Enhancement of Intracellular Proline Level in Cells of Anacystis Nidulans (Cyanobacteria) Exposed to Deleterious Concentrations of Copper¹

The intracellular proline level in Anacystis nidulans cells was enhanced when the cells were exposed to sublethal concentrations of Cu 2+ ; the degree of enhancement was positively related to the concentration of Cu 2+ . Analysis by high‐performance liquid chromatography confirmed that the enhancement of proline levels was the most pronounced change in the composition of the free amino acid pool during copper treatment. A direct supply of exogenous proline to the cultures lowered the inhibitory influence of Cu 2+ on the growth of cells. Further experiments showed that the supply of exogenous proline lowered the leakage of potassium ions from cells exposed to deleterious concentrations of Cu 2+ . The inhibition of potassium leakage was particularly pronounced when proline was supplied prior to Cu 2+ treatment. The present study suggests that enhanced proline protects cell membranes from being affected by deleterious concentrations of Cu 2+ .