[Effects of exogenous abscisic acid on grain filling characteristics, starch accumulation, and endogenous hormones in maize under early post-anthesis high temperature stress].

We investigated the effects of exogenous abscisic acid (ABA) on grain filling, starch accumulation, and endogenous hormones in maize (both the heat-tolerant maize variety Zhengdan 958 (ZD958) and the heat-sensitive variety Xianyu 335 (XY335)) under early post-anthesis high temperature stress by simulating high temperature stress for a period of 6 to 12 days post-anthesis in 2022 and 2023. There were three treatments: spraying water at ambient temperature as the control, spraying water at high temperature, and spraying ABA at high temperature. The results showed that early post-anthesis high temperature stress resulted in a significant reduction in grain weight and yield in maize, with XY335 showing a greater reduction than ZD958. The application of ABA mitigated the effects of high temperature stress on grain weight and yield, with the mean yield of ZD958 and XY335 over the two years being increased by 9.6% and 12.3%, respectively. High temperature stress inhibited the activities of enzymes involved in starch synthesis in the grain, resulting in reduced starch content. In contrast, ABA application after high temperature stress increased the activities of sucrose synthase, ADP-glucose pyrophosphorylase, granule-bound starch synthases, soluble starch synthase, and starch branching enzyme, thereby promoting starch accumulation. High temperature stress disturbed the balance of endogenous hormones in the grain, resulting in inhibition of grain filling, whereas ABA application mitigated the adverse effects of high temperature stress on endogenous hormone levels by increasing zeatin riboside, indole-3-acetic acid, and ABA levels and decreasing gibberellin level, which increased grain filling rate, prolonged filling duration, and improved filling characteristics. The grain filling characteristics, starch accumulation, endogenous hormone levels, and grain yield were more sensitive to exogenous ABA regulation in XY335 than in ZD958 under early post-anthesis high temperature stress. In conclusion, exogenous ABA could improve maize grain filling characteristics, promote starch accumulation, and regulate endogenous hormone levels, and ultimately increase grain weight and yield under early post-anthesis high temperature stress.