Drought Stress Tolerance In Maize Research Articles

Regulatory mechanisms used by ZmMYB39 to enhance drought tolerance in maize (Zea mays) seedlings

Drought is a significant abiotic stressor that limits maize (Zea mays L.) growth and development. Thus, enhancing drought tolerance is critical for promoting maize production. Our findings demonstrated that ZmMYB39 is an MYB transcription factor with transcriptional activation activity. Drought stress experiments involving ZmMYB39 overexpression and knockout lines indicated that ZmMYB39 positively regulated drought stress tolerance in maize. DAP-Seq, EMSA, dual-LUC, and RT-qPCR provided initial insights into the molecular regulatory mechanisms by which ZmMYB39 enhances drought tolerance in maize. ZmMYB39 directly promoted the expression of ZmP5CS1, ZmPOX1, ZmSOD2, ZmRD22, ZmNAC49, and ZmDREB2A, which are involved in stress resistance. ZmMYB39 enhanced drought tolerance by interacting with and promoting the expression of ZmFNR1, ZmHSP20, and ZmDOF6. Our study offers a theoretical basis for understanding the molecular regulatory networks involved in maize drought stress response. Furthermore, ZmMYB39 serves as a valuable genetic resource for breeding drought-resistant maize.

ZmASR1 negatively regulates drought stress tolerance in maize

Abscisic acid-, stress-, and ripening-induced (ASR) proteins in plants play a significant role in plant response to diverse abiotic stresses. However, the functions of ASR genes in maize remain unclear. In the present study, we identified a novel drought-induced ASR gene in maize (ZmASR1) and functionally characterized its role in mediating drought tolerance. The transcription of ZmASR1 was upregulated under drought stress and abscisic acid (ABA) treatment, and the ZmASR1 protein was observed to exhibit nuclear and cytoplasmic localization. Moreover, ZmASR1 knockout lines generated with the CRISPR–Cas9 system showed lower ROS accumulation, higher ABA content, and a higher degree of stomatal closure than wild-type plants, leading to higher drought tolerance. Transcriptome sequencing data indicated that the significantly differentially expressed genes in the drought treatment group were mainly enriched in ABA signal transduction, antioxidant defense, and photosynthetic pathway. Taken together, the findings suggest that ZmASR1 negatively regulates drought tolerance and represents a candidate gene for genetic manipulation of drought resistance in maize.

ZmMYB56 regulates stomatal closure and drought tolerance in maize seedlings through the transcriptional regulation of ZmTOM7

The growth and yield of essential crops, including maize, are significantly endangered by drought. Closing stomata, limiting water dissipation, and improving water use efficiency are important components of plant drought responses. In our study, the MYB-like transcription factor ZmMYB56, expressed in maize guard cells, played important roles in regulating stomatal closure and drought tolerance. Mutations in ZmMYB56 triggered elevated stomatal conductance, rapid water loss in isolated leaves, and severe drought sensitivity in plants. ZmMYB56 possesses transcriptional activation activity, and is expressed specifically in stomatal guard cells. As an R2R3 transcription factor, ZmMYB56 can bind the cis-acting element on the ZmTOM7 promoter sequence, activating its expression. Correspondingly, the ZmTOM7 transcript level is downregulated in Zmmyb56 seedlings. Transgenic Arabidopsis plants overexpressing ZmTOM7 exhibit limited stomatal conductance and elevated drought tolerance, while the ZmTOM7 mutation is linked to higher stomatal conductance and substantial drought sensitivity in maize seedlings. According to these findings, we conclude that ZmTOM7 operates as a key target gene of ZmMYB56 and is involved in ZmMYB56-regulated stomatal closure and maize drought tolerance. Our findings regarding the functional mechanisms of maize ZmMYB56 transcription factors in stomatal closure and drought stress enable a potential genetic resource for improving the drought resistance of maize.

ZmC2H2-149 negatively regulates drought tolerance by repressing ZmHSD1 in maize.

