The Effect of Deleterious Concentrations of Copper on the Photosynthesis of Chlorella pyrenoidosa

If a single salt solution of CuSO(4) is used, Cu penetrates immediately iuto the plasma of Chlorella cells, reducing the rates of photosynthesis at both high and low illumination. If CuSO(4) is added to ordinary Österlind culture-medium (pH 8) it takes some hours before any influence of deleterious concentrations of Cu is observed and initially only at light saturation. The algae must have been illuminated during the whole period. Maximum influence of CuSO(4) is found duriug the first 24 hours of treatment. A significant deleterious influence of Cu concentrations as low as about 1 μg/l is found. The influence of Cu increases with decreasing concentrations of the alga. If a culture medium at pH 5 is used instead of the ordinary one at pH 8, copper concentrations ahout 10 times as high must he used be order to obtain the same deleterious effect. An increase of the cotncentration of K reduces the influence of Cu to some extent. These facts show that the effect of deleterious concentrations of Cu in halanced solutions is not due to a marked penelration of this ion into the plasma but to a binding to the cytoplasmic membrane whereby the celts i.a. become more or less unable to divide. The cells become saturated with assimilation products which have a depressant effect on the rate of photosynthesis. Other cations compete with Cu for the "active sites" on the membranes.