Structure And Function In Photosystem II And Involvement Of Chloroplasts In Plant Apoptosis

The aim of this study is to investigate the denaturation, membrane lipids protection and recovery of photosystem II (PSII), and the involvement of chloroplasts in plant apoptosis.The first part: Protein structure, thermal stability and function of PSII in different conditions are studied using absorption, fluorescence and circular dichroism (CD) spectroscopy, differential scanning calorimetry (DSC), oxygen electrode and variable fluorescence. The main results are as follows.(1) Manganese cluster, closely related to oxygen-evolving activity, is very sensitive to heat treatment, and the protein secondary structure of the membrane proteins in PSII membranes is more stable than the excitonic interaction between chlorophyll molecules during heat treatment.(2) SDS (sodium dodecyl sulfate) perturbation can primarily affect the extrinsic proteins and OGP (n-octyl β-D-glucopyranoside) mainly influences the integral membrane proteins of PSII. Combined with DSC analysis, the results indicate that effect of perturbed extrinsic proteins on the thermal stability of PSII is different from that of the disturbed integral membrane proteins.(3) The aggregation state of the light-harvesting complex (LHCII) in PSII is related to the anomalous CD signal, and may be an important factor influencing Fo' in the heat treatment of PSII membrane.(4) Phosphatidylcholine (PC) can protect PSII membrane against heat treatment and the alterations in the unsaturated fatty acid extent in PC can cause the changes of the protection ability.(5) PC addition did not change the protein secondary structures, but could partially reactivate the reduced oxygen-evolving rate, and partly reversed the variable fluorescence parameters and the chlorophyll binding state. The results indicate that the PC environment can optimize the tertiary structures of PSII.The second part: Using a plant cell-free apoptotic system which comprised nuclei and cytosol of tobacco suspension cells, we found that spinach cytochrome f induced typical morphological and biochemical changes characteristic of apoptosis in nuclei in vitro. We suggested that chloroplast cytochrome f functioned as a novel apoptosis effector in programmed plant cell death, which may be important in green plants. In addition, the possible mechanism was discussed.