Studies on the Mechanism of Copper Toxicity in<i>Chlorella</i>

Abstract

Autotrophic growth, photosynthesis, and respiration of Chlorella sorokiniana Shihira and Krauss were inhibited by the cupric ion, but photosynthesis was more sensitive than respiration. The percent inhibition was determined by the ratio of cells to cupric ions present. Photosynthesis and respiration were inhibited within 2 and 5 min, respectively, after adding 1.0 mM cupric ions. Chlorella cells which had been incubated for a short time in concentrations of the cupric ion that completely inhibited photosynthesis were not able to grow when cultured in a fresh medium without cupric ions, indicating high concentrations of the ion may have destroyed the photosynthetic apparatus and deprived the cells of their ability for autotrophic growth. Dark preincubation of the cells, as well as high bicarbonate concentrations in the assay medium, decreased inhibition. Treatment with cupric ions reduced the cellular chlorophyll and sulfhydryl content, but anaerobiosis, a condition that increased toxicity, had little effect on the sulfhydryl content. Electron transport in photosystems I and II in intact Chlorella cells was inhibited, but the specific sites of inhibition in the photosynthetic electron transport chain could not be determined using intact cells.