Evolution des RNA ribosomaux au cours du verdissement de cotylédons de concombre en présence de 6-benzylaminopurine

Abstract

Etiolated cotyledons were excised from cucumber seedlings, maintained in darkness for 24 h in vitro, and then illuminated in the presence or in the absence of 10−5 g/ml of 6-benzylaminopurine (6-BAP) for 48 h. During incubation in the dark, 6-BAP markedly increases the incorporation of 32P into cytoplasmic rRNA and, to a lesser extent, into etioplast rRNA. 6-BAP does not significantly affect the light-induced RNA synthesis during the first 24 h of illumination. The chloroplast rRNA synthesis stops after 24 h of light in the control, but it is maintained in 6-BAP-treated cotyledons. These results are discussed in relation to previously reported cytological observations. The conclusion is reached that cytokinin mainly acts at a cytoplasmic level during the differentiation of etioplast into chloroplast.