Some of the consequences of altering cytokinin function could be highly beneficial for agriculture if synthesis of the hormone can be controlled. Because leaf senescence is delayed in the cytokinin-overproducing plants, it should be possible to extend their photosynthetic productivity. Indeed, when an ipt gene is expressed in lettuce from a senescence-inducible promoter, leaf senescence is strongly retarded, similar to the results observed in tobacco.
In addition, we were able to confirm that the lateral root meristems are likely to be the main sites of isopentenyladenosine-5'-monophosphate-dependent cytokinin synthesis, and that the aerial tissue of the plant surprisingly also was a significant source of cytokinin biosynthesis.
30/03/2006 · Cytokinin biosynthesis and perception
Interestingly, auxin mediates a very rapid negative control of the cytokinin pool by mainly suppressing the biosynthesis via the isopentenyladenosine-5'-monophosphate-independent pathway.
preventing growth but not the cytokinin-induced DNA synthesis.
N2 - The growth of plants depends on continuous function of the meristems. Shoot meristems are responsible for all the post-embryonic aerial organs, such as leaves, stems and flowers. It has been assumed that the phytohormone cytokinin has a positive role in shoot meristem function. A severe reduction in the size of meristems in a mutant that is defective in all of its cytokinin receptors has provided compelling evidence that cytokinin is required for meristem activity. Here, we report a novel regulation of meristem activity, which is executed by the meristem-specific activation of cytokinins. The LONELY GUY (LOG) gene of rice is required to maintain meristem activity and its loss of function causes premature termination of the shoot meristem. LOG encodes a novel cytokinin-activating enzyme that works in the final step of bioactive cytokinin synthesis. Revising the long-held idea of multistep reactions, LOG directly converts inactive cytokinin nucleotides to the free-base forms, which are biologically active, by its cytokinin-specific phosphoribohydrolase activity. LOG messenger RNA is specifically localized in shoot meristem tips, indicating the activation of cytokinins in a specific developmental domain. We propose the fine-tuning of concentrations and the spatial distribution of bioactive cytokinins by a cytokinin-activating enzyme as a mechanism that regulates meristem activity.
(1997), Cytokinin biosynthesis and interconversion ..
PNAS 101 : 8039-8044,
Keywords:Arabidopsis; auxin; cytokinin; biosynthesis
Abstract:One of the most long-lived models in plant science is the belief that the long-distance transport and ratio of two plant hormones, auxin and cytokinin, at the site of action control major developmental events such as apical dominance.
Where does the majority for synthesis of free cytokinin occur?
McGaw, B. A. (1995). "Cytokinin biosynthesis and metabolism". Plant Hormones: Physiology, Biochemistry and Molecular Biology. Dordrecht: Kluwer. pp.98-117.