title: Effects of cadmium on the activities of photosystems of Chlorella pyrenoidosa and the protective role of cyclic electron flow.
abstract: Cadmium (Cd) shows high toxicity to aquatic microalgae. Many studies showed that Cd inhibited activities of photosystem II (PSII) but the effects of heavy metals on photosystem I (PSI) and cyclic electron flow (CEF) were still controversial and unclear. The effects of CdCl2 on the activities of PSI, PSII and CEF in Chlorella pyrenoidosa was measured simultaneously in the present study. In presence of 200μM of Cd, ultrastructure of some cells was strongly modified. Cd exposure led to decrease of the activities of photosynthetic oxygen evolution and respiration. PSII was more sensitive to Cd treatment than PSI. Cd treatment showed significant inhibition on the photochemical quantum yield and electron transport rate of PSII. Cd increased the quantum yield of non-light-induced non-photochemical fluorescence quenching, indicating the damage of PSII. The activity of PSI showed tolerance to Cd treatment with concentration less than 100μM in the experiment. Linear electron flow (LEF) made significant contribution to the photochemical quantum yield of PSI of the untreated cells, but decreased with increasing Cd concentration. The contribution of CEF to the yield of PSI increased with increasing Cd concentration. The activation of CEF after exposure to Cd played an essential role for the protection of PSI.
authors.affiliation: Laboratory of Environmental Pollution and Bioremediation, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China.
authors.forename: Shuzhi
authors.initials: S
authors.lastname: Wang
authors.forename: Daoyong
authors.initials: D
authors.lastname: Zhang
authors.forename: Xiangliang
authors.initials: X
authors.lastname: Pan
mesh_terms: D002104:Cadmium / Q000633:toxicity*; D019256:Cadmium Chloride / Q000633:toxicity; D019069:Cell Respiration / Q000187:drug effects; D002708:Chlorella / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism* / Q000648:ultrastructure; D004579:Electron Transport / Q000187:drug effects; D004734:Energy Metabolism / Q000187:drug effects; D004785:Environmental Pollutants / Q000633:toxicity*; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism*
chemical_list: D004785:Environmental Pollutants; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002104:Cadmium; D019256:Cadmium Chloride; D010100:Oxygen
keywords: Cadmium; Chlorella pyrenoidosa; Cyclic electron flow; Photosystem I; Photosystem II