Drought Stress In Maize Research Articles

Foliar Potassium Sulfate Application Improved Photosynthetic Characteristics, Water Relations and Seedling Growth of Drought-Stressed Maize

Changing climates and frequent spells of drought have increased the risk of crop failure, especially in arid and semi-arid regions, thus multiplying the vulnerability of food-insecure populations. The exogenous application of potassium (K) can potentially ameliorate the adverse effects of drought in maize by maintaining cell osmotic potential and turgidity, provided its optimum doses are applied. The present experiment comprised two maize cultivars, viz. Islamabad Gold (drought tolerant) and Azam (drought susceptible), grown under well-watered (80% water-holding capacity (WHC)), mild drought (60% WHC) and severe drought (40% WHC) conditions. Different doses of K, viz. 0%, 1% and 2%, were also tested to screen out the most superior concentration. Drought stress markedly reduced root and shoot lengths (25% and 16%, respectively) along with their dry weights (20% and 10%, respectively). Moreover, a substantial reduction in leaf relative water content (RWC) (24%), stomatal conductance, transpiration and photosynthesis rates, chlorophyll pigments a, b and total chlorophyll contents (31%) were recorded, compared with well-watered conditions. However, foliar application of K2SO4 at 2% concentration outperformed other doses by improving growth attributes, RWC (10%), total chlorophyll (9%) and proline (12%) under severe drought conditions. Our findings confirmed the effectiveness of foliage-applied K2SO4 in ameliorating drought effects in rainfed maize; however, more doses and sources of K could be tested for developing it as a potent source to cope with water stress.

Ameliorative Effects of Calcium Sprays on Yield and Grain Nutritional Composition of Maize (Zea mays L.) Cultivars under Drought Stress

Drought stress is seriously affecting maize production. To investigate the influence of calcium (Ca) foliar application on maize production and chemical composition of grains under drought stress, two experiments were carried out at Cairo University Research Station, Giza, Egypt, during the summer seasons of 2018 and 2019. The experimental design was split-split plot design with a completely randomized blocks arrangement with three replications. Water regimes were assigned to the main plots [100 (control), 75, and 50% of estimated evapotranspiration]. Calcium levels (zero and 50 mg/L) were assigned to the sub plots. Maize cultivars (SC-P3444, Sammaz-35 and EVDT) were assigned to the sub-sub plots. Three maize cultivars were sprayed with Ca solution concentration (50 mg/L) under normal and drought conditions. The control treatment (0 mg/L) was sprayed with an equal amount of distilled water for comparison. Results indicated a significant decrease in total yield and grain characteristics [protein, ash, total sugars, nitrogen (N), phosphorus (P), potassium (K), and iron (Fe) contents] as a response of drought. Calcium foliar application significantly increased maize yield, protein, ash, carbohydrates, starch, total sugars, and ionic contents of grains, except for manganese (Mn), under all irrigation levels. Based on the drought tolerance index (DTI), only cultivar SC-P3444 showed drought tolerance while cultivars Sammaz-35 and EVDT were sensitive to drought stress. Foliar application of Ca on SC-P3444 cultivar achieved the highest grain yield per hectare (8061 kg) under the water regime of 100% of the total evapotranspiration, followed by Sammaz-35 (7570 kg), and EVDT (7191 kg) cultivars. At the water regime of 75% of estimated evapotranspiration (75% irrigation), Ca foliar application increased grain yield by 16, 13 and 14% in SC-P3444, Sammaz-35, and EVDT, respectively. At the water regime of 50% of the estimated evapotranspiration (50% irrigation), Ca foliar application increased grain yield by 17, 16, and 13% in SC-P3444, Sammaz-35, and EVDT, respectively. In brief, Ca had a clear impact on productivity and grain quality with important implications for maize yield under normal and water stress conditions. Our findings demonstrate that foliar application of Ca enabled drought stressed maize plants to survive better under stress. The most water stress tolerant cultivar was SC-P3444 followed by Sammaz-35 and EVDT under drought stress.

