Comparison of the Polypeptide Compositions of the Internal Membranes of Chloroplasts, Etioplasts and Ribosome-Deficient Heat-Bleached Plastids from Rye Leaves

Abstract

When rye seedlings ( Secale cereale L.) are grown at a non-permissive temperature of 32°C in light 70S ribosome-deficient and chlorotic leaves are formed, due to a previously described preferential high-temperature-sensitivity of the plastidic ribosome formation that allows the selective elimination of the chloroplastic protein synthesis. From bleached ribosome-deficient plastids obtained from 32°-grown rye leaves the internal membranes were isolated. Their polypeptide composition was analysed by sodium dodecylsulfate polyacrylamide gel electrophoresis and compared to that of the internal membranes of chloroplasts and etioplasts from leaves grown at a permissive temperature of 22°C. For about 50% of the major polypeptides of normal chloroplast thylakoids corresponding polypeptide bands of equal electrophoretic mobility occurred in the internal membranes of the ribosome-deficient plastids, thereby indicating that they were of cytoplasmic origin. The bleached plastids contained also numerous additional membrane polypeptides which did not occur in chloroplast thylakoids. Several of those were characteristic for etioplast membranes from 22°-grown leaves. The etioplast internal membranes contained most of the chloroplast thylakoid polypeptides and a number of specific additional polypeptides. The α- and β-subunits of the coupling factor CF 1 were present in chloroplasts and etioplasts from 22°-grown leaves but missing in the bleached plastids of 32°-grown leaves. Both the etioplasts and the bleached ribosome-deficient plastids contained a polypeptide corresponding in its electrophoretic mobility to that of the main apoprotein (relative molecular mass 69,100) of the chlorophyllprotein complex I. The apoprotein of the chlorophyll-protein complex II (relative molecular mass 24,600) was missing in etioplasts but present, though in relatively small amount, in the ribosome-deficient plastids.