Differential effects of daytime and nighttime high temperatures at the grain formation stage on starch structure and properties in waxy maize

High temperature (HT) is a critical abiotic stress factor that negatively impacts yield and quality of maize worldwide. Although the effects of HT during key growth stages are extensively documented, the distinct influences of daytime versus nighttime HT on the physicochemical properties of waxy maize starch remain largely unexplored. This study investigated the effects of daytime and nighttime HT on the on the starch physicochemical properties in two waxy maize hybirds. Temperature treatments included ambient temperature (NN), daytime HT (DH), nighttime HT (NH), and whole-day HT (DNH), which were applied from 1 to 15 days after pollination. The three HT stresses significantly inhibited starch synthesis and accumulation, increased the number of pores on the starch granule surface, enlarged starch granule size, enhanced relative crystallinity, and shortened the chain length and reduced the branching degree of amylopectin. The most severe effects were observed under DNH, followed by DH. DH and DNH reduced starch pasting viscosity and gelatinization enthalpy while increasing starch retrogradation through mechanisms involving enlargement of granule size, increased relative crystallinity, and reduced branching and chain length of amylopectin. NH increased gelatinization enthalpy and retrogradation and decreased starch pasting viscosity primarily by shortening the chain length of amylopectin. By elucidating the mechanisms through which daytime and nighttime HT affect starch physicochemical properties, this study provides valuable insights into optimizing waxy maize production in response to climate change challenges.