained similar content of ascorbate (AsA) and glutathione (GSH), whereas the reduced substrate content of which were significantly higher in LT-tolerant accessions. Consistently, activities of ascorbate peroxidase and dehydroascorbate reductase, the enzyme components that responsible for the AsA-GSH recycling, were much higher in LT-tolerant lines. Transcription profile revealed the increased expression of ZmVTC2 gene in LT-tolerant inbred line, which was rate limited step in AsA biosynthesis. These data indicates that the coordinated improvement of AsA biosynthesis and AsA-GSH recycling increase the pool size of the total antioxidants, which ameliorate LT-induced oxidative stress during maize seed germination. Full article