Heat denaturation is an important technique in the study of the structure and function of photosynthetic proteins. Heat denaturation of photosystem II (PSII) membrane was studied using circular dichroism (CD) spect...Heat denaturation is an important technique in the study of the structure and function of photosynthetic proteins. Heat denaturation of photosystem II (PSII) membrane was studied using circular dichroism (CD) spectroscopy, differential scanning calorimetry (DSC) and oxygen electrode. Complete loss of oxygen evolving activity of the PSII membrane was observed at temperatures below 45℃ . The decrease of excitonic interaction between chlorophyll molecules occurred more rapidly than the change of the protein secondary structure of the PSII membrane at temperatures above 45℃ . The results indicate that the protein secondary structure of the membrane proteins in PSII membranes is more stable than the excitonic interaction between chlorophyll molecules during heat denaturation. 展开更多
The effect of varying pH on the photosystem II (PSII) membrane was studied using absorption and steady state fluorescence spectroscopy, and using a variable fluorescence technique. pH variations induced significan...The effect of varying pH on the photosystem II (PSII) membrane was studied using absorption and steady state fluorescence spectroscopy, and using a variable fluorescence technique. pH variations induced significant changes in the chlorophyll states of the PSII membrane, but no effect was seen on the chlorophyll fluorescence parameter F ′ v/ F ′ m. For acidic pH conditions, protein structures of the PSII membrane were slightly altered, whilst at alkaline pH levels, large changes in the protein structure of the PSII membrane were detected. The results indicate that the microenvironment around Cys in the PSII membrane is very susceptible to alkaline pH conditions, and that in the acid (4≤pH<7) and alkaline (9≥pH>7) regions, pH variation has no effect on the protein structures of the PSII reaction center (RC).展开更多
Strong light decreases the rate of photosynthesis and assimilates production of crop plants. Plants with different carbon reduction cycles respond differently to strong light stress. However, variation in photoinhibit...Strong light decreases the rate of photosynthesis and assimilates production of crop plants. Plants with different carbon reduction cycles respond differently to strong light stress. However, variation in photoinhibition in leaves with different photosynthetic characteristics in maize is not clear. In this experiment, we used the first leaves (with an incomplete C4 cycle) and fifth leaves (with a complete C4 cycle) of maize plants as well as the fifth leaves (C3 cycle) of tobacco plants as a reference to measure the photosynthetic rate (PN) and chlorophyll a parameters under strong light stress. During treatment, PN, the maximal fluorescence (Fm), the maximal quantum yield of PSII photochemistry (Fv/Fm), and the number of active photosystem II (PSII) reaction centers per excited cross-section (RC/CSm) declined dramatically in all three types of leaves but to different degrees. PN, Fm, Fv/Fm, and RC/CSm were less inhibited by strong light in C4 leaves. The results showed that maize C4 leaves with higher rates of photosynthesis are more tolerant to strong light stress than incomplete C4 leaves, and the carbon reduction cycle is more important to photoprotection in C4 leaves, while state transition is critical in incomplete C4 leaves.展开更多
基金Supported by the State Key Basic Research and Development Plan (No.G19980 10 10 0 ) the National Natural Science Foundation of China(No.3 9890 3 90 )
文摘Heat denaturation is an important technique in the study of the structure and function of photosynthetic proteins. Heat denaturation of photosystem II (PSII) membrane was studied using circular dichroism (CD) spectroscopy, differential scanning calorimetry (DSC) and oxygen electrode. Complete loss of oxygen evolving activity of the PSII membrane was observed at temperatures below 45℃ . The decrease of excitonic interaction between chlorophyll molecules occurred more rapidly than the change of the protein secondary structure of the PSII membrane at temperatures above 45℃ . The results indicate that the protein secondary structure of the membrane proteins in PSII membranes is more stable than the excitonic interaction between chlorophyll molecules during heat denaturation.
基金Supported by the State Key Basic Research and Developm ent Plan (No. G19980 10 10 0 ) and the National Natural Science Foundation of China (No.39890 390 )
文摘The effect of varying pH on the photosystem II (PSII) membrane was studied using absorption and steady state fluorescence spectroscopy, and using a variable fluorescence technique. pH variations induced significant changes in the chlorophyll states of the PSII membrane, but no effect was seen on the chlorophyll fluorescence parameter F ′ v/ F ′ m. For acidic pH conditions, protein structures of the PSII membrane were slightly altered, whilst at alkaline pH levels, large changes in the protein structure of the PSII membrane were detected. The results indicate that the microenvironment around Cys in the PSII membrane is very susceptible to alkaline pH conditions, and that in the acid (4≤pH<7) and alkaline (9≥pH>7) regions, pH variation has no effect on the protein structures of the PSII reaction center (RC).
文摘Strong light decreases the rate of photosynthesis and assimilates production of crop plants. Plants with different carbon reduction cycles respond differently to strong light stress. However, variation in photoinhibition in leaves with different photosynthetic characteristics in maize is not clear. In this experiment, we used the first leaves (with an incomplete C4 cycle) and fifth leaves (with a complete C4 cycle) of maize plants as well as the fifth leaves (C3 cycle) of tobacco plants as a reference to measure the photosynthetic rate (PN) and chlorophyll a parameters under strong light stress. During treatment, PN, the maximal fluorescence (Fm), the maximal quantum yield of PSII photochemistry (Fv/Fm), and the number of active photosystem II (PSII) reaction centers per excited cross-section (RC/CSm) declined dramatically in all three types of leaves but to different degrees. PN, Fm, Fv/Fm, and RC/CSm were less inhibited by strong light in C4 leaves. The results showed that maize C4 leaves with higher rates of photosynthesis are more tolerant to strong light stress than incomplete C4 leaves, and the carbon reduction cycle is more important to photoprotection in C4 leaves, while state transition is critical in incomplete C4 leaves.
