Effects Of High Temperature On The Nitrogen Metabolism Enzymes Activities And Protein Contents In Rice Grain-filling Stage

The experiment selected the rice varieties Koshihikari (Japonica rice) and IR72 (Indica rice) as the materials, and used the PGX illuminable incubators which are multistage and programmable to construct high temperature environment (35℃/29℃) as treatment, while the natural normal temperature environment as the control check in rice grain-filling to research the effects of high temperature on the value of SPAD in functional leaves, nitrogen metabolism enzymes activities and nutritional quality in grains. The results were as followes.The value of SPAD in functional leaves (flag leaf and second leaf) changed as unimodal curve in rice grain-filling stage. And the average value of SPAD in functional leaves decreased extremely remarkably under the high temperature.The soluble protein contents in grains decreased gradually in rice grain-filling stage. The average contents of soluble protein in grains increased extremely remarkably in rice grain-filling stage under the high temperature.The GS and GOGAT activities in grains changed as unimodal curve in rice grain-filling stage. The average activities (the average of 5 times mensurated, the same followed) of GS in koshihikari grains decreased remarkably under the high temperature, which decreased extremely remarkably in IR72 grains. And the average activities of GOGAT in koshihikari grains were increased remarkably under the high temperature, which were increased extremely remarkably in IR72 grains. The peak time of GS activities in both varieties were moved up under the high temperature, while only the peak time of GOGAT activities in Koshihikari were moved up.The GOT and GPT activities in grains were descending during the grain-filling stage. The average activities of GOT and GPT in koshihikari grains increased remarkably under the high temperature, which increased extremely remarkably in IR72 grains.The rice protein contents increased extremely remarkably under the high temperature. The protein content in koshihikari was 93.100 mg/g under the high temperature, which was increased by 42.86% to the normal temperature, and the protein content in IR72 was 89.533 mg/g under the high temperature, which increased by 50.81% to the normal temperature. The amino acid constituents contents increased extremely remarkably under the high temperature. The total amino acid contents (except the Trp) in koshihikari increased by 66.71% under the high temperature, and which increased by 59.40% in IR72, and the essential amino acid contents increased by 67.89% and 61.03%, the lysine contents increased by 57.84% and 57.60%, respectively.There existed extremely remarkably positive correlation between the value of SPAD in functional leaves and GS activities, and remarkably or extremely remarkably negative correlation between the value of SPAD in functional leaves and GOT activities, GPT activities. But no remarkably correlation existed between the value of SPAD in functional leaves and GOGAT activities during rice grain-filling stage.There existed extremely remarkably negative correlation between soluble protein contents and GS activities, and remarkably or extremely remarkably positive correlation between soluble protein contents and GOGAT activities, GOT activities, GPT activities, and extremely remarkably positive correlation between soluble protein contents and protein contents, amino acid contents. There existed extremely remarkably negative correlation between GS activities and protein contents, amino acid contents. But no remarkably correlation existed between GOGAT activities and protein contents and amino acid contents. There existed extremely remarkably positive correlation between GOT activities, GPT activities and protein contents, amino acid contents. And there existed extremely remarkably positive correlation between GOGAT activities and GOT activities, GPT activities. In summary, the high temperature had accelerated the decomposition of chlorophyll in functional leaves, and strengthened the grain nitrogen metabolism in rice grain-filling stage, and caused the obviously enhancement of protein contents and amino acid contents. The decline of GS activities in grains did not restrain the synthesis of protein under the high temperature in rice grain-filling stage, so we presumed that the GS in grains was not the key enzyme in nitrogen metabolism in rice grain-filling stage. There existed extremely remarkably positive correlation between GOGAT activities and GOT activities, GPT activities, but no remarkably correlation existed between GOGAT activities and protein contents, amino acid contents, so we presumed that it would need the further research to demonstrate whether the GOGAT in grains was the key enzyme to restrain the synthesis of protein or not. There existd remarkably positive correlation between GOT activities, GPT activities and protein contents and amino acid contents. so we presumed that the GOT and GPT in grains were the key enzymes in the synthesis of protein.