Next Article in Journal
Marker-Assisted Improvement of Bread Wheat Variety HD2967 for Leaf and Stripe Rust Resistance
Next Article in Special Issue
Role of Spermidine in Photosynthesis and Polyamine Metabolism in Lettuce Seedlings under High-Temperature Stress
Previous Article in Journal / Special Issue
SNP Based Trait Characterization Detects Genetically Important and Stable Multiple Stress Tolerance Rice Genotypes in Salt-Stress Environments
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Plants
Volume 11
Issue 9
10.3390/plants11091151
plants-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Melatonin Mitigates Drought Induced Oxidative Stress in Potato Plants through Modulation of Osmolytes, Sugar Metabolism, ABA Homeostasis and Antioxidant Enzymes

by
Ahmed Abou El-Yazied
1,
Mohamed F. M. Ibrahim
2,*,
Mervat A. R. Ibrahim
3,
Ibrahim N. Nasef
4,
Salem Mesfir Al-Qahtani
5,
Nadi Awad Al-Harbi
5,
Fahad Mohammed Alzuaibr
6,
Abdullah Alaklabi
7,
Eldessoky S. Dessoky
8,
Nadiyah M. Alabdallah
9,
Mohamed M. A. Omar
3,
Mariam T. S. Ibrahim
3,
Amr A. Metwally
1,
Karim. M. Hassan
1 and
Said A. Shehata
2
1
Department of Horticulture, Faculty of Agriculture, Ain Shams University, Cairo 11566, Egypt
2
Department of Agricultural Botany, Faculty of Agriculture, Ain Shams University, Cairo 11566, Egypt
3
Department of Biochemistry, Faculty of Agriculture, Ain Shams University, Cairo 11566, Egypt
4
Department of Horticulture, Faculty of Agriculture, Suez Canal University, Ismailia 41522, Egypt
5
Biology Department, University College of Tayma, Tabuk University, P.O. Box 741, Tabuk 47512, Saudi Arabia
6
Department of Biology, Faculty of Science, University of Tabuk, P.O. Box 741, Tabuk 71491, Saudi Arabia
7
Department of Biology, Faculty of Science, University of Bisha, P.O. Box 551, Bisha 61922, Saudi Arabia
8
Department of Biology, College of Science, Taif University, P.O. Box 11099, Taif 21944, Saudi Arabia
9
Department of Biology, College of Science, Imam Abdulrahman Bin Faisal University, P.O. Box 1982, Dammam 31441, Saudi Arabia
*
Author to whom correspondence should be addressed.
Plants 2022, 11(9), 1151; https://doi.org/10.3390/plants11091151
Submission received: 9 April 2022 / Revised: 21 April 2022 / Accepted: 22 April 2022 / Published: 24 April 2022
(This article belongs to the Special Issue Physiological and Molecular Mechanisms of Plant Responses to Abiotic Stress)
Browse Figures
Versions Notes

Abstract

:
The effect of melatonin (MT) on potato plants under drought stress is still unclear in the available literature. Here, we studied the effect of MT as a foliar application at 0, 0.05, 0.1, and 0.2 mM on potato plants grown under well-watered and drought stressed conditions during the most critical period of early tuberization stage. The results indicated that under drought stress conditions, exogenous MT significantly (p ≤ 0.05) improved shoot fresh weight, shoot dry weight, chlorophyll (Chl; a, b and a + b), leaf relative water content (RWC), free amino acids (FAA), non-reducing sugars, total soluble sugars, cell membrane stability index, superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (G-POX), and ascorbate peroxidase (APX) compared to the untreated plants. Meanwhile, carotenoids, proline, methylglyoxal (MG), H2O2, lipid peroxidation (malondialdehyde; MDA) and abscisic acid (ABA) were significantly decreased compared to the untreated plants. These responses may reveal the protective role of MT against drought induced carbonyl/oxidative stress and enhancing the antioxidative defense systems. Furthermore, tuber yield was differentially responded to MT treatments under well-watered and drought stressed conditions. Since, applied-MT led to an obvious decrease in tuber yield under well-watered conditions. In contrast, under drought conditions, tuber yield was substantially increased by MT-treatments up to 0.1 mM. These results may imply that under water deficiency, MT can regulate the tuberization process in potato plants by hindering ABA transport from the root to shoot system, on the one hand, and by increasing the non-reducing sugars on the other hand.

1. Introduction

Drought stress or water scarcity is one of the most restricted factors to growth and productivity of several plant species [1,2,3]. It poses a serious threat to food security in many regions worldwide [4]. Moreover, frequent climatic change and global warming can cause severe increments in the rate of evapotranspiration [5]. In this context, it is expected that by 2050, drought stress will cause serious problems for more than 50% of arable lands [6]. In higher plants, drought stress can be involved in a wide spectrum of complex events at morphological, physiological, biochemical and molecular levels [7,8,9,10]. These influences include hindering of stomatal conductance, CO2 fixation, transpiration rate, nutrients’ transport, and restriction of electron transport chain (ETC) leading to a significant disturbance in photosynthesis and respiration [11,12,13,14]. Besides, drought stress affects hormonal balance, various signaling processes and collapses cell membranes’ structure and dysfunction [15,16,17,18]. All of these destructive effects are widely correlated with elevating the concentration of reactive oxygen species (ROS) which cause oxidative damages to protein, lipids, and nucleic acids [19].
Melatonin (MT; N-acetyl-5-methoxy-tryptamine) is a naturally synthesized compound in animals, plants and microbes [20]. It is able to delay senescence, stimulating root growth, regulation fruit ripening and protecting photosynthetic systems [21,22]. Moreover, it has been found that exogenous melatonin can improve plant tolerance to various abiotic stresses i.e., heat stress [23], chilling [24], heavy metals [25], salinity [26], and drought [27,28,29]. Since applied MT can prevent the oxido-nitrositive induced damages by reducing the cytotoxic effects of reactive oxygen and/or nitrogen species (ROS/RNS) [20]. Additionally, MT plays an important role in the methylglyoxal (MG) detoxification [30] and enhancing plant water relations by stimulating the osmolytes’ biosynthesis [27]. Furthermore, MT can reinforce the photosynthesis efficiency [31] by affecting the transcription key genes that are involved in chlorophyll metabolism [23], upregulating the enzymes of Calvin’s cycle [32] and maintaining the plant cell redox status [33]. Melatonin is also an important regulator of gene expression related to phytohormones and their metabolism in plants i.e., indole-3-acetic acid (IAA), GAs, cytokinins (CKs), ABA, jasmonic acid (JA), nitric oxide (NO), ethylene (C2H4) and salicylic acid [21].
Methylglyoxal is a reactive carbonyl species causing oxidative stress under various abiotic stresses [34]. It can also serve as a signaling molecule under stress responses and tolerance [35,36]. Under severe stress conditions, it is considered a toxic molecule that can restrict plant growth, developmental, photosynthesis, and seed germination, [36]. Methylglyoxal detoxification depends on two glyoxalase enzymes (Gly I and Gly II) which can be boosted by exogenous melatonin under abiotic stress conditions [30,37].
The potato (Solanum tuberosum L.) is one of the most valuable edible crops worldwide [38,39]. It is sensitive to drought stress during different growth stages and tuber development due to the shallow root system that reduces its ability for water uptake and speed recovery after stress conditions [3,40]. Tuber initiation (tuberization) is most critical growth stage in potato plants [41,42]. Tuberization is a complex developmental and physiological process in potato plants. It requires an increase in ABA and non-reducing sugars leading to inhibition of stolon elongation and starting of tuber formation [43]. Several previous studies revealed that tuberization in potato plants and productivity can be affected by exogenous compounds i.e., plant growth regulators, antioxidants and osmo-protectants under various abiotic stress conditions [44,45,46].
Generally, the effect of exogenous MT on potato tuberization under drought stress is still unclear in literatures. Therefore, we conducted this study to investigate the possible protective effects of exogenous MT on drought-stressed potato plants and to understand its relation to the tuberization process by regulating the endogenous ABA (the key plant hormone under drought stress and tuberization process) and maintaining the concentration of non-reducing sugars (the major form for sugar transport and starch synthesis in tubers).

2. Results

2.1. Effect of Melatonin on Plant Growth and Photosynthetic Pigments

Plants exposed to drought stress revealed a significant (p ≤ 0.05) decrease in growth parameters and photosynthetic pigments compared to the well-watered plants (Figure 1). However, exogenous MT enhanced shoot fresh weight, shoot dry weight, Chl a, Chl b and total chlorophyll in both water stressed and non-stressed plants. Generally, the highest significant results were obtained by the treatment of 0.1 mM MT in this respect. Conversely, MT treatments revealed divergent effects on carotenoids under water stressed and non-stressed conditions. In this context, carotenoids were significantly enhanced by MT treatments specifically at 0.05 and 0.1 mM under well-watered conditions. In contrast, under drought stress, all MT-treatments significantly reduced carotenoids compared to the untreated plants. These responses may imply that MT has a dual impact on the metabolism of terpenoids’ pathway (the major pathway of carotenoids and ABA biosynthesis in higher plants) in potato plants under sufficient and deficit water supply.

