Interactions entre le cycloheximide et la 6-benzylaminopurine au cours du verdissement de cotylédons de concombre

Abstract

Etiolated cotyledons of cucumber (Cucumis sativus L.) were isolated and incubated for 15 h in the dark and 48 h in the light in the presence of 10−6 g/mL 6-benzylaminopurine (6-BAP) or 3.10−6 and 10−5 g/mL cycloheximide (CHX). Cotyledons were permanently maintained on these compounds or transferred from one medium to the other after the dark period or after 6 h of the light. 6-BAP stimulates both chlorophyll synthesis and plastid differentiation. Chlorophyll synthesis is more affected than differentiation in the presence of CHX. Only some thylakoids are present in plastids treated permanently with CHX at 10−5 g/mL. At 3.10−6 g/mL, CHX inhibits the development of the stroma thylakoids and the granal stacks. The effect of CHX is particularly important during the 1st h of light; it is partially reversible. During the treatment with 6-BAP followed by CHX (or conversely), the ultrastructural effect of 10−5 g/mL CHX is removed if 6-BAP is given before the inhibitor. After 48 h the plastid ultrastructure depends particularly on the compound applied during the 1st h of light. 6-BAP and CHX are not competitive during chlorophyllogenesis. 6-BAP increases and CHX decreases the incorporation of 32P into cytoplasmic and etioplastic rRNA during the dark. During the light, 6-BAP increases the incorporation in chloroplastic rRNA only and CHX decreases the incorporation in cytoplasmic rRNA only. The modes of action of CHX and its relations with 6-BAP are discussed.