Title: Potassium application regulates nitrogen metabolism and osmotic adjustment in cotton (Gossypium hirsutum L.) functional leaf under drought stress

Root Reduction Caused Directly or Indirectly by High Application of Nitrogen Fertilizer Was the Main Cause of the Decline in Biomass and Nitrogen Accumulation in Citrus Seedlings

Citrus is the largest fruit crop around the world, while high nitrogen (N) application in citrus orchards is widespread in many countries, which results not only in yield, quality and environmental issues but also slows down the establishment of citrus canopies in newly cultivated orchards. Thus, the objective of this study was to investigate the physiological inhibitory mechanism of excessive N application on the growth of citrus seedlings. A pot experiment with the citrus variety Orah (Orah/Citrus junos) at four N fertilization rates (0, 50, 100, and 400 mg N/kg dry soil, denoted as N0, N50, N100, and N400, respectively) was performed to evaluate the changes of root morphology, biomass, N accumulation, enzyme activities, and so on. The results showed that the N400 application significantly reduced the total biomass (from 14.24 to 6.95 g/Plant), N accumulation (from 0.65 to 0.33 g/Plant) and N use efficiency (92.69%) in citrus seedlings when compared to the N100 treatment. The partial least squares pathway model further showed that the decline of biomass and N accumulation by high N application were largely attributed to the reduction of root growth through direct and indirect effects (the goodness of fit under the model was 0.733.) rather than just soil N transformation and activity of root N uptake. These results are useful to optimize N management through a synergistic N absorption and utilization by citrus seedlings.

Elevated tolerance of both short-term and continuous drought stress during reproductive stages by exogenous application of hydrogen peroxide on soybean

The global production of soybean, among other drought-susceptible crops, is reportedly affected by drought periods, putting more pressure on food production worldwide. Drought alters plants' morphology, physiology and biochemistry. As a response to drought, reactive oxygen species (ROS) concentrations are elevated, causing cellular damage. However, lower concentrations of ROS were reported to have an alleviating role through up-regulating various defensive mechanisms on different levels in drought-stressed plants. This experiment was set up in a controlled environment to monitor the effects of exogenous spray of different (0, 1, 5 and 10 mM) concentrations of H2O2 on two soybean genotypes, i.e., Speeda (drought-tolerant), and Coraline (drought-susceptible) under severe drought stress conditions (induced by polyethylene glycol) during flowering stage. Furthermore, each treatment was further divided into two groups, the first group was kept under drought, whereas drought was terminated in the second group at the end of the flowering stage, and the plants were allowed to recover. After 3 days of application, drought stress significantly decreased chlorophyll-a and chlorophyll-b, total carotenoids, stomatal conductance, both optimal and actual photochemical efficiency of PSII (Fv/Fm and Df/Fm, respectively), relative water content, specific leaf area, shoot length and dry weight, and pod number and fresh weight, but significantly increased the leaf concentration of both proline and total soluble sugars, the root length, volume and dry weight of both genotypes. The foliar application of 1 mM and 5 mM H2O2 on Speeda and Coraline, respectively enhanced most of the decreased traits measurably, whereas the 10 mM concentration did not. The group of treatments where drought was maintained after flowering failed to produce pods, regardless of H2O2 application and concentration, and gradually deteriorated and died 16 and 19 days after drought application on Coraline and Speeda, respectively. Overall, Speeda showed better performance under drought conditions. Low concentrations of foliar H2O2 could help the experimented soybean genotypes better overcome the influence of severe drought during even sensitive stages, such as flowering. Furthermore, our findings suggest that chlorophyll fluorescence and the cellular content of proline and soluble sugars in the leaves can provide clear information on the influence of both drought imposition and H2O2 application on soybean plants.

Melatonin improves drought stress tolerance of pepper (Capsicum annuum) plants via upregulating nitrogen metabolism

While ameliorating effects of melatonin (MT) on abiotic stress tolerance in plants are widely reported, the mechanism that underlies this process remains elusive. This work investigated mechanisms by which MT improved drought tolerance in pepper (Capsicum annuum ) plants. A foliar spray of 0.1mM MT treatment was applied to plants grown at 80% and 40% of full field capacity for 3days. Drought stress caused a significant decrease in plant dry weight, relative water content, leaf water potential, PSII efficiency (F v /F m ratio), chlorophyll, soluble protein, leaf and root nitrogen content. Drought increased hydrogen peroxide, malondialdehyde (MDA), nitrate, ammonium, free amino acids, soluble sugars, proline and glycine betaine. Drought also increased peroxidase (POD), glutathione S-transferase (GST) and catalase (CAT) activities, electrolyte leakage (EL) and methylglyoxal (MG). MT pre-treatment reduced oxidative stress and improved nitrogen metabolism by activating various enzymes such as nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthetase (GOGAT) and glutamine dehydrogenase (GDH) activities. It also activated enzymes related to the glyoxalase system (Gly I and Gly II) and decreased NO3 - , NH4 + and free amino acid content. Our study suggests a cost-effective and sustainable solution to improve crop productivity in water-limited conditions, by enhancing plant growth, photosynthesis and nitrogen content.

Improving seed germination and physiological characteristics of maize seedlings under osmotic stress through potassium nano-silicate treatment

Introduction

Osmotic stress can significantly affect the survival and functioning of living organisms, particularly during vulnerable stages such as seed germination and seedling growth. To address this issue, advanced technologies like nanofertilizers have been developed to improve soil conditions and enhance plant growth in stressed ecosystems due to their multiple effects and efficient consumption.

Methods

The objective of this study was to investigate the impact of potassium nano-silicate (PNS) on the physiological characteristics of maize seedlings and seed germination under various levels of osmotic stress induced by polyethylene glycol (PEG). The study considered two factors: two levels of PNS concentration (500 and 1000 ppm) and PEG-6000 solution with different osmotic stress levels (-2, -4, -6, and -8 bars).

Results and discussion

The results demonstrated that the application of PNS at a concentration of 1000 ppm led to increased radicle length and hypocotyl length as well as fresh weight of maize seedlings. Furthermore, PNS at a concentration of 1000 ppm had a more beneficial effect on the germination rate of maize seedlings under osmotic stress compared to 500 ppm. Additionally, the application of PNS under osmotic stress conditions resulted in an increase in various physiological parameters, including protein content, chlorophyll a, chlorophyll b, total chlorophyll content, proline content, and the activity of catalase (CAT) and ascorbate peroxidase (AXPO) enzymes. These findings indicate that the use of PNS can have a positive impact on the physiological characteristics of maize seedlings and seed germination under osmotic stress conditions. Overall, this technology has the potential to enhance crop growth and yield in stressed ecosystems. By improving the survival and function of plants during vulnerable stages, such as seed germination and seedling growth, the application of PNS can contribute to more resilient agricultural practices and promote sustainable food production in challenging environments.

AnWRKY29 from the desert xerophytic evergreen Ammopiptanthus nanus improves drought tolerance through osmoregulation in transgenic plants

As a significant transcription factor family in plants, WRKYs have a crucial role in responding to different adverse environments. They have been repeatedly demonstrated to contribute to drought resistance. However, no systematic exploration of the WRKY family has been reported in the evergreen shrub Ammopiptanthus nanus under drought conditions. Here, we showed that AnWRKY29 expression is strongly induced under drought stress. AnWRKY29 belongs to the group IIe of WRKY gene family. To characterize the function of AnWRKY29, we generated transgenic plants overexpressing this gene in Arabidopsis thaliana. We determined that AnWRKY29 overexpression of mainly improves the drought resistance of transgenic plants to water stress by reducing water loss, preventing electrolyte leakage, and increasing the absorption of inorganic ions. In addition, the AnWRKY29 transgenic plants synthesized more trehalose under water stress. The overexpression of AnWRKY29 also enhanced the antioxidant and osmoregulation capacity of transgenic plants by increasing the activities of catalase, peroxidase and superoxide dismutase, thus increasing the scavenging of reactive oxygen species and propylene glycol synthesis aldehyde oxidase. In summary, our study shows that AnWRKY29 plays an important role in the drought tolerance pathway in plants.

Genetic regulation of nitrogen use efficiency in Gossypium spp

Cotton (Gossypium spp.) is the most important fibre crop, with desirable characteristics preferred for textile production. Cotton fibre output relies heavily on nitrate as the most important source of inorganic nitrogen (N). However, nitrogen dynamics in extreme environments limit plant growth and lead to yield loss and pollution. Therefore, nitrogen use efficiency (NUE), which involves the utilisation of the 'right rate', 'right source', 'right time', and 'right place' (4Rs), is key for efficient N management. Recent omics techniques have genetically improved NUE in crops. We herein highlight the mechanisms of N uptake and assimilation in the vegetative and reproductive branches of the cotton plant while considering the known and unknown regulatory factors. The phylogenetic relationships among N transporters in four Gossypium spp. have been reviewed. Further, the N regulatory genes that participate in xylem transport and phloem loading are also discussed. In addition, the functions of microRNAs and transcription factors in modulating the expression of target N regulatory genes are highlighted. Overall, this review provides a detailed perspective on the complex N regulatory mechanism in cotton, which would accelerate the research toward improving NUE in crops.