2.2. Effect of Melatonin on RWC and Osmolytes

Exogenous MT exhibited a significant (p ≤ 0.05) improvement in leaf relative water content (RWC) free amino acids (FAA) compared to the untreated plants under both water stressed and non-stressed conditions (Figure 2A,B). In this respect, the highest significant results were obtained by the treatment of 0.1 mM MT under both irrigation conditions. Despite proline was not affected by different MT-treatments under well-watered conditions, an obvious and significant (p ≤ 0.05) decrease in proline was observed with increasing the concentration of MT under drought stress conditions (Figure 2C). Moreover, reducing, non-reducing and total soluble sugars were differentially affected by MT- treatments under both watering levels (Figure 2D–F). Under well-watered conditions, MT-treated plants displayed an obvious increase in reducing sugars. However, an opposite trend was observed in the non-reducing sugars. These changes slightly affected the concentration of total soluble sugars. In contrast, under drought stress, the general trend was that MT-treated plants at 0.05 and 0.1 mM exhibited an obvious increase in non-reducing sugars and total soluble sugars in parallel with a slight decrease in the reducing sugars. These findings imply that under drought stress condition, exogenous MT at the suitable concentrations (0.05 and 0.1 mM) may induce the sucrose biosynthesis (non-reducing sugar) which is considered the most transported form of soluble sugars. This effect may help potato plants to produce more tubers under water stress condition.

2.3. Effect of Melatonin on Cell Membrane Stability Index (CMSI), Methylglycoxal (MG), H2O2 and Lipid Peroxidation

To evaluate the drought induced damages that occurred to plants in this study, CMSI, MG, H2O2, and MDA were estimated (Figure 3). Under well-watered condition, no significant changes were observed between all MT treatments in respect to MG and MDA. Meanwhile, MT at 0.2 and 0.1 mM resulted in the highest and lowest values of CMSI and H2O2; respectively. On the other hand, plants exposed to drought stress demonstrated a significant (p ≤ 0.05) decrease in CMSI, while, MG, H2O2 and MDA were significantly and dramatically increased in leaf tissues. Exogenous MT at all investigated concentrations significantly enhanced CMSI compared to the untreated plants either under well-watered or water-stressed conditions. On the contrary, MT-treated plants exhibited a significant decrease in MG, H2O2 and MDA under water deficit. In this respect, the lowest values were achieved by the treatments of MT at 0.1 and 0.2 mM compared to the untreated plants.

2.4. Effect of Melatonin on the Activities of Antioxidant Enzymes

Regarding the antioxidant enzymes activities (Figure 4), it was observed that under water-stressed conditions, the activities of SOD, CAT, G-POX and APX were significantly (p ≤ 0.05) increased in potato plants compared to those of well-watered conditions. Moreover, the results showed that no significant differences were detected between MT-treated and non-treated plants in respect to SOD, CAT, and APX under well-watered conditions. Meanwhile, G-POX activity was increased in all MT-treated plants compared to the control under well-watered conditions. Under water shortage, applied MT led to a significant increase in the activities of all studied antioxidant enzymes. The highest activities of CAT and G-POX were obtained by the treatment of 0.2 mM MT, while, the treatment of 0.1 mM MT achieved the maximum findings in respect to SOD and APX.

2.5. Effect of Melatonin on ABA Concentration and Its Relationship with RWC

The results of this study cleared that ABA was lower in potato plants under well-watered conditions compared with water-stressed conditions (Figure 5A). In addition, exogenous MT has no significant (p ≤ 0.05) effect on ABA content in potato under well-watered conditions. Under water-stressed conditions, ABA content was significantly affected by MT treatments. Also, 0.1 mM MT gave the lowest ABA content, followed by 0.2 mM, while the highest ABA content was recorded with control. Also, our results revealed that there is a linear and significant (p ≤ 0.01) negative correlation between RWC and ABA content in potato plants (Figure 5B).

2.6. Effect of Melatonin on Tuber Yield

There was a highly significance difference between the effect of MT treatments on potato tuber yield under well-watered and drought stress conditions (Figure 6). Interestingly, applied-MT reduced the tuber yield compared to untreated plants under well-watered conditions, conversely, MT treatments up to 0.1 mM maximized tuber yield under water-stressed conditions. However, the treatment of 0.2 mM significantly inhibited tuber yield under drought stress condition.

