Greater impact of pre-flowering high temperature stress on nutrient content in purple sweet waxy maize grains compared to post-flowering stress

Abstract

Purple sweet waxy maize is valued for its distinctive nutritional profile and flavor. High temperature stress, which can occur at any developmental stage, poses a significant threat to maize production. Understanding its effects on maize quality is essential for developing effective strategies to cope with climate change. This study investigated the effects of high temperature stress during pre-flowering (V12-T and VT-T) and post-flowering (VT+10-T) stages on the nutritional composition of purple sweet waxy maize grains in 2022 and 2023. Compared to natural temperature conditions (CK), high temperature stress increased the activity of flavonoid 3′-hydroxylase (F3′-H), thereby promoting anthocyanin synthesis, however, it significantly reduced grain weight and anthocyanin accumulation. Specifically, V12-T, VT-T, and VT+10-T treatments reduced the mean anthocyanin accumulation over two years by 22.45 %, 43.70 %, and 12.76 %, respectively, with the VT-T treatment resulting in the greatest decline. High temperature stress also disrupted sucrose and starch metabolism, inhibited starch synthesis in endosperm cells and reduced the two-year mean starch content by 24.06 %, 40.94 %, and 21.46 % for the V12-T, VT-T, and VT+10-T treatments, respectively. In addition, it decreased starch paste viscosity and thermal stability, and increased surface porosity and depression of starch granules, thereby compromising starch quality. High temperature stress decreased the contents of albumin, globulin, and gluten, while increasing prolamin content, which has lower nutritional value. Overall, high temperature stress significantly affected the accumulation and quality of key grain components, including anthocyanins, starch, and protein fractions, by disrupting multiple physiological and biochemical processes, particularly sucrose and starch metabolism. Notably, high temperature stress during the pre-flowering stage, especially at the VT stage, caused the most severe negative effects.