The Effect of Deleterious Concentrations of Mercury on the Photosynthesis and Growth of Chlorella pyrenoidosa

The effect of mercury ions on the photosynthesis and growth of Chlorella pyrenoidosa in a balanced medium has been studied and compared with the effect of copper. In many ways Hg treated algae behave like algae treated with Cu in concentrations of the same molarity, but important deviations occur. Hg acts at a lower and in a more narrow range of concentrations than does Cu due to a more specific binding. The depressing effect of Hg is not counteracted by other cations such as potassium and sodium, and iron has only a slight effect. Cell division is stopped after Hg addition and there is no accumulation of assimilation products. On the contrary the cells become pale yellow. Preliminary studies indicate a light-independent leakage in the cytoplasmatic membrane leading to an outflow of potassium ions. This is the primary action of both Hg and Cu poisoning, but the leakage does not seem to be correlated with the decrease of photosynthesis. After a lapse of time — dependent on the mercury/cell concentration ratio — a detoxication takes place probably due to the binding of Hg to “insensitive sites” in the cells. Probable mechanisms for the action of Hg on photosynthesis and growth are discussed.