title: Simultaneous analysis of photosystem responses of Microcystis aeruginoga under chromium stress.
abstract: Chromium (Cr) is a toxic metal that poses a great threat to aquatic ecosystems. Information is limited on coinstantaneous responses of photosystems I (PSI) and II (PSII) to Cr(VI) stress due to lack of instruments that can simultaneously measure PSI and PSII activities. In the present study, responses of quantum yields of energy conversion and electron transport rates of PSI and PSII in Microcystis aeruginosa cells to Cr(VI) stress were simultaneously analyzed by a DUAL-PAM-100 system. Quantum yield of cyclic electron flow (CEF) under Cr(VI) stress and its physiological role in alleviating toxicity of Cr(VI) were also analyzed. At 5 mg L(-1) Cr(VI), quantum yield and electron transport rate of PSII decreased significantly, and light-induced non-photochemical fluorescence quenching lost. Cr(VI) also inhibited efficiency of PSII to use energy under high light more than of PSI. PSII showed lower maximal electron transport rate and light adaptability than PSI. Electron transport rate of PSI was higher and decreased less than that of PSII, implying less sensitivity of PSI to high light and Cr(VI). Energy dissipation through non-light-induced non-photochemical fluorescence quenching increased with increasing Cr(VI) concentration. CEF was stimulated under Cr(VI) treatment and made a significant contribution to quantum yield and electron transport of PSI, which was essential for protection of PSI from stresses of Cr(VI) and high light.
authors.affiliation: State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China.
authors.forename: Shuzhi
authors.initials: S
authors.lastname: Wang
authors.forename: Fulong
authors.initials: F
authors.lastname: Chen
authors.forename: Shuyong
authors.initials: S
authors.lastname: Mu
authors.forename: Daoyong
authors.initials: D
authors.lastname: Zhang
authors.forename: Xiangliang
authors.initials: X
authors.lastname: Pan
authors.forename: Duu-Jung
authors.initials: DJ
authors.lastname: Lee
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D002857:Chromium / Q000633:toxicity*; D004579:Electron Transport / Q000187:drug effects; D005453:Fluorescence; D008027:Light; D046931:Microcystis / Q000187:drug effects* / Q000378:metabolism; D045331:Photosystem I Protein Complex / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000502:physiology*; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D014874:Water Pollutants, Chemical; D002857:Chromium; D002734:Chlorophyll