Tolerance to Drought and Salt Stress in Plants

Mining salt tolerance genes is significant for breeding high-quality salt-tolerant rice varieties in order to improve the utilization of saline–alkaline land. In this study, 173 rice accessions were measured for their germination potential (GP), germination rate (GR), seedling length (SL), root length (RL), germination potential relative to salt damage rate (GPR), germination rate relative to salt damage rate (GRR), seedling length relative to salt damage rate (SLR), relative salt damage rate at the germination stage (RSD) and comprehensive relative salt damage rate in the early seedling stage (CRS) under normal and salt stress conditions. Genome-wide association analysis was performed with 1,322,884 high-quality SNPs obtained by resequencing. Eight quantitative trait loci (QTLs) related to salt tolerance traits at the germination stage were detected in 2020 and 2021. They were related to the GPR (qGPR2) and SLR (qSLR9), which were newly discovered in this study. Three genes were predicted as salt tolerance candidate genes: LOC_Os02g40664, LOC_Os02g40810, and LOC_Os09g28310. At present, marker-assisted selection (MAS) and gene-edited breeding are becoming more widespread. Our discovery of candidate genes provides a reference for research in this field. The elite alleles identified in this study may provide a molecular basis for cultivating salt-tolerant rice varieties. Full article

Polygonum cuspidatum, an important medicinal plant, is rich in resveratrol and polydatin, but it frequently suffers from drought stress in the nursery stage, which inhibits the plant’s growth, active components concentrations, and the price of rhizome in the later stage. The purpose of this study was to analyze how exogenous 100 mM melatonin (MT) (an indole heterocyclic compound) affected biomass production, water potential, gas exchange, antioxidant enzyme activities, active components levels, and resveratrol synthase (RS) gene expression of P. cuspidatum seedlings growing under well-watered and drought stress conditions. The 12-week drought treatment negatively affected the shoot and root biomass, leaf water potential, and leaf gas exchange parameters (photosynthetic rate, stomatal conductance, and transpiration rate), whereas the application of exogenous MT significantly increased these variables of stressed and non-stressed seedlings, accompanied by higher increases in the biomass, photosynthetic rate, and stomatal conductance under drought versus well-watered conditions. Drought treatment raised the activities of superoxide dismutase, peroxidase, and catalase in the leaves, while the MT application increased the activities of the three antioxidant enzymes regardless of soil moistures. Drought treatment reduced root chrysophanol, emodin, physcion, and resveratrol levels, while it dramatically promoted root polydatin levels. At the same time, the application of exogenous MT significantly increased the levels of the five active components, regardless of soil moistures, with the exception of no change in the emodin under well-watered conditions. The MT treatment also up-regulated the relative expression of PcRS under both soil moistures, along with a significantly positive correlation between the relative expression of PcRS and resveratrol levels. In conclusion, exogenous MT can be employed as a biostimulant to enhance plant growth, leaf gas exchange, antioxidant enzyme activities, and active components of P. cuspidatum under drought stress conditions, which provides a reference for drought-resistant cultivation of P. cuspidatum. Full article

