A stereochemical model for cytokinin activity

Korszun, Z. R.; Knight, Christopher G.; Chen, C.-M.

doi:10.1016/0014-5793(89)81216-5

Cited by 18 publications

(10 citation statements)

References 18 publications

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“…Residues 36-47 and 148-159, which have weak electron densities, are drawn with dotted lines. rather than the N7-H form as found in the crystals of several cytokinins (see Korszun et al 1989). As expected, the cytokinin/Cdk2 co-crystals confirm the cytokinin stmcture-activity studies (for review see Skoog et al 1967, Letham 1978, Iwamura et al 1980 in that the N7, N3, and N9 of the purine must remain free of substitution because of the hydrogen bonds formed by these nitrogen atoms.…”

Section: -Alkyl-ba Derivativessupporting

confidence: 72%

The aromatic cytokinins

Strnad

1997

Physiologia Plantarum

200

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After the discovery of kinetin (Miller et al. 1956, J. Am. Chem. Soc. 78: 1345–1350) there was a flurry of syntheses that led to the finding of 6‐benzylaminopurine (BA), an active and easily obtainable cytokinin. Much research into cytokinin physiology was subsequently done with this substance. Further, the isolation and unequivocal identification of natural BA and the high biological activity of its meta‐hydroxylated analogues stimulated the search for other natural aromatic cytokinins. Screening was accomplished by ELISA of HPLC fractions using antisera against ortho‐ and meta‐hydroxybenzyladenosine. Subsequent isolation and decisive identification by mass spectrometry led to discovery of a broad spectrum of endogenous plant growth substances structurally similar to a highly active compound, meta‐topolin (6‐[3‐hydroxybenzyl‐amino]purine), and to its less active analogue, ortho‐topolin (6‐[2‐hydroxybenzyl‐amino]purine). The structures of such aromatic cytokinins suggest considerably different biosynthetic pathways from that of zeatin and related isoprenoid cytokinins. From a physiological viewpoint, aromatic cytokinin metabolism can be classified under four main headings analogous to isoprenoid cytokinins: interconversion, hydroxylation, conjugation, and oxidative degradation. This review attempts to put into context what is known about 9‐alkyl‐BAs and compares their metabolism in regard to the practical use of cytokinins in agriculture and biotechnology. The recently discovered unusual specificity of additionally C2,N9‐disubstituted aromatic cytokinins toward cell cycle kinases, suggests that these cytokinin‐derived growth regulators may selectively inhibit certain steps of the cell cycle. The functional overlap of the aromatic cytokinins with those of their isoprenoid counterparts and cytokinin inhibitors, in relation to growth and developmental processes in plants, has yet to be determined.

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Section: -Alkyl-ba Derivativessupporting

confidence: 72%

The aromatic cytokinins

Strnad

1997

Physiologia Plantarum

200

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“…Those study showed the dihedral angle between adenine and furfuryl residues plane to be 76-79 • [26][27][28][29][30].…”

Section: Synthesis and Structure Of Kinetinmentioning

confidence: 99%

Kinetin—A multiactive molecule

Barciszewski

Massino²,

Clark

2007

International Journal of Biological Macromolecules

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“…CK were extracted from whole pods (fer- Figure 1. The stereochemical conformation of (trans)Z and (cis)Z (adapted from Korszun et al, 1989). Open oval, C; gray oval, N; checkered oval, O; black oval, H. tilized ovaries, 1 DAPS, 30-50 mg dry weight), embryo with cotyledons, endospermic fluid and seed coat (14 DAPS; 4-84 mg dry weight), and cotyledons (30, 40, and 50 DAPS; 16-85 mg dry weight for GC-MS-SIM and 500-900 mg dry weight for full-scan GC-MS).…”

Section: Plant Materialsmentioning

confidence: 99%

“…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).…”

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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

109

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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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A stereochemical model for cytokinin activity

Abstract: The three-dimensional structures of several cytokinins were compared and a stereochemical model for cytokinin activity is proposed. This model is used to explain the difference in activity of c/s-and trans-zeatin.

Cited by 18 publications

References 18 publications

The aromatic cytokinins

The aromatic cytokinins

Kinetin—A multiactive molecule

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

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