Characterizing the impact of high temperature during the grain filling on phytohormone levels, enzyme activities and metabolic profiles of the early indica-rice variety.

Global warming results in high temperature stress (HTS), which presents severe challenges for the worldwide modern agricultural production and will have significant impacts on the yield and quality of crops. Accumulation of photosynthetic products, activities of the sucrose-starch metabolism related enzymes, phytohormone levels and metabolic profiling using LC-MS were analysed in the flag leaves and/or the in the developing grains treated with HTS during the grain filling stage of an indica-rice. HTS induced significant yield loss, and caused grain quality reduction with less amylose contents. HTS reduced photosynthetic product accumulation in flag leaves and less starch accumulation in the developing grains, compared to that under normal temperatures. The activities of sucrose-starch metabolism related enzymes were dis-regulated in developing grains grown under HT. Moreover, phytohormone homeostasis in the flag leaves and developing grains was also dramatically disturbed by HT. Metabolic profiling detected many metabolites had remarkably different relative fold abundances at different timepoints in the developing grains under HT versus those under normal temperatures, these metabolites enriched in different HTS-responding pathways. The changed phytohormone ratio and auxin levels might associate with the reduced photosynthetic product and its translocation, and ultimately reduced starch accumulation in the developing grains. The detected metabolites might play different roles in responding to the influence of HTS in developing grains at different development stages. These results provide theoretical reference and the basis for regulation of rice production with higher quality and yields when grown under HT.