Effect of selenate on growth and photosynthesis of Chlamydomonas reinhardtii

• Published in: Aquatic toxicology 2007-06, Vol.83 (2), p.149-158
• Main Authors: Geoffroy, Laure, Gilbin, Rodolphe, Simon, Olivier, Floriani, Magali, Adam, Christelle, Pradines, Catherine, Cournac, Laurent, Garnier-Laplace, Jacqueline
• Format: Article
• Language: English
• Subjects: Algae; Animal, plant and microbial ecology; Animals; Applied ecology; Biological and medical sciences; Chlamydomonas reinhardtii; Chlamydomonas reinhardtii - drug effects; Chlamydomonas reinhardtii - growth & development; Chlamydomonas reinhardtii - physiology; Chlorophyll; Chlorophyll fluorescence; chloroplasts; cytotoxicity; dose response; Dose-Response Relationship, Drug; Ecotoxicology, biological effects of pollution; electron transfer; Eukaryota - drug effects; Fluorescence; Freshwater; Fundamental and applied biological sciences. Psychology; General aspects; Growth - drug effects; in vitro studies; photosynthesis; Photosynthesis - drug effects; Phytoplankton; plant growth; reaction inhibition; Selenate; selenates; Selenic Acid; Selenium - analysis; Selenium Compounds - toxicity; TEM analysis; Time Factors; Toxicity; toxicity testing; transmission electron microscopy; ultrastructure; Water Pollutants, Chemical - toxicity; water pollution
• ISSN: 0166-445X; 1879-1514
• DOI: 10.1016/j.aquatox.2007.04.001

Algal communities play a crucial role in aquatic food webs by facilitating the transfer of dissolved inorganic selenium (both an essential trace element and a toxic compound for a wide variety of organisms) to higher trophic levels. The dominant inorganic chemical species of selenium in freshwaters are selenite (SeO 3 2−) and selenate (SeO 4 2−). At environmental concentrations, selenite is not likely to have direct toxic effects on phytoplankton growth [Morlon, H., Fortin, C., Floriani, M., Adam, C., Garnier-Laplace, J., Boudou, A., 2005a. Toxicity of selenite in the unicellular green alga Chlamydomonas reinharditii: comparison between effects at the population and sub-cellular level. Aquat. Toxicol. 73(1), 65–78]. The effects of selenate, on the other hand, are poorly documented. We studied the effects of selenate on Chlamydomonas reinhardtii growth (a common parameter in phytotoxicity tests). Growth inhibition (96-h IC 50) was observed at 4.5 ± 0.2 μM selenate ( p < 0.001), an effective concentration which is low compared to environmental concentrations. Growth inhibition at high selenium concentrations may result from impaired photosynthesis. This is why we also studied the effects of selenate on the photosynthetic process (not previously assessed in this species to our knowledge) as well as selenate's effects on cell ultrastructure. The observed ultrastructural damage (chloroplast alterations, loss of appressed domains) confirmed that chloroplasts are important targets in the mechanism of selenium toxicity. Furthermore, the inhibition of photosynthetic electron transport evaluated by chlorophyll fluorescence induction confirmed this hypothesis and demonstrated that selenate disrupts the photosynthetic electron chain. Compared to the classical ‘growth inhibition’ parameter used in phytotoxicity tests, cell diameter and operational photosynthetic yield were more sensitive and may be convenient tools for selenate toxicity assessment in non-target plants.