Drought is a major abiotic stress that limits maize production worldwide. Therefore, it is of great importance to improve drought tolerance in crop plants for sustainable agriculture. In this study, we examined the roles of Cys2 /His2 zinc-finger-proteins (C2H2-ZFPs) in maize's drought tolerance as C2H2-ZFPs have been implicated for plant stress tolerance. By subjecting 150 Ac/Ds mutant lines to drought stress, we successfully identified a Ds-insertion mutant, zmc2h2-149, which shows increased tolerance to drought stress. Overexpression of ZmC2H2-149 in maize led to a decrease in both drought tolerance and crop yield. DAP-Seq, RNA-Seq, Y1H and LUC assays additionally showed that ZmC2H2-149 directly suppresses the expression of a positive drought tolerance regulator, ZmHSD1 (hydroxysteroid dehydrogenase 1). Consistently, the zmhsd1 mutants exhibited decreased drought tolerance and grain yield under water deficit conditions compared to their respective wild-type plants. Our findings thus demonstrated that ZmC2H2-149 can regulate ZmHSD1 for drought stress tolerance in maize, offering valuable theoretical and genetic resources for maize breeding programmes that aim for improving drought tolerance.

Molecular mechanism analysis of ZmRL6 positively regulating drought stress tolerance in maize

MYB-related genes, a subclass of MYB transcription factor family, have been documented to play important roles in biological processes such as secondary metabolism and stress responses that affect plant growth and development. However, the regulatory roles of MYB-related genes in drought stress response remain unclear in maize. In this study, we discovered that a 1R-MYB gene, ZmRL6, encodes a 96-amino acid protein and is highly drought-inducible. We also found that it is conserved in both barley (Hordeum vulgare L.) and Aegilops tauschii. Furthermore, we observed that overexpression of ZmRL6 can enhance drought tolerance while knock-out of ZmRL6 by CRISPR-Cas9 results in drought hypersensitivity. DAP-seq analyses additionally revealed the ZmRL6 target genes mainly contain ACCGTT, TTACCAAAC and AGCCCGAG motifs in their promoters. By combining RNA-seq and DAP-seq results together, we subsequently identified eight novel target genes of ZmRL6 that are involved in maize's hormone signal transduction, sugar metabolism, lignin synthesis, and redox signaling/oxidative stress. Collectively, our data provided insights into the roles of ZmRL6 in maize’s drought response.

Leaf extract of neem (Azadirachta indica Adr. Juss.) modulates morphological and biochemical characteristics in maize (Zea mays L.) under water deficit stress

Foliar spray of neem (Azadirachta indica Adr. Juss.) leaf extract was exogenously applied at pre-flowering stage to examine the changes in growth and physio-biochemical characteristics of two maize cultivars (Sultan and Sadaf) under different water regimes (100%, 75% and 60% field capacity). Water deficit conditions significantly reduced shoot fresh weight (SFW), shoot dry weight (SDW), root fresh weight (RFW), root dry weight (RDW), shoot length, root length, chlorophyll b, total soluble proteins and free proline, but it significantly increased ascorbic acid (AsA) and total phenolics in both maize cultivars. Foliar-applied leaf neem extract significantly improved SFW, SDW, RFW, RDW, shoot length, chlorophyll b and ascorbic acid concentrations, but it significantly minimized hydrogen peroxide (H2O2) contents. Application of 1.0% neem extract was effective in improving chlorophyll b and AsA contents, whereas 2.0% neem extract was beneficial for total soluble proteins and MDA contents. Of both maize cultivars, cv. Sultan was found to be drought sensitive and cv. Sadaf as drought tolerant. Exogenous application of leaf neem extract was suggested to be effective in enhancing drought stress tolerance in maize by improving plant growth and oxidative defense system.

Integration of mRNA and microRNA analysis reveals the molecular mechanisms underlying drought stress tolerance in maize (Zea mays L.).