Photosynthetic performance and biomass at different growth stages of the salt-sensitive KDML105 rice cultivar, three improved lines (RD73, CSSL8-94, and TSKC1-144), and the salt-tolerant standard genotype (Pokkali) were investigated under non-saline, semi-saline, and the heavy-saline field conditions in the northeast of Thailand. In the non-saline field, net photosynthesis rates (P_n) of all genotypes remained high from the early vegetative stage to the milky stage and then dramatically reduced at maturity. In contrast, in both saline fields, P_n was the highest at the early vegetative stage and continuously declining until maturity. Leaf chlorophyll content remained high from the early vegetative to milky stage then reduced at maturity for all three field conditions. During the reproductive phase, P_n of KDML105 and the improved lines were reduced by 4–17% in the heavy-saline field, while that of Pokkali was increased (11–19% increase over that of the non-saline). Pokkali also showed a prominent increase in water use efficiency (WUE) under salinity. Nevertheless, rice leaves under saline conditions maintained the PSII integrity, as indicated by the pre-dawn values of maximum quantum yield of PSII photochemistry (F_v/F_m) of higher than 0.8. Pokkali under the semi-saline and the heavy-saline conditions exhibited 51% and 27% increases in final biomass, and 64% and 42% increases in filled grain weight plant⁻¹, respectively. In the semi-saline condition, RD73, TSKC1-144, CSSL8-94, and KDML105 showed moderate salt tolerance by displaying 24%, 18.6%, 15%, and 11.3% increases in final biomass, and 24%, 4%, 13%, and 6% increases in filled grain weight plant⁻¹, respectively. In contrast, in the heavy-saline field, final biomass of RD73, KDML105, CSSL8-94, and TSKC1-144 showed 48%, 45%, 38%, and 36% reductions from that in the non-saline field, while the filled grain weight plant⁻¹ were reduced by 45%, 58%, 35%, and 32%, respectively. This indicated that the improved lines carrying drought- and/or salt-tolerance genes achieved an increased salt tolerance level than the parental elite cultivar, KDML105. Full article

The effects of climate change in coastal semi-arid and arid Mediterranean areas are intense. Green roofs planted with native plant species that are able to withstand saline conditions can contribute to supporting climate-change adaptation and species preservation in wetlands, enhancing the character of local landscapes and reducing disaster risk. Considering the limited availability of water resources, there is increasing interest in the use of seawater for irrigation, particularly near coastal areas. The growth of a native Mediterranean halophyte, Arthrocnemum macrostachyum, on a simulated extensive green roof system with six different irrigation treatments with or without seawater for 97 days is presented. The irrigation treatments included tap water every 4 or 8 days, seawater every 4 or 8 days, and seawater alternated with tap water every 4 or 8 days. The plants’ growth indices, heights, ground-cover surface areas, and relative shoot water content, as well as the electrical conductivity of the green roof’s substrate leachates (EC_L), were measured at regular intervals. Overall, the plants irrigated with tap water every 4 days and the plants irrigated with seawater alternated with tap water every 4 days showed the greatest growth amongst the different irrigation treatments, while the plants irrigated with seawater or seawater alternated with tap water every 8 days showed the least growth. Furthermore, the plants irrigated with tap water every 8 days or seawater every 4 days showed intermediate growth. To conserve water, irrigation with seawater alternated with tap water every 4 days is proposed. To further conserve water, irrigation every 4 days with seawater only is also proposed. Full article

Information on industrial hemp (Cannabis sativa) water use and water stress is sparse. We studied water stress impact in two essential-oil hemp cultivars (‘Wife’ and ‘Cherry’) prompted by anecdotal differences in growth and water use. In a greenhouse setting, we measured water relations, water use, growth, and essential oil (CBD-cannabidiol and THC-delta-9 tetrahydrocannabinol) concentrations. Water stress did not significantly affect THC and CBD concentrations, but both cultivars responded to water stress by reducing transpiration through notably different mechanisms. ‘Cherry’ had more anisohydric behavior, maintaining high stomatal conductance (Gs) and more negative leaf water potential until root zone water depletion triggered partial afternoon stomatal closure to moderate stress, resulting in lower flower and CBD yield. By contrast, water-stressed ‘Wife’ rapidly defoliated half its leaf area in balance with less applied water and so maintained high Gs and flower yield on par with well-watered plants, suggesting potential for deficit irrigation to conserve water and reduce post-harvest vegetation management. Differences in water use translated to provisionally suggested crop coefficients of 1 for ‘Cherry’ and 1.3–1.5 for ‘Wife’, but further research is needed. Because hemp is genetically diverse, and cultivar naming conventions are currently lax, further germplasm screening and research are needed to determine the extent to which either conservative ‘Cherry’ or the water-stress defoliation response of ‘Wife’ is found in the larger population of hemp cultivars. Full article

