Activities of sucrose to starch metabolizing enzymes during grain filling in late sown wheat under water stress

Tolerance to water deficit in relation to activities of sucrose-to- starch metabolizing enzymes and starch accumulation was studied in the grains of contrasting wheat (Triticum aestivum L.) genotypes (WH1021 and WH1080; tolerant) and (WH711 and HD2687; susceptible) under late planting conditions. The activities of starch metabolizing enzymes i.e. sucrose synthase (SuSase), ADP-glucose pyrophosphorylase (AGPase), soluble starch synthase (SSS) and starch branching enzymes (SBE) were substantially enhanced by water deficit in all genotypes at early to mid-grain filling stage showing peaks at 14 to 21 days after anthesis (DAA); while decreased significantly at mid-late grain filling stage with maximum decline at 35 DAA. Activities of all the enzymes under study showed maximum decline in activity (28.4–60%) in susceptible genotype WH711; whereas WH1021 proved to be most tolerant one with minimum decline in enzyme activity (14.9–32.8%). Starch content was also markedly reduced (21%) in WH711 due to drought while WH1021 reported 12% decline corresponding well with enzyme activity. A faster pre-mature cessation of starch deposition occurred in susceptible wheat genotypes compared to tolerant ones. A significant and positive correlation of the enzyme activities with starch accumulation (r = 0.491–0.555 at P0.05 for SuSase, AGPase, SSS and r = 0.638 at P0.01 for SBE) under well watered conditions indicated that enhancing the activities of the enzymes would lead to increase in starch accumulation and thus faster grain filling. Genotype WH1021 proved to be most efficient based on comparatively higher enzyme activity and least yield penalty under late planting conditions combined with water scarcity.