The Metabolism and Translocation of Zeatin in Intact Radish Seedlings1

Gordon, Margaret E.; Letham, D. S.; Parker, Charles W.

doi:10.1093/oxfordjournals.aob.a084871

Cited by 56 publications

(22 citation statements)

References 15 publications

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“…Some, but not all, of the symptoms produced in a plant nodulated by strain IC3342 could be mimicked by feeding the cytokinin BAPR (our unpublished data). Observed differences in the symptoms induced by IC3342 nodulation and those induced by BAPR (15,24), and that reduction of ZR to DZR occurs actively in pea roots and nodules (5). In the above explanation, it is assumed that the pathway of cytokinin biosynthesis in cultured Rhizobium cells is the same as in the symbiotic association.…”

Section: Discussionmentioning

confidence: 99%

Evidence for Cytokinin Involvement in Rhizobium (IC3342)-Induced Leaf Curl Syndrome of Pigeonpea (Cajanus cajan Millsp.)

Upadhyaya¹,

Parker²,

Letham³

et al. 1991

Plant Physiol.

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A uniquely abnormal shoot development (shoot tip-bending, leaf curling, release from apical dominance, and stunted growth) in pigeonpea (Cajanus cajan Millsp) induced by a nodulating Rhizobium strain, IC3342, is thought to be due to a hormonal imbalance. Amaranthus betacyanin bioassay indicated that xylem exudate and leaf extracts from pigeonpea plants with Rhizobiuminduced leaf curl symptoms contained high concentrations of cytokinin relative to those in normal plants. Radioimmunoassay (RIA) of samples purified with high performance liquid chromatography revealed that zeatin riboside (ZR) and dihydrozeatin riboside (DZR) concentrations in xylem sap from plants with leaf curl symptoms were 7 to 9 times higher than those in the sap from symptomless, nodulated plants. The sap from symptomless plants nodulated by a Curl-mutant had ZR and DZR concentrations comparable to those in the normal plant sap. RIA indicated that the respective concentrations of zeatin and N6-isopentenyladenine in culture filtrates of the curl-inducing strain IC3342 were 26 and 8 times higher than those in filtrates of a related normal nodulating strain (ANU240). Gas chromatographic-mass spectrometric analyses revealed similar differences. Gene-specific hybridization and sequence comparisons failed to detect any homology of IC3342 DNA to Agrobacterium tumefaciens or Pseudomonas savastanoi genetic loci encoding enzymes involved in cytokinin biosynthesis.The interaction of Rhizobium with legumes has many features in common with plant parasitic infection and development (31). While the pathogenic Agrobacterium-plant interaction leads to production of nondifferentiated plant tissue, the Rhizobium-legume interaction usually leads to the development of highly organized root nodule tissue. A role for phytohormones in parasitic, bacterial-plant interactions is becoming more evident as a result of the discovery of genes involved in hormone biosynthesis or metabolism in those bacteria. Crown gall on most dicotyledonous plants, induced

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Section: Discussionmentioning

confidence: 99%

Evidence for Cytokinin Involvement in Rhizobium (IC3342)-Induced Leaf Curl Syndrome of Pigeonpea (Cajanus cajan Millsp.)

Upadhyaya¹,

Parker²,

Letham³

et al. 1991

Plant Physiol.

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“…Radioactivity in chromatographic zones was determined by liquid scintillation counting according to Gordon et al (1974). TLC zones were eluted with meth- anol/water (1:1) to characterize the metabolites present by rechromatography or by enzymic degradation.…”

Section: Characterization Of Chromatographic Fractionsmentioning

confidence: 99%

Regulators of cell division in plant tissues. XXX. Cytokinin metabolism in relation to radish cotyledon expansion and senescence

