Secretory granules in the cytoplasm of a wall-less mutant of Chlamydomonas reinhardtii contain processed light-harvesting complex apoproteins and HSP70

Abstract

Large, electron dense granules are present within vacuoles in the cytoplasm of Chlamydomonas reinhardtii cw15arg7A cells. Immunocytochemical electron microscopy revealed labeling of these granules when sections of cells were incubated with antibodies specific for apoproteins (Lhcb) of the light-harvesting chlorophyll a/b complex (LHCII). The granules were also labeled with antibodies against the cytosolic molecular chaperone Hsp70. Purified granules contained Hsp70 and processed, mature forms of Lhcb as minor constituents. Appearance of processed Lhcb in the vacuole suggests that these proteins were products of retrograde movement resulting from aborted import into the chloroplast. Immunoreactive granules were released from the cell following fusion of the vacuolar and plasma membranes.