title: Photosynthetic and cellular toxicity of cadmium in Chlorella vulgaris.
abstract: The toxic effects of cadmium (Cd) on the green alga Chlorella vulgaris were investigated by following the response to Cd of various toxicity endpoints (cell growth, cell size, photochemical efficiency of PSII in the light or Φ(PSII), maximal photochemical efficiency or Fv/Fm, chlorophyll a fluorescence, esterase activity, and cell viability). These toxicity endpoints were studied in laboratory batch cultures of C. vulgaris over a long-term 96-h exposure to different Cd concentrations using flow cytometry and pulse amplitude modulated fluorometry. The sequence of sensitivity of these toxicity endpoints was: cell yield >> Φ(PSII) ≈ esterase activity > Fv/Fm > chlorophyll a fluorescence ≈ cell viability. It is shown that cell apoptosis or cell death only accounted for a minor part of the reduction in cell yield even at very high algistatic free Cd²⁺ concentrations, and other mechanisms such as blocked cell divisions are major contributors to cell yield inhibition. Furthermore, cadmium may affect both the electron donors and acceptors of the electron transport chain at high free Cd²⁺ concentration. Finally, the resistance of cells to cell death was size-dependent; medium-sized cells had the highest toxicity threshold. The present study brings new insights into the toxicity mechanisms of Cd in C. vulgaris and provides a detailed comparison of the sensitivity of various Cd toxicity endpoints.
authors: MOE Laboratory for Earth Surface Process, College of Urban & Environmental Sciences, Peking University, Beijing, China.
authors: Hui-Ling
authors: HL
authors: Ou-Yang
authors: Xiang-Zhen
authors: XZ
authors: Kong
authors: Michel
authors: M
authors: Lavoie
authors: Wei
authors: W
authors: He
authors: Ning
authors: N
authors: Qin
authors: Qi-Shuang
authors: QS
authors: He
authors: Bin
authors: B
authors: Yang
authors: Rong
authors: R
authors: Wang
authors: Fu-Liu
authors: FL
authors: Xu
mesh_terms: D002104:Cadmium / Q000633:toxicity*; D002470:Cell Survival / Q000187:drug effects; D048408:Chlorella vulgaris / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D004950:Esterases / Q000378:metabolism; D005453:Fluorescence; D010788:Photosynthesis / Q000187:drug effects; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D014874:Water Pollutants, Chemical; D002104:Cadmium; D002734:Chlorophyll; D004950:Esterases; D000077194:Chlorophyll A
keywords: Cadmium; Cellular toxicity; Chlorella vulgaris; Flow cytometry; Photosynthetic toxicity