Discrepancy Of Physiology And Biochemistry During Leaf Senescence Process In Stay Green Maize Breedline And The Regulation By N-fertilizer Treatment

In this research we compared the discrepancy of physiology and biochemistry druing plant senescence in different stay green maize breedlines, as well as the regulation of two level N-fertilizer treatment. The combination experiments including field plot experiment and potted plant growing methods, providing non-fertilization and normal fertilization treatment was conducted using stay green and non-stay green maize breedline. In addition, with the using of chlorophyll a fluorescence transient and light absorbance at 820 nm, we analysed the main reason of decline in photosynthetic performance during leaf senescence process. The main results as follow:1. Non-stay green type photosynthetic performance showed rapidly decline trend in grain-filling stage after anthesis, the main reason was that the electron transport chain after PSII reaction center has been serious damaged, which blocked the electron transport from PSII to PSI and suppressed the conversion between light energy and chemical energy. Consequently, that led the carboxylation system performance markedly decreased.2. The performance of electron transport chain after PSII reaction center in non-stay green type was decreased rapidly at the grain-filling stage, that resulted in a large number electron accumulation in receptor side of PSII reaction center and resulted in the phenomenon of light energy overmuch. Then it could rise the content of active-oxygen up markedly. Thereby, that accelerated the performance decline of the PSII and affected the utilization efficiency of light energy by leaf.3. After anthesis, the activity of RuBPcase and PEPcase in non-stay green maize breedline was significantly reduced. Compared to stay green type, Which ability of carbohydrate synthesis in carboxylation system has declined markedly. Three protective enzymes SOD, POD and CAT activity in active-oxygen scavenging system were significantly lower than the rate of stay green type, but MDA content increased significantly. The ability of scavenging active-oxygen in non-stay green maize breedline was significantly lower than that of stay green type.4. The ability of nitrogen accumulation after output in stay green type was stronger than non-stay green type, in which the protein content stayed a high level after anthesis and maintained the stability of the photosynthetic organ, accordingly. All of above can prolong and enhance the high value continuance of photosynthetic in stay green type, which is the one of the reasons to promote high and stable yield in stay green type.5. Nitrogenous fertilizer enhanced the performance of PSII reaction center and the electron transport chain after it in non-stay green type, but the performance increase rate of electron transport chain after PSII reaction center was lower, so the co-ordination between the two photosystem was not significant increase. Therefore, photosynthetic performance of non-stay green type was increased by nitrogenous fertilizer treatment, but the short duration of photosynthetic high-value and low intensity of the photosynthesis were not changed. The performance of electron transport chain after PSII reaction center of stay green type was significantly increased markedly by nitrogenous fertilizer treatment, therefore PSI can be supplied enough electron by PSII, which is bound to strengthen the two co-ordination between the two photosystem, thus which maintained a long-term performance of photosynthesis in stay green one. 6. The regulation to non-stay green type by nitrogenous fertilizer treatment were significantly higher than stay green one, especially in the later grain-filling stage. The nitrogenous fertilizer increased protein content of leaf as well as photosynthetic performance, which significantly increased the production of non-stay green type. Compared with stay green style, the non-stay green style was a obviously high efficiency of nitrogen. However, non-stay green type was restricted by its gene, that showed the decline of photosynthetic performance was significantly greater than the stay green type after grain-filling stage, so the yield of non-stay green type was still significantly lower than the stay green one.In conclusion, in the leaf senescence process the performance of electron transport chain after PSII reaction center of non-stay green type was rapidly decline, which was one of important reasons that the reduction of in photosynthetic performance and grain yield. Nitrogen enhanced photosynthetic performance mainly through improving the co-coordination between two photosystem, despite the nitrogen significantly enhanced the PSII reaction center of non-stay green type, but the performance of electron transport chain after it was not increased markedly by nitrogen regulation, so it is not sensitive to improved the co-cooperation photosystem. Therefore non-stay green type did not have the high yield potential.