Identification of an N-Glucoside of cis-Zeatin from Potato Tuber Sprouts

Nicander, Björn; Björkman, Per‐Olof; Tillberg, Elisabeth

doi:10.1104/pp.109.2.513

Cited by 18 publications

(11 citation statements)

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“…Although it is becoming increasingly clear that cis ‐Z and its derivatives are bonafide natural constituents of many plant tissues, the physiological significance of these zeatin isomers in plant development remains unknown. Previous studies have established that cis ‐isomers of zeatin‐type cytokinins exist in specific tissues and organs of potato ( Mauk and Langille 1978; Nicander et al 1995) and limited data suggested that, like its trans ‐counterpart, cis ‐ZR exhibits biological activity in potato cuttings. In the present study, evidence has been presented which demonstrates that: (1) both cis ‐Z and its riboside occur in potato tuber extracts, (2) endogenous levels of cis ‐Z (but not cis ‐ZR) increase in tuber tissues prior to the termination of dormancy and the onset of sprout growth, and (3) exogenous cis ‐Z promotes the premature termination of tuber dormancy ( Figs 1, 2 and 3).…”

Section: Discussionmentioning

confidence: 99%

“…In addition, exogenous cis ‐ZR was shown to promote tuberization on non‐induced potato rhizomes (stolons). More recently, an N ‐glucoside of cis ‐Z was isolated from potato tuber sprouts ( Nicander et al 1995). It was identified as the 9‐glucoside of cis ‐Z by a variety of criteria including gas‐chromatography mass spectrometry.…”

Section: Introductionmentioning

confidence: 99%

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Changes in cis‐zeatin and cis‐zeatin riboside levels and biological activity during potato tuber dormancy

Suttle

Banowetz

2000

Physiologia Plantarum

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20°C) prior to use, the rise in endogenous cis-Z was less The effects of postharvest storage duration and temperature on endogenous cis-zeatin (cis-Z) and cis-zeatin riboside (cis-dramatic and more protracted; increasing twofold after 53 days of storage. No change in cis-Z riboside content was ZR) levels in potato (Solanum tuberosum L.) tubers were observed in these tubers during this period. Dose-response determined in relation to tuber bud dormancy. The tubers used in these studies were completely dormant for at least 81 studies using either cis-Z or trans-Z demonstrated a time-dependent increase in cytokinin sensitivity during postharvest days of storage. Thereafter, tuber bud dormancy diminished storage. Immediately after harvest, dormant tubers were in-gradually and after 165 days of postharvest storage, the tubers were completely non-dormant. Immediately after har-sensitive to both zeatin isomers. Thereafter, tubers exhibited a dose-dependent increase in premature sprouting following vest, endogenous levels of cis-Z and cis-ZR were approxiinjection with either cytokinin isomer. After injection into mately 25 pmol (g fresh weight) − 1 and 8 pmol (g fresh dormant tubers, cis-[8-14 C]-zeatin was metabolized primarily weight) − 1 , respectively. In tubers exiting dormancy but stored at a growth-inhibiting temperature (3°C), endogenous to adenine/adenosine and cis-Z riboside. Seven days after injection, less than 10% of the recovered radioactivity was levels of cis-Z rose over threefold after 25 days of storage associated with trans-ZR. These results are consistent with a and remained elevated for the duration of the study. Levels of role for endogenous cis-Z (and its derivatives) in the regula-cis-ZR remained essentially constant during this same period. tion of potato tuber dormancy. In tubers transferred to a growth permissive temperature stored crop and result in financial losses to producers and processors in excess of several hundred million dollars annually.At the cellular level, tuber meristem dormancy is a result of an inhibition of cell division (Macdonald and Osborne 1988). Meristematic cells in the tuber buds (eyes) are arrested in the G 1 -phase of the cell cycle prior to the onset of DNA replication (Campbell et al. 1996). The resumption of bud growth following the termination of dormancy is accompanied by a large increase in DNA synthesis and in the number of cells traversing the cell cycle.The molecular processes regulating meristem dormancy in plants remain unknown (see Bewley 1997). However, there