3. Discussion

Drought is one of the devasting abiotic stresses that facing the cultivation of plants in throughout the world, limiting the growth and reducing the yield of plants. Drought sensitive vegetables, such as potato can be seriously affected by water shortage. Researchers around the world have made great efforts to overcome and alleviate the effect of this problem. In this context, some chemicals such as salicylic acid, jasmonic acid and γ-aminobutyric acid etc. have been extensively studied to induce drought tolerance in plants [47,48,49]. Similarly, melatonin as a new plant growth regulator has been suggested to mitigate a wide array of abiotic stresses [50]. Also, previous studies have revealed that exogenous melatonin can positively affect the productivity of various plant species [51,52,53]. In this study, the role of melatonin in alleviating water stress in potato plants was investigated. Melatonin treatment improved the fresh weight of potato plants and dry weight under water-stressed conditions compared with the untreated plants. These effects imply that exogenous melatonin as foliar application induced the tolerance to water stress in potato plants. Consistent with our results, Ye, et al. [54] found that melatonin improved the leaf area and shoot dry weight of maize seedlings under water stress. Moreover, the present study demonstrated that melatonin enhanced the chlorophyll content in potato plants under drought stress. Similarly, the activity of photosynthesis and photosystem II in rice seedlings were improved by exogenous melatonin. These responses were associated with increasing the activities of antioxidant enzymes leading to reduce the accumulation of ROS and MDA in plant cells [55]. Chlorophyll plays an important role in the light energy transmission and absorption [56], thereby synthesizing carbohydrates can be related to enhancing plant growth and productivity [57]. The results of this study indicated that 0.1 mM of melatonin was more effective in increasing chlorophyll and maximizing the yield of potato under water-stressed conditions. This effect could be attributed to increase the photosynthetic efficiency and protecting potato plants from drought induced oxidative damage. The physiological processes in the leaves of plant, such as transpiration, photosynthesis and respiration are regulated by leaf stomata through opening and closing which is affected by water balance and the pathways of complex signal transduction [8,45]. Relative water content (RWC) is an important physiological marker for the water status and plant’s ability to survive under drought stress conditions. In this study, water stress significantly reduced the RWC in the untreated plants. However, the exogenous melatonin as foliar application attenuated the reduction in RWC of treated potato. This suggests that melatonin improves the function of stomatal by stimulation of plant to reopen its stomata [28], and enhances the photosynthetic rate, allowing the RWC to increase under drought stress conditions. Also, Ahmad, et al. [51] found that length, width and area of stomata and pore numbers were reduced in maize seedlings under drought stress conditions compared to the control and MT-treated plants. In addition, the closure of stomata to prevent loss of water from the leaf by evapotranspiration may be due to the abscisic acid accumulation [58].
Several plant species, i.e., maize [59], tomato [27], green beans [1], and potato [7] can create a potential strategy to adapt stress conditions by maintaining osmotic potential. This effect can be occurred due to the accumulation of osmolyte substances, i.e., soluble sugars, free amino acids, soluble protein and proline. In this respect, in maize seedlings, proline has been found to scavenge OH• radicals and quenches singlet oxygen to protect the membrane cells, protein and DNA from damage by ROS under abiotic stress [51]. The results of the present study showed that soluble sugars, free amino acids and proline content of MT-treated plants were significantly enhanced under water-stressed conditions compared to the untreated plants. These findings indicate that melatonin can stimulate the production of osmotic solvents to minimize water loss and protect the cell membrane under water-stressed conditions.
Exposure of plants to environmental stresses leads to generate the reactive oxygen species (ROS), including singlet oxygen (O12), hydrogen peroxide (H2O2), hydroxyl radicals (OH), alkoxy radicals (RO), superoxide anion radicals (O−2). These toxic molecules may react with proteins, deoxyribonucleic acid and lipids triggering oxidative damage in plant cell [60]. In the same line, the results showed that hydrogen peroxide (H2O2) increased in potato under water-stressed conditions compared to the well-watered conditions. Meanwhile, exogenous melatonin significantly reduced H2O2 accumulation compared to the control under drought stress conditions. Also, a high significant reduction was detected in malondialdehyde (MDA) content in MT-treated plants compared to the untreated ones. Moreover, cell membrane stability index (CMSI) of potato was improved by MT treatments under water-stressed. Furthermore, the study of Li et al. [58] indicated that MT was effective in decreasing ROS under drought stress conditions. Therefore, the present study suggests that MT acts as an antioxidant and plays a vital role in overcoming the oxidative damage.
Methylglycoxal (MG) is an emerging signaling molecule in abiotic stress responses and tolerance in plants, is produced as a result of glycolysis in cells. Under normal conditions, MG remains at very low level. While, under stress conditions, MG accumulates to higher level. However, MG at low level, regulates the opening and closing stomata, reactive oxygen species production, concentration of cytosolic calcium ion and many stress-responsive genes expression. Whereas, MG high levels act as a toxic molecule, inhibits growth development processes, such as seed germination, root growth and photosynthesis, so, MG is considered as biochemical marker for abiotic stress tolerance in plants [61]. Our results indicated that MG significantly increased under water-stressed conditions, however, MT-treatment at a rate of 0.1 mM maintains MG at low level. This result cleared that 0.1 mM of melatonin is the best concentration to induce drought stress tolerance in potato plants.
Sueroxide dismutase (SOD), catalase (CAT), guiacol peroxidase (G-POX) and ascorbate peroxidase (APX) are essential protective enzymes related to the enzymatic defense system, effectively decomposing ROS and reducing H2O2 levels in plants [27,62,63]. Under stress conditions such as water deficit, plants evolve the mechanisms of tolerance to resist abiotic stress via activation several antioxidant enzymes, including SOD, CAT, G-POX and APX to protect the cell against oxidative damage [56]. The key of action mode of these enzymes is the balance between them, where SOD scavenges ROS and converts superoxide anion radicals (O−2) to O2 and H2O2, and then G-POX and CAT breakdown H2O2 to water [64]. In the present study, under water-stressed conditions, all antioxidant enzymes activities were significantly increased compared to the well-watered conditions. However, exogenous MT maximized the activities of SOD, CAT, G-POX and APX compared to control under water-stressed conditions. Whereas; H2O2 content decreased, the reduction of H2O2 may relate to antioxidant enzymes activity in MT-treated plants. Similarly, MT treatment improved CAT, SOD and G-POX activity in maize under drought stress [65]. These findings suggest that MT may play a crucial role in the activity of antioxidant enzymes and protecting plant cells from damage under drought stress.
Concerning the yield of potato, inevitably, water-stressed conditions had a negative effect and reduced the tuber yield of potato, but exogenous melatonin foliar application at a rate of 0.1 mM significantly increased tuber yield compared to control and another two concentrations. This indicates that melatonin has a vital role in tuber development under water stress by regulating the formation of growth regulators and non-reducing sugars. From the previous studies, melatonin and ABA function antagonistically or synergistically in order to regulate many processes in plants under stress conditions [58,66]. In this study, under drought stress, MT-treated plants showed a significant decrease in ABA compared to the untreated plants. This effect could be attributed to enhance leaf water status and antioxidant capacity of MT-treated plants. Several lines of evidence confirmed that, tuberization in potato plants is a developmental stage correlated with reducing of gibberellin (GA3) and increasing of sucrose. Also, there is an antagonism between ABA and GA3 in the presence of sucrose [43]. Indeed, ABA stimulates the tuber formation in potato via inhibition of stolon elongation, as prerequisite for formation process [67]. Also, there is a negative correlation between tuberization and reducing sugars content, while sucrose induces the tuberization by causing a hormonal changes in potato plants [68], sucrose induces the tuber-specific genes expression [69], acts as secondary messengers which have the ability to regulate the growth and development under abiotic and biotic stresses. Moreover, it is well documented that the photosynthetic carbon metabolites can be transported in plant as sucrose [70]. Hence, our study suggests that melatonin induces the potato tuberization and tubers formation and enhances tubers development under water-stressed conditions by increasing the non-reducing sugars and inhibition ABA transport from the root to shoot system leading to improving the tuber yield.

4. Material and Methods

4.1. Plant Material and Growth Conditions

Imported basic seed potatoes (Solanum tuberosum L.; CV, Hermes, Scotland) were kept for 3 weeks in a ventilated room until sprouting. After that, the homogenous seed tubers in size and form (35–40 mm) were planted in plastic pots (40 cm diameter) filled with 16 kg pre-washed sand (one sprouted tuber/pot). All pots were kept under greenhouse conditions during the period from 19 January to 10 May 2021. Air minimum and maximum temperatures and relative humidity (Table 1) were recorded inside the greenhouse using a digital Thermo/Hygrometer Art placed in the middle of the greenhouse (No.30.5000/30.5002, TFA; Wertheim, Baden-Württemberg, Germany).

4.2. Treatments and Experimental Layout

To investigate the effect of exogenous melatonin (MT) as a foliar application on potato plants grown under well-watered and drought stressed conditions, plants were sparyed with MT (Bio Basic, Markham, York, Ontario, Canada) at 0.05, 0.1 and 0.2 mM. Addationally, distilled water was sprayed as a control. Tween-20 at 0.05% (v/v) as a wetting agent was used with all foliar treatments. The total number of pots (144) was divided into two major groups to apply the irrigation treatments (72 pots to apply the drought stress and 72 pots to apply the well-watered level). The timeline infographic for the treatments and sampling was shown in Figure 7. Each major group was divided into four subgroups to apply the different foliar treatments of MT (18 pots/subgroup). Each pot containing a single plant was weekly sprayed with 20 mL of specific MT concentration for 5 times at 42, 49, 56, 63, and 70 days after planting respectively. The progressive drought stress was applied during the most critical period of potato tuberization. Irrigation was stopped for 10 days (55–64 days after planting), rehydration was applied once with full strength Hogland’s solution at 65 days after planting; then irrigation was stopped again for 10 days (66–75 days after planting). However, the well-watered plants were irrigated seven times during this period (six times with tap water and one time with full strength Hogland’s solution as shown in Figure 7. The experimental layout was a Complete Randomized Design (CRD) including 3 replicates × 6 pots × 4 melatonin × 2 irrigation. Two pots from each replicate were left to the end of experiment at 110 days after planting to evaluate the tuber yield/plant.

4.3. Determination of Growth Parameters

When plants reached the maximum vegetative growth stage at 75 days after planting, two pots from each replicate were gathered to evaluate the growth parameters. Shoot fresh weight was immediately estimated after sampling using a digital balance, whereas shoot dry weight was determined by drying the samples in an air-forced ventilated oven at 105 °C.

4.4. Determination of Leaf Photosynthetic Pigments

The concentration of chlorophyll (Chl) a and b, and carotenoids in fresh leaves was determined spectrophotometrically according to Lichtenthaler and Wellburn [71]. Fresh weight (0.05 g) of fully expanded young leaves was used for pigment extraction in 80% acetone. The extract of pigments was measured versus a blank of pure 80% acetone at 663, 644, and 452.5 nm for Chla, Chlb, and carotenoid contents, respectively.

4.5. Determination of Relative Water Content (RWC), Osmolytes and Soluble Sugars

Leaf relative water content (RWC) was estimated according to Abd El-Gawad et al. [1]. Leaf discs from 6 of fully expanded leaves were weighed (FW) and placed immediately in distilled water for 2 h at 25 °C then the turgid weight (TW) was recorded. After that discs were fully dried in an oven at 110 °C for 24 h (DW). Relative water content (RWC) was calculated using the following formula:
RWC   ( % ) = FW − DW TW − DW   × 100
Free amino acids were determined using the ninhydrin reagent according to the method of Hamilton, et al. [72]. Proline concentration was determined by the method of ninhydrin reagent as described by Bates, et al. [73]. Total soluble sugars were estimated using the anthrone method [74], whereas, the reducing sugars were determined using the dinitrosalicylic acid method [75], and the non-reducing sugars content was estimated using the difference between the total soluble sugar content and the reducing sugars.

