Interaction of cytokinins and phenethylamines in cell-free enzyme systems and plant callus cultures Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/pv63g2938

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  • 1-Phenyl-3-(2-Thiazoly1)-2-Thiourea (PTTU), has been reported to inhibit dopamine-fi-hydroxylase (a copper-containing enzyme involved in the pathway of biosynthesis of adrenaline in animal systems). In the present study, PTTU has been shown to have cytokinin activity in the tobacco bioassay. The cytokinin activity of PTTU suggested that cytokinin-active N⁶-substituted adenine derivatives might be effective in inhibiting the activity of dopamine-β-hydroxylase. Tests of a number of cytokinin-active adenine derivatives have demonstrated that most of these compounds inhibit the activity of cell-free preparations of dopamine-b-hydroxylase. N⁶-cyclohexylmethyladenine (the most effective of the compounds) was as active as PTTU in inhibiting the enzyme. The cytokinin N⁶- (Δ²-isopentenyl)adenine (i⁶Ade) was one of compounds effective in inhibiting dopamine-,B-hydroxylase. No inhibition of the enzyme was obtained with the corresponding N³ substituted compound, N³- (Δ²-isopentenyl)adenine (triacanthine). The ability of dopamine-β-hydroxylase to degrade labeled i⁶Ade was tested using a variety of conditions, but no evidence was obtained of any enzymatic attack of the enzyme on this compound. Tyramine (a substrate of dopamine-β-hydroxylase), was tested as a competitive substrate for the enzyme-catalyzed degradation of i⁶Ade- 2,8 -³H by cytokinin oxidase (an enzyme involved in the degradation of cytokinins in plant tissues). Some inhibition of i⁶Ade degradation was observed at very high tyramine concentrations. The biological activities of phenethylamines were tested in several plant tissue culture systems. Tyramine and hordenine (N,Ndimethyltyramine) did not show cytokinin activity in the tobacco callus bioassay. Octopamine, tyramine, hordenine, and phenylethylamine inhibited the growth of callus tissues of cytokinin-dependent Nicotiana tabacum and promoted the formation of a dark pigment by the callus tissues. Cytokinin-dependent callus tissues of Phaseolus genotypes, which require high levels of cytokinins, were less sensitive than the tobacco callus to the inhibitory effects of the phenethylamines. The growth inhibitory effect of tyramine in the cytokinin-dependent callus tissues of tobacco was completely reversed by increased concentrations of kinetin. The possible mechanisms of interaction of cytokinins and phenethylamine derivatives in tobacco callus cultures are discussed.
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