Letham

Gollnow

1985

J Plant Growth Regul

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Abstract. Kinetic studies of formation of glucosides of 6-benzylaminopurine (BAP) in excised radish cotyledons indicated that the 3-, 7-, and 9-glucosides (N-glucosides) were each formed directly from BAP. The 7-and 9-glucosides of BAP and the 7-glucoside of zeatin exhibited great stability in the cotyledons, but the 3-glucoside was converted to free BAP and to the 7-and 9-glucosides of BAP. When 3H-labeled zeatin was supplied to developed cotyledons, at high concentrations (100 I~M), 7-glucosylzeatin was the principal metabolite, but an appreciable proportion of the extracted 3H was due to O-glucosylzeatin. In immature cotyledons, as used in the radish cotyledon cytokinin bioassay, this O-glucoside was shown to be converted into zeatin 7-glucoside probably via free zeatin.Metabolism of BAP and zeatin in radish cotyledons was studied in relation to cytokinin-induced cotyledon expansion. Cytokinin N-glucosides were not metabolites responsible for the observed cytokinin-induced expansion, and were not detoxification products, or deactivation products formation of which was coupled with cytokinin action. However, the free base, its riboside, and nucleotide were possible active forms of BAP associated with cotyledon expansion. The possible significance of cytokinin N-glucosides is discussed.Senescent and nonsenescent cotyledons differed in their metabolism of BAP, zeatin, and zeatin riboside. Senescence was associated principally with a reduction in ability to form 7-glucosylzeatin, enhanced metabolism to adenine derivatives, and an inability to form appreciable amounts of 3-glucosyl-BAP.A two-dimensional thin layer chromatography (TLC) system, based on adjoining layers of cellulose and silica gel, for separating zeatin metabolites

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“…The biological functions of zeatin metabolites (such as 0-and N-glucosides [4,5,8,24], lupinic acid [11,21,25], glucosylribosylzeatin [29], nucleoside and nucleotides [10,28] (16). P. vulgaris x P. acutifolius crosses result in embryos which develop to the cotyledonary stage but also do not reach maturity.…”

Section: Discussionmentioning

confidence: 99%

Cytokinin Metabolism in Phaseolus Embryos

Lee¹,

Mok²,

Mok³

et al. 1985

Plant Physiol.

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The metabolism of trans-18-'4Cjzeatin was examined in embryos of Phaseolus vulgaris cv Great Northern (GN) and P. lunatus cv Kingston (K) in an attempt to detect genetic variations in organized plant tissues. Metabolites were fractionated by HPLC, and identified by chemical and enzymic tests Metabolism of '4CiZeatin. Immature embryos at three developmental stages (measuring 3, 6, and 9 mm in length) were dissected from the pods under sterile condition. The embryos corresponded to late heart and early and mid cotyledonary stages at the respective length. ['4C]Zeatin (0.05 MCi, 0.002 umol) dissolved in 250 ,d of H20 was applied aseptically to 250 mg of immature embryos. The vials were sealed and maintained at 27°C in the dark for 2, 4, and 8 h. In addition, embryos were incubated with radioactively labeled zeatin dissolved in 0.05 M Tris-HCI (pH 6.0) buffer with all other conditions identical to those described above. To determine the amount of radioactivity recovered at time 0, ['4C]zeatin was applied and metabolites extracted immediately. This determination was made for the three sizes of embryos of both genotypes. Each experiment was repeated at least once and averages of two experiments are presented.To extract metabolites, the embryos were homogenized with a Tissuemizer equipped with a Microprobe Shaft (Tekmar) in 2.5 parts (v/w) of cold 95% ethanol. Cell debris was removed by successive filtration through Whatman paper No. 1 and Millipore filters (0.45 ,um). The ethanol extract was taken to dryness in vacuo at 35°C, redissolved in 4 ml of 50% (v/v) ethanol, and centrifuged at 23,500g for 20 min. The supernatant was condensed in vacuo to 100 Ml with a speed vac concentrator (Savant). The sample was then analyzed directly by HPLC. A Beckman Model 110 dual pump HPLC system with a prepacked column of reversed-phase C18 (Ultrasphere ODS 5 gm, 4.6 x 250 mm; Altex) was used. The aqueous buffer consisted of 0.2 M acetic acid, adjusted to pH 3.5 with TEA. Samples were eluted with a 635 www.plantphysiol.org on May 10, 2018 -Published by Downloaded from

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The Metabolism and Translocation of Zeatin in Intact Radish Seedlings1

Cited by 56 publications

References 15 publications

Evidence for Cytokinin Involvement in Rhizobium (IC3342)-Induced Leaf Curl Syndrome of Pigeonpea (Cajanus cajan Millsp.)

Evidence for Cytokinin Involvement in Rhizobium (IC3342)-Induced Leaf Curl Syndrome of Pigeonpea (Cajanus cajan Millsp.)

Regulators of cell division in plant tissues. XXX. Cytokinin metabolism in relation to radish cotyledon expansion and senescence

Cytokinin Metabolism in Phaseolus Embryos

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