Regulation of polyphenol catabolism in amelioration of high-temperature stress vis-a-vis antioxidant defense system in wheat

Sensitivity of reproductive stage to high temperature was investigated in twenty wheat genotypes (three tall traditional-C ones, seven elite-PBW ones, nine advanced-BWL ones and one landrace-Himachal Local 1) using various biochemical indices under high-temperature stress. Effect of high temperature on activities of antioxidant enzymes and contents of phenolic compounds in relation to transformation of free sugars to starch in developing grains of wheat genotypes was studied by raising the crop under timely sown (November) and late planting (December) conditions. During metabolomic profiling, it was confirmed that sugars, amino acids and proteins accumulated in different wheat genotypes under high temperature with decrease in starch content. Disruption of starch biosynthesis resulted in their favored utilization in nitrogen metabolism leading to higher amino acid and protein accumulation as depicted by the negative correlation between starch and proteins (p <= 0.05) under heat stress. Phenolic compounds, viz. total polyphenols, phenolic acids, flavonols, anthocyanins and proanthocyanidins, were increased under stress conditions. Increase in polyphenolic content could be associated with the activation of phenylalanine ammonia lyase enzyme involved in shikimic acid pathway in wheat grains. A significant correlation (p <= 0.01) of total polyphenols and proanthocyanidins was observed with the activity of catalase (r = 0.59) and polyphenol oxidase (r = 0.27), respectively. Advanced lines, namely BWL 1664, 3504 and 6250, performed better with less decrease in yield under heat stress which was attributed to low reduction in starch content.