Potassium fertilizer improves drought stress alleviation potential in sesame by enhancing photosynthesis and hormonal regulation

Soil-potassium (K) low availability and drought stress are limiting factors to crop productivity in arid and semiarid regions. A pot experiment with four K soil supplies (0, 60, 120 and 180 K₂O kg ha^-1) and exposed to drought stress with 50 ± 5% field capacity was performed to investigate the function of K in protecting sesame plants from the adverse effects of drought based on the related physio-biochemical traits. The water stress was applied during flowering by withholding water for 6 days, and then rewatering to a well-watered level (75 ± 5% field capacity). Results showed that drought stress substantially reduced leaf relative water content (RWC), stomatal conductance (G_s), transpiration rate (T_r), photosynthetic rate (P_n), maximum PSII yield (F_v/F_m), and actual quantum yield of PSII (Ф_PSII), leading to greater non-photochemical quenching (qN) and stomatal limitation (L_s), thereby resulting in a decreased yield in contrast with well-watered sesame plants. Incidentally, K was more effective in promoting yield production under drought stress relative to well-watered conditions, and the optimal K application was 120 kg ha^-1, which primarily attributed to the enhanced photosynthetic and plant water retaining ability. Specifically, plants receiving K supply showed greater leaf gas exchange traits, higher F_v/F_m and Ф_PSII values, and superior water use efficiency as compared to K-deficiency plants in both water regimes. Moreover, K can ameliorate the adverse effects of drought by improving salicylic acid (SA) while conversely decreasing abscisic acid (ABA) and jasmonic acid (JA) concentrations that are involved in controlling stomatal closure. It is noted that significant correlations between the seed yield, gas exchange parameters, and aforementioned endogenous hormones were observed. In conclusion, the K application can improve the sesame plant's potential to maintain functionality regarding photosynthetic response and phytohormone regulation under drought stress, and ultimately, enhancing the sesame's productivity.

Potassium deficiency causes more nitrate nitrogen to be stored in leaves for low-K sensitive sweet potato genotypes

In order to explore the effect of potassium (K) deficiency on nitrogen (N) metabolism in sweet potato (Ipomoea batatas L.), a hydroponic experiment was conducted with two genotypes (Xushu 32, low-K-tolerant; Ningzishu 1, low-K-sensitive) under two K treatments (-K, <0.03 mM of K⁺; +K, 5 mM of K⁺) in the greenhouse of Jiangsu Normal University. The results showed that K deficiency decreased root, stem, and leaf biomass by 13%-58% and reduced whole plant biomass by 24%-35%. Compared to +K, the amount of K and K accumulation in sweet potato leaves and roots was significantly decreased by increasing root K⁺ efflux in K-deficiency-treated plants. In addition, leaf K, N, ammonium nitrogen (NH₄ ⁺-N), or nitrate nitrogen (NO₃ ^--N) in leaves and roots significantly reduced under K deficiency, and leaf K content had a significant quadratic relationship with soluble protein, NO₃ ^--N, or NH₄ ⁺-N in leaves and roots. Under K deficiency, higher glutamate synthase (GOGAT) activity did not increase amino acid synthesis in roots; however, the range of variation in leaves was larger than that in roots with increased amino acid in roots, indicating that the transformation of amino acids into proteins in roots and the amino acid export from roots to leaves were not inhibited. K deficiency decreased the activity of nitrate reductase (NR) and nitrite reductase (NiR), even if the transcription level of NR and NiR increased, decreased, or remained unchanged. The NO₃ ^-/NH₄ ⁺ ratio in leaves and roots under K deficiency decreased, except in Ningzishu 1 leaves. These results indicated that for Ningzishu 1, more NO₃ ^- was stored under K deficiency in leaves, and the NR and NiR determined the response to K deficiency in leaves. Therefore, the resistance of NR and NiR activities to K deficiency may be a dominant factor that ameliorates the growth between Xushu 32 and Ningzishu 1 with different low-K sensitivities.

Phosphorous Supplementation Alleviates Drought-Induced Physio-Biochemical Damages in Calligonum mongolicum

Calligonum mongolicum is a phreatophyte playing an important role in sand dune fixation, but little is known about its responses to drought and P fertilization. In the present study, we performed a pot experiment to investigate the effects of P fertilization under drought or well-watered conditions on multiple morpho-physio-biochemical attributes of C. mongolicum seedlings. Drought stress leads to a higher production of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), leading to impaired growth and metabolism. However, C. mongolicum exhibited effective drought tolerance strategies, including a higher accumulation of soluble sugars, starch, soluble protein, proline, and significantly higheractivities of peroxidase (POD) and catalase (CAT) enzymes. P fertilization increased the productivity of drought-stressed seedlings by increasing their growth, assimilative shoots relative water content, photosynthetic pigments, osmolytes accumulation, mineral nutrition, N assimilation, and reduced lipid peroxidation. Our findings suggest the presence of soil high P depletion and C. mongolicum high P requirements during the initial growth stage. Thus, P can be utilized as a fertilizer to enhance the growth and productivity of Calligonum vegetation and to reduce the fragility of the hyper-arid desert of Taklamakan in the context of future climate change.

Molecular mechanism of Cu metal and drought stress resistance triggered by Porostereum spadiceum AGH786 in Solanum lycopersicum L

Rapid industrialization and global warming have threatened the plants with multiple abiotic stresses, such as heavy metals and drought stress. For crop cultivation, the conventional approach of cleaning the soils by excavation is very costly and not feasible for large scale. Establishing toxin-free and drought-resistant crops is a major challenge in the environment under natural and anthropogenic pressure. In the past decades, copper contamination of agricultural land has become an emerging concern. For dry land reclamation, several new strategies, including bioremediation (phytoremediation and microbial remediation), have been used. Owing to the potential of Cu hyperaccumulators, the current project aims to enhance the drought tolerance and the phytoremediation potential of Solanum lycopersicum L. with the inoculation of copper and 12% polyethylene glycol (PEG)-induced drought stress-tolerant endophytic fungus Porostereum spadiceum AGH786 under the combined stress of copper heavy metal and PEG-induced drought stress. When S. lycopersicum L. was watered with individual stress of copper (Cu) concentration (400 ppm) in the form of copper sulfate (CuSO₄.5H₂O), 12% PEG-induced drought stress and the combined stress of both negatively affected the growth attributes, hormonal, metabolic, and antioxidant potential, compared with control. However, the multistress-resistant AGH786 endophytic fungus ameliorated the multistress tolerance response in S. lycopersicum L. by positively affecting the growth attributes, hormonal, metabolic, and antioxidant potential, and by restricting the root-to-shoot translocation of Cu and inducing its sequestration in the root tissues of affected plants. AGH786-associated plants exhibited a reduction in the severity of copper (Cu) and drought stress, with higher levels of SlCOPT (Cu transporters) and SlMT (metallothionine) gene expressions in root and shoot tissues, indicating that AGH786 contributed to resistance to copper metal toxicity and drought stress in the host S. lycopersicum L.

Potassium in plant physiological adaptation to abiotic stresses

Potassium (K) is an integral part of plant nutrition, playing essential roles in plant growth and development. Despite its abundance in soils, the limitedly available form of K ion (K⁺) for plant uptake is a critical factor for agricultural production. Plants have evolved complex transport systems to maintain appropriate K⁺ levels in tissues under changing environmental conditions. Adequate stimulation and coordinated actions of multiple K⁺-channels and K⁺-transporters are required for nutrient homeostasis, reproductive growth, cellular signaling and stress adaptation responses in plants. Various contemporary studies revealed that K⁺-homeostasis plays a substantial role in plant responses and tolerance to abiotic stresses. The beneficial effects of K⁺ in plant responses to abiotic stresses include its roles in physiological and biochemical mechanisms involved in photosynthesis, osmoprotection, stomatal regulation, water-nutrient absorption, nutrient translocation and enzyme activation. Over the last decade, we have seen considerable breakthroughs in K research, owing to the advances in omics technologies. In this aspect, omics investigations (e.g., transcriptomics, metabolomics, and proteomics) in systems biology manner have broadened our understanding of how K⁺ signals are perceived, conveyed, and integrated for improving plant physiological resilience to abiotic stresses. Here, we update on how K⁺-uptake and K⁺-distribution are regulated under various types of abiotic stress. We discuss the effects of K⁺ on several physiological functions and the interaction of K⁺ with other nutrients to improve plant potential against abiotic stress-induced adverse consequences. Understanding of how K⁺ orchestrates physiological mechanisms and contributes to abiotic stress tolerance in plants is essential for practicing sustainable agriculture amidst the climate crisis in global agriculture.

Biochar-based molybdenum slow-release fertilizer enhances nitrogen assimilation in Chinese flowering cabbage (Brassica parachinensis)

Low molybdenum (Mo) bioavailability in acidic soil obstructs vegetable nitrogen assimilation and thus increases the health risk of vegetable ingestion due to nitrate accumulation. Constantly providing available Mo in acidic soil is a challenge for decreasing nitrate accumulation in vegetables. In this study, three Mo application methods, including biochar-based Mo slow-release fertilizer (Mo-biochar), seed dressing, and basal application, were investigated to enhance Mo bioavailability in acidic soil and nitrogen assimilation in Chinese flowering cabbage (Brassica parachinensis). The results showed that Mo-biochar constantly and sufficiently supplied Mo nutrients throughout the growing period of Brassica parachinensis, as evidenced by the soil available Mo, plant Mo uptake, and Mo values. The improved Mo supply was attributed to the alleviation of acidic soil (pH from 5.10 to 6.99) and the slow release of Mo adsorbed on biochar. Mo-biochar increased the nitrate reductase (NR) activity by 238.6% and glutamate dehydrogenase activity by 27.5%, indicating an enhancement of the rate-limiting steps of nitrogen assimilation, especially for nitrate reduction and amino acid synthesis. The increase in Mo-containing NR could be directly ascribed to the high level of Mo in Brassica parachinensis. Compared with the control, the nitrate content of Brassica parachinensis decreased by 42.9% due to the nitrate reduction induced by increased NR. Additionally, Mo-biochar was beneficial to vegetable growth and quality. In contrast, the transformation from NO₃^- to NH₄⁺ was blocked with Mo seed dressing and basal application because of low Mo bioavailability in the soil, resulting in a high nitrate content in Brassica parachinensis. Conclusively, Mo-biochar can slowly release Mo and improve the neutral environment for Mo bioavailability, which is an effective strategy to mitigate the high nitrate accumulation of vegetables planted in acidic soil.

