Distribution, biological activities, metabolism, and the conceivable function of cis-zeatin-type cytokinins in plants

Silvia Gajdošová, Lukáš Spíchal, Miroslav Kamínek, Klára Hoyerová, Ondřej Novák, Petre I. Dobrev, Petr Galuszka, Petr Klíma, Alena Gaudinová, Eva Žižková, Jan Hanuš, Martin Dančák, Bohumil Trávníček, Bedřich Pešek, Martin Krupička, Radomíra Vaňková, Miroslav Strnad, Václav Motyka

Klíčová slova: Arabidopsis thaliana, cis-zeatin, cytokinin, cytokinin oxidase/dehydrogenase, growth-limiting conditions, oat, tobacco BY-2 cells, trans-zeatin
Abstrakt: Cytokinins (CKs) are plant hormones affecting numerous developmental processes. Zeatin and its derivatives are the most important group of isoprenoid CKs. Zeatin occurs as two isomers: while trans-zeatin (transZ) was found to be a bioactive substance, cis-zeatin (cisZ) was reported to have a weak biological impact. Even though cisZ derivatives are abundant in various plant materials their biological role is still unknown. The comprehensive screen of land plants presented here suggests that cisZ-type CKs occur ubiquitously in the plant kingdom but their abundance might correlate with a strategy of life rather than with evolutionary complexity. Changing levels of transZ and cisZ during Arabidopsis ontogenesis show that levels of the two zeatin isomers can differ significantly during the life span of the plant, with cisZ-type CKs prevalent in the developmental stages associated with limited growth. A survey of the bioassays employed illustrates mild activity of cisZ and its derivatives. No cis↔trans isomerization, which would account for the effects of cisZ, was observed in tobacco cells and oat leaves. Differences in uptake between the two isomers resulting in distinct bioactivity have not been detected. In contrast, cisZ and transZ have a different metabolic fate in oat and tobacco. Analysis of a CK-degrading enzyme, cytokinin oxidase/dehydrogenase (CKX), reveals that Arabidopsis possesses two isoforms, AtCKX1 expressed in stages of active growth, and AtCKX7, both of which have the highest affinity for the cisZ isomer. Based on the present results, the conceivable function of cisZ-type CKs as delicate regulators of CK responses in plants under growth-limiting conditions is hypothesized.
DOI: Autoři z ÚEB: Alena Gaudinová, Klára Hoyerová, Miroslav Kamínek, Petr Klíma, Václav Motyka, Bedřich Pešek, Radomíra Vaňková, Eva Pokorná