Soybean fixes atmospheric nitrogen through the symbiotic rhizobia bacteria that inhabit root nodules. Drought stress negatively affect symbiotic nitrogen fixation (SNF) in soybean. The main objective of this study was to identify allelic variations associated with SNF in short-season Canadian soybean varieties under drought stress. A diversity panel of 103 early-maturity Canadian soybean varieties was evaluated under greenhouse conditions to determine SNF-related traits under drought stress. Drought was imposed after three weeks of plant growth, where plants were maintained at 30% field capacity (FC) (drought) and 80% FC (well-watered) until seed maturity. Under drought stress, soybean plants had lower seed yield, yield components, seed nitrogen content, % nitrogen derived from the atmosphere (%Ndfa), and total seed nitrogen fixed compared to those under well-watered conditions. Significant genotypic variability among soybean varieties was found for yield, yield parameters, and nitrogen fixation traits. A genome-wide association study (GWAS) was conducted using 2.16 M single nucleotide single nucleotide polymorphisms (SNPs) for different yield and nitrogen fixation related parameters for 30% FC and their relative performance (30% FC/80% FC). In total, five quantitative trait locus (QTL) regions, including candidate genes, were detected as significantly associated with %Ndfa under drought stress and relative performance. These genes can potentially aid in future breeding efforts to develop drought-resistant soybean varieties. Full article

DREB is a plant-specific transcription factor family that plays a pleiotropic regulatory role in response to abiotic stresses such as drought and cold. In this study, we identified 51 DREB genes of Camellia oleifera. These CoDREBs ranged from 88 to 518 amino acids (average/median 259/237 aa). The predicted molecular weights (MW) of the CoDREB proteins ranged from 9.7 kDa to 59.6 kDa, and the isoelectric points (pI) ranged from 4.62 to 10.44. A gene structure analysis showed that 43/51 (84.3%) CoDREBs were intronless, and the number of exons varied from one to three. Then, we focused on the response of CoDREB genes in terms of plant drought and cold acclimation. Under short-/long-term drought stress, CoDREB1.2/4.1/4.4/4.8/4.12/4.15/5.1/5.3/5.5/6.2 have different regulations in response to long-term drought response, and CoDREB1.4/2.5/4.6/4.1/6.3/6.5 specifically in the short term. Additionally, in response to mild/severe drought and followed by recovery, we found that CoDREBs may be involved in a complex drought-responsive regulatory network. Under cold stress, CoDREB5.2 and CoDREB6.5 are significantly up-regulated, and CoDREB may participate in the regulation of the low-temperature response of C. oleifera. Full article

In order to investigate the relationship between hydraulic lift and drought tolerance in potato, four cultivars differing in drought susceptibilities were selected, and a pot experiment with three different irrigation conditions was carried out in a randomized complete block design. Under irrigation conditions (WW), hydraulic lift of soil water was not observed in the upper pots. Under half-irrigation (DW) and drought (DD) conditions, the water content increased in the upper pots, along with a change in root-related traits, higher biomass, and lower proline (Pro) and malondialdehyde (MDA) concentrations observed in the drought-tolerant cultivars (Longshu NO.3 and Xindaping), whereas the drought-sensitive cultivars (Favorita and Atlantic) had contrary results. As the degree of drought stress increased, the phenomenon of hydraulic lift was inhibited completely, along with a reduction in soil water content and biomass and an increase in Pro and MDA accumulation. Genotypes of Longshu NO.3 and Xindaping exhibited higher tolerance to drought stress than Favorita and Atlantic under drought conditions. In addition, similar results were also obtained for the determination of plant height, leaf water content, root activity, and root–shoot ratio. This study revealed that there was a phenomenon of hydraulic redistribution among different potato cultivars, along with hydraulic lift strongly associated with the root growth, biomass allocation, and other physiological traits that potentially confer drought resistance. Full article