Improving Drought Stress Tolerance in Ramie (Boehmeria nivea L.) Using Molecular Techniques

Ramie is one of the most significant fiber crops and contributes to good quality fiber. Drought stress (DS) is one of the most devastating abiotic factors which is accountable for a substantial loss in crop growth and production and disturbing sustainable crop production. DS impairs growth, plant water relation, and nutrient uptake. Ramie has evolved a series of defense responses to cope with DS. There are numerous genes regulating the drought tolerance (DT) mechanism in ramie. The morphological and physiological mechanism of DT is well-studied; however, modified methods would be more effective. The use of novel genome editing tools like clustered regularly interspaced short palindromic repeats (CRISPR) is being used to edit the recessive genes in crops to modify their function. The transgenic approaches are used to develop several drought-tolerant varieties in ramie, and further identification of tolerant genes is needed for an effective breeding plan. Quantitative trait loci (QTLs) mapping, transcription factors (TFs) and speed breeding are highly studied techniques, and these would lead to the development of drought-resilient ramie cultivars. The use of hormones in enhancing crop growth and development under water scarcity circumstances is critical; however, using different concentrations and testing genotypes in changing environments would be helpful to sort the tolerant genotypes. Since plants use various ways to counter DS, investigating mechanisms of DT in plants will lead to improved DT in ramie. This critical review summarized the recent advancements on DT in ramie using novel molecular techniques. This information would help ramie breeders to conduct research studies and develop drought tolerant ramie cultivars.

Nitrogen and potassium application effects on productivity, profitability and nutrient use efficiency of irrigated wheat (Triticum aestivum L.)

The development of robust nutrient management strategies have played a crucial role in improving crop productivity, profitability and nutrient use efficiency. Therefore, the implementation of efficient nutrient management stratigies is important for food security and environmental safety. Amongst the essential plant nutrients, managing nitrogen (N) and potassium (K) in wheat (Triticum aestivum L.) based production systems is citically important to maximize profitable production with minimal negative environmental impacts. We investigated the effects of different fertilizer-N (viz. 0–240 kg N ha^-1; N₀-N₂₄₀) and fertilizer-K (viz. 0–90 kg K ha^-1; K₀-K₉₀) application rates on wheat productivity, nutrient (N and K) use efficiency viz. partial factor productivity (PFP_N/K), agronomic efficiency (AE_N/K), physiological efficiency (PE_N/K), reciprocal internal use efficiency (RIUE_N/K), and profitability in terms of benefit-cost (B-C) ratio, gross returns above fertilizer cost (GRAFC) and the returns on investment (ROI) on fertilizer application. These results revealed that wheat productivity, plant growth and yield attributes, nutrients uptake and use efficiency increased significantly (p<0.05)with fertilizer-N application, although the interaction effect of N x K application was statistically non-significant (p<0.05). Fertilizer-N application at 120 kg N ha^-1 (N₁₂₀) increased the number of effective tillers (8.7%), grain yield (17.3%), straw yield (15.1%), total N uptake (25.1%) and total K uptake (16.1%) than the N₈₀. Fertilizer-N application significantly increased the SPAD reading by ~4.2–10.6% with fertilizer-N application (N₈₀-N₂₄₀), compared with N₀. The PFP_N and PFP_K increased significantly with fertilizer-N and K application in wheat. The AE_N varied between 12.3 and 22.2 kg kg^-1 with significantly higher value of 20.8 kg kg^-1 in N₁₂₀. Fertilizer-N application at higher rate (N₁₆₀) significantly decreased the AE_N by ~16.3% over N₁₂₀. The N₁₂₀treatment increased the AE_K by ~52.6% than N₈₀ treatment. Similarly the RIUE_N varied between 10.6 and 25.6 kg Mg^-1 grain yield, and increased significantly by ~80.2% with N₁₂₀ as compared to N₀ treatment. The RIUE_K varied between 109 and 15.1 kg Mg^-1 grain yield, and was significantly higher in N₁₂₀ treatment. The significant increase in mean gross returns (MGRs) by ~17.3% and mean net returns (MNRs) by ~24.1% increased the B-C ratio by ~15.1% with N₁₂₀ than the N₈₀ treatment. Fertilizer-N application in N₁₂₀ treatment increased the economic efficiency of wheat by ~24.1% and GRAFC by ~16.9%. Grain yield was significantly correlated with total N uptake (r = 0.932**, p<0.01), K uptake (r = 0.851**), SPAD value (r = 0.945**), green seeker reading (r = 0.956**), and the RIUE_N (r = 0.910**). The artificial neural networks (ANNs) showed highly satisfactory performance in training and simulation of testing data-set on wheat grain yield. The calculated mean absolute error (MAE), mean absolute percentage error (MAPE) and root mean square error (RMSE) for wheat were 0.0087, 0.834 and 0.052, respectively. The well trained ANNs model was capable of producing consistency for the training and testing correlation (R² = 0.994**, p<0.01) between the predicted and actual values of wheat grain yield, which implies that ANN model succeeded in wheat grain yield prediction.

Ethanol Positively Modulates Photosynthetic Traits, Antioxidant Defense and Osmoprotectant Levels to Enhance Drought Acclimatization in Soybean

Drought is a major environmental threat to agricultural productivity and food security across the world. Therefore, addressing the detrimental effects of drought on vital crops like soybean has a significant impact on sustainable food production. Priming plants with organic compounds is now being considered as a promising technique for alleviating the negative effects of drought on plants. In the current study, we evaluated the protective functions of ethanol in enhancing soybean drought tolerance by examining the phenotype, growth attributes, and several physiological and biochemical mechanisms. Our results showed that foliar application of ethanol (20 mM) to drought-stressed soybean plants increased biomass, leaf area per trifoliate, gas exchange features, water-use-efficiency, photosynthetic pigment contents, and leaf relative water content, all of which contributed to the improved growth performance of soybean under drought circumstances. Drought stress, on the other hand, caused significant accumulation of reactive oxygen species (ROS), such as superoxide and hydrogen peroxide, and malondialdehyde, as well as an increase of electrolyte leakage in the leaves, underpinning the evidence of oxidative stress and membrane damage in soybean plants. By comparison, exogenous ethanol reduced the ROS-induced oxidative burden by boosting the activities of antioxidant enzymes, including peroxidase, catalase, glutathione S-transferase, and ascorbate peroxidase, and the content of total flavonoids in soybean leaves exposed to drought stress. Additionally, ethanol supplementation increased the contents of total soluble sugars and free amino acids in the leaves of drought-exposed plants, implying that ethanol likely employed these compounds for osmotic adjustment in soybean under water-shortage conditions. Together, our findings shed light on the ethanol-mediated protective mechanisms by which soybean plants coordinated different morphophysiological and biochemical responses in order to increase their drought tolerance.

Polyamines Metabolism Interacts with γ-Aminobutyric Acid, Proline and Nitrogen Metabolisms to Affect Drought Tolerance of Creeping Bentgrass

Due to increased global warming and climate change, drought has become a serious threat to horticultural crop cultivation and management. The purpose of this study was to investigate the effect of spermine (Spm) pretreatment on metabolic alterations of polyamine (PAs), γ-aminobutyric acid (GABA), proline (Pro), and nitrogen associated with drought tolerance in creeping bentgrass (Agrostis stolonifera). The results showed that drought tolerance of creeping bentgrass could be significantly improved by the Spm pretreatment, as demonstrated by the maintenance of less chlorophyll loss and higher photosynthesis, gas exchange, water use efficiency, and cell membrane stability. The Spm pretreatment further increased drought-induced accumulation of endogenous PAs, putrescine, spermidine, and Spm, and also enhanced PAs metabolism through improving arginine decarboxylases, ornithine decarboxylase, S-adenosylmethionine decarboxylase, and polyamine oxidase activities during drought stress. In addition, the Spm application not only significantly improved endogenous GABA content, glutamate content, activities of glutamate decarboxylase and α-ketoglutarase, but also alleviated decline in nitrite nitrogen content, nitrate reductase, glutamine synthetase, glutamate synthetase, and GABA aminotransferase activities under drought stress. The Spm-pretreated creeping bentgrass exhibited significantly lower ammonia nitrogen content and nitrite reductase activity as well as higher glutamate dehydrogenase activity than non-pretreated plants in response to drought stress. These results indicated beneficial roles of the Spm on regulating GABA and nitrogen metabolism contributing towards better maintenance of Tricarboxylic acid (TCA) cycle in creeping bentgrass. Interestingly, the Spm-enhanced Pro metabolism rather than more Pro accumulation could be the key regulatory mechanism for drought tolerance in creeping bentgrass. Current findings provide a comprehensive understanding of PAs interaction with other metabolic pathways to regulate drought tolerance in grass species.

