<i>trans</i>-Ribosylzeatin

Miura, George A.; Hall, Ross H.

doi:10.1104/pp.51.3.563

Cited by 50 publications

(14 citation statements)

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“…2iP and 2iPA can undergo three basic reactions: (a) cleavage of the isopentenyl side chain, leading to complete inactivation of the CK (Terrine and Laloue, 1980); (b) ring substitution, resulting in a lower activity of the CK (Laloue et al, 1977); and (c) hydroxylation of the terminal methyl group in the side chain, leading to an increase in CK activity (Miura and Hall, 1973). Our results show that externally applied 2iP and 2iPA undergo a rapid oxidative cleavage of the side chain.…”

Section: Dlscusslonmentioning

confidence: 99%

Analysis of Cytokinin Metabolism in ipt Transgenic Tobacco by Liquid Chromatography-Tandem Mass Spectrometry

1996

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The endogenous levels of the major, naturally occurring cytokinins in fisum safivum ribulose-I ,5-bisphosphate carboxylase small subunit promoter-isopentenyl transferase gene (Pssu-ipt)-transformed tobacco (Nicotiana tabacum L.) callus were quantified using electrospray-liquid chromatography-tandem mass spectrometry during a 6-week subcultivation period. An ipt gene was expressed under control of a tetracycline-inducible promoter for a more detailed study of cytokinin accumulation and metabolism. Activation of the ipt in both expression systems resulted in the production of mainly zeatin-type cytokinins. No accumulation of isopentenyladenine or isopentenyladenosine was observed. In Pssu-ipt-transformed calli, as well as in the tetracycline-inducible ipt leaves, metabolic inactivation occurred through O-glucoside conjugation. No significant elevation of cytokinin Kglucosides levels was observed. Side-chain reduction to dihydrozeatin-type cytokinins was observed in both systems. The levels of the endogenous cytokinins varied in time and were subject to homeostatic regulatory mechanisms. Feeding experiments of ipt transgenic callus with [3Hlisopentenyladenine and [3Hlisopentenyladenosine mainly led to labeled adenine-like compounds, which are degradation products from cytokininoxidase activity. lncorporation of radioactivity in zeatin riboside was observed, although to a much lesser extent.

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Section: Dlscusslonmentioning

confidence: 99%

Analysis of Cytokinin Metabolism in ipt Transgenic Tobacco by Liquid Chromatography-Tandem Mass Spectrometry

1996

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“…Cell-free extracts from this organism can convert AMP and dimethylallyl-pyrophosphate (DMAPP) to the free cytokinins isopentenyladenosine-5Ј-monophosphate (iPMP) and the corresponding nucleoside (isopentenyladenosine, iPA). This finding, and studies on the metabolism of isopentenyl-type cytokinins (7,8), led to the proposal that iPMP is also the primary cytokinin intermediate in plants, and zeatin cytokinins are formed by hydroxylation of iPMP and its derivatives (9, 10) ( Fig. 1).…”

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An alternative cytokinin biosynthesis pathway

Åstot

Doležal

Nordström

et al. 2000

Proc. Natl. Acad. Sci. U.S.A.

126

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Studies of de novo cytokinin biosynthesis in isopentenyltransferase (ipt)-transformed Arabidopsis thaliana, involving in vivo deuterium labeling and mass spectrometry, showed that the biosynthetic rate of zeatinriboside-5 -monophosphate was around 66-fold higher than that of isopentenyladenosine-5 -monophosphate (iPMP), the proposed primary product of the Agrobacterium ipt. Double tracer analysis, using [ 2 H6] isopentenyladenosine and deuterium oxide, provided evidence for an alternative, iPMPindependent, biosynthetic pathway for zeatin-type cytokinins, present in both ipt-expressing and wild-type Arabidopsis thaliana. Reduction of the biosynthetic flux in the alternative pathway by use of mevastatin, an inhibitor for 3-hydroxy-3-methylglutaryl CoA reductase, indicated a terpenoid origin for the side-chain precursor of the iPMP independent pathway. C ytokinins are an important class of plant growth regulators, defined by their ability to promote cell division in tissue culture in the presence of auxins (1, 2). Virtually all naturally occurring cytokinins identified to date are adenine species substituted at N 6 with an isoprenoid or aromatic side chain. In this text, cytokinins will refer solely to the isoprenoid cytokinin bases and their sugar conjugates. Cytokinins affect many plant developmental processes including cell division, cell differentiation, chlorophyll senescence, and apical dominance (3).Efforts to elucidate the biosynthetic origin of cytokinins in plants have been inconclusive. Early suggestions that tRNA degradation could be the major source of free, active cytokinins (4) were disproved when calculations of tRNA turnover rates showed that a tRNA-independent de novo biosynthetic pathway also must be present in plants (5). A major breakthrough was the discovery of a cytokinin biosynthetic enzyme in the slime mold, Dictyostelium discoideum (6). Cell-free extracts from this organism can convert AMP and dimethylallyl-pyrophosphate (DMAPP) to the free cytokinins isopentenyladenosine-5Ј-monophosphate (iPMP) and the corresponding nucleoside (isopentenyladenosine, iPA). This finding, and studies on the metabolism of isopentenyl-type cytokinins (7,8), led to the proposal that iPMP is also the primary cytokinin intermediate in plants, and zeatin cytokinins are formed by hydroxylation of iPMP and its derivatives (9, 10) ( Fig. 1).Later, the product of the T-DNA gene 4 (ipt) of the crown gall-forming bacterium, Agrobacterium tumefaciens, also was described as a DMAPP:AMP isopentenyltransferase (ipt) (11,12). AMP was found to be the preferred adenylic substrate for the Agrobacterium ipt enzyme but searches for alternative side-chain donors have been limited. However, when de novo biosynthesis in crown gall tissue of Vinca rosea was traced with 14 C-adenine, in vivo production of iPMP was undetectable, whereas zeatinriboside-5Ј-monophospate (ZMP) production was strong (13). After studies of 14 C-isopententyladenine metabolism in this system, it was proposed that the very low levels of iPMP were caused by rapi...

