Effects Of High Temperature On Grain Starch Size Distribution And Sucrose Degradation,Storage Protein Accumulation Metabolism In Rice(Oryza Sativa L.)

The high-temperature stress resulted in a significant decrease in seed setting rate and a decrease in the eating quality and nutritional quality of rice during grain-filling stage.In this study,two temperature treatments(HT and NT)at filling stage were imposed to rice plants under the controlled temperature chambers.Rice varieties with different qualities were used as materials to investigate the effect of high temperature on starch granule size distribution,sucrose metabolism and storage protein accumulation in rice grains.The main findings are as follows:1.High temperature(HT)is the major environmental factor affecting grain starch properties of cooking rice cultivars.However,little information has been available on the effect of environmental temperature on the particle size distribution of starch granules in rice plant.In this paper,five indica rice genotypes,including the wild type(9311)and its four mutants differing in amylose content(AC),were used to investigate the effect of environmental temperature on the particle size distribution of starch granule,as well as its relation to AC and gelatinization properties of rice starch.The result showed that HT increased the average diameter of starch granules,and had a marked impact on the particle size distribution of starch granules.However,influence of HT on GT and particle size distribution of starch granules was relatively independent of their alteration in AC level for different rice genotypes.Therefore,HT-induced increase in the average diameter of starch granules and LSG percentage was strongly responsible for the higher starch gelatinization temperature and inferior cooked palatability of HT-ripening rice grains,which be not inherently associated with their varying AC level.2.The grain filling process involves a series of biochemical reactions with sucrose decomposition and starch synthesis as the core.Sucrose decomposition is the first step in the process of starch synthesis.However,the effects of high temperature on sucrose degradation in rice grain were reported rarely during grain filling.In this study,we investigated the effects of high temperature during the filling stage on the transcriptional expression of sucrose degradation related genes in rice grains,using different rice cultivars with different sensitivity to high temperature.The results showed that sucrose synthase(SUS)gene and the content of fructose were up-regulated while sucrose invertase(INV)gene and the content of glucose were down-regulated expression.Therefore,sucrose synthase plays a major role in the degradation of sucrose under high temperature stress.3.Protein is the second storage material of rice sophomore,and a main factor to determine the nutritional quality of rice.Some studies have reported that protein disulfide isomerase(PDI)affects the accumulation of rice storage protein,and high temperature stress can also cause increased protein content of rice,but the reason for the increase of protein content were investigated with little research.In this study,we investigated the relationship between the high temperature-induced increase in protein content and the PDI level with the plants of WT,PDI-RNAi and PDI-OE,involving the technology of SDS-PAGE,Western blot and real-time fluorescence quantitative.The results showed that high temperature treatment resulted in the increase of total protein content and mature subunits,the decrease of glutelin precursors and the up-regulated expression of PDI and glutelin synthase genes;the change range of PDI-OE was higher than that of WT and the opposite for PDI-RNAi.Therefore,the enhance of PDI would also increase the content of protein in rice grain under high temperature stress.