title: Distribution, biological activities, metabolism, and the conceivable function of cis-zeatin-type cytokinins in plants.
abstract: 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.
authors.affiliation: Laboratory of Hormonal Regulations in Plants, Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Rozvojová 263, 16502 Prague 6, Czech Republic.
authors.forename: Silvia
authors.initials: S
authors.lastname: Gajdosová
authors.forename: Lukás
authors.initials: L
authors.lastname: Spíchal
authors.forename: Miroslav
authors.initials: M
authors.lastname: Kamínek
authors.forename: Klára
authors.initials: K
authors.lastname: Hoyerová
authors.forename: Ondrej
authors.initials: O
authors.lastname: Novák
authors.forename: Petre I
authors.initials: PI
authors.lastname: Dobrev
authors.forename: Petr
authors.initials: P
authors.lastname: Galuszka
authors.forename: Petr
authors.initials: P
authors.lastname: Klíma
authors.forename: Alena
authors.initials: A
authors.lastname: Gaudinová
authors.forename: Eva
authors.initials: E
authors.lastname: Zizková
authors.forename: Jan
authors.initials: J
authors.lastname: Hanus
authors.forename: Martin
authors.initials: M
authors.lastname: Dancák
authors.forename: Bohumil
authors.initials: B
authors.lastname: Trávnícek
authors.forename: Bedrich
authors.initials: B
authors.lastname: Pesek
authors.forename: Martin
authors.initials: M
authors.lastname: Krupicka
authors.forename: Radomíra
authors.initials: R
authors.lastname: Vanková
authors.forename: Miroslav
authors.initials: M
authors.lastname: Strnad
authors.forename: Václav
authors.initials: V
authors.lastname: Motyka
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000254:growth & development; D018554:Avena / Q000378:metabolism; D055162:Biocatalysis; D001681:Biological Assay; D001692:Biological Transport; D002478:Cells, Cultured; D007536:Isomerism; D010088:Oxidoreductases / Q000378:metabolism; D010802:Phylogeny; D018515:Plant Leaves / Q000378:metabolism; D010944:Plants / Q000201:enzymology / Q000378:metabolism*; D020033:Protein Isoforms; D012639:Seeds / Q000378:metabolism; D015398:Signal Transduction; D013379:Substrate Specificity; D013997:Time Factors; D014026:Nicotiana / Q000166:cytology / Q000201:enzymology; D014316:Tritium / Q000378:metabolism; D015026:Zeatin / Q000235:genetics / Q000378:metabolism*
chemical_list: D020033:Protein Isoforms; D014316:Tritium; D015026:Zeatin; D010088:Oxidoreductases; C019984:cytokinin oxidase