Cytokinin N-glucosylation inhibitors suppress deactivation of exogenous cytokinins in radish, but their effect on active endogenous cytokinins is counteracted by other regulatory mechanisms |
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Authors: | Blagoeva Elitsa Dobrev Petre I Malbeck Jirí Motyka Václav Strnad Miroslav Hanus Jan Vanková Radomíra |
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Institution: | Laboratory of Hormonal Regulations in Plants, Institute of Experimental Botany AS CR, Rozvojová135, CZ-16502 Prague 6, Czech Republic; Department of Plant Physiology, Faculty of Science, Charles University, Vini?ná2, CZ-12844 Prague 2, Czech Republic; Laboratory of Growth Regulators, Institute of Experimental Botany AS CR &PalackýUniversity, ?lechtitel?11, CZ-78371 Olomouc, Czech Republic; Isotope Laboratory, Institute of Experimental Botany AS CR, Víde?ská1083, CZ-14220 Prague 4, Czech Republic |
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Abstract: | The prolongation of the effect of exogenous cytokinins by inhibition of their inactivation was studied in Raphanus sativus L. cv. Rampouch. As in radish the main way of cytokinin inactivation is their N- glucosylation, inhibitors of this pathway, papaverine, theophylline and olomoucine, as well as two olomoucine analogues, bohemine and roscovitine, were tested. The latter ones, which function as potent inhibitors of cyclin-dependent kinases, have also been found to effectively inhibit cytokinin N- glucosylation. Incubation (24 h) of de-rooted radish seedlings with inhibitors resulted in c . 50% decrease of the conversion of model cytokinins, 3H]dihydrozeatin and 3H]N6-benzyladenine, to the corresponding 7 N- glucosides. Simultaneously the level of the non-metabolized cytokinin bases was elevated. The activity of cytokinin oxidase/dehydrogenase (EC 1.5.99.12) was suppressed in a dose dependent manner. The concentration of physiologically active endogenous cytokinins was not increased significantly by inhibitor application. The inhibition of N- glucosylation was in the case of olomoucine, bohemine and roscovitine accompanied by the accumulation of physiologically nonactive cis -zeatin derivatives. The impact of inhibitors on the endogenous cytokinin pool seems to be balanced by the mechanisms involved in the maintenance of cytokinin homeostasis. |
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