Expression patterns of the ZmASR family during simulated drought stress in maize

AbstractMaize (Zea mays L.) is an important food crop. Maize production is adversely affected by abiotic stress, especially drought stress. The screening and characterization of the roles of stress‐related genes in maize are thus essential for improving abiotic stress resistance. Abscisic acid‐stress‐ripening (ASR)‐induced proteins with abscisic acid/water deficit stress (ABA/WDS) domains are a class of plant‐specific transcription factors that play an important role in plant development, growth, and abiotic stress responses. In this study, nine members of the ASR‐induced protein in maize (ZmASR) family were predicted and analyzed in maize in terms of gene structure, subcellular localization, amino acid sequence, physical and chemical properties, secondary structure, tertiary structure, and phosphorylation modification sites by bioinformatics. Analysis of regulatory promoter elements was performed to provide additional information about their distinctive tissue‐specific expression and possible functions. To further investigate the function of these proteins in maize, the expression levels of ZmASRs in different tissues and in response to different drought stress treatments were analyzed using quantitative real‐time polymerase chain reaction (qRT‐PCR). The results showed that the nine members of the maize ZmASR family have very different expression levels in different organs and under different degrees of drought stress. Moreover, the expression levels of the nine members in the same organ also varied greatly with leaf age. These findings provide a reference for functional research of the maize ZmASR gene family. Our findings have important theoretical and practical significance for cultivating new drought‐resistant maize varieties and promoting the development of the maize industry.

Cover crop effects on maize drought stress and yield

Cover crops have been proposed as a tool for adapting cropping systems to drought stress caused by climate change. However, little research has directly evaluated whether cover crops reduce drought stress in the following cash crop. We grew maize in both ambient and imposed drought conditions following four functionally diverse cover crops and a fallow control in a two-site-year study. We looked for evidence that cover crops reduced drought stress by improving cash crop water access or nitrogen (N) status. The study was embedded in an organic cropping systems trial in Pennsylvania, USA. Cover crops and manure fertilizer were incorporated with full inversion tillage.Overall, cover crops neither ameliorated nor exacerbated drought stress in the following maize crop. There was no interaction between cover crop and moisture treatment in a mixed model ANOVA predicting maize kernel yield in either year. Drought reduced yield by 33 % in 2014 and 17 % in 2015. Cereal rye (Secale cereale L. cv. Aroostook) reduced yield relative to cover crop treatments that contained legumes by up to 43 %. There were no other yield differences among cover crop treatments, including the fallow control. Our results are likely influenced by the short legacy of cover cropping (only one or two preceding cover crops) and the use of full inversion tillage. Cover crops may have greater potential to reduce maize drought stress after long-term use, in systems with less soil disturbance, and when residues are retained on the soil surface. Further research is needed to assess the potential for cover crops and other soil-building practices to reduce drought stress by increasing infiltration rates, improving soil water-holding capacity, enhancing cash crop root exploration, and reducing evaporation from the soil surface.Multiple lines of evidence in this study lead to a new hypothesis: cropping systems that rely on cover crops and other organic amendments for N supply may be at risk for N limitation under drought. First, drought reduced mineralization of N from cover crop residues, especially cereal rye. Second, drought reduced maize N status when topsoil drying was more severe. Since cover crop residues and manure were concentrated in the plow layer (top 20 cm) and maize roots extended into the subsoil, topsoil drying may have reduced N mineralization more than crop water uptake. Further research is needed to determine whether and under what circumstances the hypothesized effect meaningfully reduces crop yield.

