The Metabolism and Biological Activity of a 9-Substituted Cytokinin

Abstract

In order to test the metabolic stability of 9-substituted cytokinins, 6-benzylamino-9-methyl purine has been synthesized and labeled with 14C in the 9-methyl carbon or doubly labeled with 14C in the 9-methyl carbon and 3H in the methylene moiety of the side chain. Although the 6-benzylamino-9-methylpurine is chemically stable, cytokinin-requiring tissues begin removing the 9-substituent in as little as 10 minutes. Among the various metabolic products is free benzylaminopurine. Thus, the biological activity of 9-substituted cytokinins could be accounted for by their conversion to the free base.The widespread presence of cytokinins in the transfer RNA of animals, plants, and microorganisms is well established (see review by Key [14]). Furthermore, in those cases where the primary structure is known, the cytokinin is found immediately adjacent to the presumed anticodon (1,5,17). The continuing debate as to whether or not the physiological activity of exogenously supplied cytokinins is mediated by their presence in tRNA seems to have been recently resolved by the work of Chen and Hall (4). Here it was shown that the potent cytokinin N6-(A2-isopentenyl) adenosine occurs in the tRNA of cultivated tobacco tissue even though the tissue requires an exogenous cytokinin in order to grow. The fact that the cytokinin supplied in the medium is not the metabolic precursor of the cytokinin in the tRNA argues that the role of the former is distinct in at least some important way from that of the latter.This work, however, cannot be used as evidence against the notion that exogenous cytokinins act through their observed incorporation into polynucleotides (7, 9, 10). One would need to demonstrate that cytokinins which are prevented from entering into nucleotide formation nevertheless retain all of their biological activity. It occurred to us that the use of blocking agents at the 9 position of the purine moiety would result in compounds which might yield information concerning the relation between nucleotide formation and biological activity of the I

Short Term Metabolism of Urea and Purine Cytokinins

“…The mass spectra of BA and benzyladenosine (Fig. 3) are consistent with their structure assignment (9).…”

The Mode of Incorporation of 6-Benzylaminopurine into Tobacco Callus Transfer Ribonucleic Acid

“…The validity of this report is subject to limitations in procedures employed. Fox et al- (15) claim that the 9-methyl group is released from the 6-benzylamino-9-methylpurine in contact with tobacco and soybean callus and that in tests on tobacco tissue some 6-benzylaminopurine was recovered. Recently, Elliott and Murray (10) have reported that bzl6Ade2 is not incorporated into tRNA but that bzl6A, apparently arising from transbenzylation of an adenosine in the tRNA, is found at a level of one molecule of bzl6A/750-2210 molecules of tRNA in soybean tissue grown on medium supplemented with bzl6Ade.…”

Biological activity of several 9-nonglycosidic-substituted natural cytokinins

“…7, Letham et al 1983). If those reactions were very fast, as with the oxidation of the 9-methyl group to carbon dioxide in the 9-methyl cytokinins, the derivatives would exhibit the properties of the parent (Fox et al 1971, Pietraface and Blaydes 1981, Shaw et al 1968. It follows then, if one cytokinin is not as active as another and they have the same activity-concentration slopes, they are probably binding to the same receptor and the differences in activity reflect the differences in affinity.…”