Drought is among the most serious environmental issue globally, and seriously affects the development, growth, and yield of crops. Maize (Zea mays L.), an important crop and industrial raw material, is planted on a large scale worldwide and drought can lead to large-scale reductions in maize corn production; however, few studies have focused on the maize root system mechanisms underlying drought resistance. In this study, miRNA–mRNA analysis was performed to deeply analyze the molecular mechanisms involved in drought response in the maize root system under drought stress. Furthermore, preliminary investigation of the biological function of miR408a in the maize root system was also conducted. The morphological, physiological, and transcriptomic changes in the maize variety “M8186” at the seedling stage under 12% PEG 6000 drought treatment (0, 7, and 24 h) were analyzed. With prolonged drought stress, seedlings gradually withered, the root system grew significantly, and abscisic acid, brassinolide, lignin, glutathione, and trehalose content in the root system gradually increased. Furthermore, peroxidase activity increased, while gibberellic acid and jasmonic acid gradually decreased. Moreover, 32 differentially expressed miRNAs (DEMIRs), namely, 25 known miRNAs and 7 new miRNAs, and 3,765 differentially expressed mRNAs (DEMRs), were identified in maize root under drought stress by miRNA-seq and mRNA-seq analysis, respectively. Through combined miRNA–mRNA analysis, 16 miRNA–target gene pairs, comprising 9 DEMIRs and 15 DEMRs, were obtained. In addition, four metabolic pathways, namely, “plant hormone signal transduction”, “phenylpropane biosynthesis”, “glutathione metabolism”, and “starch and sucrose metabolism”, were predicted to have important roles in the response of the maize root system to drought. MiRNA and mRNA expression results were verified by real-time quantitative PCR. Finally, miR408a was selected for functional analysis and demonstrated to be a negative regulator of drought response, mainly through regulation of reactive oxygen species accumulation in the maize root system. This study helps to elaborate the regulatory response mechanisms of the maize root system under drought stress and predicts the biological functions of candidate miRNAs and mRNAs, providing strategies for subsequent mining for, and biological breeding to select for, drought-responsive genes in the maize root system.

Recent Advances for Drought Stress Tolerance in Maize (Zea mays L.): Present Status and Future Prospects.

Drought stress has severely hampered maize production, affecting the livelihood and economics of millions of people worldwide. In the future, as a result of climate change, unpredictable weather events will become more frequent hence the implementation of adaptive strategies will be inevitable. Through utilizing different genetic and breeding approaches, efforts are in progress to develop the drought tolerance in maize. The recent approaches of genomics-assisted breeding, transcriptomics, proteomics, transgenics, and genome editing have fast-tracked enhancement for drought stress tolerance under laboratory and field conditions. Drought stress tolerance in maize could be considerably improved by combining omics technologies with novel breeding methods and high-throughput phenotyping (HTP). This review focuses on maize responses against drought, as well as novel breeding and system biology approaches applied to better understand drought tolerance mechanisms and the development of drought-tolerant maize cultivars. Researchers must disentangle the molecular and physiological bases of drought tolerance features in order to increase maize yield. Therefore, the integrated investments in field-based HTP, system biology, and sophisticated breeding methodologies are expected to help increase and stabilize maize production in the face of climate change.

Genome-wide identification of HD-ZIP transcription factors in maize and their regulatory roles in promoting drought tolerance.

Drought is the main limiting factor of maize productivity, therefore improving drought tolerance in maize has potential practical importance. Cloning and functional verification of drought-tolerant genes is of great importance to understand molecular mechanisms under drought stress. Here, we employed a bioinformatic pipeline to identify 42 ZmHDZ drought responsive genes using previously reported maize transcriptomic datasets. The coding sequences, exon-intron structure and domain organization of all the 42 genes were identified. Phylogenetic analysis revealed evolutionary conservation of members of the ZmHDZ genes in maize. Several regulatory elements associated with drought tolerance were identified in the promoter regions of ZmHDZ genes, indicating the implication of these genes in plant response to drought stress. 42 ZmHDZ genes were distributed unevenly on 10 chromosomes, and 24 pairs of gene duplications were the segmental duplication. The expression of several ZmHDZ genes was upregulated under drought stress, and ZmHDZ9 overexpressing transgenic plants exhibited higher SOD and POD activities and higher accumulation of soluble proteins under drought stress which resulted in enhanced developed phenotype and improved resistance. The present study provides evidence for the evolutionary conservation of HD-ZIP transcription factors homologs in maize. The results further provide a comprehensive insight into the roles of ZmHDZ genes in regulating drought stress tolerance in maize.

