Observations on Components of Photosystem II During the Greening of Select Mutants of Scenedesmus

Abstract

The formation of photosystem II of the photosynthetic apparatus was studied in five different developmental mutants of the green alga, Scenedesmus obliquus . These strains are characterized by their ability to synthesize chlorophyll only in the light and by specific differences in their photosystem II (PS-II) capacity and composition when fully developed. Cells from mutants C-2A, LF1-YI-RVT1 and WT-LHC 1 -Y3 form a functional PS-II upon transfer from darkness into light whereas those of strains C-2A-10 and LF1-Y1 do not develop PS-II activity under any conditions. Analysis of a variety of chloroplast reactions with the latter two strains showed that they lack the PS-II reaction center only minimally. 35 S labeling during light-induced chloroplast development revealed that only C-2A-10 and LF1-Y1 failed to develop the normal D1 protein (32 kDa polypeptide In LF1-Y1, only the unprocessed form (34 kDa) of this protein was synthesized and, as was noted for the original mutant LF-1, is inactive as a PS-II reaction center component. During development of C-2A-10, which appears to be pleiotropic in its PS-II deficiency, this protein is not synthesized and the PS-II core antenna polypeptides (the 48 and 44 kDA polypeptides) and a 14.5 kDa polypeptide also appear to be synthesized in lesser amounts or not to be synthesized at all. No other changes in PS-II chloroplast membrane components were noted in these studies, which would implicate other polypeptides in PS-II function of Scenedesmus .