Changes in Carbon and Nitrogen Metabolites before, at, and after Anthesis for Wheat Cultivars in Response to Reduced Soil Water and Zinc Foliar Application

Water deficit stress is one of the major constraints for commercial agriculture, as it disturbs the metabolic processes in plant. Identification of carbon and nitrogen receptors that act on drought resistance helps in breeding for drought resistance varieties. Zn fertilizer can regulate multiple antioxidant defense systems at the transcriptional level in response to drought. Two field experiments were conducted in 2018–2019 and 2019–2020 seasons to explore the effectiveness of foliar application of zinc oxide on soluble sugar, soluble proteins, and free amino acids under normal irrigation and drought-stressed environments. Three Egyptian wheat cultivars (Triticum aestivum L.) were used. The experimental design was split-plot in RCBD with three replications, applying zinc oxide levels to the whole plot and the split plots. Leaf samples were taken for analysis before anthesis, at anthesis, and after anthesis. Application of Zn increased soluble sugars. However, the free amino acids were higher under irrigation, reached the maximum at anthesis, and decreased sharply after 2 weeks from anthesis. The ranking of cultivars for the three metabolites differed according to plant stage, reflecting the response to Zn and years. Correlations between metabolites according to Zn were positive. The findings suggest the potential of foliar application of Zn to alleviate drought stress.