Exogenously Applied Proline Modulates Drought Tolerance in Maize (Zea mays L)

Improving drought stress tolerance in maize is essential to increase its production and yield worldwide. Thus, the present study was conducted to investigate the improvement of drought tolerance in maize (Zea mays L.) by exogenous application of proline (25 and 50mM) on two maize varieties. Maize plants were subjected to drought stress at various phases of plant growth under pot culture conditions and proline was applied as foliar spray. Water deficit stress caused a significant decrease (by approximately 25%) in growth and yield of both maize varieties by decreasing plant height, cob length, dry root weight, grains per cob and 100-grain weight. Water deficit stress also decreased chlorophyll and intercellular proline contents, and antioxidant enzyme activities viz. catalase (CAT), guaiacol peroxidase (POX) and ascorbate peroxidase (APX). Exogenous application of proline (50 mM) was found to be more effective in increasing growth and yield of both varieties. These increases were positively associated with increased levels (by at least 15%) of chlorophyll and intracellular proline, and enhanced activities of CAT, POX and APX enzymes in both varieties. Interaction effects of exogenous proline and water deficit stress were significant in aspects of higher growth and yields and enhanced levels of chlorophyll, intracellular proline and antioxidant enzyme activities. Therefore, it is concluded that foliar application of proline improves drought tolerance by modulating chlorophyll and intracellular proline contents, and antioxidant enzyme activities.

Effect of naphthyl acetic acid foliar spray on the physiological mechanism of drought stress tolerance in maize (Zea Mays L.)

Owing to climate change, there has been an alarming increase in drought conditions, which has led to an expected increase in the loss of water in soil and water bodies. Moreover, the concomitant climatic disasters are causing severe crop losses worldwide. The designed experiment is aimed to determine the potential effect of naphthyl acetic acid (NAA) foliar spray and how it neutralizes the adverse effects of different drought stress levels (5d, 7d, 10d, 12d and 15d drought) on two maize varieties namely Pakhari and Jalal. A pot experiment was conducted in the Department of Botany, Bacha Khan University Charsadda, during the maize growing season in 2014. Results indicated that the drought-sensitive variety Pakhari is markedly affected, as observed from their reduced level of antioxidant enzymes including peroxidase, superoxide dismutase and catalase along with osmoprotectants including proline and sugar content at the lowest drought stress level of 5 days compared with that observed in the drought-tolerant variety Jalal. Furthermore, a marked decrease in the leaf water status 0.05–0.415 g−1, chlorophyll and carotenoid contents are associated with an increase in the accumulation of sugar, proline and antioxidant enzyme activities under drought stress. Analysis of variance between genotype, drought stress and NAA treatment was performed, and the results were considered significant at p<0.05, except for the germination rate index (GRI), total biomass (TB), carotenoid content (CC), seed vigor index (SVI-II), soluble protein content (SPT) and superoxide dismutase (SOD). Variance analysis was performed to examine the interactions between drought and NAA treatment,and the results were found to be significant at p < 0.05 for seed vigor index (SVI-I, SVI-II), root–shoot ratio (RSR), leaf area index (LAI), leaf area ratio (LAR), TB, chlorophyll ‘a’ (CA), chlorophyll ‘b’ (CB), CC, peroxidase (POD) and SOD content under high drought stress (15d) irrespective of SVI-I, CB, POD, SOD, RSR, CB, SSC and SPC under low drought (5d) conditions. It has been concluded from the obtained results that maize varieties exhibit tolerance when subjected to low levels of drought stress; however, high drought stress (15d) reduces crop yield via high osmotic potential, which poses an alarming threat to Pakistani agriculturists in the forthcoming climate change.

