Short Term Metabolism of Urea and Purine Cytokinins

Abstract

Approximately 20 to 25% of the cytokinin benzyladenine (BA) taken up by soybean tissues in culture is converted to a stable, long-lived derivative which contains BA as part of its structure. This derivative may be metabolically related to 6-benzylamino 9-,B-D-ribofuranosylpurine 5'-monophosphate (BAMP). In in vivo incubations of 2 hours or less, we recover only BA, benzyladenosine, and BAMP. Benzyladenosine never accounts for more than 10% of the total radioactivity while BAMP builds up to about 20% of the total within 2 to 4 hours. After this period it begins to disappear, and a new, unidentified substance arises at a rate which roughly parallels the loss of BAMP. After about 48 hours this substance, which has good cytokinin activity, accounts for some 20 to 25% of the total radioactivity and persists at this level for at least 60 days. In the meantime the remainder of the BA, as well as benzyladenosine and BAMP, disappear completely. In addition, evidence is presented which suggests that the urea cytokinins are not active as such but first are metabolically transformed into other substances. Despite the increasing amount of evidence demonstrating the presence of molecules with cytokinin activity in the transfer RNA of a wide variety of organisms (see review by Key [12]), the biological roles of these substances remain obscure. Particularly puzzling is the finding (2) that, even in plant tissues which require an exogenous cytokinin source for in vitro growth, molecules with potent cytokinin activity exist as naturally occurring constituents of the tRNA. One is led to believe that the exogenous cytokinin has at least one biological role quite distinct from the cytokinin in situ.To investigate this role, one needs to know the short term metabolic fate of a cytokinin in a tissue which requires an exogenous source of these substances in order to grow. There are, unfortunately, very few sufficiently detailed studies of the low molecular weight metabolites of the cytokinins in the literature. McCalla et al. (15) investigated the soluble metabolites of 6-benzylaminopurine in Xanthium leaves and concluded that the riboside was the major metabolite. In addition, small amounts of what was apparently the 5'-ribonucleotide

Interaction of Kinetin and Calcium in Relation to Their Effect on Stimulation of Ethylene Production

“…Recently, the short term metabolism of 6-benzylaminopurine (benzyladenine) in soybean tissue culture (6) or potato tuber slices (4) has been demonstrated. 6-Benzylaminopurine riboside and 6-benzylaminopurine ribotide were identified as products of the conversion of benzyladenine within 2 to 4 hr.…”

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

“…Adenine-8-'4C (8.4 mg, 1 mCi, 16.0 mCi/mmole), 8.4 mg (0.062 mmole) freshly prepared benzylamine hydrochloride, and 0.5 ml (46 mmole) of freshly distilled benzylamine were heated in a sealed ampoule at 175 C overnight. The contents of the ampoule were then transferred to a 15-ml centrifuge tube.…”

“…There (28), van Onckelen et al (32), and Fox et al (13,14) reported the incorporation of cytokinins into sRNA although the purity of some of the sRNA was later questioned by Key (19). Dyson (8) and Srivastava (31) into both tRNA and rRNA, whereas Hall (16), Richmond et al (26), and Bezemer-Sybrandy et al (3) failed to detect any incorporation into RNA. Kende and Tavares (18), on the basis of measurements of incorporation of radioactive 6-benzylaminopurine and 6-benzylamino-9-methylpurine into soybean callus, claim that the methyl substituent in the 9 position inhibited incorporation of the latter cytokinin into RNA without inhibiting its biological activity.…”

“…The 2-isopentenyl pyrophosphate is derived from mevalonic acid (5, 25), but mevalonic acid itself does not satisfy the cytokinin requirements of the plant tissues (23). Studies on the short term metabolism of bzl6Ade have shown that it is in part degraded and in part rapidly transformed to its riboside and ribotide and more slowly to a stable 7-glucofuranosyl derivative (3,7,9).…”

The Formation, Isolation, and Biological Activity of a Cytokinin 7-Glucoside

“…In previous communications, it has been established that the cytokinin, 6-benzylaminopurine, is metabolized in relatively short time periods by cytokinin-requiring soybean tissues to yield three compounds containing the BA9 moiety in the soluble, nonpolynucleotide fraction (2,6). Two the these, 6-benzylamino-9-/8-D-ribofuranosylpurine and 6-benzylamino-9-fl-D-ribofuranosylpurine-5'-monophosphate, as well as BA itself, are relatively short lived and disappear within 120 hr, when the tissue is given an initial pulse of BA.…”