CHARACTERISTICS OF THE ASSEMBLY OF THE 33 KDA OXYGEN-EVOLVING COMPLEX PROTEIN IN THE ETIOPLASTS AND THE DEVELOPING CHLOROPLASTS OF BARLEY SEEDLINGS

In barley etioplasts, extrinsic 33 and 24 kDa proteins (OEC33 and 24) and cytochrome (cyt) b-559 were accumulated predominantly as the polypeptides of Photosystem (PS) II. OEC33 was located at the thylakoid lumen of the etioplasts, without being tightly bound to the membranes. OEC33 and cyt b-559 were not crosslinked by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimides and hexamethylene diisocyanate in the etioplasts, suggesting no complex formation between OEC33 and cyt b-559. Two-dimensional gel electrophoresis of chloroplasts in greening process employing Softes 12 (the mixture of sodium poly(oxyethylene) lauryl ether sulfate and lauryl dimethylamine oxide) and sodium dodecyl sulfate showed that PS II core complexes (D1,D2,cyt b-559,CP43,CP47) are formed by coordinated assembly of the constituent polypeptides and no intermediate complexes of PS II is formed in the developing chloroplasts. Measurement of photoreduction of 2,6-dichloroindophenol with the premature chloroplasts suggests that the preexisting OEC33 in the etioplasts binds efficiently to the newly assembled PS II cores. Fractionation assay of the thylakoids with digitonin implied that the stoichiometry of polypeptides in the PS II core complex is kept, at least in the appressed region, during the greening, but the PS II complexes without extrinsic proteins are present in the non-appressed region, especially at the early stage of chloroplast development. These results suggest that OEC33 binds preferentially to the PS II core complexes in the appressed thylakoids and stabilizes the juvenile PS II.