Differential effects of copper and cadmium exposure on toxicity endpoints and gene expression in Chlamydomonas reinhardtii

Abstract

Abstract-The toxicity of cadmium to aquatic organisms is well known, but the mechanisms of toxicity are not as clearly understood. In the present study, Cd bioassay experiments incorporating both traditional endpoints and novel thiol-based endpoints were conducted with Chlamydomonas reinhardtii. The results were compared with results from previous bioassay experiments to probe the apparent contrasting biochemical mechanisms of toxicity of copper and cadmium as expressed in cellular glutathione and the glutathione cycle. Total glutathione and reduced to oxidized glutathione ratio (GSH/GSSG) measurements were remarkably different in Cd-compared with Cu-exposed cells. Whereas total glutathione in cells decreased with increasing Cu concentration, Cd caused dramatic increases. Total glutathione increased by 4.5-fold with 80 nM Cd treatment over concentrations in Cd-free controls. Glutathione reductase (GR) enzyme activity was positively correlated (r 2 Cu ¼ 0.96, r 2 Cd ¼ 0.85) with glutathione concentrations for both metals. Measurements of mRNA for GR were increased 2-fold in response to Cd exposure (80 nM) and correlated well with GR enzyme activity. Glutathione concentrations and GR enzyme activity are useful endpoints for both Cu and Cd toxicity in algae, even though the metals elicit opposing responses. We conclude that Cu decreases glutathione concentrations by inhibiting GR enzyme activity. In contrast, Cd stimulates GR enzyme activity and increases glutathione concentrations as cells respond to Cd-induced stress by producing increased antioxidant capacity. The present study demonstrates that determining the glutathione response in cells is important for understanding the metalspecific mechanisms of toxicity and that these associated novel endpoints may be useful metrics for accurately predicting toxicity.

Sensing the dynamics of oxidative stress using enhanced absorption in protein-loaded random media

“…3d) which depends on the Cd(II) concentration, antioxidant levels can balance efficiently the accumulation of the ROS within the cell (phase II). Indeed up-regulation of intracellular antioxidant glutathione levels in C. reinhardtii after exposure to 80 nM of Cd(II) was observed for a comparable exposure time29. Our data agree also with proteomic studies showing up-regulation of antioxidant proteins such as L-ascorbate peroxidase or superoxide dismutase in C. reinhardtii once exposed to 150 μM of Cd(II)30.…”

Physiological characterization of cadmium‐exposed Chlamydomonas reinhardtii

“…As recently shown, actin protein quantities and expression levels were not influenced by cadmium treatment (Gillet et al . 2006; Stoiber, Shafer & Armstrong 2010). After checking stable expression level of actin again, it was used as reference also in this study.…”

“…RuBisCo was not used as housekeeping gene because cadmium influences its protein quantity enormously (Gillet et al 2006), which can be caused by differential expression and is probably correlated to cadmium storage in chloroplasts (Nagel et al 1996). As recently shown, actin protein quantities and expression levels were not influenced by cadmium treatment (Gillet et al 2006;Stoiber, Shafer & Armstrong 2010). After checking stable expression level of actin again, it was used as reference also in this study.…”

Copper excess-induced large reversible and small irreversible adaptations in a population of Chlamydomonas reinhardtii CW15 (Chlorophyta)

“…The pro-oxidative action of copper ions in algal photosynthetic systems has been reported by many researchers [54][55][56]. Lupi et al [43] described increased copper ion toxicity (40 µM Cu 2+ ) when light intensity was increased from 100 to 150 W m −2 in Chlorella vulgaris cultures.…”