Cytokinin-Induced Changes in Transfer RNA Species

Abstract

Ribonucleic acids, particularly transfer RNAs, exhibit cytokinin bioassay activity. Isolated RNA of rat and sheep liver, and cultured tobacco cells is active in promoting growth of carrot phloem callus while the DNA of these respective tissues is inactive (Bellamy, 1966). Hydrolysates of sRNA, but not ribosomal RNA, from roots and shoots of germinating sweet corn possesses strong cytokinin activity in the carrot root tissue culture assay (Letham and Ralph, 1967). Highly purified tRNA of yeast, rat liver, E. coli (Skoog et al., 1966), chick embryo, calf and human liver (Robbins et al., 1967) stimulates cell division and differentiation. Again, rRNA from similar tissues exhibited no cytokinin activity. RNA rich in seryl-, isoleucyl-, and tyrosyl-tRNAs are very high in cytokinin activity in contrast to arginyl2-, glycyl-, phenylalanyl-, valyl-, and alanyl-tRNAs which had little growth promoting activity (Skoog et al., 1966). Thus, tRNA is the only known nucleic acid fraction active in cytokinesis and more specifically only certain tRNA species are functional. It is calculated that one molecule of isopentenyladenine (IPA) per 20 molecules of tRNA could account for the cytokinin activity of the tRNA fraction (Skoog et al., 1966).