LOCALIZATION OF LIGHT-HARVESTING COMPLEX APOPROTEINS IN THE CHLOROPLAST AND CYTOPLASM DURING GREENING OF CHLAMYDOMONAS-REINHARDTII AT 38-DEGREES-C

Assembly of the major light-harvesting complex (LHC II) and developmen t of photosynthetic function were examined during the initial phase of thylakoid biogenesis in Chlamydomonas reinhardtii cells at 38 degrees C. Continuous monitoring of LHC II fluorescence showed that these pro cesses were initiated immediately upon exposure of cells to light. How ever, mature-size apoproteins of LHC II (Lhcb) increased in amount in an alkali-soluble (nonmembrane) fraction in parallel with the increase in the membrane fraction. Alkali-soluble Lhcb were not integrated int o membranes when protein synthesis was inhibited, suggesting that they were not active intermediates in LHC II assembly, nor were they recov ered in a purified chloroplast preparation. Immunocytochemical analysi s of greening cells revealed Lhcb inside the chloroplast near the enve lope and in clusters deeper in the organelle. Antibody binding also de tected Lhcb in granules within vacuoles in the cytosol, and Lhcb were recovered in granules purified from greening cells. Our results sugges t that the cytosolic granules serve as receptacles of Lhcb synthesized in excess of the amount that can be accommodated by thylakoid membran e formation within the plastid envelope.