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

Abstract

Etiolated cotyledons of cucumber (Cucumis sativus L.) were incubated for 15 h in the dark followed by 72 h in the light in the presence of 10−6 g/ml 6-benzylaminopurine (6-BAP) or 10−4 g/ml chloramphenicol (CHL). These compounds were applied either permanently or only during the dark period, the first 6 h in the light, or the following 66 h in the light. In all cases 6-BAP stimulates both chlorophyll synthesis and plastid differentiation and increases the area of appressed thylakoids. CHL decreases the rate of chlorophyll synthesis only if given during the whole incubation period (dark + light). However, CHL always inhibits the development of the stroma thylakoids and increases both the number of stacked thylakoids per grana and the size of these thylakoids. During the first 6 h in the light, the structure and pigment content of plastids submitted to 6-BAP and CHL (or conversely) appear to be regulated by the compound applied in the dark period. The changes observed in the following light period (after 6 h) depend on the compound present during this period. These results, and those obtained with the two compounds acting simultanously, indicate that the action of these molecules is localized at different cellular levels. The modes of interaction between 6-BAP and CHL are discussed with reference to a biometrical analysis of some structural parameters of plastids.