Cytokinin‐controlled polyribosome formation and protein synthesis in cucumber cotyledons

Abstract

An increased proportion of ribosomes forming polyribosomes and an increased activity of polyribosomes in protein synthesis in vitro were found in dark‐grown kinetin‐treated cucumber cotyledons (Cucumis sativus L. cv. Monastyrski) as compared with untreated controls. The stimulation occurred also under an osmotic stress which suppressed the kinetin stimulation of the cotyledon growth, indicating an independence of the effect from the promotion of growth. Analysis of the ribosomal profiles as well as experiments with [3H]‐adenosine showed that kinetin neither changed the total amount of ribosomal material nor enhanced the label incorporation into the polyribosomes. Inhibitors of transcription and of polyadenylation did not affect the kinetin stimulation of the polyribosome level. Aurin tricarboxylic acid (inhibitor of initiation) markedly suppressed the stimulatory effect of kinetin on the polyribosome formation. It is suggested that the increase in polyribosomes in response to kinetin results from the kinetin effect at the translational level by increasing the rate of initiation through an enhancement of the affinity of ribosomes for the messenger RNA.