Sugar beet (Beta vulgaris L.) is cultivated in temperate climates worldwide to produce sugar. The production of sugar beet and other plants is in danger due to the world’s increasingly salinized soils. Although different sugar beet genotypes exist at various ploidy levels, most of them are diploid (2X) with 18 chromosomes. The majority of polyploid plants have different variations, morphologies, and anatomy. Diploid and polyploid plants especially have different morphology, physiology, cellularity, and biochemistry. As a result, polyploidy has been identified as an essential component in determining plant salt tolerance. To evaluate the effects of salt (NaCl) stress on sugar beet genotypes, diploid (2X), triploid (3X), and tetraploid (4X) genotypes were exposed to 0 (control), 50, and 150 mM NaCl concentrations for seven weeks. Under control conditions, the diploid (2X) genotype showed higher growth performance compared to the tetraploid (4X) and triploid (3X) genotypes, respectively. Regarding germination and early-stage growth performance, a reduction of about 50% was observed in the diploid (2X) genotype under salt stress compared to the control condition. The diploid (2X) genotype showed higher germination, a greater salt tolerance index, and better seedling growth performance than the other ploidy levels. Late-stage growth, leaf length, leaf width, leaf area, cytological findings, and total chlorophyll content were all shown to be higher and less reduced (around 30%) under salt stress in diploid (2X) genotypes. Even though all of the findings in this study showed a decrease when plants were exposed to salt (NaCl), the diploid (2X) ploidy level plants displayed more robust growth and development than the triploid (3X) and tetraploid (4X) genotypes. Full article

In crops, drought stress reduces the photosynthetic rate and gamete function through oxidative damage. Earlier studies showed that nanoceria possesses an antioxidant property; however, the ability of nanoceria to alleviate drought-stress-stimulated oxidative damage in pulse crops has not been studied. Therefore, experiments were conducted to assess the impacts of nanoceria on drought-induced oxidative damage in mungbean [Vigna radiata (L.) Wilczek]. We hypothesize that foliar application of nanoceria under drought stress can scavenge the excess produced reactive oxygen species (ROS) due to its inherent properties which could result in increased photosynthesis and reproductive success of mungbean. Three experiments were conducted under well-watered and limited-moisture conditions. The traits associated with oxidative damage, photosynthesis, reproductive success, and yield were recorded. Results showed that for mungbean, the optimum concentration of nanoceria for foliar spray was 100 mg L⁻¹. Field and pot culture experiments showed that foliar application of nanoceria under drought decreased the superoxide radical content (29%), hydrogen peroxide content (28%), and membrane damage (35%) over water spray. Nanoceria increased the photosynthetic rate (38%), pod-set percentage (16%), and seed weight m⁻² (44%) in drought-stressed plants compared to control plants. The increased photosynthetic rate by nanoceria spray under drought stress is associated with lesser oxidative damage and stomatal limitation caused by nanoceria’s inherent ROS-scavenging ability. Hence, foliar application of nanoceria at the rate of 100 mg L⁻¹ under drought stress could increase mungbean seed yield per plant through increased photosynthetic rate and pod-set percentage. Full article

Iris domestica is a popular gardening plant. Although the species is considered tolerant to drought, its growth and development are often affected by drought conditions. Therefore, revealing the regulatory mechanisms of drought tolerance in this species will aid in its cultivation and molecular breeding. In this study, morpho-physiological and transcriptome analyses of the roots of I. domestica plants were performed under persistent drought conditions. Peroxidase activity, proline content, and tectoridin content increased under sustained drought conditions. Transcriptome analysis showed that the roots of I. domestica seedlings respond to drought mainly by regulating the expression of drought-resistant genes and biosynthesis of secondary metabolites. This study provides basic data for identifying drought response mechanisms in Iris domestica. Full article