English

β-expansin 2 (EXPB2) gene induces drought tolerance in different plant species including maize. Different epigenetic mechanisms like DNA methylation, histone modification and RNA interference affect the gene activities under stress conditions. DNA methylation, an important epigenetic mechanism, could be involved in the regulation of ZmEXPB2 gene under drought stress in maize. Plants of drought sensitive variety „Jalal‟ were grown till 4th leaf stage under well-watered conditions. At 5th leaf stage, plants were divided in two groups i.e., well-watered (100% water holding capacity) or drought stress (0% water holding capacity for 15 days). Plants subjected to drought stress showed clear signs of stress by significant decrease in fresh weight of whole plant, 6th leaf length, stunted secondary root growth and increased primary root length. DNA methylation profile of three regions (denoted as -1.7 k, -1.3 k and -0.8 k) in the promoter of ZmEXPB2 gene, of root DNA, were evaluated. Under well-watered conditions, heterogeneity in DNA methylation profile along the promoter sequence was observed. Regions -1.7 k and -1.3 k were methylated whereas the region -0.8 k was nonmethylated. After the comparison of DNA methylation profile of well-watered and drought stress plants, no change in -1.7 k and -0.8 k regions was observed. However, the -1.3k region had significant decrease in the DNA methylation at symmetric cytosine sites i.e., cytosine-guanine (CG) dinucleotides and cytosine-adenine/cytosine/thymine-guanine (CHG where H = A, C or T) trinucleotide and significant increase at asymmetric cytosine sites (CHH) under the stress condition. In addition, significant increase in the gene expression of ZmEXPB2 under drought was also observed. In conclusion, drought stress conditions induce DNA hypomethylation at CG, and CHG sites and DNA hypermethylation at CHH sites in the middle region of the promoter of ZmEXPB2 gene. This shift can be associated with the up regulation of ZmEXPB2 gene which in turn increased primary root length as a plant stress response mechanism. © 2021 Friends Science Publishers

Effects of Improving Evapotranspiration Parameterization Scheme on WOFOST Model Performance in Simulating Maize Drought Stress Process

To solve the problem on poor performance of crop growth model in simulating crop growth process under water stress, three schemes including improving evapotranspiration parameterization scheme with Penman-Monteith method, building dynamic crop coefficient (Kc) and considering simultaneously two above-mentioned solutions which are respectively named as the PM, CC and PMCC schemes are used to improve WOFOST model. Their effects on model performance in simulating maize drought stress process are evaluated based on experiments of different sowing dates on 20 April, 30 April and 10 May conducted in Jinzhou in the year with normal precipitation (2012) and the dry year (2015 and 2018). The results show that compared with the default model, PM scheme plays a role in increasing potential evapotranspiration and transpiration rate in 2012, while CC scheme decreases (increases) transpiration rate as Kc is larger (smaller) than the model default value 1, respectively. Three schemes hardly affect simulation accuracies of soil moisture in rooted zone, total above ground production, leaf area index (ILA) and yield. In 2015, PM scheme makes ILA, total above ground production yield and soil moisture dramatically smaller than those with the default model after the jointing stage of maize. It also increases (decreases) transpiration rate before (after) the whorl stage of maize. After improving the model with CC scheme, ILA, total above ground production, yield and soil moisture are slightly larger than those simulated by the default model after the whorl stage, and the simulated transpiration rates are smaller (larger) than those simulated by the default model before (after) the whorl stage of maize. Nevertheless, the above-mentioned variables simulated by the improved model with PMCC scheme range between those simulated by the model with PM and CC schemes, and ILA, total above ground production and yield are obviously closer to the observations. Specifically, the mean increments of simulation accuracies for all growth periods in three sowing dates are 6%, 21% and 3% for ILA and 8%, 8% and 14% for total above ground production, respectively. The simulation accuracies of yield for three sowing dates increase by 66%, 63% and 66%, respectively. In 2018, the simulation accuracies of total above ground production and yield for the sowing dates on 20 April and 30 April are obviously improved by PMCC scheme, and increase by 5%, 1% in total above ground production as well as 32%, 5% in yield. Therefore, the model performance with PMCC scheme in simulating maize growth is significantly improved under water stress.

Global Transcriptome and Weighted Gene Co-expression Network Analyses of Growth-Stage-Specific Drought Stress Responses in Maize.

