Fig. 3

Exogenous ABA priming upregulated starch synthetase activities in rice grains under heat stress. The rice plants were sprayed with distilled water, 50 μM ABA or 10 μM fluridone (FLU) at the 5th d after initial heading stage (AIH) or 12th d after initial heading stage, and then subjected to unstressed or heat stress conditions at 8–14 days after initial heading (AIH) stage or 15–21 days after initial heading stage, respectively. Rice grains at the indicated treatment times of 0 d, 3 d, 5 d and 7 d were sampled in liquid nitrogen and used to measure the starch synthetase activities. Enzyme activity levels of (A) ADP-glucose pyrophosphorylase (AGPase), (B) soluble starch synthase (SSS), (C) granule-bound starch synthase (GBSS), (D) starch branching enzyme (SBE), (E) starch debranching enzyme (DBE), and (F) sucrose synthase (SS), in rice grains, were measured at the indicated treatment days. Values are means ± SDs, n = 3. Different letters on the column represent significant differences (P < 0.05) between different treatments at the same treatment day based on Duncan’s test