4.6. Determination of Cell Membrane Stability Index, Methylglyoxal, H2O2 and Lipid Peroxidation

Cell membrane stability was estimated as described by Abd Elbar, et al. [76] with some modifications. Eight leaf discs with 1.8 cm diameter were incubated in 10 mL deionized water for 24 h on a shaker. After that EC1 values of contents were measured by EC meters (DOH-SD1, TC-OMEGA, USA/Canada). Then, samples were autoclaved at 120 °C for 20 min to determine the values of EC2. Cell membrane stability index was calculated using the following equation:
MSI = [ 1 − ( EC 1 EC 2 ) ] × 100
Methylglyoxal (MG) content was determined according to Hossain et al. [35] with some modifications. Fresh leaves (0.5 g) were homogenized in 3 mL of 0.5 M perchloric acid, then incubating for 15 min on ice. The mixture was centrifuged at 4 °C for 10 min at 10,000 rpm. The supernatant was decolorized by adding charcoal, kept for 15 min at room temperature, and centrifuged at 10,000 rpm for 10 min. Before using this supernatant for MG assay, it was neutralized by keeping for 15 min with saturated solution of potassium carbonate at room temperature and centrifuged again at 10,000 rpm for 10 min. The neutralized supernatant was used for MG estimation. One ml of the reaction mixture containing 250 μL of 7.2 mM 1, 2-diaminobenzene, 100 μL of 5 M perchloric acid, and 650 μL of the neutralized supernatant were added in that order. The absorbance at 335 nm was read after 25 min using a UV-spectrophotometer. Hydrogen peroxide (H2O2) concentration was estimated colorimetrically by the method of potassium iodide [77]. Malondialdehyde (MDA) was determined by thiobarbituric acid (TBA) method [78].

4.7. Assay of Antioxidant Enzymes and ABA Determination

Fresh leaves (0.2 g) were ground in 4 mL of 0.1 M ice-cold sodium phosphate buffer (pH 7.0) containing 1% (w/v) polyvinylpyrrolidon (PVP) and 0.1 mM EDTA, centrifuged at 10,000× g at 4 °C for 20 min. The supernatant was used for the next enzyme activity assays. To calculate the specific activity of different enzymes, total soluble protein was also determined in the supernatant according to Bradford [79]. Superoxide dismutase (SOD; EC 1.15.1.1) activity was evaluated according to the ability to inhibit the photochemical reduction of nitro blue tetrazolium (NBT) at 560 nm [80]. Catalase (CAT; EC 1.11.1.6) activity was assayed by monitoring the decrease in absorbance of H2O2 at 240 nm [81]. Guaiacol peroxidase (G-POX; EC1.11.1.7) activity was evaluated by observing its ability to convert guaiacol to tetraguaiacol by monitoring the increase in absorbance at 470 nm [82]. Ascorbate peroxidase (APX; EC 1.11.1.11) activity was determined based on the decrease in ascorbate at 290 nm [83]. Abscisic acid (ABA) was extracted from fresh leaf tissues according to the method of Shindy and Smith [84]. Then, High-Performance Liquid Chromatography (HPLC; SCIEX, Framingham, MA, USA) was used to complete the quantification procedure according to Nakurte, et al. [85].

4.8. Statistics

One way ANOVA procedure was followed using SAS [86] software. Means ± SD were calculated from three replicates and Duncan’s multiple range test (p ≤ 0.05) was used to determine the significant differences between means.

5. Conclusions

In conclusion, this study demonstrated the beneficial effects of melatonin (MT) in alleviating drought stress during the most critical period of early tuberization. Applied-MT decreased the harmful effects of drought induced carbonyl/oxidative stress. These effects were observed by reducing the cytotoxic biochemical cellular markers (MG, H2O2, and MDA). These responses were in parallel with enhancing plant growth, chlorophyll content, leaf water status and activities of antioxidant enzymes. Moreover, MT can differentially regulate the tuberization process under well-watered and drought stressed conditions. This regulation may be correlated with the effect of MT on increasing the non-reducing sugars on one side; and restriction of ABA transport from the root to shoot system on the other side (Figure 8). Further studies using advanced molecular techniques are required to better understand the role of MT in tuberization process and inducing different signaling pathways in potato plants under water deficiency.

