Effect of Cu²⁺, Zn²⁺, and Cd²⁺ on Flagellar Regeneration in Chlamydomonas reinhardtii

Abstract

It is well known that Chlamydomonas can regenerate flagella to their original lengths within 2-4 hr after flagellar amputation. However, flagella grow only to 50% their original lengths in the presence of 20 μg/ml cycloheximide, an inhibitor of protein synthesis. Taking advantage of these features of this organism, we can evaluate roughly the influence of pollutants upon protein synthesis or organelle morphogenesis. In this study, we examined the effects of Cu²⁺, Zn²⁺ and Cd²⁺ on flagellar regeneration using samples in culture media supplemented with heavy metals. The results suggested that Cu²⁺ and Zn²⁺ inhibit flagellar morphogenesis (assembly of flagellar components), whereas Cd²⁺ of much lower concentrations inhibits both protein synthesis in an early phase of flagellar regeneration and morphogenesis in later phases. The 4-hr EC_50s for Cd²⁺, Cu²⁺ and Zn²⁺ on flagellar regeneration were 15.8 μM, 1.1 mM and 2.2 mM, respectively. When these assessments were carried out in distilled water, EC_50s decreased 10 to 100-fold, suggesting that the effect of heavy metals depends on the water hardness. We examined effluents from eight factories in Toyama Prefecture using cells in them, and found one sample clearly inhibited flagellar regeneration. The effluent appeared to contain Zn²⁺ in a concentration as high as 200% of the effluent standard. Thus, the Chiamydomonas flagellar regeneration should be useful as an endpoint for assessing environmental water pollution with these heavy metals.