The Cytokinin Control of Protein Synthesis in Plants

Abstract

A stimulatory effect of cytokinins on protein and nucleic acid syntheses in plant tissues has been well known for a long time (Mothes et al., 1959; Wollgiehn, 1961; Roychoudhury etal., 1965; Kulaeva, 1967). A relationship of various effects of growth substances on plant development to the metabolism of nucleic acids was suggested first by Skoog (1954), and later, during the intense progress in molecular biology, a tentative idea was widely assumed that plant hormones — playing a role of effectorlike factors — act primarily at a level of DNA-directed RNA synthesis. However, despite a great number of studies, this kind of action appeared rather difficult to be prove. In the case of cytokinins, the only direct evidence was provided in a paper by Matthysse and Abrams (1970) who reported that in a cell-free system with purified chromatin or DNA from pea buds, and with Escherichia coli RNA polymerase, in the presence of a receptor protein previously isolated from the chromatin, the addition of cytokinins increased the rate of RNA synthesis. On the other hand, numerous data exist suggesting that cytokinins can stimulate protein synthesis at a post-trans-criptional or even directly at a translational level. The first assumptions about this were made after the cytokinins had been discovered in some tRNAs in the position adjacent to the anticodon (Zachau et al., 1966; Biemann et al., 1966). It was found later (Fittler and Hall, 1966; Gefter and Russell, 1969) that the presence of cytokinins in tRNA’s increases the ribosome binding affinity of the aminoacylated tRNAs, facilitating the codon recognition in the polyribosomal complexes.