Author Contributions

Conceptualization, A.A.E.-Y., M.F.M.I. and S.A.S.; methodology, I.N.N., M.A.R.I., M.M.A.O., M.T.S.I., A.A.M. and K.M.H.; software, M.F.M.I., A.A., N.M.A., M.M.A.O. and K.M.H.; validation, M.A.R.I., S.M.A.-Q., N.A.A.-H., F.M.A., A.A., M.T.S.I. and S.A.S.; formal analysis, I.N.N., M.A.R.I., N.A.A.-H., F.M.A., E.S.D., N.M.A. and A.A.M.; investigation, A.A.E.-Y., I.N.N., M.A.R.I., M.F.M.I., M.M.A.O., M.T.S.I., A.A.M. and K.M.H.; resources, S.M.A.-Q., N.A.A.-H., A.A., E.S.D. and N.M.A.; data curation, A.A.E.-Y., M.A.R.I., S.M.A.-Q., F.M.A., E.S.D., M.M.A.O. and M.T.S.I.; writing—original draft preparation, A.A.E.-Y., M.F.M.I., N.A.A.-H., A.A. and A.A.M.; writing—review and editing, M.F.M.I., I.N.N. and S.A.S.; visualization, S.M.A.-Q., N.M.A. and K.M.H.; supervision, F.M.A. and S.A.S.; project administration, S.M.A.-Q. and E.S.D.; funding acquisition, N.A.A.-H. and E.S.D. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by Ain shams University, Faculty of Agriculture, Cairo, Egypt.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors extend their appreciation to Taif University for supporting current work by Taif University Researchers Supporting Project number (TURSP-2020/85), Taif University, Taif, Saudi Arabia.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Abd El-Gawad, H.G.; Mukherjee, S.; Farag, R.; Abd Elbar, O.H.; Hikal, M.; Abou El-Yazied, A.; Abd Elhady, S.A.; Helal, N.; ElKelish, A.; El Nahhas, N. Exogenous γ-aminobutyric acid (GABA)-induced signaling events and field performance associated with mitigation of drought stress in Phaseolus vulgaris L. Plant Signal. Behav. 2021, 16, 1853384. [Google Scholar] [CrossRef] [PubMed]
  2. Elkelish, A.; El-Mogy, M.M.; Niedbała, G.; Piekutowska, M.; Atia, M.A.; Hamada, M.; Shahin, M.; Mukherjee, S.; El-Yazied, A.A.; Shebl, M. Roles of Exogenous α-Lipoic Acid and Cysteine in Mitigation of Drought Stress and Restoration of Grain Quality in Wheat. Plants 2021, 10, 2318. [Google Scholar] [CrossRef] [PubMed]
  3. Obidiegwu, J.E.; Bryan, G.J.; Jones, H.G.; Prashar, A. Coping with drought: Stress and adaptive responses in potato and perspectives for improvement. Front. Plant Sci. 2015, 6, 542. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  4. Gitz, V.; Meybeck, A.; Lipper, L.; Young, C.D.; Braatz, S. Climate change and food security: Risks and responses. Food Agric. Organ. United Nations (FAO) Rep. 2016, 110, 2–4. [Google Scholar]
  5. Yang, Z.; Zhang, Q.; Hao, X.; Yue, P. Changes in evapotranspiration over global semiarid regions 1984–2013. J. Geophys. Res. Atmos. 2019, 124, 2946–2963. [Google Scholar] [CrossRef]
  6. Kasim, W.A.; Osman, M.E.; Omar, M.N.; El-Daim, A.; Islam, A.; Bejai, S.; Meijer, J. Control of drought stress in wheat using plant-growth-promoting bacteria. J. Plant Growth Regul. 2013, 32, 122–130. [Google Scholar] [CrossRef]
  7. Abd Elhady, S.A.; El-Gawad, H.G.A.; Ibrahim, M.F.; Mukherjee, S.; Elkelish, A.; Azab, E.; Gobouri, A.A.; Farag, R.; Ibrahim, H.A.; El-Azm, N.A. Hydrogen peroxide supplementation in irrigation water alleviates drought stress and boosts growth and productivity of potato plants. Sustainability 2021, 13, 899. [Google Scholar] [CrossRef]
  8. Hasan, M.; Alabdallah, N.M.; Alharbi, B.M.; Waseem, M.; Yao, G.; Liu, X.-D.; El-Gawad, A.; Hany, G.; El-Yazied, A.A.; Ibrahim, M.F. GABA: A Key Player in Drought Stress Resistance in Plants. Int. J. Mol. Sci. 2021, 22, 10136. [Google Scholar] [CrossRef]
  9. Ibrahim, M.F.; El-Samad, A.; Ashour, H.; El-Sawy, A.M.; Hikal, M.; Elkelish, A.; El-Gawad, H.A.; El-Yazied, A.A.; Hozzein, W.N.; Farag, R. Regulation of agronomic traits, nutrient uptake, osmolytes and antioxidants of maize as influenced by exogenous potassium silicate under deficit irrigation and semiarid conditions. Agronomy 2020, 10, 1212. [Google Scholar] [CrossRef]
  10. Verslues, P.E.; Bhaskara, G.B.; Kesari, R.; Kumar, M.N. Drought tolerance mechanisms and their molecular basis. Plant Abiotic Stress 2014, 2, 15–46. [Google Scholar]
  11. Carminati, A.; Javaux, M. Soil rather than xylem vulnerability controls stomatal response to drought. Trends Plant Sci. 2020, 25, 868–880. [Google Scholar] [CrossRef] [PubMed]
  12. Cornic, G. Drought stress inhibits photosynthesis by decreasing stomatal aperture–not by affecting ATP synthesis. Trends Plant Sci. 2000, 5, 187–188. [Google Scholar] [CrossRef]
  13. Elkelish, A.; Ibrahim, M.F.; Ashour, H.; Bondok, A.; Mukherjee, S.; Aftab, T.; Hikal, M.; El-Yazied, A.A.; Azab, E.; Gobouri, A.A. Exogenous Application of Nitric Oxide Mitigates Water Stress and Reduces Natural Viral Disease Incidence of Tomato Plants Subjected to Deficit Irrigation. Agronomy 2021, 11, 87. [Google Scholar] [CrossRef]
  14. Wang, Z.; Li, G.; Sun, H.; Ma, L.; Guo, Y.; Zhao, Z.; Gao, H.; Mei, L. Effects of drought stress on photosynthesis and photosynthetic electron transport chain in young apple tree leaves. Biol. Open 2018, 7, bio035279. [Google Scholar] [CrossRef] [Green Version]
  15. Dalal, M.; Sahu, S.; Tiwari, S.; Rao, A.R.; Gaikwad, K. Transcriptome analysis reveals interplay between hormones, ROS metabolism and cell wall biosynthesis for drought-induced root growth in wheat. Plant Physiol. Biochem. 2018, 130, 482–492. [Google Scholar] [CrossRef] [PubMed]
  16. Din, A.F.; Ibrahim, M.F.; Farag, R.; El-Gawad, H.G.A.; El-Banhawy, A.; Alaraidh, I.A.; Rashad, Y.M.; Lashin, I.; El-Yazied, A.A.; Elkelish, A. Influence of polyethylene glycol on leaf anatomy, stomatal behavior, water loss, and some physiological traits of date palm plantlets grown in vitro and ex vitro. Plants 2020, 9, 1440. [Google Scholar] [CrossRef]
  17. Mahmood, T.; Khalid, S.; Abdullah, M.; Ahmed, Z.; Shah, M.K.N.; Ghafoor, A.; Du, X. Insights into drought stress signaling in plants and the molecular genetic basis of cotton drought tolerance. Cells 2019, 9, 105. [Google Scholar] [CrossRef] [Green Version]
  18. Mundree, S.G.; Baker, B.; Mowla, S.; Peters, S.; Marais, S.; Vander Willigen, C.; Govender, K.; Maredza, A.; Muyanga, S.; Farrant, J.M. Physiological and molecular insights into drought tolerance. Afr. J. Biotechnol. 2002, 1, 28–38. [Google Scholar]
  19. Ibrahim, M.; Ibrahim, H.A.; Abd El-Gawad, H. Folic acid as a protective agent in snap bean plants under water deficit conditions. J. Hortic. Sci. Biotechnol. 2021, 96, 94–109. [Google Scholar] [CrossRef]
  20. Arnao, M.B.; Hernández-Ruiz, J. Melatonin: Plant growth regulator and/or biostimulator during stress? Trends Plant Sci. 2014, 19, 789–797. [Google Scholar] [CrossRef]
  21. Arnao, M.B.; Hernández-Ruiz, J. Melatonin and its relationship to plant hormones. Ann. Bot. 2018, 121, 195–207. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  22. Chen, Q.; Qi, W.-b.; Reiter, R.J.; Wei, W.; Wang, B.-m. Exogenously applied melatonin stimulates root growth and raises endogenous indoleacetic acid in roots of etiolated seedlings of Brassica juncea. J. Plant Physiol. 2009, 166, 324–328. [Google Scholar] [CrossRef] [PubMed]
  23. Jahan, M.S.; Guo, S.; Sun, J.; Shu, S.; Wang, Y.; Abou El-Yazied, A.; Alabdallah, N.M.; Hikal, M.; Mohamed, M.H.; Ibrahim, M.F. Melatonin-mediated photosynthetic performance of tomato seedlings under high-temperature stress. Plant Physiol. Biochem. 2021, 167, 309–320. [Google Scholar] [CrossRef] [PubMed]
  24. Wang, M.; Zhang, S.; Ding, F. Melatonin mitigates chilling-induced oxidative stress and photosynthesis inhibition in tomato plants. Antioxidants 2020, 9, 218. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  25. Xu, L.; Zhang, F.; Tang, M.; Wang, Y.; Dong, J.; Ying, J.; Chen, Y.; Hu, B.; Li, C.; Liu, L. Melatonin confers cadmium tolerance by modulating critical heavy metal chelators and transporters in radish plants. J. Pineal Res. 2020, 69, e12659. [Google Scholar] [CrossRef] [PubMed]
  26. Li, J.; Liu, J.; Zhu, T.; Zhao, C.; Li, L.; Chen, M. The role of melatonin in salt stress responses. Int. J. Mol. Sci. 2019, 20, 1735. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  27. Ibrahim, M.F.; Elbar, O.H.A.; Farag, R.; Hikal, M.; El-Kelish, A.; El-Yazied, A.A.; Alkahtani, J.; El-Gawad, H.G.A. Melatonin counteracts drought induced oxidative damage and stimulates growth, productivity and fruit quality properties of tomato plants. Plants 2020, 9, 1276. [Google Scholar] [CrossRef] [PubMed]
  28. Sharma, A.; Wang, J.; Xu, D.; Tao, S.; Chong, S.; Yan, D.; Li, Z.; Yuan, H.; Zheng, B. Melatonin regulates the functional components of photosynthesis, antioxidant system, gene expression, and metabolic pathways to induce drought resistance in grafted Carya cathayensis plants. Sci. Total Environ. 2020, 713, 136675. [Google Scholar] [CrossRef]
  29. Sharma, A.; Zheng, B. Melatonin mediated regulation of drought stress: Physiological and molecular aspects. Plants 2019, 8, 190. [Google Scholar] [CrossRef] [Green Version]
  30. Li, Z.-G.; Xu, Y.; Bai, L.-K.; Zhang, S.-Y.; Wang, Y. Melatonin enhances thermotolerance of maize seedlings (Zea mays L.) by modulating antioxidant defense, methylglyoxal detoxification, and osmoregulation systems. Protoplasma 2019, 256, 471–490. [Google Scholar] [CrossRef]
  31. Huang, B.; Chen, Y.-E.; Zhao, Y.-Q.; Ding, C.-B.; Liao, J.-Q.; Hu, C.; Zhou, L.-J.; Zhang, Z.-W.; Yuan, S.; Yuan, M. Exogenous melatonin alleviates oxidative damages and protects photosystem II in maize seedlings under drought stress. Front. Plant Sci. 2019, 10, 677. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  32. Hossain, M.; Li, J.; Sikdar, A.; Hasanuzzaman, M.; Uzizerimana, F.; Muhammad, I.; Yuan, Y.; Zhang, C.; Wang, C.; Feng, B. Exogenous melatonin modulates the physiological and biochemical mechanisms of drought tolerance in tartary buckwheat (Fagopyrum tataricum (L.) Gaertn). Molecules 2020, 25, 2828. [Google Scholar] [CrossRef] [PubMed]
  33. Li, H.; Chang, J.; Chen, H.; Wang, Z.; Gu, X.; Wei, C.; Zhang, Y.; Ma, J.; Yang, J.; Zhang, X. Exogenous melatonin confers salt stress tolerance to watermelon by improving photosynthesis and redox homeostasis. Front. Plant Sci. 2017, 8, 295. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  34. Yadav, S.K.; Singla-Pareek, S.L.; Sopory, S.K. An overview on the role of methylglyoxal and glyoxalases in plants. Drug Metab. Drug Interact. 2008, 23, 51–68. [Google Scholar] [CrossRef] [PubMed]
  35. Hossain, M.A.; Hossain, M.Z.; Fujita, M. Stress-induced changes of methylglyoxal level and glyoxalase I activity in pumpkin seedlings and cDNA cloning of glyoxalase I gene. Aust. J. Crop Sci. 2009, 3, 53. [Google Scholar]
  36. Yadav, S.K.; Singla-Pareek, S.L.; Ray, M.; Reddy, M.; Sopory, S. Methylglyoxal levels in plants under salinity stress are dependent on glyoxalase I and glutathione. Biochem. Biophys. Res. Commun. 2005, 337, 61–67. [Google Scholar] [CrossRef]
