Response Of CYPPDK To Temperature In Rice Seed Germination And Phosphorylation Regulation

PPDK has the function of catalytic formation of PEP,chloroplastic PPDK C4 plants is the key enzyme of the regeneration of the primary CO2 acceptor in C4 photosynthetic pathways. The presence of PPDK in C₃ plants and in non-photosynthetic tissues in C4 plants is cytoplasmic PPDK（cyPPDK）. It was just proposed that the basic function of cyPPDK is to serve as an enzyme which can assist carbohydrate metabolism, and it can also adjust the abiotic stress adaptation. Our research group has shown that the type of PPDK in rice is mainly the cytosolic PPDK. PPDK has modified its activity by phosphorylation when participated endosperm starch accumulation processe during the grain-filling period and has regulation on chalk white formation at high temperature.In this study, we used two different temperature-sensitive cultivars（9311 and TXZ-25） and temperature treatment（34℃、24℃、18℃） at different stages of seed germination and seedling stage. The gene expression, protein content and phosphorylation level of cyPPDK were determined. The main results are as follows:1.In the process of seed germination, a large amount of cyPPDK was expressed after 48 h water absorption, and reached the maximum at 72 h and then the expression of cyPPDK gene was promoted under high temperature and suppressed at low temperature. It can detect the existence of PPDK protein during the seed germination, The expression change of PPDK in protein level was not consistent with the gene level, and the PPDK protein expression was different in response to temperature. PPDK in phosphorylation levels consistent with gene expression levels of performance, and the phosphorylation level of high temperature treatment group was higher than that of control group. The above indexes exist differences between different cultivars, 9311 higher than TXZ- 25.2.In three-leaf stage,we has found chPPDK expression in rice leaves. High temperature treatment has no effect on the expression of chPPDK in 9311,in contrast, the expression of chPPDK in TXZ-25 was decreased. However, the expression of chPPDK in the two cultivars both decreased at low temperature. The expression of PPDK in leaves is basically consistent with the expression of chPPDK gene. And the expression of phosphorylated PPDK was higher in the high temperature treatment.3. It indicated that the high temperature treatment can accelerate the process of seed germination in the two cultivars. The content of soluble sugar increased in the two cultivars under different temperature treatment, while the starch decreased.High temperature can promote the starch degradation and increase the soluble sugar content. 9311 in the process of germination, starch degradation and soluble sugar were increased more than TXZ- 25.In this study, the high temperature treatment（34℃） didn’t have an adverse effect on seed germination and seedling stage of rice, while the low temperature treatment（18℃） had obvious inhibitory effect. Preliminary results confirmed that cyPPDK and its phosphorylation in rice seed germination period is involved in the development process of rice and was affected by temperature. chPPDK Can be detected in rice seedling leaf chPPDK, its physiological functions need to be researched.