Different Studies On The Effect Of Day Versus Night High Temperature On Rice Quality And Expression Profiles Of Grain Proteins

Global warming has become an irreversible trend and had a major impact to the ecological environment and food safety, and, the potential impact of rising temperature would be further exacerbated. At present, the effect of climate warming on crop production gets much of the attention of scientists and governments in the world. The daily mean temperature is elevated owing to the climate change caused by atmospheric greenhouse gas, and the night temperature rise is more evident. The seed setting rate significantly reduced or even crop failure and quality declined were caused by heat stress in rice growing season, especially at the flowering and grain-filling stages. In recent decades, there were more researches on the high temperature on rice yield and quality at home and abroad. Studies on the rice genetic and physiological basis of high temperature have become a hot spot direction. Researches on the different effects of day and night high temperature during grain formation will have a certain reference value for fully understanding and assessing the impact of temperature increasing on rice yield and quality.In this study, four middle-season indica rice varieties '9311', Shuhui527, N22 and Texianzhan with different high temperature adaptation were selected. During rice grain-filling stage, the treatment temperatures of the control, night high temperature (NHT), and day high temperature (DHT) were 28℃/20℃,27℃/35℃, and 35℃/27℃, respectively, and, all the treatments were carried out in plant incubators and maintained for 20 days after fertilization. The different influences of NHT and DHT on rice quality and seed proteins expression profiles during grain filling were studied, to accumulate a certain foundation for revealing the different molecular ecological mechanisms of variations in rice grain formation and quality induced by DHT and NHT stress during grain filling. The main results were as follows:1. Compared with the control, the grain-filling rate and maturation of the grains from plants of all varieties exposed to high temperature were faster, and, the effect of NHT on the fresh weights was more serious than that of DHT. The accumulation of amylose was increased and suppressed by heat treatment at the early and late stage, respectively. The different influences of DHT and NHT on the amylose content during grain filling stage mainly occurred at the early grain-filling stage, which among varieties were inconsistent. High temperature treatments decreased grain weight, brown rice rate, milled rice rate, head rice rate, amylose content and gel consistency, and increased chalkiness degree. The differences between NHT and DHT or among rice varieties were just the distinct change extents of the above symptoms, and the changing amplitudes of head rice rate and chalkiness degree were larger among them. Compared with DHT, NHT exerted more serious effects on the grain weight and milled rice rate and less effect on head rice rate, while, the different effects of DHT and NHT on brown rice rate, chalkiness degree and amylose content among varieties were not consistent.2. After analyzing protein expression profiles of rice filling grains at different grain filling stages under different heat treatments by two-dimensional gel electrophoresis (2-DE),81 differentially expressed proteins in response to high temperature were determined. Through mass spectrometry analysis,66 out of 81 differentially expressed proteins were successfully identified, which were classified into eight groups according to their functions:carbohydrate metabolism, amino acid metabolism, stress and defense proteins, signal transduction, protein synthesis and destination, miscellaneous, unknown function and others function. After the expression changes in 66 differentially expressed proteins in response to different high temperature treatments analyzed, five distinct expression change patterns between NHT and DHT could be revealed. And, there were the same and specific protein expression change patterns between NHT and DHT in different varieties.3. Among all of the successfully identified proteins,11 proteins possessed 2-5 isoforms, whose expression variations were monitored at four grain filling stages in two varieties ('9311' and Texianzhan). The dynamic expression profiles of isoforms, including PPDK and pullulanase, in response to different high temperature (DHT and NHT) were displayed by proteomic approach in rice filling grains. Most of the isoforms identified displayed different expression change patterns between NHT and DHT in '9311' and Texianzhan. There were negative correlation between the expression amount of cyPPDKB isoforms and grain chalkiness degree, and it may be because of different suppressed extent of expression amount of cyPPDKB resulted in different grain chalkiness between NHT and DHT.4. High temperature stress during grain filling stimulated the differential expression of some stress and defense proteins in rice filling grains, including h-type thioredoxin (Trx h), peroxiredoxins (Prxs), Cu/Zn superoxide dismutase (Cu/ZnSOD), ascorbate peroxidase (APX), heat shock proteins (HSPs) and glyoxalasesⅠ. The expression change patterns of stress and defense proteins induced by DHT and NHT treatments were distinct. Five genes encoding stress and defense proteins including Trx h, APX,2-Cys Prx, Cu/ZnSOD and HSP70 were selected for transcripts analysis by real-time quantitative RT-PCR (qRT-PCR). The results showed that not all the protein levels were correlated with their corresponding transcript levels. However, the molecular mechanism of seed proteins involved in NHT and DHT tolerance during grain filling should be different, and the distinct stress and defense proteins played main role in rice varieties with different high temperature tolerance.5. In rice quality formation, the characteristics of high temperature adaptable rice varieties during grain-filling stage included:the expression amount of cyPPDKB was higher and suppressed extent under high temperature stress was smaller; high temperature would increase the protein expression of most of pullulanase isoforms at most grain filling stages, and, there was isoforms with more faster responses to high temperature; the expression amount of stress responsive A/B barrel domain containing protein was higher, and its isoform protein spot 60 expressed at early stage.The results in this study provided the basic data and clues for further research on revealing the different molecular ecological mechanisms of variations in rice grain formation and quality induced by DHT and NHT stress during grain filling.