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View related articles View Crossmark data Citing articles: 2 View citing articles Full Length Article Impact of osmotic stress on seedling growth observations, membrane characteristics and antioxidant defense system of different wheat genotypes

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In a controlled environment experiment, we studied how physiological changes in leaves during the vegetative phase regulate final grain yield of wheat crops in salt-affected soils. We also hypothesized that amendments such as biochar (SB) and selenium-chitosan nanoparticles (Se-NPs) can protect wheat plants from salt injury. 20-day-old wheat plants were submitted to 4-week salt stress (3000 ppm NaCl). Soybean straw biochar was mixed with soil media at planting and Se-NPs (30 ppm) was sprayed 5 days after the first salt stress treatment. At the end of 4-week Se-NPs treatment, one set of plants was harvested for studying leaf level physiological changes. The salt-stressed plants accumulated significantly high leaf Na+ (~ 13-fold increase), which trigged oxidative and osmotic damage. This salt-induced cellular injury was evident from significantly high levels of lipid membrane peroxidation and inhibited photosynthesis. Our study suggested that leaf physiological impairment in wheat plants was translated into poor biomass production and grain yield loss at crop maturity. Compared with control, salt-stressed plants produced 43% lesser biomass during vegetative phase, and 62% lesser grain yield at maturity. Amendments such as SB and Se-NPs protected the plants from salt-induced cellular injury by restricting Na+ transport toward leaf tissues. Plants treated with NaCl + SB + Se-NPs accumulated 50% less Na+ concentrations in leaves compared with NaCl-treated plants. Our study also suggested that SB and Se-NPs can restore ionic homeostasis and carbon assimilation in salt-stressed wheat by upregulating key transporter genes in leaves.

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In this study, the protective role of salicylic acid (SA) and trehalose (Tre) in relation to lipid peroxidation, membrane leakage, membrane stability index, antioxidant defense system as well as non-enzymatic antioxidants were investigated in drought stressed wheat Gemmieza-7 (drought sensitive cultivar) and Sahel-1 (drought tolerant cultivar) plants. Water stress reduced bio-membranes stability through inducing its lipid peroxidation resulting in an increment in membrane leakage with marked decrease in membrane stability index of flag leaf of both wheat cultivars during grain-filling. Moreover, it was obvious that drought significantly increased the activity of ascorbic acid oxidase (AAO), peroxidase (POD) and phenylalanine ammonia lyase (PAL) activities and induced non-significant reduction in polyphenol oxidase (PPO) activity in flag leaves of both wheat cultivars during grain-filling in comparing with well watered plants. Among cultivars, tolerant one showed higher enzymes activity than the sensitive one. Application of SA and/or Tre markedly increased AAO, POD and PAL activities and non-significant decrease in PPO activity in flag leaf of water stressed wheat plants. Generally, SA and Tre treatment appeared to be the most effective treatment in counteracting the negative effects of water stress and Sahel-1 appeared to induce better results than Gemmieza-7 and proved to be more tolerant.Drought stress caused significant increase in the amount of total phenols and flavonoids in flag leaf of both cultivars during grain-filling where the sensitive plants accumulated more total phenols and flavonoids contents than the tolerant one. Furthermore, water stress increased the non-photosynthetic pigment content of the two wheat cultivars particularly drought sensitive one during grain filling. These results suggest that the exogenous application of SA and/or Tre assisted the plants to become more tolerant to drought stress-induced oxidative damage by upregulating the membrane characteristics and enhancing their antioxidant defense system as well as non-enzymatic antioxidants.

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Irrigation of wheat plants with seawater (10 and 25 %) led to significant increases in free and bound abscisic acid (ABA) in leaves, especially at 25 %. The relative water content (RWC) and water use efficiency (calculated from grain yield, WUEG, or from biomass yield, WUEB) of the seawater‐irrigated plants were lower than those of the control. Grain pre‐soaking in gibberellic acid (GA3), indole‐3‐acetic acid (IAA) or ABA reduced the levels of accumulated ABA (free and bound) produced by seawater irrigation. The stress imposed by seawater generally reduced yield and yield components of wheat plants and the effect was more pronounced at the higher level of seawater irrigation (25 %). Furthermore, seawater treatments decreased the carbohydrate content and increased the protein content of the developing grains. The effect of seawater treatments on ion concentrations in the developing grains was not consistent. The application of growth bioregulators appeared to mitigate the effect of seawater salinity stress on wheat productivity. GA3 was the most effective hormone in this regard. The economic yield (grain yield) had a strong positive correlation with RWC, WUEG, WUEB, plant height, shoot fresh and dry weight, grain number/main spike, kernel weight and harvest index.