Melatonin enhances drought stress tolerance in maize through coordinated regulation of carbon and nitrogen assimilation

Melatonin is a pleiotropic regulatory molecule in plants and is involved in regulating plant tolerance to drought stress. Here, we conducted transcriptomic and physiological analyses to identify metabolic processes associated with the enhanced tolerance of the melatonin-treated maize (Zea mays L.) seedlings to water deficit. Maize seedlings were foliar sprayed with either 50 μM melatonin or water and exposed to drought stress for 12 d in growth chambers. Drought stress significantly suppressed seedling growth, and melatonin application partially alleviated this growth inhibition. RNA-Seq analysis revealed that genes whose expression was significantly altered by melatonin were mainly related to carbon (C) and nitrogen (N) metabolism. Analysis of transcriptomics, enzyme activity, and metabolite content data, melatonin-treated plants exhibited a higher level of relatively stable C and N metabolism than untreated plants; this phenotype of melatonin-treated plants was associated with their higher photosynthesis, sucrose biosynthesis, N assimilation, and protein biosynthesis capacities under drought stress. Overall, our results suggest that melatonin enhances drought stress tolerance in maize through coordinated regulation of C and N metabolism.

Silicon Defensive Role in Maize (Zea mays L.) against Drought Stress and Metals-Contaminated Irrigation Water

Irrigation water rarity and its contamination with toxic metals are increasing gradually and have become imperious issues for the environment at personal and governmental levels. Silicon (Si) can increase plant tolerance to abiotic stressors and beneficially affect plant growth and productivity. The main purpose of the current study was to investigate the effect of Si as a foliar application on growth, photosynthetic efficiency, plant-water status, metals accumulation, water-use efficiency (WUE) and yield of maize grown under drought and metals-contaminated irrigation water stresses. We conducted two-season field experiments in 2017 and 2018 summer seasons on maize grown under two irrigation regimes (Full irrigation (FI = 100%) and deficit irrigation (DI20% = 80%) of crop evapotranspiration) combined with 0 (Si0), 2 (Si2), and 4 (Si4) mM of Si in form of Na2SiO3 applied at 40 and 60 days after planting as a foliar application. In both seasons, maize plants were irrigated with metals-contaminated redundant water (Ni2+; 5.5 ppm, Cd2+; 0.27 ppm, and Cr3+; 5 ppm). Exogenous application of Si increased drought stress tolerance in maize by enhancing photosynthetic efficiency, stomatal conductance (gs) and cell membrane integrity as evaluated by membrane stability index. These results were positively reflected in improving plant growth, WUE, and productivity along with decreasing accumulation of Ni+2, Cd+2, and Cr+3 in leaves and grains under drought stress by metals-contaminated irrigation water. Deficit irrigation and metal-contaminated irrigation water conditions reduced growth and productivity of maize plants. However, foliar application of Si was effective in enhancing the physiological performance, water use efficiency, and productivity of maize under drought and/or contaminated irrigation water conditions. Therefore, Si may, in future, find value as a potential plant growth stimulant under different abiotic stresses.

Rapid method of screening for drought stress tolerance in maize (Zea mays L.)

Drought stress is the major production constraint in rainfed maize. Screening for drought tolerance is severely affected by the lack of a simple and reliable phenotyping technique. The objective of this study was to standardize a simple hydroponic based drought screening technique in maize. In this context, one week old uniform seedlings of 55 inbreds and 5 hybrids were transferred to hydroponic solution in the glass house. The seedlings were allowed to acclimatize for next one week in hydroponic solution. The drought stress was imposed by removing seedlings from nutrient solution and exposed to air for 6 and 4 hours daily for a period of 5 and 4 consecutive days in hybrids and inbreds, respectively. Data were recorded on all shoot and root parameters, and based on stress symptoms, a drought tolerance score was given to each genotype. The percent deductions in shoot and root fresh weight from non-stress to stress ranged from 11.7 to 84.4 and 2.1 to 77.5, respectively. Six inbred lines, namely, DQL790-4, CML334, CM140, CML422, CM125 and HKI488 and three hybrids namely DMRH1306, DMRH1410 and PMH4 were found drought tolerant. The effectiveness of this screening technique was compared and confirmed using pots screening as well as by expression profiling of key antioxidant genes (Sod2, Sod4, Sod9 and Apx1) playing role in drought stress tolerance. This phenotyping technique is very short, low cost and simple which can be utilized in preliminary drought screening for large set of maize germplasm and mapping populations.

