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

Day heat (DH) and night heat (NH) stresses severely damage starch structure and quality, with DH having a greater impact. DH primarily affects starch granule size, relative crystallinity, and starch branching degree; NH primarily shortens amylopectin chains and retains more branching. Whole-day heat stress exerts a cumulative effect, causing more severe damage to starch than DH or NH. High temperature (HT) is a critical abiotic stress factor that negatively impacts maize yield and quality 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. In this study, the effects of daytime and nighttime HT on the physicochemical properties of waxy maize starch were investigated using two waxy maize hybrids as materials. 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 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. 1