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Changes in cis‐zeatin and cis‐zeatin riboside levels and biological activity during potato tuber dormancy

Suttle

Banowetz

2000

Physiologia Plantarum

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“…Naturally occurring cytokinins are adenine derivatives with a side chain at the N 6 -position; cytokinins with a hydroxylated isoprenoid side chain such as trans-zeatin, first identified in maize (2), are major constituents in plants. Studies on the biosynthesis and metabolism of cytokinins have centered on trans-zeatin, although cis-zeatin and its derivatives have been isolated from a number of species including potato (3,4), Mercurialis (5), hops (6), rice (7)(8)(9), wheat (10), oats (10), and chickpeas (11). This emphasis on the trans isomers may be attributed to their higher biological activity.…”

mentioning

confidence: 99%

A maize cytokinin gene encoding an O -glucosyltransferase specific to cis -zeatin

Martin

Mok

Habben

et al. 2001

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

127

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Zeatin is a naturally occurring cytokinin. Biosynthesis and metabolism studies of zeatin have been directed mostly at the trans isomer, although cis-zeatin and its riboside occur as major components in some plant species. It is not known whether parallel regulatory pathways exist for the two isomers. Based on the sequence of the gene ZOG1 encoding a trans-zeatin O-glucosyltransferase from Phaseolus (EC 2.4.1.203), a cis-zeatin-specific Oglucosyltransferase was isolated from maize. This gene, cisZOG1, contains an ORF of 1,401 nucleotides encoding a protein of 51.1 kDa with 41% identity to the Phaseolus ZOG1 protein. Unexpectedly, the maize enzyme recognizes as substrates cis-zeatin and UDP-glucose but not cis-ribosylzeatin, trans-zeatin, or trans-ribosylzeatin. This finding indicates the existence of cis-specific regulatory elements in plants and suggests that cis-zeatin and derivatives may be more important in cytokinin homeostasis than currently recognized. C ytokinins are essential hormones for plant growth. In addition to promoting cell division and differentiation in tissue culture, cytokinins regulate a host of developmental events in whole plants such as bud formation, leaf expansion, delay of senescence, promotion of seed germination, and chloroplast formation (reviewed in ref. 1). Naturally occurring cytokinins are adenine derivatives with a side chain at the N 6 -position; cytokinins with a hydroxylated isoprenoid side chain such as trans-zeatin, first identified in maize (2), are major constituents in plants. Studies on the biosynthesis and metabolism of cytokinins have centered on trans-zeatin, although cis-zeatin and its derivatives have been isolated from a number of species including potato (3, 4), Mercurialis (5), hops (6), rice (7-9), wheat (10), oats (10), and chickpeas (11). This emphasis on the trans isomers may be attributed to their higher biological activity.Two pathways for cytokinin biosynthesis have been proposed. The first is the direct pathway, involving formation of N 6 -isopentenyladenosine monophosphate from AMP and dimethylallyl pyrophosphate, followed by hydroxylation of the side chain to form trans-zeatin-type cytokinins. In support of this pathway, isopentenyltransferase activity in tobacco (12) and hydroxylation activity in cauliflower (13) have been reported. The discovery of the Agrobacterium ipt gene (14, 15) lends support to the existence of a similar biosynthetic pathway in plants. However, plant genes encoding such enzymes have not been identified, and indirect evidence suggests the existence of a biosynthetic pathway for zeatin without isopentenyl intermediates (16, 17). The second, indirect pathway involves release of cytokinins by turnover of tRNAs containing cis-zeatin. Because cis-zeatin is much less active in bioassays, conversion to the trans isomer by enzymes such as the cis-trans isomerase of zeatin (18) Here we report the isolation and characterization of a gene encoding a cis-zeatin specific O-glucosyltransferase from maize. The finding of a gene and enzyme sp...