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“…Evidence from various microorganisms shows that i6A and ms2i6A are the two major cytokinins found in their tRNAs (2,6,27). However, c-io6A and ms2io6A have been found in culture filtrates of certain plant pathogens (16,17,20), and recently Thimmappaya and Cherayil (29) 3 Abbreviations: i6A: N6-(A2-isopentenyl)adenosine or 6-(3-methyl-2-butenylamino)-9-/3-D-ribofuranosylpurine; t-io6A: ribosyl-trans-zeatin or 6-(4-hydroxy-3-methyl-trans-2-butenylamino)-9-/3-D-ribofuranosylpurine; c-io6A: ribosyl-cis-zeatin or 6-(4-hydroxy-3-methyl-cis-2-butenylamino)-9-,8--ribofuranosylpurine; ms2i6A: 2-methylthio-NO-isopentenyladenosine or 6-(3-methyl-2-butenylamino)-2-methylthio-9-13D-ribofuranosylpurine; ms2io6A: ribosyl-2-methylthiozeatin or 6-(4-hydroxy-3-methyl-2-butenylamino)-2-methylthio-9-f-D-ribofuranosylpurine; CTAB: cetyltrimethylammonium bromide; KE: kinetin equivalent, defined as the ,ug of kinetin (6-furfurylaminopurine) required to give the same activity as the test sample under the specified conditions. tRNA preparations.…”

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Subcellular Localization of Cytokinins in Transfer Ribonucleic Acid

1977

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Evidence on the localization of cytokinins in chloroplast tRNA was obtained by comparison of Euglena gracilis var. bacillaris light-grown and dark-grown wild type cultures and chloroplast-bleached mutant strains. The several cytokinins characteristic of tRNA were separated by Sephadex LH-20 column chromatography of the hydrolysates and were quantitatively determined by tobacco bioassays of the eluates. The results indicate that 6-(3-methyl-2-butenylamino)-9-l3-D-ribofuranosylpurine (i6A) is formed in both the cytoplasmic and chloroplast tRNA, whereas 6-(4-hydroxy-3-methyl-cis-2-butenylamino)-9-fl-D-ribofuranosylpurine (c-io6A) is produced mainly in the cytoplasmic tRNA and 6-(4-hydroxy-3-methyl-2-butenylamiao)-2-methylthio-9-fi-D-ribofuranosylpurine (ms2io6A) is localized exdusively in chloroplast tRNA. The restriction of the methiolation reaction to the chloropbst is supported by results of radioisotope experiments showing that 3S-labeled MgSO4 is incorported into ms2io6A in the wild type cultures, but not in the chloroplast-bleached mutant strains.Preparations of unfractionated tRNAs from various sources of wide evolutionary divergence have been shown to contain cytokinin-active nucleosides (3,12,26). To date, the four major active nucleosides which have been identified in tRNAs are i6A,3 c-io6A, ms2i6A, and ms2io6A. Evidence from various microorganisms shows that i6A and ms2i6A are the two major cytokinins found in their tRNAs (2,6,27). However, c-io6A and ms2io6A have been found in culture filtrates of certain plant pathogens (16,17,20), and recently Thimmappaya and Cherayil (29) 3 Abbreviations: i6A: N6-(A2-isopentenyl)adenosine or 6-(3-methyl-2-butenylamino)-9-/3-D-ribofuranosylpurine; t-io6A: ribosyl-trans-zeatin or 6-(4-hydroxy-3-methyl-trans-2-butenylamino)-9-/3-D-ribofuranosylpurine; c-io6A: ribosyl-cis-zeatin or 6-(4-hydroxy-3-methyl-cis-2-butenylamino)-9-,8--ribofuranosylpurine; ms2i6A: 2-methylthio-NO-isopentenyladenosine or 6-(3-methyl-2-butenylamino)-2-methylthio-9-13D-ribofuranosylpurine; ms2io6A: ribosyl-2-methylthiozeatin or 6-(4-hydroxy-3-methyl-2-butenylamino)-2-methylthio-9-f-D-ribofuranosylpurine; CTAB: cetyltrimethylammonium bromide; KE: kinetin equivalent, defined as the ,ug of kinetin (6-furfurylaminopurine) required to give the same activity as the test sample under the specified conditions. tRNA preparations. Hall et al. (13) have reported c-io6A and i6 A as constituents of plant tRNA, namely from corn kernels, spinach, and frozen peas. Wheat germ tRNA contains four cytokinins, i6A, io6A, and their methylthio derivatives (5). Pea root tRNA hydrolysates have been shown to contain mainly io6A and i6A (25). Vreman et al. (30,31) have reported the presence of i6A, ms2i6A, c-io6A, c-ms2io6A, and t-ms2io06A in tRNA hydrolysates from pea shoots. Thus, the cytokinins show greater diversity in plant tRNAs than in animal tRNAs or than generally found in tRNAs of microorganisms. The presence of different cytokinins in tRNAs of a single organism raises questions as to their origin and pos...

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trans-Ribosylzeatin

Cited by 50 publications

References 17 publications

Analysis of Cytokinin Metabolism in ipt Transgenic Tobacco by Liquid Chromatography-Tandem Mass Spectrometry

Analysis of Cytokinin Metabolism in ipt Transgenic Tobacco by Liquid Chromatography-Tandem Mass Spectrometry

An alternative cytokinin biosynthesis pathway

Subcellular Localization of Cytokinins in Transfer Ribonucleic Acid

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