Potassium application enhances drought tolerance in sesame by mitigating oxidative damage and regulating osmotic adjustment

Potassium (K) is known for alleviating the negative effects of abiotic stresses on plants. To explore the functions of K in controlling reactive oxygen species (ROS), antioxidant activities, and osmoregulation in sesame under drought stress, a pot experiment was conducted with three K levels (0, 60, and 120 kg ha^-1, recorded as K0, K1, and K2, respectively) and exposed to well-watered (WW, 75% ± 5% soil relative water content) and drought-stressed (DS, 50% ± 5% soil relative water content) conditions. The results showed that DS stimulated the production of ROS such as increased hydrogen peroxide (H₂O₂), leading to lipid peroxidation as characterized by higher malondialdehyde (MDA) and, consequently, resulting in the decline in relative water content (RWC) and photosynthetic pigments as compared with WW plants. These adverse effects were exacerbated when drought stress was prolonged. Concurrently, K application alleviated the magnitude of decline in the RWC, chlorophyll a, and chlorophyll b, and plants applied with K exhibited superior growth, with the optimal mitigation observed under K2 treatment. Additionally, DS plants treated with K exhibited lower lipid peroxidation, higher antioxidant activities, and increased osmotic solute accumulation in comparison with plants under K deficiency, which suggested that exogenous K application mitigated the oxidative damages and this was more prominent under K2 treatment. Noteworthily, proline and soluble protein, respectively, dominated in the osmotic regulation at 3 and 6 days of drought stress according to the analysis of the quantitative comparison among different osmotically active solutes. Based on the correlation of the aforementioned traits and the analysis of variance on the interaction effects of drought stress and potassium, we propose that superoxide dismutase (SOD), glutathione reductase (GR), and MDA could be critical indicators in balancing ROS detoxification and reproduction. In summary, our studies suggest that optimized K application keeps a balance between the production of antioxidants and ROS and simultaneously affects osmoregulation to alleviate the damage from drought stress.

Potassium fertilization improves growth, yield and seed quality of sunflower (Helianthus annuus L.) under drought stress at different growth stages

Water scarcity is a major concern for sunflower production in the semi-arid and arid regions of the world. Potassium (K) application has been found effective to alleviate the influence of drought stress; however, the impact of drought stress on seed quality of sunflower has not been reported frequently. Therefore, a field experiment was performed to determine the optimum K requirement for mitigating the adverse effects of water stress and improving growth and seed quality of spring-planted sunflower. Sunflower plants were exposed to water stress at different growth stages, i.e., I_o = no stress (normal irrigation), I₁ = pre-anthesisi stress (irrigation skipped at pre-anthesis stage), I₂ = anthesis stress (irrigation skipped at anthesis stage) and I₃ = post-anthesis stress (irrigation skipped at post-anthesis stage). Potassium was applied at four different rates, i.e., K_o = 0, K₁ = 50, K₂ = 100 and K₃ = 150 kg ha^-1. The results revealed that water stress at pre- and post-anthesis stages significantly reduced plant height, head diameter, number of achenes, oleic acid contents, and phosphorus (P) uptake. However, pre-anthesis stress improved linoleic acid contents. Treatment I_oK₃ (stress-free with 150 kg ha^-1 K) was optimum combination for 1000-achene weight, biological and achene yields, oil contents, protein contents, and N and P uptake. Results indicated that a higher amount of K and irrigation resulted in higher yield, whereas yield and yield components decreased with early-stage water stress. Nevertheless, potassium application lowered the impacts of waters stress compared to no application. Keeping in view these results, it is recommended that sunflower must be supplied 150 kg ha^-1 K in arid and semi-arid regions to achieve higher yield and better seed quality.

Hydrogen sulfide (H2S) and potassium (K+) synergistically induce drought stress tolerance through regulation of H+-ATPase activity, sugar metabolism, and antioxidative defense in tomato seedlings

Exogenous potassium (K⁺) and endogenous hydrogen sulfide (H₂S) synergistically alleviate drought stress through regulating H⁺-ATPase activity, sugar metabolism and redox homoeostasis in tomato seedlings. Present work evaluates the role of K⁺ in the regulation of endogenous H₂S signaling in modulating the tolerance of tomato (Solanum lycopersicum L. Mill.) seedlings to drought stress. The findings reveal that exposure of seedlings to 15% (w/v) polyethylene glycol 8000 (PEG) led to a substantial decrease in leaf K⁺ content which was associated with reduced H⁺-ATPase activity. Treatment with sodium orthovanadate (SOV, PM H⁺-ATPase inhibitor) and tetraethylammonium chloride (TEA, K⁺ channel blocker) suggests that exogenous K⁺ stimulated H⁺-ATPase activity that further regulated endogenous K⁺ content in tomato seedlings subjected to drought stress. Moreover, reduction in H⁺-ATPase activity by hypotaurine (HT; H₂S scavenger) substantiates the role of endogenous H₂S in the regulation of H⁺-ATPase activity. Elevation in endogenous K⁺ content enhanced the biosynthesis of H₂S through enhancing the synthesis of cysteine, the H₂S precursor. Synergistic action of H₂S and K⁺ effectively neutralized drought stress by regulating sugar metabolism and redox homoeostasis that resulted in osmotic adjustment, as witnessed by reduced water loss, and improved hydration level of the stressed seedlings. The integrative role of endogenous H₂S in K⁺ homeostasis was validated using HT and TEA which weakened the protection against drought stress induced impairments. In conclusion, exogenous K⁺ and endogenous H₂S regulate H⁺-ATPase activity which plays a decisive role in the maintenance of endogenous K⁺ homeostasis. Thus, present work reveals that K⁺ and H₂S crosstalk is essential for modulation of drought stress tolerance in tomato seedlings.

Shoot potassium content provides a physiological marker to screen cotton genotypes for osmotic and salt tolerance

Drought and salinity are considered two major abiotic stresses that diminish cotton production worldwide. Studying common morphological and physiological responses in cotton cultivars may help plant biologists to develop and apply standard screening criteria for either of these stresses and for their combination. Therefore, this research aimed to assess the suitability of several physiological parameters as diagnostic to report on osmotic and salinity tolerance in six elite cotton genotypes. Data for relative growth rate (RGR), RGR-reduction, potassium (K⁺) concentrations in roots, xylem sap and shoots, stomatal conductance (g_s) and net photosynthesis rate (P_n) were assessed. Based on RGR and RGR-reduction, we observed an association between osmotic tolerance and salinity tolerance of cotton genotypes. Furthermore, this study found that tolerant cotton genotypes were better able to maintain high RGR, tissue K⁺, and gas exchange under both hyperosmotic and saline conditions. Shoot K⁺ levels showed high negative correlations with both osmotic and salinity stress and emerged as a convenient and suitable parameter to assess cotton tolerance to either stress.Novelty statementCotton (Gossypium hirsutum) is a leading fiber crop that is cultivated in more than 52 countries. Much of the land where cotton is grown faces co-occurring drought and salinity abiotic stress which negatively impacts cotton yield and fiber quality. In the present study, cotton genotypes were identified with tolerance to both hyperosmolarity and salinity. Furthermore, we show that shoot potassium content is a diagnostic trait that reports on both osmotic and salinity stress and hence a convenient tool for screening cotton germplasm.

Exogenous Potassium (K+) Positively Regulates Na+/H+ Antiport System, Carbohydrate Metabolism, and Ascorbate-Glutathione Cycle in H2S-Dependent Manner in NaCl-Stressed Tomato Seedling Roots

Potassium (K⁺) is one of the vital macronutrients required by plants for proper growth and blossoming harvest. In addition, K⁺ also plays a decisive role in promoting tolerance to various stresses. Under stressful conditions, plants deploy their defense system through various signaling molecules, including hydrogen sulfide (H₂S). The present investigation was carried out to unravel the role of K⁺ and H₂S in plants under NaCl stress. The results of the study show that NaCl stress caused a reduction in K⁺ and an increase in Na⁺ content in the tomato seedling roots which coincided with a lower H⁺-ATPase activity and K⁺/Na⁺ ratio. However, application of 5 mM K⁺, in association with endogenous H₂S, positively regulated the Na⁺/H⁺ antiport system that accelerated K+ influx and Na+ efflux, resulting in the maintenance of a higher K⁺/Na⁺ ratio. The role of K⁺ and H₂S in the regulation of the Na⁺/H⁺ antiport system was validated by applying sodium orthovanadate (plasma membrane H⁺-ATPase inhibitor), tetraethylammonium chloride (K⁺ channel blocker), amiloride (Na⁺/H⁺ antiporter inhibitor), and hypotaurine (HT, H₂S scavenger). Application of 5 mM K⁺ positively regulated the ascorbate–glutathione cycle and activity of antioxidant enzymes that resulted in a reduction in reactive oxygen species generation and associated damage. Under NaCl stress, K⁺ also activated carbohydrate metabolism and proline accumulation that caused improvement in osmotic tolerance and enhanced the hydration level of the stressed seedlings. However, inclusion of the H₂S scavenger HT reversed the effect of K⁺, suggesting H₂S-dependent functioning of K⁺ under NaCl stress. Therefore, the present findings report that K⁺, in association with H₂S, alleviates NaCl-induced impairments by regulating the Na⁺/H⁺ antiport system, carbohydrate metabolism, and antioxidative defense system.

Potassium Fertilization Stimulates Sucrose-to-Starch Conversion and Root Formation in Sweet Potato (Ipomoea batatas (L.) Lam.)

