Increasing the abscisic acid level in maize grains induces precocious maturation by accelerating grain filling and dehydration

Elevated levels of abscisic acid (ABA) are closely associated with cereal grain filling under water deficit. However, grain dehydration during grain filling has received little attention. In this paper, three experiments with drought stress and exogenous ABA treatments were conducted to investigate the relationship between ABA and grain dehydration in maize (Zea mays L.) during the grain-filling period. The results indicated that exogenous ABA application and drought stress led to the same tendency of the grain ABA concentration, carbohydrate concentration and dehydration rate to increase but the moisture content to decrease. Moreover, the time to reach the maximum grain-filling rate was advanced, and the grain-filling period was shortened. In in vitro culture experiments, the sucrose-to-starch conversion was promoted, mainly influenced by sucrose synthase, ADP-glucose pyrophosphorylase (AGPase), and soluble starch synthase during the middle grain-filling stage, and the improvement in starch synthesis was possibly induced by AGPase. Correlation analysis showed that the ABA level was significantly negatively correlated with the moisture content and positively correlated with the starch level. A close and notably negative correlation was observed between the grain moisture content and starch level. In summary, adequate grain ABA promoted sucrose-to-starch conversion, shortened the duration of grain filling and accelerated grain dehydration, resulting in precocious grain maturation.