  37. Siddiqui, M.H.; Alamri, S.; Alsubaie, Q.D.; Ali, H.M. Melatonin and gibberellic acid promote growth and chlorophyll biosynthesis by regulating antioxidant and methylglyoxal detoxification system in tomato seedlings under salinity. J. Plant Growth Regul. 2020, 39, 1488–1502. [Google Scholar] [CrossRef]
  38. Ezekiel, R.; Singh, N.; Sharma, S.; Kaur, A. Beneficial phytochemicals in potato—A review. Food Res. Int. 2013, 50, 487–496. [Google Scholar] [CrossRef]
  39. Ibrahim, H.A.; Ibrahim, M.; Bondok, A. Improving Growth, Yield and Resistance to Viral Diseases of Potato Plants Through Modifying Some Metabolites Using Zinc Sulphate and Jasmonic Acid. J. Hortic. Sci. Ornam. Plants 2016, 8, 161–172. [Google Scholar]
  40. Diaz-Valencia, P.; Melgarejo, L.M.; Arcila, I.; Mosquera-Vásquez, T. Physiological, biochemical and yield-component responses of Solanum tuberosum L. Group Phureja genotypes to a water deficit. Plants 2021, 10, 638. [Google Scholar] [CrossRef]
  41. Boguszewska-Mańkowska, D.; Pieczyński, M.; Wyrzykowska, A.; Kalaji, H.; Sieczko, L.; Szweykowska-Kulińska, Z.; Zagdańska, B. Divergent strategies displayed by potato (Solanum tuberosum L.) cultivars to cope with soil drought. J. Agron. Crop Sci. 2018, 204, 13–30. [Google Scholar] [CrossRef] [Green Version]
  42. Sprenger, H.; Kurowsky, C.; Horn, R.; Erban, A.; Seddig, S.; Rudack, K.; Fischer, A.; Walther, D.; Zuther, E.; Köhl, K. The drought response of potato reference cultivars with contrasting tolerance. Plant Cell Environ. 2016, 39, 2370–2389. [Google Scholar] [CrossRef] [PubMed]
  43. Xu, X.; van Lammeren, A.A.; Vermeer, E.; Vreugdenhil, D. The role of gibberellin, abscisic acid, and sucrose in the regulation of potato tuber formation in vitro. Plant Physiol. 1998, 117, 575–584. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  44. Gong, H.-L.; Chen, Q.-Q. Exogenous sucrose protects potato seedlings against heat stress by enhancing the antioxidant defense system. J. Soil Sci. Plant Nutr. 2021, 21, 1511–1519. [Google Scholar] [CrossRef]
  45. Ibrahim, M.; Ibrahim, H.A. Assessment of selenium role in promoting or inhibiting potato plants under water stress. J. Hortic. Sci. Ornam. Plants 2016, 8, 125–139. [Google Scholar]
  46. Liu, P.; Xu, N.; Liu, R.; Liu, J.; Peng, Y.; Wang, Q. Exogenous proline treatment inhibiting enzymatic browning of fresh-cut potatoes during cold storage. Postharvest Biol. Technol. 2022, 184, 111754. [Google Scholar] [CrossRef]
  47. Ilyas, N.; Gull, R.; Mazhar, R.; Saeed, M.; Kanwal, S.; Shabir, S.; Bibi, F. Influence of salicylic acid and jasmonic acid on wheat under drought stress. Commun. Soil Sci. Plant Anal. 2017, 48, 2715–2723. [Google Scholar] [CrossRef]
  48. Kareem, F.; Rihan, H.; Fuller, M.P. The effect of exogenous applications of salicylic acid on drought tolerance and up-regulation of the drought response regulon of Iraqi wheat. J. Crop Sci. Biotechnol. 2019, 22, 37–45. [Google Scholar] [CrossRef]
  49. Yong, B.; Xie, H.; Li, Z.; Li, Y.-P.; Zhang, Y.; Nie, G.; Zhang, X.-Q.; Ma, X.; Huang, L.-K.; Yan, Y.-H. Exogenous application of GABA improves PEG-induced drought tolerance positively associated with GABA-shunt, polyamines, and proline metabolism in white clover. Front. Physiol. 2017, 8, 1107. [Google Scholar] [CrossRef] [Green Version]
  50. Zhang, N.; Sun, Q.; Zhang, H.; Cao, Y.; Weeda, S.; Ren, S.; Guo, Y.-D. Roles of melatonin in abiotic stress resistance in plants. J. Exp. Bot. 2015, 66, 647–656. [Google Scholar] [CrossRef] [Green Version]
  51. Ahmad, S.; Muhammad, I.; Wang, G.Y.; Zeeshan, M.; Yang, L.; Ali, I.; Zhou, X.B. Ameliorative effect of melatonin improves drought tolerance by regulating growth, photosynthetic traits and leaf ultrastructure of maize seedlings. BMC Plant Biol. 2021, 21, 368. [Google Scholar] [CrossRef] [PubMed]
  52. Martinez, V.; Nieves-Cordones, M.; Lopez-Delacalle, M.; Rodenas, R.; Mestre, T.C.; Garcia-Sanchez, F.; Rubio, F.; Nortes, P.A.; Mittler, R.; Rivero, R.M. Tolerance to stress combination in tomato plants: New insights in the protective role of melatonin. Molecules 2018, 23, 535. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  53. Mir, A.R.; Siddiqui, H.; Alam, P.; Hayat, S. Melatonin modulates photosynthesis, redox status, and elemental composition to promote growth of Brassica juncea—a dose-dependent effect. Protoplasma 2020, 257, 1685–1700. [Google Scholar] [CrossRef] [PubMed]
  54. Ye, J.; Wang, S.; Deng, X.; Yin, L.; Xiong, B.; Wang, X. Melatonin increased maize (Zea mays L.) seedling drought tolerance by alleviating drought-induced photosynthetic inhibition and oxidative damage. Acta Physiol. Plant. 2016, 38, 48. [Google Scholar] [CrossRef]
  55. Han, Q.-H.; Huang, B.; Ding, C.-B.; Zhang, Z.-W.; Chen, Y.-E.; Hu, C.; Zhou, L.-J.; Huang, Y.; Liao, J.-Q.; Yuan, S. Effects of melatonin on anti-oxidative systems and photosystem II in cold-stressed rice seedlings. Front. Plant Sci. 2017, 8, 785. [Google Scholar] [CrossRef]
  56. Imran, M.; Latif Khan, A.; Shahzad, R.; Aaqil Khan, M.; Bilal, S.; Khan, A.; Kang, S.-M.; Lee, I.-J. Exogenous melatonin induces drought stress tolerance by promoting plant growth and antioxidant defence system of soybean plants. AoB Plants 2021, 13, plab026. [Google Scholar] [CrossRef]
  57. Zhao, C.; Guo, H.; Wang, J.; Wang, Y.; Zhang, R. Melatonin Enhances Drought Tolerance by Regulating Leaf Stomatal Behavior, Carbon and Nitrogen Metabolism, and Related Gene Expression in Maize Plants. Front. Plant Sci. 2021, 12, 779382. [Google Scholar] [CrossRef]
  58. Li, H.; Guo, Y.; Cui, Q.; Zhang, Z.; Yan, X.; Ahammed, G.J.; Yang, X.; Yang, J.; Wei, C.; Zhang, X. Alkanes (C29 and C31)-mediated intracuticular wax accumulation contributes to melatonin-and ABA-induced drought tolerance in watermelon. J. Plant Growth Regul. 2020, 39, 1441–1450. [Google Scholar] [CrossRef]
  59. Anjum, S.A.; Ashraf, U.; Tanveer, M.; Khan, I.; Hussain, S.; Shahzad, B.; Zohaib, A.; Abbas, F.; Saleem, M.F.; Ali, I. Drought induced changes in growth, osmolyte accumulation and antioxidant metabolism of three maize hybrids. Front. Plant Sci. 2017, 8, 69. [Google Scholar] [CrossRef]
  60. Farooq, M.; Wahid, A.; Kobayashi, N.; Fujita, D.; Basra, S. Plant drought stress: Effects, mechanisms and management. In Sustainable Agriculture; Springer: Berlin/Heidelberg, Germany, 2009; pp. 153–188. [Google Scholar]
  61. Hoque, T.S.; Hossain, M.A.; Mostofa, M.G.; Burritt, D.J.; Fujita, M.; Tran, L.-S.P. Methylglyoxal: An emerging signaling molecule in plant abiotic stress responses and tolerance. Front. Plant Sci. 2016, 7, 1341. [Google Scholar] [CrossRef] [Green Version]
  62. Ramadan, K.M.; Alharbi, M.M.; Alenzi, A.M.; El-Beltagi, H.S.; Darwish, D.B.E.; Aldaej, M.I.; Shalaby, T.A.; Mansour, A.T.; El-Gabry, Y.A.E.-G.; Ibrahim, M.F. Alpha Lipoic Acid as a Protective Mediator for Regulating the Defensive Responses of Wheat Plants against Sodic Alkaline Stress: Physiological, Biochemical and Molecular Aspects. Plants 2022, 11, 787. [Google Scholar] [CrossRef] [PubMed]
  63. Youssef, M.H.; Raafat, A.; El-Yazied, A.A.; Selim, S.; Azab, E.; Khojah, E.; El Nahhas, N.; Ibrahim, M.F. Exogenous Application of Alpha-Lipoic Acid Mitigates Salt-Induced Oxidative Damage in Sorghum Plants through Regulation Growth, Leaf Pigments, Ionic Homeostasis, Antioxidant Enzymes, and Expression of Salt Stress Responsive Genes. Plants 2021, 10, 2519. [Google Scholar] [CrossRef] [PubMed]
  64. Hu, Z.; Fan, J.; Xie, Y.; Amombo, E.; Liu, A.; Gitau, M.M.; Khaldun, A.; Chen, L.; Fu, J. Comparative photosynthetic and metabolic analyses reveal mechanism of improved cold stress tolerance in bermudagrass by exogenous melatonin. Plant Physiol. Biochem. 2016, 100, 94–104. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  65. Li, Z.; Su, X.; Chen, Y.; Fan, X.; He, L.; Guo, J.; Wang, Y.; Yang, Q. Melatonin improves drought resistance in maize seedlings by enhancing the antioxidant system and regulating abscisic acid metabolism to maintain stomatal opening under PEG-induced drought. J. Plant Biol. 2021, 64, 299–312. [Google Scholar] [CrossRef]
  66. Fu, J.; Wu, Y.; Miao, Y.; Xu, Y.; Zhao, E.; Wang, J.; Sun, H.; Liu, Q.; Xue, Y.; Xu, Y. Improved cold tolerance in Elymus nutans by exogenous application of melatonin may involve ABA-dependent and ABA-independent pathways. Sci. Rep. 2017, 7, 39865. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  67. Vreugdenhil, D.; Struik, P.C. An integrated view of the hormonal regulation of tuber formation in potato (Solanum tuberosum). Physiol. Plant. 1989, 75, 525–531. [Google Scholar] [CrossRef]
  68. Šimko, I. Sucrose application causes hormonal changes associated with potato tuber induction. J. Plant Growth Regul. 1994, 13, 73–77. [Google Scholar] [CrossRef]
  69. Dutt, S.; Manjul, A.S.; Raigond, P.; Singh, B.; Siddappa, S.; Bhardwaj, V.; Kawar, P.G.; Patil, V.U.; Kardile, H.B. Key players associated with tuberization in potato: Potential candidates for genetic engineering. Crit. Rev. Biotechnol. 2017, 37, 942–957. [Google Scholar] [CrossRef]
  70. Hammond, J.P.; White, P.J. Sucrose transport in the phloem: Integrating root responses to phosphorus starvation. J. Exp. Bot. 2008, 59, 93–109. [Google Scholar] [CrossRef]
  71. Lichtenthaler, H.K.; Wellburn, A.R. Determinations of total carotenoids and chlorophylls a and b of leaf extracts in different solvents. Biochem. Soc. Trans. 1983, 11, 591–592. [Google Scholar] [CrossRef] [Green Version]
  72. Hamilton, P.B.; Van Slyke, D.D.; Lemish, S. The gasometric determination of free amino acids in blood filtrates by the ninhydrin-carbon dioxide method. J. Biol. Chem. 1943, 150, 231–250. [Google Scholar] [CrossRef]
  73. Bates, L.S.; Waldren, R.P.; Teare, I.D. Rapid determination of free proline for water-stress studies. Plant Soil 1973, 39, 205–207. [Google Scholar] [CrossRef]
  74. Yemm, E.W.; Willis, A.J. The estimation of carbohydrates in plant extracts by anthrone. Biochem. J. 1954, 57, 508–514. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  75. Miller, G.L. Use of Dinitrosalicylic Acid Reagent for Determination of Reducing Sugar. Anal. Chem. 1959, 31, 426–428. [Google Scholar] [CrossRef]
  76. Abd Elbar, O.H.; Elkelish, A.; Niedbała, G.; Farag, R.; Wojciechowski, T.; Mukherjee, S.; Abou-Hadid, A.F.; El-Hennawy, H.M.; Abou El-Yazied, A.; Abd El-Gawad, H.G. Protective Effect of γ-Aminobutyric Acid Against Chilling Stress During Reproductive Stage in Tomato Plants Through Modulation of Sugar Metabolism, Chloroplast Integrity, and Antioxidative Defense Systems. Front. Plant Sci. 2021, 12, 663750. [Google Scholar] [CrossRef] [PubMed]