Drought stress critically endangers the growth and development of crops. Glutathione S-transferase plays a vital role in response to abiotic stress. However, there are few studies on the role of glutathione S-transferase in maize drought stress. In this study, the significantly downregulated expression of ZmGST26 in roots under drought stress was analyzed by qRT-PCR. Promoter analyses showed that there were several cis-acting elements related to drought stress and that were involved in oxidative response in the promoter region of ZmGST26. Subcellular localization results showed that ZmGST26 was localized in the nucleus. The transgenic lines of the Arabidopsis over-expressing ZmGST26 were more sensitive to drought stress and ABA in seed germination and inhibited ABA-mediated stomatal closure. Under drought stress, phenotypic analyses showed that the germination rate, root length and survival rate of ZmGST26 overexpressing lines were significantly lower than those of wild-type lines. The determination of physiological and biochemical indexes showed that the water loss rate, malondialdehyde, O₂⁻ and H₂O₂ of the overexpression lines significantly increased compared with wild-type Arabidopsis, but the antioxidant enzyme activities (CAT, SOD and POD), and proline and chlorophyll contents were significantly reduced. Subsequently, the qRT-PCR analysis of drought stress-related gene expression showed that, under drought stress conditions, the expression levels of DREB2A, RD29A, RD29B and PP2CA genes in ZmGST26 overexpression lines were significantly lower than those in wild-type Arabidopsis. In summary, ZmGST26 reduced the drought resistance of plants by aggravating the accumulation of reactive oxygen species in Arabidopsis. Full article

The potential of using pre-stress NaCl or CaCl₂ applications to confer a cross-tolerance to a water deficit was evaluated in periwinkle. The plants initially received five applications of NaCl (0, 30 and 50 mM), or CaCl₂ (15 and 25 mM) via irrigation, and then they were cultivated under different water deficit regimes (80, 50 and 20% available water content). The water deficit induced smaller and denser stomata. It promoted a water use efficiency, a proline content and antioxidant enzyme activity. However, it downgraded the aesthetic value (plant stature, flower size and vegetation greenness), magnified the stem bending probability and strongly decreased the floral longevity. It additionally impeded the growth by reductions in the leaf area and photosynthesis. Plants undergoing a water deficit maintained a lower hydration and expressed oxidative damage symptoms, including enhanced chlorophyll and membrane degradation. As the water deficit intensified, these effects were more pronounced. Pre-stress CaCl₂ or NaCl applications generally restored most of the water severity-induced effects, with the former being more effective. For CaCl₂, the highest concentration (25 mM) was generally optimal, whereas NaCl was the lowest concentration (30 mM). In conclusion, pre-stress CaCl₂ or NaCl applications effectively confer a cross-tolerance to the water deficit by promoting the aesthetic value and extending the floral longevity, with the promotive effects being incremental as the water deficit becomes more severe. Full article

The search for soybean genotypes more adapted to abiotic stress conditions is essential to boost the development and yield of the crop in Brazil and worldwide. In this research, we propose a new approach using the concept of distance (or similarity) in a vector space that can quantify changes in the morphological traits of soybean seedlings exposed to stressful environments. Thus, this study was conducted to select soybean genotypes exposed to stressful environments (saline or drought) using similarity based on Manhattan distance and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method. TOPSIS is a multi-criteria decision method for selecting the best alternative using the concept of distance. The use of TOPSIS is essential because the genotypes are not absolutely similar in both treatments. That is, just the distance measure is not enough to select the best genotype simultaneously in the two stress environments. Drought and saline stresses were induced by exposing seeds of 70 soybean genotypes to −0.20 MPa iso-osmotic solutions with polyethylene glycol–PEG 6000 (119.6 g L⁻¹) or NaCl (2.36 g L⁻¹) for 14 days at 25 °C. The germination rate, seedling length, and seedling dry matter were measured. We showed here how the genotypic stability of soybean plants could be quantified by TOPSIS when comparing drought and salinity conditions to a non-stressful environment (control) and how this method can be employed under different conditions. Based on the TOPSIS method, we can select the best soybean genotypes for environments with multiple abiotic stresses. Among the 70 tested soybean genotypes, RK 6813 RR, ST 777 IPRO, RK 7214 IPRO, TMG 2165 IPRO, 5G 830 RR, 98R35 IPRO, 98R31 IPRO, RK 8317 IPRO, CG 7464 RR, and LG 60177 IPRO are the 10 most stable genotypes under drought and saline stress conditions. Owing to high stability and gains with selection verified for these genotypes under salinity and drought conditions, they can be used as genitors in breeding programs to obtain offspring with higher resistance to antibiotic stresses. Full article