Research On Flag Leaf Senescence And Photosynthetic Membrane Protein Complexes Function Changes Yield Hybrid Rice "Liangyoupeijiu.

The purpose of this research is to explore the content variation of photosynthetic membrane (i.e. thylakoid membrane) protein complexes and their relationship with light energy absorption, transformation and transfer in flag leaves of high-yield hybrid rice Liangyoupeijiu during senescence.The present paper made a preliminary exploration on the method of Blue-Native polyacrylamide gel-electrophoresis (BN-PAGE), which was used to separate the thylakoid membrane protein complexes of rice leaves. The intact chloroplasts were isolated and purified by Percoll gradient centrifugation. Then the thylakoid membrane proteins were solubilized at n-dodecyl-β-D-maltoside. Using5%～12%gradient Blue-native PAGE,9protein complex bands could be exhibited on the gel. They contained the major high molecular weight protein complexes in the photosynthetic membrane. Diversity of these proteins between different rice varieties could also be showed. Using1D BN-PAGE as the fist dimension and SDS-Urea-PAGE as the second dimension, a total of51protein spots could be observed on2D-gel, which were the subunits of thylakoid membrane protein complexes in Liangyoupeijiu flag leaves. This method provided favorable conditions for the proteomics research of rice photosynthetic apparatus in responsing the adversity.To discuss the changing pattern of photosynthetic membrane during senescence, high-yield hybrid rice Liangyoupeijiu was grown in the field and the flag leaves were collected at jointing stage, heading stage, flowering stage, filling stage, milky stage and dough stage. Through Chlorophyll a fluorescence transient, physiological and biochemical techniques, we studied the function of photosynthetic membrane. The content changes of thylakoid membrane protein complexes were also investigated by BN-PAGE.The results showed that:1. Chlorophyll content, photosynthesis and thylakoid membrane protein content of flag leaves rose and peaked at heading stage, then began to decline. It still maintained a high level at flowering and filling stage, and the significant decline-appeared untill the stage of milky and wax ripeness. 2. The stability of each protein complexes (i.e. inverse degradation rate) during leaf senescence was different in the following order:LHCⅡ> PSⅡ core> PSⅠ core> ATPase&Cyt b6/f> LHC Ⅰ.3. Protein complexes and electron transport activity of PS Ⅰ declined later but more quickly than those of PS Ⅱ.4. The decreased chlorophyll alb ratio could be explained by the relative enrichment of light-harvesting antenna to reaction center with senescence. The stable LHC Ⅱ kept the high level of absorbing energy in the late of flag leaf growth, which may play an important role in adjusting the energy distribution and dissipation during leaf senescence.In summary, combined photosynthetic physiology and biochemistry method with proteomics method, we explained the relationship between degradation of thylakoid membrane protein complexes and changes of photoreaction during senescence. It might have great significance in the research of hybrid rice premature aging.