  77. Velikova, V.; Yordanov, I.; Edreva, A. Oxidative stress and some antioxidant systems in acid rain-treated bean plants: Protective role of exogenous polyamines. Plant Sci. 2000, 151, 59–66. [Google Scholar] [CrossRef]
  78. Heath, R.L.; Packer, L. Photoperoxidation in isolated chloroplasts: I. Kinetics and stoichiometry of fatty acid peroxidation. Arch. Biochem. Biophys. 1968, 125, 189–198. [Google Scholar] [CrossRef]
  79. Bradford, M.M. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal. Biochem. 1976, 72, 248–254. [Google Scholar] [CrossRef]
  80. Beyer, W.F., Jr.; Fridovich, I. Assaying for superoxide dismutase activity: Some large consequences of minor changes in conditions. Anal. Biochem. 1987, 161, 559–566. [Google Scholar] [CrossRef]
  81. Cakmak, I.; Strbac, D.; Marschner, H. Activities of hydrogen peroxide-scavenging enzymes in germinating wheat seeds. J. Exp. Bot. 1993, 44, 127–132. [Google Scholar] [CrossRef]
  82. Dias, M.A.; Costa, M.M. Effect of low salt concentrations on nitrate reductase and peroxidase of sugar beet leaves. J. Exp. Bot. 1983, 34, 537–543. [Google Scholar] [CrossRef]
  83. Nakano, Y.; Asada, K. Hydrogen peroxide is scavenged by ascorbate-specific peroxidase in spinach chloroplasts. Plant Cell Physiol. 1981, 22, 867–880. [Google Scholar]
  84. Shindy, W.W.; Smith, O.E. Identification of plant hormones from cotton ovules. Plant Physiol. 1975, 55, 550–554. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  85. Nakurte, I.; Keisa, A.; Rostoks, N. Development and Validation of a Reversed-Phase Liquid Chromatography Method for the Simultaneous Determination of Indole-3-Acetic Acid, Indole-3-Pyruvic Acid, and Abscisic Acid in Barley (Hordeum vulgare L.). J. Anal. Methods Chem. 2012, 2012, 103575. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  86. SAS. SAS/STAT User’s Guide: Release 6, 3rd ed.; SAS Inst. Inc.: Cary, NC, USA, 1988. [Google Scholar]
Plants 11 01151 g001 550
Figure 1. Effect of exogenous melatonin (MT; 0, 0.05, 0.1 and 0.2 mM) on shoot fresh weight (A), shoot dry weight (B), Chl a (C), Chl b (D), Chl a + b (E) and carotenoids (F) of potato plants grown under drought stress during the early stage of tuberization. Bars represent standard deviation (SD) of the means (n = 3). Different letters indicate significant differences among the treatments at p ≤ 0.05, according to Duncan’s multiple range test. Chl, chlorophyll.
Figure 1. Effect of exogenous melatonin (MT; 0, 0.05, 0.1 and 0.2 mM) on shoot fresh weight (A), shoot dry weight (B), Chl a (C), Chl b (D), Chl a + b (E) and carotenoids (F) of potato plants grown under drought stress during the early stage of tuberization. Bars represent standard deviation (SD) of the means (n = 3). Different letters indicate significant differences among the treatments at p ≤ 0.05, according to Duncan’s multiple range test. Chl, chlorophyll.
Plants 11 01151 g001
Plants 11 01151 g002 550
Figure 2. Effect of exogenous melatonin (MT; 0, 0.05, 0.1 and 0.2 mM) on leaf relative water content; RWC (A), free amino acids; FAA (B), proline (C), reducing sugars (D), non-reducing sugars (E) and total soluble sugars (F) of potato plants grown under drought stress during the early stage of tuberization. Bars represent standard deviation (SD) of the means (n = 3). Different letters indicate significant differences among the treatments at p ≤ 0.05, according to Duncan’s multiple range test.
Figure 2. Effect of exogenous melatonin (MT; 0, 0.05, 0.1 and 0.2 mM) on leaf relative water content; RWC (A), free amino acids; FAA (B), proline (C), reducing sugars (D), non-reducing sugars (E) and total soluble sugars (F) of potato plants grown under drought stress during the early stage of tuberization. Bars represent standard deviation (SD) of the means (n = 3). Different letters indicate significant differences among the treatments at p ≤ 0.05, according to Duncan’s multiple range test.
Plants 11 01151 g002
Plants 11 01151 g003 550
Figure 3. Effect of exogenous melatonin (MT; 0, 0.05, 0.1 and 0.2 mM) on cell membrane stability index; CMSI (A), methylglycoxal; MG (B), H2O2; (C), malondialdehyde; MDA (D) of potato plants grown under drought stress during the early stage of tuberization. Bars represent standard deviation (SD) of the means (n = 3). Different letters indicate significant differences among the treatments at p ≤ 0.05, according to Duncan’s multiple range test.
Figure 3. Effect of exogenous melatonin (MT; 0, 0.05, 0.1 and 0.2 mM) on cell membrane stability index; CMSI (A), methylglycoxal; MG (B), H2O2; (C), malondialdehyde; MDA (D) of potato plants grown under drought stress during the early stage of tuberization. Bars represent standard deviation (SD) of the means (n = 3). Different letters indicate significant differences among the treatments at p ≤ 0.05, according to Duncan’s multiple range test.
Plants 11 01151 g003
Plants 11 01151 g004 550
Figure 4. Effect of exogenous melatonin (MT; 0, 0.05, 0.1 and 0.2 mM) on superoxide dismutase; SOD (A), catalase; CAT (B), guaiacol peroxidase; G-POX (C), ascorbate peroxidase; APX (D) of potato plants grown under drought stress during the early stage of tuberization. Bars represent standard deviation (SD) of the means (n = 3). Different letters indicate significant differences among the treatments at p ≤ 0.05, according to Duncan’s multiple range test.
Figure 4. Effect of exogenous melatonin (MT; 0, 0.05, 0.1 and 0.2 mM) on superoxide dismutase; SOD (A), catalase; CAT (B), guaiacol peroxidase; G-POX (C), ascorbate peroxidase; APX (D) of potato plants grown under drought stress during the early stage of tuberization. Bars represent standard deviation (SD) of the means (n = 3). Different letters indicate significant differences among the treatments at p ≤ 0.05, according to Duncan’s multiple range test.
Plants 11 01151 g004
Plants 11 01151 g005 550
Figure 5. Effect of exogenous melatonin (MT; 0, 0.05, 0.1 and 0.2 mM) on abscisic acid; ABA (A), the relationship between ABA concentration and leaf relative water content; RWC (B) of potato plants grown under drought stress during the early stage of tuberization. Bars represent standard deviation (SD) of the means (n = 3). Different letters indicate significant differences among the treatments at p ≤ 0.05, according to Duncan’s multiple range test. ** (p ≤ 0.01).
Figure 5. Effect of exogenous melatonin (MT; 0, 0.05, 0.1 and 0.2 mM) on abscisic acid; ABA (A), the relationship between ABA concentration and leaf relative water content; RWC (B) of potato plants grown under drought stress during the early stage of tuberization. Bars represent standard deviation (SD) of the means (n = 3). Different letters indicate significant differences among the treatments at p ≤ 0.05, according to Duncan’s multiple range test. ** (p ≤ 0.01).
Plants 11 01151 g005
Plants 11 01151 g006 550
Figure 6. Effect of exogenous melatonin (MT; 0, 0.05, 0.1 and 0.2 mM) on tuber yield of potato plants grown under drought stress during the early stage of tuberization. Bars represent standard deviation (SD) of the means (n = 3). Different letters indicate significant differences among the treatments at p ≤ 0.05, according to Duncan’s multiple range test.
Figure 6. Effect of exogenous melatonin (MT; 0, 0.05, 0.1 and 0.2 mM) on tuber yield of potato plants grown under drought stress during the early stage of tuberization. Bars represent standard deviation (SD) of the means (n = 3). Different letters indicate significant differences among the treatments at p ≤ 0.05, according to Duncan’s multiple range test.
Plants 11 01151 g006
Plants 11 01151 g007 550
Figure 7. The timeline infographic for the treatments of melatonin as a foliar application and sampling of potato plants subjected to the well watered conditions and progressive drought stress during the tuberization stage.
Figure 7. The timeline infographic for the treatments of melatonin as a foliar application and sampling of potato plants subjected to the well watered conditions and progressive drought stress during the tuberization stage.
Plants 11 01151 g007
Plants 11 01151 g008 550
Figure 8. Simplified model for the suggested effect of exogenous melatonin as foliar spray on potato plants grown under drought stress during the early stage of tuberization. In drying soil, ABA that is synthesized in roots can be carried by xylem stream to the shoot system leading to stomata closing and reducing the rate of transpiration. Moreover, soluble sugars tends to accumulate in shoots as reducing sugars (not suitable form to sugar transport) leading to decrease the rate of tuberization. Conversely, melatonin treatments led to decrease ABA in shoots as resulting to enhancement of leaf water status and antioxidant capacity. This effect may also be explained by restriction of ABA transport from root to the shoot system. Furthermore, MT-treated plants tended to accumulate the non-reducing sugars (the most suitable form to sugar transport and starch synthesis) leading to improve the tuberization. ETC, electron transport chain in chloroplast and mitochondria; ABA, abscisic acid; MG, methylglyoxal; ROS, reactive oxygen species.
Figure 8. Simplified model for the suggested effect of exogenous melatonin as foliar spray on potato plants grown under drought stress during the early stage of tuberization. In drying soil, ABA that is synthesized in roots can be carried by xylem stream to the shoot system leading to stomata closing and reducing the rate of transpiration. Moreover, soluble sugars tends to accumulate in shoots as reducing sugars (not suitable form to sugar transport) leading to decrease the rate of tuberization. Conversely, melatonin treatments led to decrease ABA in shoots as resulting to enhancement of leaf water status and antioxidant capacity. This effect may also be explained by restriction of ABA transport from root to the shoot system. Furthermore, MT-treated plants tended to accumulate the non-reducing sugars (the most suitable form to sugar transport and starch synthesis) leading to improve the tuberization. ETC, electron transport chain in chloroplast and mitochondria; ABA, abscisic acid; MG, methylglyoxal; ROS, reactive oxygen species.
Plants 11 01151 g008
Table
Table 1. Summary of the monthly mean climate condition, maximum (Tmax) and minimum (Tmin), mean (Tave) temperatures and relative humidity (RH), inside the greenhouse.
Table 1. Summary of the monthly mean climate condition, maximum (Tmax) and minimum (Tmin), mean (Tave) temperatures and relative humidity (RH), inside the greenhouse.
MonthTmaxTminTaveRH (%)
January23.911.417.662.6
Febrauary26.213.119.665.2
March27.413.920.665.7
April33.715.624.660.2
May38.524.231.458.6
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