Drought is the major abiotic stress threatening maize (Zea mays L.) production globally. Despite recent scientific headway in deciphering maize drought stress responses, the overall picture of key genes, pathways, and co-expression networks regulating maize drought tolerance is still fragmented. Therefore, deciphering the molecular basis of maize drought tolerance remains pertinent. Here, through a comprehensive comparative leaf transcriptome analysis of drought-tolerant hybrid ND476 plants subjected to water-sufficient and water-deficit treatment conditions at flared (V12), tasseling (VT), the prophase of grain filling (R2), and the anaphase of grain filling (R4) crop growth stages, we report growth-stage-specific molecular mechanisms regulating maize drought stress responses. Based on the transcriptome analysis, a total of 3,451 differentially expressed genes (DEGs) were identified from the four experimental comparisons, with 2,403, 650, 397, and 313 DEGs observed at the V12, VT, R1, and R4 stages, respectively. Subsequently, 3,451 DEGs were divided into 12 modules by weighted gene co-expression network analysis (WGCNA), comprising 277 hub genes. Interestingly, the co-expressed genes that clustered into similar modules exhibited diverse expression tendencies and got annotated to different GO terms at different stages. MapMan analysis revealed that DEGs related to stress signal transduction, detoxification, transcription factor regulation, hormone signaling, and secondary metabolites biosynthesis were universal across the four growth stages. However, DEGs associated with photosynthesis and amino acid metabolism; protein degradation; transport; and RNA transcriptional regulation were uniquely enriched at the V12, VT, R2, and R4 stages, respectively. Our results affirmed that maize drought stress adaptation is a growth-stage-specific response process, and aid in clarifying the fundamental growth-stage-specific mechanisms regulating drought stress responses in maize. Moreover, genes and metabolic pathways identified here can serve as valuable genetic resources or selection targets for further functional validation experiments.

A natural antisense transcript acts as a negative regulator for the maize drought stress response gene ZmNAC48.

Although plant-specific NAC transcription factors play crucial roles in response to abiotic stress, few reports describe the regulation of NAC genes in maize (Zea mays) by the cis-natural antisense transcripts (cis-NATs). In this study, 521 NAC genes from Gramineae were classified, of which 51 NAC genes contained cis-NATs. ZmNAC48 and cis-NATZmNAC48 co-localized to the same cell nucleus, and both transcripts responded to drought stress. Arabidopsis plants overexpressing ZmNAC48 had improved drought tolerance, lower rate of water loss, enhanced stomatal closure, and higher rates of survival. Transient expression in both maize protoplasts and tobacco leaves indicated that cis-NATZmNAC48 reduced ZmNAC48 expression. Western blotting and ribosome profiling analyses confirmed that cis-NATZmNAC48 lacked protein coding potential. Furthermore, the cis-NAT-derived small-interfering RNAs (nat-siRNAs) generated from the overlapping regions of ZmNAC48 and cis-NATZmNAC48 were detected in maize and transgenic Arabidopsis. Cis-NATZmNAC48 overexpressing maize showed higher water loss rate, increased stomatal opening, and had more dead leaves. Expression of ZmNAC48 and nat-siRNA was decreased in these plants. Taken together, our study indicates that both ZmNAC48 and cis-NATZmNAC48 are involved in plant drought stress responses, and that the double-stranded RNA-dependent mechanism is involved in the interaction between cis-NATZmNAC48 and ZmNAC48. Additionally, cis-NATZmNAC48 may negatively regulate ZmNAC48 to affect stomatal closure of maize.

The quantitative proteomic analysis provides insight into the effects of drought stress in maize

Drought stress is one of the major environmental factors that limit maize yield in agriculture. However, few studies have analyzed how proteins respond to different degrees of drought at the proteome level. In this study, physiological characteristics and comparative tandem mass tag proteomics were used to analyze the responses of maize seedlings to mild and severe drought stresses in pot experiments. A total of 104 and 464 proteins were differentially expressed under mild and severe drought, respectively, but only 30 proteins were overlapped. Further Gene Ontology enrichment analysis showed maize can adapt to mild drought by activating antioxidant system and photorespiration. Under severe drought stress, photosystem and protein synthesis-related proteins were downregulated indicating severe drought damaged the photosynthetic apparatus. The plant biomass under drought stress was also reduced sharply compared to control. Taken together, our study provides insights into proteomic information of maize leaves under increasing drought stress.

Modulation of cell cycle progression and chromatin dynamic as tolerance mechanisms to salinity and drought stress in maize.

Salinity and drought are the major abiotic stresses that disturb several aspects of maize plants growth at the cellular level, one of these aspects is cell cycle machinery. In our study, we dissected the molecular alterations and downstream effectors of salinity and drought stress on cell cycle regulation and chromatin remodeling. Effects of salinity and drought stress were determined on maize seedlings using 200 mM NaCl (induced salinity stress), and 250 mM mannitol (induced drought stress) treatments, then cell cycle progression and chromatin remodeling dynamics were investigated. Seedlings displayed severe growth defects, including inhibition of root growth. Interestingly, stress treatments induced cell cycle arrest in S-phase with extensive depletion of cyclins B1 and A1. Further investigation of gene expression profiles of cell cycle regulators showed the downregulation of the CDKA, CDKB, CYCA, and CYCB. These results reveal the direct link between salinity and drought stress and cell cycle deregulation leading to a low cell proliferation rate. Moreover, abiotic stress alters chromatin remodeling dynamic in a way that directs the cell cycle arrest. We observed low DNA methylation patterns accompanied by dynamic histone modifications that favor chromatin decondensation. Also, the high expression of DNA topoisomerase 2, 6 family was detected as consequence of DNA damage. In conclusion, in response to salinity and drought stress, maize seedlings exhibit modulation of cell cycle progression, resulting in the cell cycle arrest through chromatin remodeling.

Allometric relationships between nitrogen uptake and transpiration to untangle interactions between nitrogen supply and drought in maize and sorghum

Abstract Worldwide supply of water and nitrogen (N) are critical to crop yield with multiple interactions that need to be untangled. We used an allometric framework to quantify the dynamic relationships between crop growth, transpiration and N uptake in maize (Zea mays L.) and sorghum (Sorghum bicolor L.) using published data from experiments in France, New Zealand and United States. Our analysis highlighted a two-fold effect of drought on crop growth: a direct effect whereby crop growth is reduced proportionally to the reduction in transpiration, and an indirect effect mediated by a drought-induced crop N deficit, quantified as N nutrition index (NNI), the ratio between actual and critical plant N concentration (the minimum plant N concentration for achieving maximum crop mass). Under drought, sorghum maintained NNI and transpiration efficiency (biomass per unit of transpiration) whereas both NNI and transpiration efficiency declined in drought-stressed maize in comparison to well-watered crops. Nitrogen uptake per unit of transpiration (N/T) is a valuable trait for analyzing the combined effect of water and N deficit on water use efficiency (biomass per unit of evapotranspiration). However, both N/T and crop N concentration decline allometrically with biomass, hence comparisons of genotypes, environments and management practices would be biased unless they are scaled by crop biomass.

Starch biosynthesis contributes to the maintenance of photosynthesis and leaf growth under drought stress in maize.

To understand the growth response to drought, we performed a proteomics study in the leaf growth zone of maize (Zea mays L.) seedlings and functionally characterized the role of starch biosynthesis in the regulation of growth, photosynthesis and antioxidant capacity, using the shrunken-2 mutant (sh2), defective in ADP-glucose pyrophosphorylase. Drought altered the abundance of 284 proteins overrepresented for photosynthesis, amino acid, sugar and starch metabolism, and redox-regulation. Changes in protein levels correlated with enzyme activities (increased ATP synthase, cysteine synthase, starch synthase, RuBisCo, peroxiredoxin, glutaredoxin, thioredoxin and decreased triosephosphate isomerase, ferredoxin, cellulose synthase activities, respectively) and metabolite concentrations (increased ATP, cysteine, glycine, serine, starch, proline and decreased cellulose levels). The sh2 mutant showed a reduced increase of starch levels under drought conditions, leading to soluble sugar starvation at the end of the night and correlating with an inhibition of leaf growth rates. Increased RuBisCo activity and pigment concentrations observed in WT, in response to drought, were lacking in the mutant, which suffered more oxidative damage and recovered more slowly after re-watering. These results demonstrate that starch biosynthesis contributes to maintaining leaf growth under drought stress and facilitates enhanced carbon acquisition upon recovery.

Dry-Caribbean Bacillus spp. Strains Ameliorate Drought Stress in Maize by a Strain-Specific Antioxidant Response Modulation.

Drought is a global problem for crop productivity. Therefore, the objective of this research was to evaluate five dry-Caribbean Bacillus spp. strains in drought stress amelioration in maize plants. Maize seeds were single-strain inoculated and sown in pots under greenhouse conditions. After 12 days, plants were subjected to 33 days of drought conditions, i.e., 30% of soil field capacity, and then collected to measure leaf and root dry biomass, plant height, antioxidant enzymes, proline accumulation, and P+, Ca2+, and K+ uptake. Results correlated drought stress amelioration with the inoculation of Bacillus spp. strains XT13, XT38 and XT110. Inoculated plants showed increases in dry biomass, plant height, and K+ and P+ uptake. The overall maize antioxidant response to bacterial inoculation under drought stress showed dependence on proline accumulation and decreases in ascorbate peroxidase and glutathione reductase activities. Moreover, results suggest that this stress amelioration is driven by a specific plant-strain correlation observed in antioxidant response changes in inoculated plants under stress. Also, there is a complex integration of several mechanisms, including plant growth-promotion traits and nutrient uptake. Hence, the use of dry-Caribbean plant growth-promoting Bacillus strains represents an important biotechnological approach to enhance crop productivity in arid and semi-arid environments.

Transgenic overexpression of rubisco subunits and the assembly factor RAF1 are beneficial to recovery from drought stress in maize

Finding ways to increase Rubisco activity in crops to improve photosynthesis has long been a key objective. We have developed maize plants with transgenic overexpression of Rubisco subunits and Rubisco assembly factor 1 (RAF1) that resulted in higher Rubisco content, photosynthetic capacity and dry biomass under non-stressed growth conditions. The question remains, however, whether the transgenes conferring these effects could confer a growth penalty under stress conditions, given the nitrogen sink that Rubisco represents. In the present study, control and transgenic maize lines either overexpressing RAF1, both large and small subunits of Rubisco (LSSS), or all three (RAF1-LSSS), were subjected to mild, and severe drought conditions, and then re-watered. The results demonstrate that RAF1-LSSS, which has increased Rubisco abundance relative to the control, was slightly more affected than wild-type Rubisco level plants in terms of gas exchange and chlorophyll content after 14 days of stress. After returning plants to well-watered conditions, however, RAF1-LSSS displayed a more robust recovery compared to other genotypes. We attribute this to its high Rubisco content and the low malondialdehyde content noted prior to recovery, which indicates reduced oxidative degradation of lipids. Strong recovery was also observed in lines overexpressing RAF1 alone, in contrast with its lack of improved performance under non-stressed conditions. In contrast, LSSS displayed improved growth under non-stressed conditions, but showed a clear growth penalty during stress along with poor recovery. Taken together, our results suggest that while the high-Rubisco trait is neutral during water stress, recovery is more rapid once the stress is removed.

Coordinated regulation of carbon and nitrogen assimilation confers drought tolerance in maize (Zea mays L.)

Drought is a major limiting factor affecting crop productivity. To gain a comprehensive understanding of transcriptomic reprogramming under drought stress in maize (Zea mays L.), we performed physiological and transcriptomic analysis of leaf tissues of two maize cultivars, LY66 and LY99, subjected to a progressively severe drought and subsequent recovery. LY66 exhibited greater drought tolerance and recovery than LY99. RNA-Seq analysis showed that differentially expressed genes mainly enriched in pathways involved in carbon (C) and nitrogen (N) metabolism, and plant hormone signal transduction. As judged from RNA-Seq data, enzyme activity, and metabolite contents, LY66 maintained a higher relatively stable C and N metabolism than LY99, which were related to higher photosynthesis and sucrose biosynthesis capacity, higher N assimilation and protein biosynthesis capacity under drought stress, respectively. Interestingly, the expression of several genes encoding key enzymes involved in auxin biosynthesis and signaling were activated to higher levels in LY66 than in LY99 under drought stress. Our results indicate that LY66 exhibits coordinated regulation of C and N assimilation, possibly involved in phytohormone signaling pathways, which enhances drought stress tolerance.

Lignin-based hydrogel alleviates drought stress in maize

Global water shortage is a crisis for all living systems, including agricultural cropping systems. Water absorbent hydrogels from synthetic polymers can retain moisture from irrigation or rainfall and release it in response to crop water demands, but have a limited functional lifespan and may release byproducts that are harmful to plants or pollute the soil environment. Hydrogels fabricated from plant-based polymers are more suitable for agricultural cropping systems because they could improve the soil water availability to the crop and gradually biodegrade to harmless carbon dioxide and water. The objective of this work was to determine how biodegradable lignin hydrogel affected the soil water availability to maize grown under drought conditions. The lignin hydrogel was applied at 0.3 % and 0.6 % (by weight) in pots subjected to water deficit or sufficiency, and compared to sodium polyacrylate hydrogel that was applied at the same rates. Maize plants were taller, had greater phosphorus content and more biomass when grown in soil with lignin hydrogel and sodium polyacrylate hydrogel than without hydrogel. Furthermore, soil receiving 0.6 % lignin hydrogel produced significantly (P < 0.05) greater maize biomass and relative leaf water content, with an 86 % reduction in leaf proline content and 10 % less electrolyte leakage under severe drought conditions than without hydrogel. There was more soil soluble Na and Na uptake by maize in the sodium polyacrylate-amended soil due to solubilization of the Na+ ions from the sodium polyacrylate. We recommend lignin hydrogel as a soil additive to increase water availability to crops experiencing drought stress that will not release undesirable byproducts into the cropping system.

Alleviation of drought stress in maize (Zea mays L.) by using endogenous endophyte Bacillus subtilis in North West Himalayas

ABSTRACT In the present study, we reported the isolation and molecular characterisation of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-producing endophyte and its effect on alleviating drought stress in maize. Ten morphologically distinct indigenous plant growth-promoting rhizobacteria (PGPR) from maize roots and rhizosphere were screened for multiple plant growth-promoting (PGP) traits, and of ten, two strains (DHK and B1N1) possessing maximum PGP traits were evaluated at three water stress regimes in maize: (i) 80% field capacity (FC), (ii) 60% FC, and (iii) 40% FC for 45 days, starting 15 days after sowing to the maturity. Inoculation of DHK strain with maize at 80% FC induced a significant increase in plant biomass (root biomass, 86.67%; shoot biomass, 111.63%) together with decreased reactive oxygen species and increased activity of antioxidant enzymes (superoxide dismutase, 14.11 U/g fresh weight; peroxidase, 1.14 U/g fresh weight and catalase; 14.91 U/g fresh weight) compared to uninoculated control at same water regime (80% FC). The derivative strain also significantly accrued nutrients in maize and enhanced total chlorophyll and amino acid content in comparison with non-inoculated plants. 16S rDNA analysis of DHK strain revealed its lineage to Bacillus subtilis. Present investigations demonstrated the potential of the bacterial partner in alleviating drought stress in maize.

Transcriptomic Analysis of Female Panicles Reveals Gene Expression Responses to Drought Stress in Maize (Zea mays L.)

Female panicles (FPs) play an important role in the formation of yields in maize. From 40 days after sowing to the tasseling stage for summer maize, FPs are developing and sensitive to drought. However, it remains unclear how FPs respond to drought stress during FP development. In this study, FP differentiation was observed at 20 and 30 days after drought (DAD) and agronomic trait changes of maize ears were determined across three treatments, including well-watered (CK), light drought (LD), and moderate drought (MD) treatments at 20, 25, and 30 DAD. RNA-sequencing was then used to identify differentially expressed genes (DEGs) in FPs at 30 DAD. Spikelets and florets were suppressed in LD and MD treatments, suggesting that drought slows FP development and thus decreases yields. Transcriptome analysis indicated that 40, 876, and 887 DEGs were detected in LD/CK, MD/CK, and MD/LD comparisons. KEGG pathway analysis showed that ‘biosynthesis of other secondary metabolites’ and ‘carbohydrate metabolism’ were involved in the LD response, whereas ‘starch and sucrose metabolism’ and ‘plant hormone signal transduction’ played important roles in the MD response. In addition, a series of molecular cues related to development and growth were screened for their drought stress responses.

Enhancement of proline content and antioxidant enzyme activities induced by drought stress in maize (&lt;i&gt;Zea mays L.&lt;/i&gt;) by application of compost

In sub-Saharan Africa, soil degradation and recurrent droughts are major obstacles to a sustainable agriculture. This study aimed at investigating the effect of compost addition to soil on proline content and activities of the antioxidant enzymes [catalase (CAT), ascorbate peroxidase (APX)] in maize plants, under drought stress conditions. The test was carried out in 20L plastic pots containing either sandy soil or sandy soil with the fertilizer, under natural conditions. The water deficit was induced at male blooming and milky grain stages. Plant irrigation was done by successive weighing of the pots during which the control is reduced to the same weight corresponding to 70% of the useful water reserve (UWR), while the stressed treatment maintains the water content at 30% of the UWR for 10 days. At the end of the stress period, the proline content, the CAT and APX activities in the leaves were determined through a spectrophotometry. The results show an important accumulation of proline and increase in enzymatic activity induced by water deficit in plants grown on compost (p = 0.00000 at p &lt; 0.05). This study provides evidence for a beneficial effect of compost application in enhancing drought tolerance of maize.Keywords: Drought stress; compost; proline; antioxidant enzymes; Zea mays L.

Nano-ZnO alleviates drought stress via modulating the plant water use and carbohydrate metabolism in maize

ABSTRACT The wide application of zinc oxide (ZnO) nanoparticles inevitably facilities their release into the terrestrial and agricultural ecosystems, severely affecting crop production. The effects of nano-ZnO (100 mg L−1) on stomatal morphology, gas exchange and key carbon metabolism enzyme activities were investigated in drought-stressed and well-watered maize. Drought stress limited the plant growth, caused stomatal closure, decreased the net photosynthetic rate, while increased the osmolyte concentrations. In drought-stressed maize, the application of nano-ZnO (100 mg L−1) alleviated photosynthetic pigment degradation and benefited the stomatal movement, maintained a higher net photosynthetic rate, and enhanced water use efficiency, promoting the drought tolerance in maize. In addition, the nano-ZnO increased the activities of UDP-glucose pyrophosphorylase, phosphoglucoisomerase and cytoplasmic invertase by 17.8%, 391.5% and 126%, respectively, which enhanced the starch and sucrose biosynthesis and glycolysis metabolism in leaves under drought stress. Manipulation of primary carbohydrate metabolism through nano-ZnO induced regulation of the key enzymes activity benefited the drought tolerance in maize. The nano-ZnO application (100 mg L−1) alleviates the negative effect of drought stress via improving photosynthetic carbon assimilation of maize.