The Physiological Pathway of High Temperature Effects on Rice Quality Formation during Grain-Filling Stage
Date Issued
2008
Date
2008
Author(s)
Lin, Chin-Ju
Abstract
Rice plants frequently expose to high temperature during grain-filling stage in Taiwan. It renders chalky grain appearance and results in lower rice quality. Moreover, with the influence of global warming in recent years, high temperature has become a major challenge for rice production in Taiwan. Previous studies usually focus on the high temperature effects of enzyme activities involved in starch or protein biosynthetic pathway and the content/composition alteration of these storage products. Few documents, however, report the possible physiological pathways or molecular mechanisms related to energy/physiological status which lead to poor grain quality formation under high temperature. The present study focused on the physiological pathway of high temperature effects on rice quality during grain-filling stage, and expected to reveal the relation between high temperature and rice quality formation. The current study also hoped to confirm the possibility of ameliorating high temperature negative effects on rice quality via root temperature regulation. he results showed that under high temperature oxygen depletion inside rice caryopsis may limit ATP synthesis. Moreover, high temperature induced rapid growth of caryopsis but also speeded up its chlorophyll degradation, and so decreased the extra supply for oxygen and energy by photosynthesis during grain-filling state. High temperature also accelerated the aging of flag leaf, the major source organ for grain filling, thus may cause the shortage of photosynthetic assimilate. According to gene expression analysis for energy metabolism related genes, glycolysis and fermentation pathways were elevated by high temperature, and therefore meight accelerate the starch degradation to provide more sugar substrates for both pathways. Alcohol fermentation pathway rather than organic acids fermentation was elevated by high temperature which might avoid further acidification in caryopsis. In addition high temperature enhanced the H2O2 production, one of reactive oxygen species, and enhanced expressions of genes encoding antioxidants, such as SOD and CATB, indicating the existence of oxidative stress and homeostasis in caryopsis under high temperature. Lipid peroxidation, nuclear DNA fragmentation and endosperm cell death were also found to be promoted under high temperature. These phenomenons seemed to be caused by oxidative stress. Above physiological reactions might in turn interfere the synthesis and accumulation of starch or storage protein during grain-filling stage, and finally lead to rice chalky appearance formation. Moreover, lowering root temperature could ameliorate these effects exerted by high temperature with respect of analyzed physiological traits. igh temperature also regulated the expression of some stress-related gene, including up-regulated GLOI, RAB24, OsSAMDC, but down-regulated PDI, cyPPDKB expressions. It reveals that these gene-related molecular mechanisms may also participate in physiological responses to high temperature.he results in this study revealed that the physiological pathway between high temperature and rice quality formation seems to be complicate. The present study provided a basic frame; however, it still needs more works to elucidate the relationship among different pathways.
Subjects
Oryza sativa
high temperature
chalky
Type
thesis
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