Polypeptide binding to plastid envelopes during chloroplast development

Abstract

Pulse-chase experiments using [(35)S]methionine with various light and dark regimes have been used to follow in situ polypeptide accumulation during plastid development in Avena sativa (var. Mostyn). Subsequent isolation and later fraction of the etioplasts, etio-chloroplasts or chloroplasts into envelope, stroma lamellae, thylakoid and supernatant (stromal) fractions has enabled a survey of the movement of label between the different fractions. These studies show that considerable and sometimes quite rapid plastidic protein interchange takes place even in the unilluminated etiolated tissue but this increases markedly as greening commences and that the synthesis and transport of polypeptides required for thylakoid assembly is a light-dependent process. Labelled polypeptides from each fraction were resolved by SDS-polyacrylamide gel electrophoresis, sectioned and counted. The well-washed envelope fractions contained several labelled polypeptides, one of which had an estimated molecular weight of 13,500 daltons. Upon subsequent tryptic digest of this envelope material and finger-printing by high voltage electrophoresis and paper chromatography, the distribution of 9 of the tryptic peptides was similar to that of tryptic peptides derived from authentic small sub-unit of Fraction I protein from Avena. This apparent attachment of the small sub-unit of Fraction I protein to the envelope may be part of the mechanism of transport of this protein from the cytoplasm to the stroma of the developing plastid.