title: A purine nucleoside phosphorylase in Solanum tuberosum L. (potato) with specificity for cytokinins contributes to the duration of tuber endodormancy.
abstract: StCKP1 (Solanum tuberosum cytokinin riboside phosphorylase) catalyses the interconversion of the N9-riboside form of the plant hormone CK (cytokinin), a subset of purines, with its most active free base form. StCKP1 prefers CK to unsubstituted aminopurines. The protein was discovered as a CK-binding activity in extracts of tuberizing potato stolon tips, from which it was isolated by affinity chromatography. The N-terminal amino acid sequence matched the translation product of a set of ESTs, enabling a complete mRNA sequence to be obtained by RACE-PCR. The predicted polypeptide includes a cleavable signal peptide and motifs for purine nucleoside phosphorylase activity. The expressed protein was assayed for purine nucleoside phosphorylase activity against CKs and adenine/adenosine. Isopentenyladenine, trans-zeatin, dihydrozeatin and adenine were converted into ribosides in the presence of ribose 1-phosphate. In the opposite direction, isopentenyladenosine, trans-zeatin riboside, dihydrozeatin riboside and adenosine were converted into their free bases in the presence of Pi. StCKP1 had no detectable ribohydrolase activity. Evidence is presented that StCKP1 is active in tubers as a negative regulator of CKs, prolonging endodormancy by a chill-reversible mechanism.
authors: *Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, U.K.
authors: Jennifer R
authors: JR
authors: Bromley
authors: *Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, U.K.
authors: Barbara J
authors: BJ
authors: Warnes
authors: *Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, U.K.
authors: Christine A
authors: CA
authors: Newell
authors: *Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, U.K.
authors: Jamie C P
authors: JC
authors: Thomson
authors: *Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, U.K.
authors: Celia M
authors: CM
authors: James
authors: †Department of Life Sciences, Imperial College London, London SW7 2AZ, U.K.
authors: Colin G N
authors: CG
authors: Turnbull
authors: *Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, U.K.
authors: David E
authors: DE
authors: Hanke
mesh_terms: D000595:Amino Acid Sequence; D003583:Cytokinins / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D057445:Plant Dormancy / Q000502:physiology*; D010936:Plant Extracts / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D014674:Plant Proteins, Dietary / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D035281:Plant Tubers / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011683:Purine-Nucleoside Phosphorylase / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D011198:Solanum tuberosum / Q000201:enzymology* / Q000235:genetics; D013997:Time Factors
chemical_list: D003583:Cytokinins; D010936:Plant Extracts; D014674:Plant Proteins, Dietary; D011683:Purine-Nucleoside Phosphorylase