John Wiley & Sons, Ltd.

Photosynthetic and cellular toxicity of cadmium in Chlorella vulgaris

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 ФPSII, 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 >> ФPSII ≈ esterase activity > Fv/Fm > chlorophyll a fluorescence ≈ cell viability. It is shown that 1) 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 that other mechanisms such as blocked cell divisions are major contributors to cell yield inhibition; 2) Cd may affect both the electron donors and acceptors of the electron transport chain at high free Cd2+ concentration, and 3) the resistance of cells to cell death was size‐dependent, and medium‐sized cells had the highest toxicity threshold. This work 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. Environ Toxicol Chem © 2013 SETAC

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