Distribution, biological activities, metabolism, and the conceivable function of XXXX -type cytokinins in plants.

@entity286 @entity72407 @entity958 @entity72408 @entity12307 @entity30119 @entity72406 @entity30973
Cytokinins (CKs) are plant hormones affecting numerous developmental processes. @entity30973 and its derivatives are the most important group of @entity12307 CKs. Zeatin occurs as two isomers: while @entity30119 (transZ) was found to be a bioactive substance, @entity72406 (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 @entity958 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 @entity286 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 @entity286 . Analysis of a CK-degrading enzyme, cytokinin oxidase/dehydrogenase (CKX), reveals that @entity958 possesses two isoforms, @entity72407 expressed in stages of active growth, and @entity72408 , 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.
