Subcellular distribution of cadmium in the unicellular green alga Chlamydomonas reinhardtii

As previously reported, cadmium strongly inhibits photosynthesis in the unicellular green alga Chlamydomonas reinhardtii. A cadmium-tolerant mutant with impaired photosynthesis has been isolated recently. Therefore, we have investigated tile subcellular distribution of Cd-109(2+) in the cell-wall deficient C. reinhardtii mutant strain CW15. The cytosol only contained about 10% of the incorporated Cd-109(2+). The predominant proportion of Cd2+, however was found in the purified chloroplasts (more than 50%), although a considerable part of the chloroplasts was destroyed during the disrupture of the cells. Fractionation of (poly)peptide-bound and free Cd-109(2+) by Sephadex G75 chromatography revealed essentially the same distribution for the lysates of purified chloroplasts as for the cytosol. A considerable proportion of the incorporated Cd-109(2+) was sequestered by complex formation with oligopeptides both in the cytosol and in the chloroplasts.