Cytokinin-promoted Polyribosome Formation in Excised Cucumber Cotyledons

Abstract

Polyribosome (polysome) levels based on total ribosomal materials in excised etiolated cotyledons of Cucumis sativus L. cv. Ohio were examined during incubation with or without N 6 -benzyladenine (BA) in the dark. Within the first 2 h after excision, polysome levels in both cotyledons with and without BA increased about 5-fold. The polysome level in control cotyledons subsequently declined, approximating the initial level after 12-18h. In BA-treated cotyledons, however, it remained high during the entire period of incubation. BA application to the water-pretreated (18h) cotyledons also increased the polysome level and did not affect RNase activity or RNA content. BA-promoted polysome formation was inhibited by α-amanitin and cordycepin but not by 5-fluorouracil. These results are consistent with the hypothesis that cytokininpromoted polysome formation depends on de novo synthesis of mRNA but not of rRNA.