A purine nucleoside phosphorylase in <i>Solanum tuberosum</i> L. (potato) with specificity for cytokinins contributes to the duration of tuber endodormancy

Bromley, Jennifer R.; Warnes, Barbara J.; Newell, C. A.; Thomson, Jamie C. P.; James, C. M.; Turnbull, Colin; Hanke, David E.

doi:10.1042/bj20130792

Cited by 17 publications

(10 citation statements)

References 49 publications

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“…In plant systems, this enzyme is known as adenosine nucleosidase EC 3.2.2.7, also referred to as uridine‐ribohydrolase in Arabidopsis thaliana . More recently, an additional enzyme capable of facilitating the same reaction from CK riboside to FB was identified in Solanum tuberosum (potato)—referred to as purine nucleoside phosphorylase (EC 2.4.2.1) . While there are currently no known nucleoside hydrolases in mammals, purine nucleoside phosphorylases (PNPs) have been characterized in mammalian systems .…”

Section: Discussionmentioning

confidence: 99%

“…48 More recently, an additional enzyme capable of facilitating the same reaction from CK riboside to FB was identified in Solanum tuberosum (potato)-referred to as purine nucleoside phosphorylase (EC 2.4.2.1). 49 While there are currently no known nucleoside hydrolases in mammals, purine nucleoside phosphorylases (PNPs) have been characterized in mammalian systems. [50][51][52] Therefore, we propose this enzyme may be responsible for the conversion of iPR into iP in HeLa cells as observed in this study.…”

Section: Hela Ck Metabolismmentioning

confidence: 99%

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Phytohormone metabolism in human cells: Cytokinins are taken up and interconverted in HeLa cell culture

et al. 2019

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Cytokinins (CKs) encompass a group of phytohormones, known to orchestrate many critical processes in plant development. Excluding Archaea, CKs are pervasive among all kingdoms, but much less is reported about their metabolism beyond plants. Recent evidence from mammalian tissues indicates the presence of six additional CK forms beyond the previously identified, single mammalian CK, N6‐isopentenyladenosine (i6A). There is limited understanding of CK biosynthesis pathways in mammalian systems; therefore, human cervical cancer (HeLa) cells were used to further characterize CK processing by tracking the interconversion of CKs into their various structural derivatives in mammalian cells in a time‐course study. Through high‐performance liquid chromatography‐positive electrospray ionization‐tandem mass spectrometry (HPLC‐(+ESI)‐MS/MS), we document changes in the functional profiles of endogenous CKs in a human cell line following metabolism by HeLa cell cultures. The nucleotide CK fraction (iPRP) was found exclusively within the cell pellet (0.34 pmol/106 cells), and the active free base (FB) form (iP) and riboside fraction (iPR) were found in greater abundance extracellularly (1.67 and 0.10 nmol/L respectively). For further confirmation, we demonstrate that HeLa cells metabolize an exogenously supplied CK, N6‐benzyladenosine (BAR). In the HeLa culture supernatant, a 12‐fold decrease in BAR concentration was observed within the first 24 hours of incubation accompanied by a fivefold increase in the FB form, N6‐benzyladenine (BA). These findings support the hypothesis that HeLa cells have the enzymatic pathways required for the metabolism of both endogenous and exogenous CKs.

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Section: Discussionmentioning

confidence: 99%

Section: Hela Ck Metabolismmentioning

confidence: 99%

Phytohormone metabolism in human cells: Cytokinins are taken up and interconverted in HeLa cell culture

et al. 2019

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“…Excretion, perception, and degradation of extracellular ATP. pmANT1 (44), plasma membrane adenine nucleotide transporter; APY3 (45), apyrase 3; 59 NT (46), 59-nucleotidase; ENT3 (47), equilibrative nucleoside transporter 3; NSH3 (48), nucleoside hydrolase 3, AZG1/2 (49), azaguanine resistant 1 / azaguanine resistant 2, DORN1 (50), does not respond to nucleotides 1. and ribose-1-phosphate in the presence of phosphate, and that can also work in the synthesis direction of ribosides (Bromley et al, 2014). The enzyme preferred cytokinins/cytokinin ribosides over adenine/adenosine as substrates and is supposedly involved in cytokininmediated tuber endodormancy.…”

Section: Connections To Cytokinin Homeostasismentioning

confidence: 99%

Nucleotide Metabolism in Plants

2019

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“…Extracellular cytokinins are transported from remote sites or released from neighboring cells. The possible interconversion of cytokinin bases (tZ) and cytokinin ribosides (tZR) in the apoplast by a purine nucleoside phosphorylase (PNP) (Bromley et al ., ) is indicated. The model predicts one cytokinin signaling pathway starting from AHK receptors located at the plasma membrane (PM) as shown by dashed blue arrows.…”

Section: Towards An Integrative Concept For Cytokinin Receptor Signalingmentioning

confidence: 99%

“…Only root‐derived tZ transported through the xylem could become directly active at the surface of cells in the shoot. It may also be degraded in the apoplast by a CKX enzyme, transformed into the corresponding riboside by extracellular purine nucleoside phosphorylase (PNP) (Bromley et al ., ) or be imported in the cytoplasm by a PUP transporter. The signal generated by tZ at the PM would reach the cell nucleus through the two‐component signaling system shown in Fig.…”

Section: Towards An Integrative Concept For Cytokinin Receptor Signalingmentioning

confidence: 99%

Cytokinin signaling: from the ER or from the PM? That is the question!

2018

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Content Summary41I.Introduction41II.Historical outline42III.Recent developments43IV.Towards an integrative concept for cytokinin receptor signaling48Acknowledgements51References51 Summary Cytokinin signaling plays an important role in plant growth and development, and therefore its molecular characteristics are under extensive study. One characteristic is the subcellular localization of cytokinin signal initiation. This localization determines both the pathway for hormone delivery to the receptor, as well as molecular aspects of signal transfer to the primary cellular targets. Subcellular sites for the onset of cytokinin signaling are still uncertain and experimental data are in part controversial. A few years ago, cytokinin receptors were shown to be localized predominantly in the membrane of the endoplasmic reticulum (ER) and to possess some features, such as their pH activity profile, typical for intracellular proteins. Very recently, new data corroborating the functionality of ER‐located cytokinin receptors were reported. However, other work argued for cytokinin perception to occur at the plasma membrane (PM). Here, we discuss in detail these partially conflicting data and present an integrative model for cytokinin perception and signaling. In our opinion, the prevailing evidence argues for the ER being the predominant site of cytokinin signal perception but also that signal initiation at the PM might be relevant in some circumstances as well. The roles of these pathways in long‐distance, paracrine and autocrine cytokinin signaling are discussed.

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A purine nucleoside phosphorylase in Solanum tuberosum L. (potato) with specificity for cytokinins contributes to the duration of tuber endodormancy

Abstract: We found that the potato gene StCKP1 encodes an enzyme interconverting two forms of the plant hormone CK (cytokinin), an activator of tuber development. We showed that StCKP1 prolonged dormancy in potato tubers. If tubers were chilled, the extra dormancy disappeared.

Cited by 17 publications

References 49 publications

Phytohormone metabolism in human cells: Cytokinins are taken up and interconverted in HeLa cell culture

Phytohormone metabolism in human cells: Cytokinins are taken up and interconverted in HeLa cell culture

Nucleotide Metabolism in Plants

Cytokinin signaling: from the ER or from the PM? That is the question!

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