ROLE OF PROLINE ACCUMULATION IN RESPONSE TO TOXIC COPPER IN CHLORELLASP. (CHLOROPHYCEAE) CELLS

The green alga Chlorella sp. (strain 2350) was found to accumulate pro line, up to a maximum of 0.027 fmol . cell(-1), under stressful concen trations of cupric ions. The function of the accumulated proline was s tudied with respect to its effect on copper (Cu) uptake. By induction with salt stress, cells with various levels of intracellular proline w ere used for this study. It is shown that the amount of Cu taken zip b y the cells was reduced when the intracellular proline levels were enh anced. When proline was exogenously supplied prior to Cu treatment, th e adsorption of Cu was markedly reduced. When exogenous proline was su pplied after Cu treatment, it resulted in a remarkable desorption of t he adsorbed Cu immediately after the addition of proline. The results of the present study indicate that proline may exert some action on th e cell surface and suggest that one function of accumulated proline is to reduce the uptake of metal ions. The accumulation of proline may b e related to a tolerance mechanism for dealing with Cu stress.