title: Cytokinin N-glucosylation inhibitors suppress deactivation of exogenous cytokinins in radish, but their effect on active endogenous cytokinins is counteracted by other regulatory mechanisms.
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, [(3)H]dihydrozeatin and [(3)H]N(6)-benzyladenine, to the corresponding 7N-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.
authors.affiliation: Laboratory of Hormonal Regulations in Plants, Institute of Experimental Botany AS CR, Rozvojová 135, CZ-16502 Prague 6, Czech Republic.
authors.forename: Elitsa
authors.initials: E
authors.lastname: Blagoeva
authors.forename: Petre I.
authors.initials: PI
authors.lastname: Dobrev
authors.forename: Jirí
authors.initials: J
authors.lastname: Malbeck
authors.forename: Václav
authors.initials: V
authors.lastname: Motyka
authors.forename: Miroslav
authors.initials: M
authors.lastname: Strnad
authors.forename: Jan
authors.initials: J
authors.lastname: Hanus
authors.forename: Radomíra
authors.initials: R
authors.lastname: Vanková