Metabolism of Cytokinin

Chen, Chong-Maw; Kristopeit, Susan M.

doi:10.1104/pp.67.3.494

Cited by 66 publications

(9 citation statements)

References 15 publications

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“…4) as evidenced by the observation that IP causes a significant increase in the endogenous concentration of BA and a reduction in the level of 7G-BA. This result was expected since the enzymes responsible for cytokinin conversion play a role in the metabolism of purine bases, ribosides, and ribotides in general (2)(3)(4)(5).…”

Section: Discussionmentioning

confidence: 80%

Cytokinins and Flower Bud Formation in Vitro in Tobacco

Krieken¹,

Croes²,

Smulders³

et al. 1990

Plant Physiol.

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Explants from flower stalks of Nicotiana tabacum L. were cultured on different cytokinins to induce flower bud formation. All cytokinins tested except zeatin and zeatin-riboside induced the same maximal number of flower buds. Benzyladenine, benzyladenosine, and dihydrozeatin were the most active compounds whereas isopentenyladenosine and isopentenyladenine acted at a 20-fold higher concentration. These data suggest that the active cytokinins bind to the same receptor with different affinities. The presence of benzyladenine in the medium was necessary only during the first 2 days of culture (initiation period). The equilibrium between benzyladenine and its conjugates (the riboside, glucoside, and nucleotides) after a 4-day pulse was independent of the benzyladenine concentration whether it was inductive or noninductive for bud formation. The level of all derivatives was proportional to the benzyladenine concentration in the medium. Isopentenyladenine was used as a competitive inhibitor of benzyladenine conjugation. Isopentenyladenine concentrations that were too low for bud formation led to a synergistic increase in bud number when applied together with benzyladenine. Isopentenyladenine decreased benzyladenine uptake and conjugation. In spite of the lower uptake, the concentration of free benzyladenine inside the explants was higher in the presence of isopentenyladenine than in its absence whereas the concentration of the 7-glucoside of benzyladenine was lower. It was concluded that the free cytokinin base is the main active compound.The regeneration of organs in small explants from plant tissues offers the possibility to study differentiation on tissues spatially isolated from the whole plant. In this way the qualitative and quantitative response to auxins and cytokinins involved in the regulation of developmental processes can be studied. In tobacco, both the effects of the concentrations and of the ratios of these plant growth regulators on the induction and frequency of roots and/or shoots ( 16) or flower buds (20) have been described. In attempting to understand the mechanism of action of these plant growth regulators, it is important to relate the number of regenerated organs to the actual endogenous auxin and cytokinin concentrations. These concentrations cannot be determined from the amount of growth ' Present address: Department of Botany, University of Guelph, Guelph, Ontario N1G 2W1, Canada. 565regulator taken up because of the conversion of the biologically active molecules into derivatives of unknown activity or no activity at all (1,6,8,9,12,23,24). The cytokinin conjugates formed are glucosides, ribosides, and ribotides. Generally, the glucosides are considered stable and inactive. In contrast, the free base and perhaps also the ribosides and ribotides are active (1 1, 13).Little research has been performed on cytokinin metabolism in relation to developmental processes in plants. Van der Krieken et al. (22) (18), is very well suited to study cytokinin metabolism in relation to flower b...

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Section: Discussionmentioning

confidence: 80%

Cytokinins and Flower Bud Formation in Vitro in Tobacco

Krieken¹,

Croes²,

Smulders³

et al. 1990

Plant Physiol.

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“…Nucleotide diphosphate sugars cleaved at essentially the same rate are UDP-D-glucose, UDP-D-galactose, UDP-N-Vol. 285 Mittal et al (1988); 4, Ostergaard et al (1991); 5, Polya & Ashton (1973); 6, Polya (1974Polya ( , 1975; 7, Chen & Kristopeit (1981); 8, Carter & Tipton (1986); 9, Burch & Stuchburry (1986); 10, Sharma et al (1986) acetyl-D-glucosamine or UDP-N-acetyl-D-galactosamine. The enzyme shows an absolute requirement for a divalent cation.…”

Section: Soluble Formsmentioning

confidence: 99%

5′-Nucleotidase: molecular structure and functional aspects

Zimmermann

1992

Biochemical Journal

798

701

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“…Hence, we refer to these enzymes as adenosine phosphateIPTs. Subsequent conversion of iPRMP to iP is catalyzed by 5Ј-nucleotidase and adenosine nucleosidase (10,11). The conversion of iP into tZ is catalyzed by microsomal trans-hydroxylase, which is probably a P450 monooxygenase (12).…”

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confidence: 99%

Distinct Isoprenoid Origins of cis- and trans-Zeatin Biosyntheses in Arabidopsis

Kasahara

Takei

Ueda

et al. 2004

Journal of Biological Chemistry

179

137

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Plants produce the common isoprenoid precursors isopentenyl diphosphate and dimethylallyl diphosphate (DMAPP) through the methylerythritol phosphate (MEP) pathway in plastids and the mevalonate (MVA) pathway in the cytosol. To assess which pathways contribute DMAPP for cytokinin biosynthesis, metabolites from each isoprenoid pathway were selectively labeled with 13 C in Arabidopsis seedlings. Efficient 13 C labeling was achieved by blocking the endogenous pathway genetically or chemically during the feed of a 13 C labeled precursor specific to the MEP or MVA pathways. Liquid chromatography-mass spectrometry analysis demonstrated that the prenyl group of trans-zeatin (tZ) and isopentenyladenine is mainly produced through the MEP pathway. In comparison, a large fraction of the prenyl group of cis-zeatin (cZ) derivatives was provided by the MVA pathway. When expressed as fusion proteins with green fluorescent protein in Arabidopsis cells, four adenosine phosphate-isopentenyltransferases (AtIPT1, AtIPT3, AtIPT5, and AtIPT8) were found in plastids, in agreement with the idea that the MEP pathway primarily provides DMAPP to tZ and isopentenyladenine. On the other hand, AtIPT2, a tRNA isopentenyltransferase, was detected in the cytosol. Because the prenylated adenine moiety of tRNA is usually of the cZ type, the formation of cZ in Arabidopsis seedlings might involve the transfer of DMAPP from the MVA pathway to tRNA. Distinct origins of large proportions of DMAPP for tZ and cZ biosynthesis suggest that plants are able to separately modulate the level of these cytokinin species.Cytokinins (CKs), 1 a group of phytohormones, have profound physiological roles in plants, e.g. promotion of cell division, release of lateral buds from apical dominance, and delay of senescence. The biological activity, signal transduction, and metabolism of CKs have long been studied (1). However, it remains unclear how different classes of CKs are produced in plants and whether such classes of CKs play different roles in plant development. Most natural CKs are derivatives of N 6

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Metabolism of Cytokinin

Cited by 66 publications

References 15 publications

Cytokinins and Flower Bud Formation in Vitro in Tobacco

Cytokinins and Flower Bud Formation in Vitro in Tobacco

5′-Nucleotidase: molecular structure and functional aspects

Distinct Isoprenoid Origins of cis- and trans-Zeatin Biosyntheses in Arabidopsis

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