Genome-wide association study and genomic prediction analyses of drought stress tolerance in China in a collection of off-PVP maize inbred lines

Phenotypic evaluation of the drought-tolerant traits and identification of the genetic markers associated with these traits in diverse germplasms are essential for developing drought-tolerant germplasm through molecular breeding. A collection of 210 off-PVP (no longer subject to Plant Variety Protection) maize inbred lines introduced from the USA (ALs) were genotyped using a low-coverage sequencing method and phenotyped in eight environments (location × year × treatment) in China. The CV of phenotypic data for six target traits varied from 5.34 to 20.69% under well-watered (WW) conditions and from 5.46 to 35.98% under drought-stressed (WS) conditions. ALs exhibited higher grain yield per plot (GY) under the WS conditions and premature characteristic compared with the local checks, which are important breeding targets in drought tolerance. Two subgroups, SS and NSS, were identified in this collection based on population structure analysis, PCA, and an NJ tree. A total of 413 trait-associated SNPs under the WW conditions and 696 SNPs under the WS conditions were detected in a GWAS (genome-wide association study) analysis, with the phenotypic variation explained by each SNP to the target traits varied from 10.02 to 25.40%. In the genomic prediction (GP) analysis, the prediction models incorporating trait-marker associations showed higher prediction accuracies than the prediction models using an equivalent number of randomly selected SNPs for all the six traits evaluated under both the WW and WS conditions. The results observed in this study provide valuable information for understanding the genetic variation of drought stress tolerance in maize, and show great potential to improve drought stress tolerance in maize via genomic selection.

Foliar calcium spray confers drought stress tolerance in maize via modulation of plant growth, water relations, proline content and hydrogen peroxide activity

ABSTRACTWater and nutrient restrictions are the factors that limiting growth of maize in arid/semi-arid climate. Calcium (Ca2+) uptake is affected severely under drought stress (DS). The objectives of this study were to investigate the effects of DS and foliar applied Ca2+ on growth, physiological, biochemical, yield and grain-nutrient content in two maize cultivars i.e. drought-tolerantDekalb-6525 and drought-sensitive Yousafwala-hybrid. The study comprised of two phases; firstly the best rate of Ca2+ (20, 40 and 60 mg L−1) was evaluated. Secondly, optimized rate of Ca2+ (40 mg L−1) was used to assess physio-biochemical and yield responses of maize under DS. The applied DS caused significant reduction in maize growth, water-status, photosynthesis and grain nutrient contents. Foliar Ca2+ markedly improved plant growth, water-potential (18%), turgor-potential (75%), photosynthesis (45%), stomatal-conductance (47%), transpiration rate (43%) and accumulation of total soluble sugars (20%) along with decline in H2O2 content (23%) in both cultivars under DS. Furthermore, optimized rate of Ca2+ improved maize grain yield and quality under water-deficit conditions. Cultivar Dekalb-6525 presented significant response to Ca2+ over Yousafwala-hybrid. Results of the study surmise that foliar supply of Ca2+ is an effective approach to make plants vigorous to thrive under limited-water supply.

Exogenous application of urea and a urease inhibitor improves drought stress tolerance in maize (Zea mays L.).

Drought is believed to cause many metabolic changes which affect plant growth and development. However, it might be mitigated by various inorganic substances, such as nitrogen. Thus, the study was carried out to investigate the effect of foliar-applied urea with or without urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) on a maize cultivar under drought stress simulated by 15% (w/v) polyethylene glycol 6000. Foliar-applied urea resulted in a significant increase in plant dry weight, relative water content, and photosynthetic pigments under water stress condition. Furthermore, the activities of superoxide dismutase (SOD), peroxidase (POD), and hydrogen peroxidase (CAT), were enhanced with all spraying treatments under drought stress, which led to decreases in accumulation of hydrogen peroxide (H2O2), superoxide anion ([Formula: see text]) and malondialdehyde (MDA). The contents of soluble protein and soluble sugar accumulated remarkably with urea-applied under drought stress condition. Moreover, a further enhancement in above metabolites was observed by spraying a mixture of urea and urease inhibitor as compared to urea sprayed only. Taken together, our findings show that foliar application of urea and a urease inhibitor could significantly enhance drought tolerance of maize through protecting photosynthetic apparatus, activating antioxidant defense system and improving osmoregulation.