El-Yazied, A.A.; Ibrahim, M.F.M.; Ibrahim, M.A.R.; Nasef, I.N.; Al-Qahtani, S.M.; Al-Harbi, N.A.; Alzuaibr, F.M.; Alaklabi, A.; Dessoky, E.S.; Alabdallah, N.M.; et al. Melatonin Mitigates Drought Induced Oxidative Stress in Potato Plants through Modulation of Osmolytes, Sugar Metabolism, ABA Homeostasis and Antioxidant Enzymes. Plants 2022, 11, 1151. https://doi.org/10.3390/plants11091151

AMA Style

El-Yazied AA, Ibrahim MFM, Ibrahim MAR, Nasef IN, Al-Qahtani SM, Al-Harbi NA, Alzuaibr FM, Alaklabi A, Dessoky ES, Alabdallah NM, et al. Melatonin Mitigates Drought Induced Oxidative Stress in Potato Plants through Modulation of Osmolytes, Sugar Metabolism, ABA Homeostasis and Antioxidant Enzymes. Plants. 2022; 11(9):1151. https://doi.org/10.3390/plants11091151

Chicago/Turabian Style

El-Yazied, Ahmed Abou, Mohamed F. M. Ibrahim, Mervat A. R. Ibrahim, Ibrahim N. Nasef, Salem Mesfir Al-Qahtani, Nadi Awad Al-Harbi, Fahad Mohammed Alzuaibr, Abdullah Alaklabi, Eldessoky S. Dessoky, Nadiyah M. Alabdallah, and et al. 2022. "Melatonin Mitigates Drought Induced Oxidative Stress in Potato Plants through Modulation of Osmolytes, Sugar Metabolism, ABA Homeostasis and Antioxidant Enzymes" Plants 11, no. 9: 1151. https://doi.org/10.3390/plants11091151

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop