Application of Polygonum minus Extract in Enhancing Drought Tolerance in Maize by Regulating Osmotic and Antioxidant System

Drought stress is a major factor affecting plant growth and crop yield production.Plant extracts as natural biostimulants hold great potential to strengthen plants to overcome drought impacts.To explore the effect of Polygonum minus extract(PME)in enhancing drought tolerance in plants,a study was set up in a glasshouse environment using 10 different treatment combinations.PME foliar application were designed in CRD and effects were closely observed related to the growth,physiology,and antioxidant system changes in maize(Zea mays L.)under well-watered and drought conditions.The seaweed extract(SWE)was used as a comparison.Plants subjected to drought stress exhibited a significant reduction in fresh weight,dry weight,relative water content(RWC),and soluble sugar,but they stimulated the phenolic,flavonoid,proline,glutathione(GSH),malondialdehyde(MDA)and antioxidant enzyme(catalase,CAT;peroxidase,POD;superoxide dismutase,SOD)activities.Foliar application of PME improved fresh and dry weight(FW:33.1%~41.4%;DW:48.0%~43.1%),chlorophyll content(Chl b:87.9%~100.76%),soluble sugar(23.6%~49.3%),and soluble protein(48.6%~56.9%)as well as antioxidant enzyme activities(CAT and POD)compared to CK under drought conditions.while decreasing the level of MDA.Notably,the mitigating effect of PME application with high concentration was more effective than those of SWE.Our study reveals that PME could alleviate drought stress by regulating osmoprotectant content and antioxidant defense system and can be used as an economical and environmentally friendly biostimulants for promoting maize growth under drought stress.

Physiological and Biochemical Mechanisms of Exogenous Calcium Chloride on Alleviating Salt Stress in Two Tartary Buckwheat(Fagopyrum tataricum)Varieties Differing in Salinity Tolerance

Salt stress is one of the most serious abiotic stresses limiting plant growth and development.Calcium as an essential nutrient element and important signaling molecule plays an important role in ameliorating the adverse effect of salinity on plants.This study aimed to investigate the impact of exogenous calcium on improving salt tolerance in Tartary buckwheat cultivars,cv.Xinong9920(salt-tolerant)and cv.Xinong9909(salt-sensitive).Four-week-old Tartary buckwheat seedlings under 100 mM NaCl stress were treated with and without exogenous calcium chloride(CaCl_(2)),Ca^(2+)chelator ethylene glycol tetraacetic acid(EGTA)and Ca^(2+)-channel blocker lanthanum chloride(LaCl_(3))for 10 days.Then,some important physiological and biochemical indexes were determined.The results showed that salt stress significantly reduced seedling growth,decreased photosynthetic pigments,inhibited antioxidants and antioxidant enzyme activities.However,it increased the reactive oxygen species(ROS)levels in the two Tartary buckwheat cultivars.Exogenous 10 mM CaCl_(2)application on salt-stressed Tartary buckwheat seedlings obviously mitigated the negative effects of NaCl stress and partially restored seedlings growth.Ca^(2+)-treated salt-stressed seedlings diplayed a suppressed accumulation of ROS,increased the contents of total chlorophyll,soluble protein,proline and antioxidants,and elevated the activities of antioxidant enzymes compared with salt stress alone.On the contrary,the addition of 0.5 mM LaCl_(3)and 5 mM EGTA on salt-stressed Tartary buckwheat seedlings exhibited the opposite effects to those with CaCl_(2)treatment.These results indicate that exogenous Ca^(2+)can enhance salt stress tolerance and Ca^(2+)supplementation may be an effective practice to cultivate Tartary buckwheat in saline soils.