Effect of Nephthyl Acetic Acid Foliar Spray on Amelioration of Drought Stress Tolerance in Maize (Zea mays L.)

ABSTRACTThe present study aimed to determine the effect of nephthyl acetic acid (NAA) on the physiological mechanism of drought tolerance in selected maize (Zea mays L.) varieties under induced drought stress at the vegetative stage. Maize seeds were sown in plastic pots (14 cm lower inside diameter, 18.5 cm upper inner diameter, 15.6 cm height, and 0.5 cm thickness) filled with 3 kg of air-dried soil and sand (3:1) in triplicate in the greenhouse of the Botany Department, Bacha Khan University, Charsadda in 2014. Results showed that the activities of antioxidant enzymes and proline accumulation were associated with the dry mass production and consequently with the drought tolerance of the maize varieties. It has been concluded that the inhibitory effects of water stress were ameliorated by exogenous application of NAA and were found to be significant for antioxidant enzymes at the vegetative stage in both varieties.

Dual Application of 24-Epibrassinolide and Spermine Confers Drought Stress Tolerance in Maize (Zea mays L.) by Modulating Polyamine and Protein Metabolism

No information is available concerning the influence of dual application of 24-epibrassinolide (EBL) and spermine (Spm) on the nitrogen metabolism in plants subjected to drought conditions. As a first report, this investigation assesses the role of EBL, Spm, and their dual application on polyamine and protein pools in water-stressed plants. It explores the ameliorative effects of these foliar applications under water deficiency. Two maize hybrids (Giza 10 and Giza 129) were treated with or without EBL and/or Spm foliar applications under well-irrigated and drought-stressed conditions (75 and 50 % of field capacity). Dual application (25 mg l−1 Spm + 0.1 mg l−1 EBL) significantly relieved the drought-induced inhibition on the activities of ribulose-1,5-bisphosphate carboxylase and nitrate reductase and the contents of relative water, nitrate, and protein, particularly in hybrid Giza 129. Changes in the content of free polyamines and in the activity of polyamine biosynthetic and catabolic enzymes were detected when water-stressed plants were treated with EBL and/or Spm. Putrescine content and arginine decarboxylase activity were significantly increased in stressed hybrid Giza 10 plants treated by the dual application. However, spermidine and Spm levels as well as ornithine decarboxylase and S-adenosylmethionine decarboxylase activities were significantly increased in stressed hybrid Giza 129 plants treated with the dual application. Diamine oxidase, polyamine oxidase, protease activity, carbonyl content, and ethylene formation were increased in response to water stress and significantly decreased when stressed plants were treated by the dual application. Total free amino acids, phenols, and flavonoids concentration were increased with the increasing water stress level; moreover, they further increased in stressed plants treated with the dual application. Overall, the combined utilization of EBL and Spm serves as complementary tools to confer plant drought tolerance by altering polyamine, ethylene, and protein levels.

Effects of salicylic acid on growth and accumulation of phenolics in Zea mays L. under drought stress

ABSTRACTThe accumulation of total soluble and cell wall-bound phenolics and total soluble proteins in Zea mays plants exposed to drought stress and foliar spray of salicylic acid (SA) at 10−4 mol/L and 10−5 mol/L was investigated. Drought stress was imposed at the four-leaf stage for 10 days (30–35% field capacity). Dehydration of maize leaves was accompanied by the accumulation of both total soluble and cell wall-bound phenolics, reduction in leaf relative water content (LRWC), and shoot and root growth attributes. Foliar spraying of SA further augmented the content of total soluble and cell wall-bound phenolics and total soluble proteins content under drought stress. SA ameliorated the adverse effects of drought stress on LRWC, shoot fresh weight, shoot dry weight, root fresh weight, root dry weight, root length and root area. The accumulation of both soluble and cell wall-bound phenolics by foliar spray of SA may be a mechanism related to SA-induced drought stress tolerance in maize. It was concluded that foliar spraying of SA at 10−5 mol/L can be highly economical and effective for modifying the effects of drought stress on maize at the four-leaf stage.