Evaluation of ascorbic acid effect on terminal heat stress responses in wheat (Triticum aestivum L.) grains

The present study was conducted to investigate the potential of exogenously applied ascorbic acid (AsA) (100, 150 and 200 ppm) as foliar spray at 70 and 90 days after sowing. Matured grains were analyzed for terminal heat stress responses during grain development in six wheat genotypes namely PBW 550, PBW 725 (released), BWL 1664, BWL 3560, BWL 5230 (advanced lines) and Himachal Local 1 (landrace) under late sown conditions. In comparison to control, 150 ppm AsA specifically showed significant upregulation of antioxidant enzymes as peroxidase, catalase, polyphenol oxidase and phenylalanine ammonia lyase in grains along with enhanced non-enzymatic antioxidants such as total polyphenols, phenolic acids, flavonols, anthocyanins and proanthocyanidins. This enhancement in the levels of non-enzymatic antioxidants could be associated with the activation of phenylalanine ammonia lyase enzyme involved in shikimic acid pathway in wheat grains. Contents of osmoprotectants like reducing sugars, sucrose and amino acids were also increased with AsA applied. Advanced lines like BWL showed higher grain yield under the effect of AsA that could be linked to the upregulated enzymatic antioxidants as well as osmoprotectants and secondary metabolites. The results revealed the efficacy of foliar applied AsA in improving the wheat performance under late sown conditions.