A field experiment was established to study sweet potato growth, starch dynamic accumulation, key enzymes and gene transcription in the sucrose-to-starch conversion and their relationships under six K2O rates using Ningzishu 1 (sensitive to low-K) and Xushu 32 (tolerant to low-K). The results indicated that K application significantly improved the biomass accumulation of plant and storage root, although treatments at high levels of K, i.e., 300-375 kg K2O ha-1, significantly decreased plant biomass and storage root yield. Compared with the no-K treatment, K application enhanced the biomass accumulation of plant and storage root by 3-47% and 13-45%, respectively, through promoting the biomass accumulation rate. Additionally, K application also enhanced the photosynthetic capacity of sweet potato. In this study, low stomatal conductance and net photosynthetic rate (Pn) accompanied with decreased intercellular CO2 concentration were observed in the no-K treatment at 35 DAT, indicating that Pn was reduced mainly due to stomatal limitation; at 55 DAT, reduced Pn in the no-K treatment was caused by non-stomatal factors. Compared with the no-K treatment, the content of sucrose, amylose and amylopectin decreased by 9-34%, 9-23% and 6-19%, respectively, but starch accumulation increased by 11-21% under K supply. The activities of sucrose synthetase (SuSy), adenosine-diphosphate-glucose pyrophosphorylase (AGPase), starch synthase (SSS) and the transcription of Susy, AGP, SSS34 and SSS67 were enhanced by K application and had positive relationships with starch accumulation. Therefore, K application promoted starch accumulation and storage root yield through regulating the activities and genes transcription of SuSy, AGPase and SSS in the sucrose-to-starch conversion.

Effects of phosphite as a plant biostimulant on metabolism and stress response for better plant performance in Solanum tuberosum

Food availability represents a major worldwide concern due to population growth, increased demand, and climate change. Therefore, it is imperative to identify compounds that can improve crop performance. Plant biostimulants have gained prominence because of their potentials to increase germination, productivity and quality of a wide range of horticultural and agronomic crops. Phosphite (Phi), an analog of orthophosphate, is an emerging biostimulant used in horticulture and agronomy. The aim of this study was to uncover the molecular mechanisms through which Phi acts as a biostimulant with potential effects of overall plant growth. Field and greenhouse experiments, using 4 potato cultivars, showed that following Phi applications, plant performance, including several physio-biochemical traits, crop productivity, and quality traits, were significantly improved. RNA sequencing of control and Phi-treated plants of cultivar Xingjia No. 2, at 0 h, 6 h, 24 h, 48 h, 72 h and 96 h after the Phi application for 24 h revealed extensive changes in the gene expression profiles. A total of 2856 differentially expressed genes were identified, suggesting that multiple pathways of primary and secondary metabolism, such as flavonoids biosynthesis, starch and sucrose metabolism, and phenylpropanoid biosynthesis, were strongly influenced by foliar applications of Phi. GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analyses associated with defense responses revealed significant effects of Phi on a plethora of defense mechanisms. These results suggest that Phi acted as a biostimulant by priming the plants, that was, by triggering dynamic changes in gene expression and modulating metabolic fluxes in a way that allowed plants to perform better. Therefore, Phi usage has the potential to improve crop yield and health, alleviating the challenges posed by the need of feeding a growing world population, while minimizing the agricultural impact on human health and environment.

Potassium Improves Drought Stress Tolerance in Plants by Affecting Root Morphology, Root Exudates and Microbial Diversity

Potassium (K) reduces the deleterious effects of drought stress on plants. However, this mitigation has been studied mainly in the aboveground plant pathways, while the effect of K on root-soil interactions in the underground part is still underexplored. Here, we conducted the experiments to investigate how K enhances plant resistance and tolerance to drought by controlling rhizosphere processes. Three culture methods (sand, water, and soil) evaluated two rapeseed cultivars’ root morphology, root exudates, soil nutrients, and microbial community structure under different K supply levels and water conditions to construct a defensive network of the underground part. We found that K supply increased the root length and density and the organic acids secretion. The organic acids were significantly associated with the available potassium decomposition, in order of formic acid > malonic acid > lactic acid > oxalic acid > citric acid. However, the mitigation had the hormesis effect, as the appropriate range of K facilitated the morphological characteristic and physiological function of the root system with increases of supply levels, while the excessive input of K could hinder the plant growth. The positive effect of K-fertilizer on soil pH, available phosphorus and available potassium content, and microbial diversity index was more significant under the water stress. The rhizosphere nutrients and pH further promoted the microbial community development by the structural equation modeling, while the non-rhizosphere nutrients had an indirect negative effect on microbes. In short, K application could alleviate drought stress on the growth and development of plants by regulating the morphology and secretion of roots and soil ecosystems.

Gradual Application of Potassium Fertilizer Elevated the Sugar Conversion Mechanism and Yield of Waxy and Sweet Fresh-Eaten Maize in the Semiarid Cold Region

Fresh-eaten maize (Zea mays L.) is favored by consumers for its unique flavor, good health, and medical effects. Heilongjiang province is a semiarid cold region with the annual output of 3.35 billion ears, and the demand for fresh eaten maize is increasing in the region. Therefore, improving its yield and quality is urgently needed in this area. In this study, two of thirty varieties (waxy maize Jin-262 and sweet maize Jingke-183) were used and five proportions of potassium (K2O, 120 kg/ha) were applied at sowing, jointing, and large trumpet stages to identify the high yield and quality of fresh-eaten maize under a semiarid cold ecological condition in Daqing, Heilongjiang province, China, during 2017-2018. The results from the screening of eighteen maize varieties showed that waxy maize Jin-262 and sweet maize Jingke-183 had higher starch content and soluble sucrose contents than those of other varieties. While the potassium proportions application during the sowing (20%), jointing (40%), and large trumpet stages (40%) had further significantly increased the starch content, soluble sugar content, sucrose content, and sucrose metabolic enzymes activities of Jin-262 and Jingke-183, however, the yields of Jin-262 and Jingke-183 had increased by applying potassium fertilizer during the sowing stages (50%) and jointing stages (50%). Considering the overall higher maize quality, we recommended the waxy maize Jin-262 and sweet maize Jingke-183 varieties along with application of 20% (sowing), 40% (jointing), and 40% (large trumpet stages) of 120 kg/ha potassium fertilizer for the improvement of grain quality of maize planting in the semiarid cold region. Otherwise, reasonable gradual potassium fertilization might be a wiser option.

RNA-Seq Provides New Insights into the Molecular Events Involved in "Ball-Skin versus Bladder Effect" on Fruit Cracking in Litchi

Fruit cracking is a disorder of fruit development in response to internal or external cues, which causes a loss in the economic value of fruit. Therefore, exploring the mechanism underlying fruit cracking is of great significance to increase the economic yield of fruit trees. However, the molecular mechanism underlying fruit cracking is still poorly understood. Litchi, as an important tropical and subtropical fruit crop, contributes significantly to the gross agricultural product in Southeast Asia. One important agricultural concern in the litchi industry is that some famous varieties with high economic value such as ‘Nuomici’ are susceptible to fruit cracking. Here, the cracking-susceptible cultivar ‘Nuomici’ and cracking-resistant cultivar ‘Huaizhi’ were selected, and the samples including pericarp and aril during fruit development and cracking were collected for RNA-Seq analysis. Based on weighted gene co-expression network analysis (WGCNA) and the “ball-skin versus bladder effect” theory (fruit cracking occurs upon the aril expanding pressure exceeds the pericarp strength), it was found that seven co-expression modules genes (1733 candidate genes) were closely associated with fruit cracking in ‘Nuomici’. Importantly, we propose that the low expression level of genes related to plant hormones (Auxin, Gibberellins, Ethylene), transcription factors, calcium transport and signaling, and lipid synthesis might decrease the mechanical strength of pericarp in ‘Nuomici’, while high expression level of genes associated with plant hormones (Auxin and abscisic acid), transcription factors, starch/sucrose metabolism, and sugar/water transport might increase the aril expanding pressure, thereby resulting in fruit cracking in ‘Nuomici’. In conclusion, our results provide comprehensive molecular events involved in the “ball-skin versus bladder effect” on fruit cracking in litchi.

Morpho-physiological and molecular characterization of drought tolerance traits in Gossypium hirsutum genotypes under drought stress

Drought stress is one of the major abiotic stresses affecting lint yield and fibre quality in cotton. With increase in population, degrading natural resources and frequent drought occurrences, development of high yielding, drought tolerant cotton cultivars is critical for sustainable cotton production across countries. Six Gossypium hirsutum genotypes identified for drought tolerance, wider adaptability and better fibre quality traits were characterized for various morpho-physiological and biochemical characters and their molecular basis was investigated under drought stress. Under drought conditions, genotypes revealed statistically significant differences for all the morpho-physiological and biochemical traits. The interaction (genotype × treatment) effects were highly significant for root length, excised leaf water loss and cell membrane thermostability indicating differential interaction of genotypes under control and stress conditions. Correlation studies revealed that under drought stress, relative water content had significant positive correlation with root length and root-to-shoot ratio while it had significant negative correlation with excised leaf water loss, epicuticular wax, proline, potassium and total soluble sugar content. Analysis of expression of fourteen drought stress related genes under water stress indicated that both ABA dependent and ABA independent mechanisms of drought tolerance might be operating differentially in the studied genotypes. IC325280 and LRA5166 exhibited ABA mediated expression of stress responsive genes and traits. Molecular basis of drought tolerance in IC357406, Suraj, IC259637 and CNH 28I genotypes could be attributed to ABA independent pathway. Based on physiological phenotyping, the genotypes IC325280 and IC357406 were identified to possess better root traits and LRA5166 was found to have enhanced cellular level tolerance. Variety Suraj exhibited good osmotic adjustment and better root traits to withstand water stress. The identified drought component trait(s) in specific genotypes would pave way for their pyramiding through marker assisted cotton breeding.

