Distribution of Cytokinin-active Ribonucleosides in Wheat Germ tRNA Species

Abstract

The distribution of cytokinin activity in wheat ( Tnticum aesdivum) germ tRNA fractionated by BD-cellulose and RPC-5 chromatography has been examined. As In other organisms, the cytokinia moieties in wheat germ tRNA appear to be restricted to tRNA species that would be expected to respond to codons ginnn with U. Only a few of the wheat germ tRNA species in this coding group actually contain cytokinin modifications.Cytokinin activity was associated with isoaccepting tRNAsr species and with a minor tRNALU species from wheat germ. All other wheat germ tRNA species corresponding to codons bnning with U were devoid of cytokinin activity in the tobacco callus bioassay.Trace amounts of the trans-isomers of io6A and ms2io6A have also been reported to be present (3,21,22). Information concerning the distribution of cytokinins with respect to particular plant tRNA species is much more limited. Ribosyl-cis-zeatin has been identified as a constituent of a minor tRNALu species from peas (8), but the distribution of cytokinin moieties in other tRNA species from this source was not examined.The (12,20). Because not all tRNA species within the U-group necessarily contain a cytokinin modification, the distribution of cytokinin moieties with respect to particular tRNA species may vary in different organisms. The cytokinin modifications of plant tRNA species are of particular interest in view of the hormonal function of cytokinins in plant systems. Cytokinin-active ribonucleosides have been isolated and identified from hydrolysates of a number of plant tRNA preparations (5,6,13,22). In addition to i6A, plant tRNA preparations typically contain ribosyl-cis-zeatin (io6A) and the 2-methylthio derivatives of these two compounds (ms2io6A and ms2i6A).

The tRNASer-isoacceptors and their genes in Nicotiana rustica: genome organization, expression in vitro and sequence analyses

“…Cis-zeatin at position 37 has been identified in tRNAs ser from wheat and Lupinus luteus [3,42] in place of N6-isopentenyl-adenosine (i6A). Due to its reduced migration as compared to i6A in the two solvent system of Nishimura [28], we conclude that cis-zeatine is also present in Nicotiana tRNAs s~.…”

Cytokinin-Active Ribonucleosides in Phaseolus RNA

“…The distribution of cytokinin-active ribonucleosides in tRNA species from etiolated P. vulgaris seedlings appears similar to that in wheat germ tRNA (20) was associated with all tRNA fractions containing serine acceptor activity. Similarly, the tRNA preparations from both plant sources contained minor tRNAIeU species that chromatographed in cytokinin-active regions of the column elution profiles.…”

“…The most detailed investigations of the distribution of cytokinin moieties with respect to individual tRNA species have been conducted with tRNA from microbial sources, but all available evidence concerning cytokinin distribution in tRNA from higher plant and animal tissues is consistent with this concept (2,6,12,(19)(20)(21). Not all tRNA species within the U group necessarily contain a cytokinin moiety.…”

“…The distribution of cytokinins in wheat germ tRNA species has recently been examined in our laboratory (20). Cytokinin activity was associated with wheat germ tRNA &r species and a minor tRNALu species, but all other wheat germ tRNA species expected to respond to codons beginning with U (tRNA YS, tRNA he, tRNATr , and tRNATY') were devoid of cytokinin activity in the tobacco callus bioassay.…”

“…Etiolated material was selected for this study to minimize the contribution of plastid tRNA species to the distribution of cytokinin activity and to provide a more direct comparison with the results obtained earlier for wheat germ tRNA. As in the case of wheat germ tRNA (20), the distribution of cytokinin moieties in tRNA species from etiolated bean seedlings appears to be more restricted than in microbial systems.…”