摘要
The effect of cadmium on the photosynthetic activity of Synechoeystis PCC 6803 was monitored in this study. The oxygen evolving capacity of Synechocystis treated with 40 M CdCl2 was depressed to 10% of the maximum in 15 min, indicating that Cd2+ penetrated rapidly into the cells and blocked the photosynthetic activity. However, neither photosystem II (PSII) nor photosystem I (PSI) activity showed a significant short-term decrease which would explain this fast decrease in the whole-chain electron transport. Thermoluminescence measurements have shown that the charge separation and stabilization in PSII remains essentially unchanged during the first few hours following the Cd2+ treatment. The electron flow through PSI was monitored by following the redox changes of the P700 reaction centers of PSI. Alterations in the oxidation kinetics of P700 in the Cd2+-treated cells indicated that Cd2+ treatment might affect the available electron acceptor pool of P700, including the CO2 reduction and accumulation in the cells. Perturbed angular correlation of rays (PAC) using the radioactive Cd-111m isotope was used to follow the Cd2+ uptake at a molecular level. The most plausible interpretation of the PAC data is that Cd2+ is taken up by one or more Zn proteins replacing Zn2+ in Synechocystis PCC 6803. Using the radioactive Cd-109 isotope, a protein of approximately 30 kDa that binds Cd2+ could be observed in sodium dodecyl sulfate polyacrylamide gel electrophoresis. The results indicate that Cd2+ might inactivate different metal-containing enzymes, including carbonic anhydrase, by replacing the zinc ion, which would explain the rapid and almost full inhibition of the photosynthetic activity in cyanobacteria.
- 出版日期2006-9