Drought-Induced Responses of Nitrogen Metabolism in Ipomoea batatas

This study investigated the effect of water stress, simulated by the polyethylene glycol (PEG-6000) method, on nitrogen (N) metabolism in leaves and roots of hydroponically grown sweet potato seedlings, Xushu 32 (X32) and Ningzishu 1 (N1). The concentrations of PEG-6000 treatments were 0%, 5% and 10% (m/v). The results showed that the drought-treated plants showed a decline leaf relative water content, and revealed severe growth inhibition, compared with the 0% treatment. Under drought stress, the decline in biomass of the leaf and stem was more noticeable than in root biomass for X32, leading to a higher root to shoot ratio. Drought stress increased the nitrate nitrogen (NO₃^--N) and protein in leaves, but reduced all the activities of N-metabolism enzymes and the transcriptional levels of nitrate reductase (NR), glutamine synthetase (GS) and glutamate synthase (GOGAT); in roots, NO₃^--N and NR had opposite trends. The leaf ammonium nitrogen (NH₄⁺-N), GS and amino acid had different trends between X32 and N1 under drought stress. Furthermore, the transcriptional level of nitrate transporter genes NRT1.1 in leaves and roots were upregulated under drought stress, except in N1 roots. In conclusion, NR determined the different response to drought in leaves for X32 and N1, and GS and GOGAT determined the response to drought in roots, respectively.

Regulation of Agronomic Traits, Nutrient Uptake, Osmolytes and Antioxidants of Maize as Influenced by Exogenous Potassium Silicate under Deficit Irrigation and Semiarid Conditions

Understanding the link between the protective role of potassium silicate (K2SiO3) against water shortage and the eventual grain yield of maize plants is still limited under semiarid conditions. Therefore, in this study, we provide insights into the underlying metabolic responses, mineral nutrients uptake and some nonenzymatic and enzymatic antioxidants that may differ in maize plants as influenced by the foliar application of K2SiO3 (0, 1 and 2 mM) under three drip irrigation regimes (100, 75 and 50% of water requirements). Our results indicated that, generally, plants were affected by both moderate and severe deficit irrigation levels. Deficit irrigation decreased shoot dry weight, root dry weight, leaf area index (LAI), relative water content (RWC), N, P, K, Ca, Fe, Zn, carotenoids, grain yield and its parameters, while root/shoot ratio, malondialdehyde (MDA), proline, soluble sugars, ascorbic acid, soluble phenols, peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), and ascorbate peroxidase (APX) were improved. The foliar applications of K2SiO3 relatively alleviated water stress-induced damage. In this respect, the treatment of 2 mM K2SiO3 was more effective than others and could be recommended to mitigate the effect of deficit irrigation on maize plants. Moreover, correlation analysis revealed a close link between yield and the most studied traits.

Chloride and amino acids are associated with K+-alleviated drought stress in tea (Camellia sinesis)

Drought is one of the main limiting factors affecting tea plant yield and quality. Previous studies have reported that K+ (potassium) application significantly alleviated drought-induced damage in tea plants. However, the intrinsic mechanisms underlying K+-alleviated drought stress are still obscure. In our study, two contrasting varieties, Taicha12 (drought tolerant) and Fuyun6 (drought sensitive), were used to investigate the intrinsic mechanisms behind K+-alleviated drought stress in tea plants. In the present study, we compared with the case of tea plants under drought: higher water and chlorophyll contents were found in drought-stressed tea plants with an external K+ supply, confirming the role of externally supplied K+ in mitigating drought stress. We also found that an adequate K+ supply promoted Cl- accumulation in the mesophyll of Taicha12 (drought tolerant) over that of in Fuyun6 (drought sensitive). Moreover, Gly, Cys, Lys and Arg were not detected in Fuyun6 under 'Drought' or 'Drought + K+' conditions. Results showed that an exogenous supply of Arg and Val significantly alleviated drought-induced damage in Fuyun6, suggesting their role in K+-alleviated drought stress in tea plants. Collectively, our results show that chloride and amino acids are important components associated with K+-alleviated drought stress in tea plants.

Influence of drought stress on pistil physiology and reproductive success of two Gossypium hirsutum cultivars differing in drought tolerance

The causes of reproductive failure under drought stress (DS) are poorly understood. We hypothesized that reproductive failure was related to drought-induced changes in pistil biochemistry. To address this hypothesis, a water deficit-induced experiment was conducted with two cotton cultivars (Dexiamian 1, drought tolerant; Yuzaomian 9110, drought sensitive). Results showed that DS decreased the photosynthesis of subtending leaf and downregulated sucrose transporter gene (GhSUT-1) expression in pistil for both cultivars, resulting in lower pistil carbon accumulation which was reflected in the decreased starch accumulation. Lower starch, as potential energy, and adenosine triphosphate (ATP), as direct energy, in droughted pistils suggested less energy for pollen tube entrance into ovules, reducing the fertilized ovule number and fertilization efficiency. Further, although pistil peroxidase activity increased under DS, a higher hydrogen peroxide (H₂ O₂ ) level still was measured in droughted pistils than well-watered pistils, damaging reproductive activities. Moreover, larger decreases in photosynthesis, pistil GhSUT-1 expression, carbon accumulation, starch and ATP contents caused by DS for Yuzaomian 9110 than Dexiamian 1, and different responses of superoxide dismutase and catalase activities, and ascorbic acid and H₂ O₂ contents to DS between the two cultivars might be the reasons causing a greater decrease in fertilization efficiency for Yuzaomian 9110 than Dexiamian 1 under DS. Thus, we suggest that decreased ovule fertilization under DS was related to the disorganized carbohydrate metabolism and inefficient antioxidant defense in droughted pistils, and the effects of DS on pistil carbohydrate metabolism and antioxidant defense were more significant for drought-sensitive cultivars than drought-tolerant cultivars.

Physiological and transcriptome analyses of the effects of exogenous dopamine on drought tolerance in apple

Water shortage is one of the main limiting factors in apple (Malus domestica Borkh.) production. Although dopamine is produced in plants and has been linked with response to abiotic stress, the underlying mechanism remains unknown. In this study, physiological analyses revealed that pretreatment with 100 μM dopamine alleviated drought stress in apple seedlings. Dopamine inhibited the degradation of photosynthetic pigments and increased net photosynthetic rate under drought stress. Dopamine also reduced H₂O₂ content, possibly through direct scavenging and by mediating the antioxidant enzyme activity. Seedlings pretreated with dopamine had higher sucrose and malic acid contents but lower starch accumulation in their leaves. RNA-Seq analysis identified 1052 differentially expressed genes (DEGs) between non-treated and dopamine-pretreated plants under drought. An in-depth analysis of these DEGs revealed that dopamine regulated the expression of genes related to metabolism of nitrogen, secondary compounds, and amino acids under drought stress. In addition, dopamine may improve apple drought tolerance by activating Ca²⁺ signaling pathways through increased expression of CNGC and CAM/CML family genes. Moreover, analysis of transcription factor expression suggested that dopamine affected drought tolerance mainly through the regulation of WRKY, ERF, and NAC transcription factors.

Chlorophyll synthesis and the photoprotective mechanism in leaves of mulberry (Morus alba L.) seedlings under NaCl and NaHCO3 stress revealed by TMT-based proteomics analyses

Chlorophyll (Chl) and effective photoprotective mechanism are important prerequisites to ensure the photosynthetic function of plants under stress. In this study, the effects of 100 mmol L^-1 NaCl and NaHCO₃ stress on chlorophyll synthesis and photosynthetic function of mulberry seedlings were studied by physiological combined with proteomics technology. The results show that: NaCl stress had little effect on the expression of Chl synthesis related proteins, and there were no significant changes in Chl content and Chl a:b ratio. However, 13 of the 15 key proteins in the process of Chl synthesis were significantly decreased under NaHCO₃ stress, and the contents of Chl a and Chl b were significantly decreased (especially Chl a). Although stomatal conductance (G_s) decreased significantly under NaCl stress, net photosynthetic rate (P_n), PSII maximum photochemical efficiency (F_v/F_m) and electron transfer rate (ETR) did not change significantly, but under NaHCO₃ stress, not only G_s decreased significantly, PSII activity and photosynthetic carbon were the same. In the photoprotective mechanism under NaCl stress, NAD(P)H dehydrogenase (NDH)-dependent cyclic electron flow (CEF) enhanced, the expression of related proteins subunit, ndhH, ndhI, ndhK, and ndhM, the key enzyme of the xanthophyll cycle, violaxanthin de-epoxidase (VDE) were up-regulated, the ratio of (A + Z)/(V + A + Z) and non-photochemical quenching (NPQ) was increased. The expressions of proteins FTR and Fd-NiR were also significant up-regulated under NaCl stress, Fd-dependent ROS metabolism and nitrogen metabolism can effectively reduce the electronic pressure on Fd. Under NaHCO₃ stress, the expressions of NDH-dependent CEF related proteins subunit (ndhH, ndhI, ndhK, ndhM and ndhN), VDE, ZE, FTR, Fd-NiR and Fd-GOGAT, were significant down-regulated, and ZE, CP26, ndhK, ndhM, Fd-NiR, Fd-GOGAT and FTR genes expression also significantly decreased, the photoprotective mechanism, like the xanthophyll cycle，CEF and Fd-dependent ROS metabolism and nitrogen metabolism might be damaged, resulting in the inhibition of PSII electron transfer and carbon assimilation in mulberry leaves under NaHCO₃ stress.

