Physiology of carbon assimilation in a green alga during exposure to and recovery from cadmium.

The flow of recently photoassimilated carbon into proteins, lipids, and polysaccharides was studied with asynchronous Selenastrum capricornutum populations during exposure to and recovery from 30 and 100 micrograms Cd.liter-1. During a 48-hr exposure to Cd, increases in Cd cell quotas were accompanied by nearly exponential decreases in growth and photosynthesis and by a disruption of the pattern of carbon allocation to macromolecules. In particular, relative to the control, the cells exposed to Cd allocated a higher percentage of carbon to the synthesis of polysaccharides. After the addition of EDTA (recovery period), Cd cell quotas decreased and growth recovery was accompanied by the recovery of photosynthesis and by an enhanced flow of carbon to lipids and proteins. The results of the experiment suggest that the measurement of the distribution of recently photoassimilated carbon into macromolecules has potential for monitoring the effects of toxic effluent discharges on primary producers.