Changes of Photosynthetic Membrane Function and Protein Complexes in Flag Leaves of Liangyoupeijiu during Leaf Senescence

Abstract

The purpose of this study was to explore the content variation of thylakoid membrane protein complexes and its relationship with light absorption,transformation and transfer in flag leaves of high-yield hybrid rice Liangyoupeijiu during senescence.A rice cultivar,Liangyoupeijiu was grown in the field.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 Blue-native polyacrylamide gel-electrophoresis(BN-PAGE).The results showed that 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 stages,and the significant decline appeared untill the stage of milky and wax ripeness.The stability of protein complexes(i.e.inverse degradation rate)during leaf senescence showed an order of LHCII PSIIcore PSIcore ATPase Cyt b6/f LHCI.Protein complexes and electron transport activity of PSI declined later but more quickly than those of PSII.The decreased chlorophyll a/b ratio could be explained by the relative enrichment of light-harvesting antenna to reaction center with leaf senescence.The stable LHCII 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.