Drought-induced disturbance of carbohydrate metabolism in anthers and male abortion of two Gossypium hirsutum cultivars differing in drought tolerance

Cotton pollen abortion, under drought stress, was closely associated with changes in anther carbohydrate metabolism, and pollen abortion rate due to drought was higher in drought-sensitive cultivars than drought-tolerant cultivars. Cotton reproductive failure under drought stress is intrinsically connected with altered male fertility, however, studies investigating the effect of drought stress on cotton male fertility are nonexistent. Thus, a drought stress experiment was conducted with two cotton cultivars, differing in drought tolerance, to study pollen fertility and anthers' physiology. Results indicated that drought stress reduced pollen fertility of both cultivars due to decreases in anther starch and adenosine triphosphate (ATP) synthesis. Lower assimilate supply capacity in conjunction with impaired activities of ADP-glucose pyrophosphorylase and soluble starch synthase were the main reasons for the decreased starch levels in drought-stressed anthers. The decreased activities of sucrose synthetase and acid invertase were responsible for the higher sucrose level in drought-stressed anthers than well-watered anthers and the changing trend of sucrose was intensified by the decreased expressions of sucrose synthase genes (GhSusA, GhSusB, GhSusD) and acid invertase genes (GhINV1, GhINV2). However, despite sucrose degradation being limited in drought-stressed anthers, glucose level was higher in droughted anthers than well-watered ones, and that might be attributed to the down-regulated respiration since decreased anther ATP levels were detected in drought-stressed plants. Furthermore, compared to the drought-tolerant cultivar, pollen fertility was more suppressed by drought stress for the drought-sensitive cultivar, and that was attributed to the larger decrease in starch and ATP contents.

Biochemical and physiological impacts of zinc sulphate, potassium phosphite and hydrogen sulphide in mitigating stress conditions in soybean

Soybean is the most widely grown oilseed in the world. It is an important source of protein and oil which are derived from its seeds. Drought stress is a major constraint to soybean yields. Finding alternative methods to mitigate the water stress for soybean is useful to maintain adequate crop yields. The aim of this study was to evaluate the morpho-physiological, biochemical and metabolic changes in soybean plants in two ontogenetic stages, under exposure to water deficit and treatment with zinc sulphate (ZS), potassium phosphite (PP) or hydrogen sulphide (HS). We carried out two independent experiments in the V4 and R1 development stages consisting of the following treatments: well-watered control (WW, 100% maximum water holding capacity, MWHC), water deficit (WD, 50% MWHC), PP + WW, PP + WD, HS + WW, HS + WD, ZS + WW and ZS + WD. The experimental design consisted of randomized blocks with eight treatments with five replicates. Morphological, physiological and metabolic analyses were performed 8 days after the start of the treatments for both experiments. We identified two tolerance mechanisms acting in response to compound application during water stress: the first involved the upregulation of antioxidant enzyme activity and the second involved the accumulation of soluble sugars, free amino acids and proline to facilitate osmotic adjustment. Both mechanisms are related to the maintenance of the photosynthetic parameters and cell membrane integrity. This report suggests the potential agricultural use of these compounds to mitigate drought effects in soybean plants.

High Nitrogen Enhance Drought Tolerance in Cotton through Antioxidant Enzymatic Activities, Nitrogen Metabolism and Osmotic Adjustment

Drought is one of the most important abiotic stresses and hampers many plant physiological processes under suboptimal nitrogen (N) concentration. Seedling tolerance to drought stress is very important for optimum growth and development, however, the enhancement of plant stress tolerance through N application in cotton is not fully understood. Therefore, this study investigates the role of high N concentration in enhancing drought stress tolerance in cotton. A hydroponic experiment supplying low (0.25 mM) and high (5 mM) N concentrations, followed by 150 g L-1 polyethylene glycol (PEG)-induced stress was conducted in a growth chamber. PEG-induced drought stress inhibited seedling growth, led to oxidative stress from excessive malondialdehyde (MDA) generation, and reduced N metabolism. High N concentrations alleviated oxidative damage and stomatal limitation by increasing antioxidant enzymatic activities, leaf relative water content, and photosynthesis in cotton seedlings under drought stress. The results revealed that the ameliorative effects of high N concentration may be ascribed to the enhancement of N metabolizing enzymes and an increase in the amounts of osmoprotectants like free amino acids and total soluble protein. The present data suggest that relatively high N concentrations may contribute to drought stress tolerance in cotton through N metabolism, antioxidant capacity, and osmotic adjustment.

Drought limits pollen tube growth rate by altering carbohydrate metabolism in cotton (Gossypium hirsutum) pistils

It has been reported that drought stress (DS) reduces cotton yield by negatively affecting reproductive activities. Some studies have investigated the effects of DS on pollen physiology and biochemistry, but studies exploring the impact of drought on pistil biochemistry and its relationship with pollen tube growth rates in vivo are scarce. In order to investigate these objectives, a greenhouse study was conducted with a drought sensitive cotton cultivar, Yuzaomian 9110. Two water treatments were imposed at flowering stage, 1. control, where plants were irrigated with optimum quantity of water and 2. DS treatment, where plants were irrigated with 50% of the optimum quantity of water. Results indicated that stored starch content at the early stage of pollen tube growth (12:00 h) was 31.6% lower in drought-stressed pistils than control pistils, and it was highly correlated with pollen tube growth rate. The decline in starch accumulation of drought-stressed pistils could be attributed to the impeded transport of photosynthetic carbon assimilates. Moreover, decreased ADP-glucose pyrophosphorylase and soluble starch synthase activities also resulted in curtailing starch accumulation in drought-stressed pistils. Furthermore, pistil sucrose concentration was significantly higher in droughted plants relative to control plants at 12:00 and 18:00 h (during the rapid growth period), which was due to lower activities of sucrose synthase and acid invertase, and the down-regulated expressions of sucrose synthase genes, GhSusA, GhSusB and GhSusD, and acid invertase genes, GhINV1 and GhINV2, in drought-stressed pistils, limiting as a result the hydrolysis of sucrose into hexose. Drought-stressed pistils sampled at 18:00 h had lower α-amylase activity compared to control pistils, resulting in decreased starch decomposition, which, in conjunction with the decreased hydrolysis of sucrose, led to lower glucose and fructose contents in drought-stressed pistils at 18:00 h. Finally, lower pyruvate level in drought-stressed pistils could not produce enough acetyl-CoA in the tricarboxylic acid cycle to yield sufficient energy (ATP) for pollen tube growth. We conclude that DS disrupts the carbohydrate balance of pistil, reducing as a consequence carbon and energy supply for pollen tube elongation in the style, which will ultimately result in reproductive failure.

Distinct leaf transcriptomic response of water deficient Eucalyptus grandis submitted to potassium and sodium fertilization

While potassium fertilization increases growth yield in Brazilian eucalyptus plantations, it could also increase water requirements, making trees more vulnerable to drought. Sodium fertilization, which has been shown to promote eucalyptus growth compared to K-deficient trees, could partially mitigate this adverse effect of potassium. However, little is known about the influence of K and Na fertilization on the tree metabolic response to water deficit. The aim of the present study was thus to analyze the transcriptome of leaves sampled from Eucalyptus grandis trees subjected to 37% rainfall reduction, and fertilized with potassium (K), sodium (Na), compared to control trees (C). The multifactorial experiment was set up in a field with a throughfall exclusion system. Transcriptomic analysis was performed on leaves from two-year-old trees, and data analyzed using multifactorial statistical analysis and weighted gene co-expression network analysis (WGCNA). Significant sets of genes were seen to respond to rainfall reduction, in interaction with K or Na fertilization, or to fertilization only (regardless of the water supply regime). The genes were involved in stress signaling, primary and secondary metabolism, secondary cell wall formation and photosynthetic activity. Our focus on key genes related to cation transporters and aquaporins highlighted specific regulation of ion homeostasis, and plant adjustment to water deficit. While water availability significantly affects the transcriptomic response of eucalyptus species, this study points out that the transcriptomic response is highly dependent on the fertilization regime. Our study is based on the first large-scale field trial in a tropical region, specifically designed to study the interaction between water availability and nutrition in eucalyptus. To our knowledge, this is the first global transcriptomic analysis to compare the influence of K and Na fertilization on tree adaptive traits in water deficit conditions.

Short-term soil-waterlogging contributes to cotton cross tolerance to chronic elevated temperature by regulating ROS metabolism in the subtending leaf

Chronic elevated temperature and soil-waterlogging events often occur concomitantly in the Yangtze River Valley; however, a clear understanding of the effects of aforementioned co-occurring stresses on antioxidant defense in cotton has not been attained. To address this, two temperature conditions during the whole flowering and boll development periods, and three soil-waterlogging levels (0, 3, 6 d) starting on the day of anthesis were established. In the current study, no siginificant difference was observed on plant performance for 3 d soil-waterlogging, whereas 6 d soil-waterlogging event and elevated temperature in isolation negatively affected plant performance (i.e. leaf area declined by 33.3% and 14.7% in AW₆ (soil waterlogging for 6 d under ambient temperature regime) and EC (soil well-watered (SRWC(75 ± 5) %) under elevated temperature for 2-3 °C) relative to AC (soil well-watered (SRWC(75 ± 5) %) under ambient temperature regime)) and induced ROS (reactive oxygen species) production and scavenging mechanisms in the subtending leaf of cotton. SOD (superoxide dismutase), CAT (catalase), and POX (peroxidase) activities were increased, and ASA (ascorbic acid) concentration was enhanced due to higher H₂O₂ (hydrogen peroxide) and O₂^- accumulations. Whereas, APX (ascorbate peroxidase), DHAR (dehydroascorbate reductase) and GR (glutathione reductase) activities were inhibited under elevated temperature regime or waterlogging event, especially in the treatment of EW₆ (soil waterlogging for 6 d under elevated temperature for 2-3 °C), which resulted in increasing H₂O₂ concentration and higher O₂^- generation rate. However, plants acclimated to a short-term waterlogging stress (3 d) performed a cross tolerance to chronic elevated temperature regime (leaf number increased by 11.4%, whereas the abscission rate decreased by 4.6% in EW₃ (soil waterlogging for 3 d under elevated temperature for 2-3 °C) compared with EC (soil well-watered (SRWC(75 ± 5) %) under elevated temperature for 2-3 °C)). Moreover, plants undergone a brief soil-waterlogging (3 d) induced higher GR activity and increased ASA concentration, along with enhanced SOD, CAT, POX activities, limiting H₂O₂ and O₂^- accumulation and reducing oxidative damage to membrane lipids as evidenced by reduced MDA (malondialdehyde) concentration when cotton was subsequently exposed to chronic elevated temperature regime.