Foliar Application of Cytokinin Modulates Gas Exchange Features,Water Relation and Biochemical Responses to Improve Growth Performance of Maize under Drought Stress

Improvement of plant performance under drought stress is crucial to sustaining agricultural productivity.The current study investigated the ameliorative effects of foliar-applied kinetin,an adenine-type cytokinin(CK),on growth and gas exchange parameters,water relations and biochemical attributes of maize plants under drought stress.Eighteen-day-old maize plants were subjected to drought by maintaining soil moisture content at 25%field capacity for 8 days followed by foliar application of kinetin at 0,75,150 and 225 mg L^(−1)(CK0,CK75,CK150 and CK225,respectively)to the plants for two-times at the 9-day interval.Results revealed that drought stress markedly reduced stem diameter,dry weight,chlorophyll content,gas exchange parameters and water balance but increased proline,malondialdehyde and soluble sugar contents,electrolyte leakage and senescence in maize leaves.Application of exogenous CK remarkably improved maize performance by modulating growth,gas exchange-and water relation-related parameters in a dose-dependent manner under drought stress.CK225 increased chlorophyll content(by 61.54%),relative water content(by 49.14%),net photosynthesis rate(by 39.94%)and transpiration rate(by 121.36%)and also delayed leaf senescence but decreased internal CO_(2)concentration(by 7.38%),water saturation deficit(by 40.40%)and water uptake capacity(by 42.49%)in both well-watered and droughtstressed plants.Nevertheless,CK application considerably decreased electrolyte leakage,proline,malondialdehyde and soluble sugar levels in drought-stressed maize plants,as also supported by heatmap and cluster analyses.Taken together,exogenous CK at proper concentration(225 mg L^(−1))successfully improved maize performance under drought conditions,thereby suggesting CK application as a useful approach to alleviate drought-induced adverse effects in maize plants,and perhaps in other important crop plants.

Nitrogen in Relation to Photosynthetic Capacity and Accumulation of Osmoprotectant and Nutrients in Brassica Genotypes Grown Under Salt Stress

Different strategies of the application of nutrients are required to overcome the adverse effects of mustard （Brassica juncea L.） in response to NaCl stress. The objective of the present study was to determine if different added levels of nitrogen （N） in growth medium could alleviate the adverse effects of salt stress on photosynthetic capacity and accumulation of osmoprotectants and nutrients. 14 days mustard seedlings of salt-sensitive （cv. Chuutki） and salt-tolerant （cv. Radha） genotypes were fed with： （i） 0 mmol L^-1 NaCl ＋ 0 mg N kg^-1 sand （control）, （ii） 90 mmol L^-1 NaCl ＋ 30 mg N kg^-1 sand, （iii） 90 mmol L^-1 NaCl ＋60 mg N kg^-1 sand, （iv） 90 mmol L^-1 NaCl ＋90 mg N kg^-1 sand and （v） 90 mmol L^-1NaCl＋ 120 mg N kg^-1 sand. Under the condition of salinity stress, N application caused a significant ameliorative effect on both genotypes with respect to growth attributes [fresh weight （FW） and dry weight （DW）] and physio-biochemical parameters [percent water content （WC）, net photosynthetic rate （PN）, stomatal conductance （gs）, total chlorophyll （Ch1）, carbonic anhydrase （CA） activity and malondialdehyde （MDA）, nitrogen （N）, potassium （K） and sodium （Na） contents, and K/Na ratio] and yield attributes （number of pods/plant, seeds/pod and seed yield/plant）. The salt-tolerant genotype exhibited maximum value for growth, physio-biochemical and yield attributes at 60 mg N kg 1 sand than that of salt-sensitive genotype. These results suggest that application of N may ameliorate most of the attributes and prove to be a physiological remedy to increase the tolerance against the ill effects of salt stress in Brassicas.