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“…An enzyme that converts cis-to transisomers, Z cis-trans-isomerase, has been partially purified and assayed in extracts of developing bean seeds (Bassil et al, 1993). Furthermore, in potato tuber sprouts, Nicander et al (1995) identified cis-Z-9-glucoside, a compound that could not have been derived directly from tRNA breakdown. Clearly, there is a need to identify the source of cis-isomers and to establish their significance, both as precursors for "active" CK and in general for regulatory roles proposed for this group of compounds.…”

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confidence: 99%

cis -Isomers of Cytokinins Predominate in Chickpea Seeds throughout Their Development1

Emery

Leport²,

Barton³

et al. 1998

Plant Physiology

108

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Trans-isomers of cytokinins (CK) are thought to predominate and have greater biological activity than corresponding cis-isomers in higher plants. However, this study demonstrates a system within which the predominant CK are cis-isomers. CK were measured at four developmental stages in developing chickpea (Cicer arietinum L. cultivar Kaniva) seeds by gas chromatography-mass spectrometry. Concentrations were highest at an early endospermic fluid stage and fell considerably when the cotyledons expanded. Seed tissues were the source for isolation of the first naturally occurring CK, trans-Z (Miller, 1961;Letham, 1963). Seeds have turned out to be a rich source of CK, and in the past 30 years investigators have described a range of different CK from seed tissues (van Staden et al., 1982). This may reflect their relatively high levels in seeds (van Staden et al., 1982), a status that is believed to indicate a role for CK in establishing developing seeds as strong assimilate sinks (Brenner and Cheikh, 1995). Despite a vast literature concerning the occurrence, form, and significance of CK in plant development, the nature and site(s) of their synthesis is yet to be established. In fact, Holland (1997) recently proposed that CK are not formed by plants at all but rather by bacterial symbionts that colonize plant tissues. Although there is good evidence for the transfer of CK synthesized by Rhizobium in legume nodules (Upadhyaya et al., 1991), a role for bacteria in providing CK to roots or shoot organs needs to be investigated more thoroughly. Because unequivocal evidence for a plant isopentenyl transferase is lacking, a persistent hypothesis, which has recently been reviewed (Prinsen et al., 1997), is that the free CK in plants are not synthesized de novo but are released during tRNA turnover.Z, [9R-MP]Z, and [9R]Z have an unsaturated isopentenyl side chain that can exist in the cis or trans conformation. The cis-isomer occurs when the hydroxyl group of the isopentenyl side chain is oriented toward the N-1 position of the purine ring, whereas in the trans-isomer the hydroxyl group is oriented away from the purine ring (Korszun et al., 1989; Fig. 1). The trans-isomers of [9R]Z and Z are by far the more commonly reported forms and are considered the predominant isomers in higher plants (McGaw and Burch, 1995;Prinsen et al., 1997). Systems in which the existence of cis-CK can be demonstrated unequivocally would be significant for two reasons. First, because cis-CK show much lower activity than trans-CK in bioassays (Kaminek, 1982) and their interconversion may constitute a mechanism for reducing CK bioactivity in vivo. Second, cis-CK provide evidence for the hypothesis that the free CK pool in higher plants may be at least partially derived from the breakdown of tRNA. The major criticism of this hypothesis has been the structural distinctness between tRNA-bound CK and free-pool CK (Letham and Palni, 1983;McGaw and Burch, 1995;Prinsen et al., 1997

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Identification of an N-Glucoside of cis-Zeatin from Potato Tuber Sprouts

Cited by 18 publications

References 13 publications

Changes in cis‐zeatin and cis‐zeatin riboside levels and biological activity during potato tuber dormancy

Changes in cis‐zeatin and cis‐zeatin riboside levels and biological activity during potato tuber dormancy

A maize cytokinin gene encoding an O -glucosyltransferase specific to cis -zeatin

cis -Isomers of Cytokinins Predominate in Chickpea Seeds throughout Their Development1

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