Evaluation of potassium solubilizing rhizobacteria (KSR): enhancing K-bioavailability and optimizing K-fertilization of maize plants under Indo-Gangetic Plains of India

Imbalanced potassium (K) fertilization in agricultural fields has led to considerable negative impacts and remains to be the foremost challenge for maize production in India-Gangetic region. Plant growth-promoting rhizobacteria, particularly potassium solubilizing rhizobacteria (KSR), could serve as inoculants and a promising strategy for enhancement of plant absorption of K hence reducing dependency on chemical fertilizers. Maize seeds were microbiolized for 30 min with KSR suspensions. In the present study, the use of chemical fertilizers along with Agrobacterium tumefaciens strain OPVS10 showed pronounced beneficial effect on growth and yield attributes in maize. There was a significant difference among different parameters studied when varying doses of K and KSR strains were applied. Results showed that the combined application of KSR strain OPVS10 with 100% RDK (recommended dose of K) was most effective in modulating growth, physio-biochemical, and yield attributes in maize thus could be regarded as a promising alternative to mineral K-fertilization. Principal component analysis (PCA) revealed that 100-grain weight and grain yield were the most important properties to improve the sustainable growth of maize. Therefore, these KSR strains have different mechanisms for modulating various activities in maize plants. Results suggested that the synergistic application of KSR strain OPVS10 with 100% RDK can be used for optimized breeding, screening, and nutrient assimilation in maize crop. Hence, this eco-friendly approach may be one of the efficient methods for reducing dependency on chemicals, which pose adverse effects on human health directly and indirectly.

Coping with drought: stress and adaptive mechanisms, and management through cultural and molecular alternatives in cotton as vital constituents for plant stress resilience and fitness

Increased levels of greenhouse gases in the atmosphere and associated climatic variability is primarily responsible for inducing heat waves, flooding and drought stress. Among these, water scarcity is a major limitation to crop productivity. Water stress can severely reduce crop yield and both the severity and duration of the stress are critical. Water availability is a key driver for sustainable cotton production and its limitations can adversely affect physiological and biochemical processes of plants, leading towards lint yield reduction. Adaptation of crop husbandry techniques suitable for cotton crop requires a sound understanding of environmental factors, influencing cotton lint yield and fiber quality. Various defense mechanisms e.g. maintenance of membrane stability, carbon fixation rate, hormone regulation, generation of antioxidants and induction of stress proteins have been found play a vital role in plant survival under moisture stress. Plant molecular breeding plays a functional role to ascertain superior genes for important traits and can offer breeder ready markers for developing ideotypes. This review highlights drought-induced damage to cotton plants at structural, physiological and molecular levels. It also discusses the opportunities for increasing drought tolerance in cotton either through modern gene editing technology like clustered regularly interspaced short palindromic repeat (CRISPR/Cas9), zinc finger nuclease, molecular breeding as well as through crop management, such as use of appropriate fertilization, growth regulator application and soil amendments.

Soil Selenium (Se) Biofortification Changes the Physiological, Biochemical and Epigenetic Responses to Water Stress in Zea mays L. by Inducing a Higher Drought Tolerance

Requiring water and minerals to grow and to develop its organs, Maize (Zea mays L.) production and distribution is highly rainfall-dependent. Current global climatic changes reveal irregular rainfall patterns and this could represent for maize a stressing condition resulting in yield and productivity loss around the world. It is well known that low water availability leads the plant to adopt a number of metabolic alterations to overcome stress or reduce its effects. In this regard, selenium (Se), a trace element, can help reduce water damage caused by the overproduction of reactive oxygen species (ROS). Here we report the effects of exogenous Se supply on physiological and biochemical processes that may influence yield and quality of maize under drought stress conditions. Plants were grown in soil fertilized by adding 150 mg of Se (sodium selenite). We verified the effects of drought stress and Se treatment. Selenium biofortification proved more beneficial for maize plants when supplied at higher Se concentrations. The increase in proline, K concentrations and nitrogen metabolism in aerial parts of plants grown in Se-rich substrates, seems to prove that Se-biofortification increased plant resistance to water shortage conditions. Moreover, the increase of SeMeSeCys and SeCys2 forms in roots and aerial parts of Se-treated plants suggest resistance strategies to Se similar to those existing in Se-hyperaccumulator species. In addition, epigenetic changes in DNA methylation due to water stress and Se treatment were also investigated using methylation sensitive amplified polymorphism (MSAP). Results suggest that Se may be an activator of particular classes of genes that are involved in tolerance to abiotic stresses. In particular, PSY (phytoene synthase) gene, essential for maintaining leaf carotenoid contents, SDH (sorbitol dehydrogenase), whose activity regulates the level of important osmolytes during drought stress and ADH (alcohol dehydrogenase), whose activity plays a central role in biochemical adaptation to environmental stress. In conclusion, Se-biofortification could help maize plants to cope with drought stress conditions, by inducing a higher drought tolerance.

Potassium: A Vital Regulator of Plant Responses and Tolerance to Abiotic Stresses

Among the plant nutrients, potassium (K) is one of the vital elements required for plant growth and physiology. Potassium is not only a constituent of the plant structure but it also has a regulatory function in several biochemical processes related to protein synthesis, carbohydrate metabolism, and enzyme activation. Several physiological processes depend on K, such as stomatal regulation and photosynthesis. In recent decades, K was found to provide abiotic stress tolerance. Under salt stress, K helps to maintain ion homeostasis and to regulate the osmotic balance. Under drought stress conditions, K regulates stomatal opening and helps plants adapt to water deficits. Many reports support the notion that K enhances antioxidant defense in plants and therefore protects them from oxidative stress under various environmental adversities. In addition, this element provides some cellular signaling alone or in association with other signaling molecules and phytohormones. Although considerable progress has been made in understanding K-induced abiotic stress tolerance in plants, the exact molecular mechanisms of these protections are still under investigation. In this review, we summarized the recent literature on the biological functions of K, its uptake, its translocation, and its role in plant abiotic stress tolerance.

GhSNAP33, a t-SNARE Protein From Gossypium hirsutum, Mediates Resistance to Verticillium dahliae Infection and Tolerance to Drought Stress

Soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor (SNARE) proteins mediate membrane fusion and deliver cargo to specific cellular locations through vesicle trafficking. Synaptosome-associated protein of 25 kDa (SNAP25) is a target membrane SNARE that drives exocytosis by fusing plasma and vesicular membranes. In this study, we isolated GhSNAP33, a gene from cotton (Gossypium hirsutum), encoding a SNAP25-type protein containing glutamine (Q)b- and Qc-SNARE motifs connected by a linker. GhSNAP33 expression was induced by H₂O₂, salicylic acid, abscisic acid, and polyethylene glycol 6000 treatment and Verticillium dahliae inoculation. Ectopic expression of GhSNAP33 enhanced the tolerance of yeast cells to oxidative and osmotic stresses. Virus-induced gene silencing of GhSNAP33 induced spontaneous cell death and reactive oxygen species accumulation in true leaves at a later stage of cotton development. GhSNAP33-deficient cotton was susceptible to V. dahliae infection, which resulted in severe wilt on leaves, an elevated disease index, enhanced vascular browning and thylose accumulation. Conversely, Arabidopsis plants overexpressing GhSNAP33 showed significant resistance to V. dahliae, with reduced disease index and fungal biomass and elevated expression of PR1 and PR5. Leaves from GhSNAP33-transgenic plants showed increased callose deposition and reduced mycelia growth. Moreover, GhSNAP33 overexpression enhanced drought tolerance in Arabidopsis, accompanied with reduced water loss rate and enhanced expression of DERB2A and RD29A during dehydration. Thus, GhSNAP33 positively mediates plant defense against stress conditions and V. dahliae infection, rendering it a candidate for the generation of stress-resistant engineered cotton.

Potassium improves photosynthetic tolerance to and recovery from episodic drought stress in functional leaves of cotton (Gossypium hirsutum L.)

To investigate whether potassium (K) application enhances the potential of cotton (Gossypium hirsutum L.) plants to maintain physiological functions during drought and recovery, low K-sensitive (Siza 3) and -tolerant (Simian 3) cotton cultivars were exposed to three K rates (0, 150, and 300 K₂O kg ha^-1) and either well-watered conditions or severe drought stress followed by a recovery period. Under drought stress, cotton plants showed a substantial decline in leaf water potential, stomatal conductance, photosynthetic rate, and the maximum and actual quantum yield of PSII, resulting in greater non-photochemical quenching and lipid peroxidation as compared to well-watered plants. However, plants under K application not only showed less of a decline in these traits but also displayed greater potential to recover after rewatering as compared to the plants without K application. Plants receiving K application showed lower lipid peroxidation, higher antioxidant enzyme activities, and increased proline accumulation as compared to plants without K application. Significant relationships between rates of photosynthetic recovery and K application were observed. The cultivar Siza 3 exhibited a more positive response to K application than Simian 3. The results suggest that K application enhances the cotton plant's potential to maintain functionality under drought and facilitates recovery after rewatering.