Morpho-Physiological,Biochemical and Molecular Adaptation of Millets to Abiotic Stresses:A Review

Abiotic stresses such as drought,heat,cold,nutrient deficiency,excess salt and hazardous metals can hamper plantgrowth and development.Intensive agriculture of only a few major staple food crops that are sensitive and intolerant to environmental stresses has led to an agrarian crisis.On the other hand,nutritionally rich,gluten free and stress tolerant plants like millets are neglected and underutilized.Millets sustain about one-third of the world’s population and show exceptional tolerance to various abiotic and biotic stresses.Millets are C4 plants that are adapted to marginal and dry lands of arid and semi-arid regions,and survive low rainfall and poor soils.Abiotic stresses significantly affect plant growth which ultimately results in reduced crop yields.However,various adaptation mechanisms have evolved in millets to withstand different stresses.This review aims at exploring various of these morphophysiological,biochemical and molecular aspects of mechanisms in millets.Morphological adaptations include short life span,smallplant height and leaf area,dense root system,adjusted flowering time,increased root and decreased shoot lengths,high tillering,and leaf folding.A high accumulation of various osmoprotectants(proline,soluble sugars,proteins)improves hyperosmolarity and enhances the activity of antioxidant enzymes(e.g.,Ascorbate peroxidase,Superoxide dismutase,Catalase,Peroxidase)providing defense against oxidative damage.Physiologically,plants show low photosynthetic and stomatal conductance rates,and root respiration which help them to escape from water stress.Molecular adaptations include the upregulation of stress-related transcriptional factors,signalling genes,ion transporters,secondary metabolite pathways,receptor kinases,phytohormone biosynthesis and antioxidative enzymes.Lack of genetic resources hampers improvement of millets.However,several identified and characterized genes for stress tolerance can be exploited for further development of millet resilience.This will provide them with an extra characteristic plant resistance to withstand environmental pressures,besides their excellent nutritional value over the conventional staple crops like rice,wheat and maize.

Alleviation of Drought Stress in Wheat Using Exogenous Ulva prolifera Extract Produced by Enzymatic Hydrolysis

Drought is one of the major abiotic stresses that affect plant growth and reduce agricultural productivity.Use of algal extract as a biostimulant is gaining increased attention from researchers.This study aimed to investigate the potential of Ulva prolifera extract(UE)as a biostimulant when enzymatically extracted under conditions of water deficit.UE treatments(0.02%,0.06%,and 0.1%)significantly improved the shoot length,root length,and dry weight of roots after 120 h of drought stress relative to that in treatment with the negative control.An increase in catalase(CAT)and peroxidase(POD)activity was also observed that resulted in improved antioxidant capacity.Application of 0.1%UE reduced the malondialdehyde(MDA)content by 30.06%compared with that in the negative control.In addition,the soluble sugar and protein content in wheat treated with 0.1%UE was increased by 23.10%and 93.51%,respectively,resulting in adjustment of the osmotic pressure.Results suggest that UE could significantly enhance the drought tolerance of wheat.This study provides a basis for increasing the value of UE as a biostimulant.

Changes in Osmotic Adjustment and Antioxidant Enzyme in Maize (<i>Zea mays L.</i>) Root Exposed to K Deficiency

Potassium (K) deficiency damaged membrane stability through irregular reactive oxygen species (ROS) caused by K deficiency stress while osmotic adjustment and antioxidant capacities play an essential role in preventing plants from osmotic stress and oxidative damages. To investigate the difference of osmoprotectants and antioxidant enzyme activities in the root, two representative maize varieties, 90-21-3 (K-tolerant) and D937 (K-sensitive), were hydroponically cultivated under normal K (+K) and K deficiency (-K) treatments in Shenyang Agriculture University, China. The results showed that root accumulation, soluble protein in root of 90-21-3 and D937 were decreased under K deficiency stress, but the root to shoot ratio, proline, free amino acid, soluble sugar, reactive oxygen species (ROS) in root for both genotypes were increased. Compared with the root of D937, the root of 90-21-3 was able to swiftly accumulate more proline, free amino acid and soluble sugar in the root when encountering K deficiency. The antioxidant enzyme activity in the root of 90-21-3, including superoxide dismutase (SOD), and catalase (CAT), peroxidase (POD), were significantly increased to counter increased levels of O2·- and H2O2 under K deficiency stress. The presented results indicated that osmotic regulator and antioxidant enzyme were actively responded to K deficiency stress, 90-21-3 (K-tolerant maize) accumulated more osmoprotectants and enhanced the activity of antioxidant enzymes to degrade ROS, alleviating oxidative stress.