Partial Purification of a cis-trans-Isomerase of Zeatin from Immature Seed of Phaseolus vulgaris L

Bassil, Nahla V.; Mok, David W. S.; Mok, Machteld C.

doi:10.1104/pp.102.3.867

Cited by 99 publications

(81 citation statements)

References 22 publications

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“…It is possible that these cytokinins are produced by AtIPT4, 6, and͞or 8, although the undetectable expression of the corresponding transcripts for these AtIPTs in vegetative tissues argues against this hypothesis. It is possible that zeatin cis-trans isomerase, activity for which has been detected in Phaseolus vulgaris (38), produces tZ-type cytokinins from cZ-type cytokinins. However, if cis-trans isomerase activity is present in the quadruple mutant, the activity must be low because tZ-type cytokinin levels were greatly reduced compared with cZ-type cytokinin levels.…”

Section: Discussionmentioning

confidence: 99%

Roles of Arabidopsis ATP/ADP isopentenyltransferases and tRNA isopentenyltransferases in cytokinin biosynthesis

Miyawaki

Tarkowski

Matsumoto-Kitano

et al. 2006

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

505

536

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Cytokinins, which are central regulators of cell division and differentiation in plants, are adenine derivatives carrying an isopentenyl side chain that may be hydroxylated. Plants have two classes of isopentenyltransferases (IPTs) acting on the adenine moiety: ATP͞ ADP isopentenyltransferases (in Arabidopsis thaliana, AtIPT1, 3, 4 -8) and tRNA IPTs (in Arabidopsis, AtIPT2 and 9). ATP͞ADP IPTs are likely to be responsible for the bulk of cytokinin synthesis, whereas it is thought that cis-zeatin (cZ)-type cytokinins are produced possibly by degradation of cis-hydroxy isopentenyl tRNAs, which are formed by tRNA IPTs. However, these routes are largely hypothetical because of lack of in vivo evidence, because the critical experiment necessary to verify these routes, namely the production and analysis of mutants lacking AtIPTs, has not yet been described. We isolated null mutants for all members of the ATP͞ADP IPT and tRNA IPT gene families in Arabidopsis. Notably, our work demonstrates that the atipt1 3 5 7 quadruple mutant possesses severely decreased levels of isopentenyladenine and trans-zeatin (tZ), and their corresponding ribosides, ribotides, and glucosides, and is retarded in its growth. In contrast, these mutants possessed increased levels of cZ-type cytokinins. The atipt2 9 double mutant, on the other hand, lacked isopentenyl-and cishydroxy isopentenyl-tRNA, and cZ-type cytokinins. These results indicate that whereas ATP͞ADP IPTs are responsible for the bulk of isopentenyladenine-and tZ-type cytokinin synthesis, tRNA IPTs are required for cZ-type cytokinin production. This work clarifies the long-standing questions of the biosynthetic routes for isopentenyladenine-, tZ-, and cZ-type cytokinin production.S ince the discovery of cytokinins as inducers of plant cell division (1) and differentiation (2), they have been recognized as central regulators of plant development (3). Cytokinins also increase nutrient sink strength, delay senescence, stimulate outgrowth from lateral buds, and inhibit cell elongation (4). The important roles for cytokinins in cell division were verified by overexpression of genes for cytokinin-degrading enzymes (cytokinin oxidases, CKXs) (5-7) and by examination of single and higher-order cytokinin-receptor null mutants (8-10).Most naturally occurring cytokinins are N 6 -isopentenyladenine (iP) derivatives. iP carries an unmodified isopentenyl side chain, whereas trans-zeatin (tZ) and cis-zeatin (cZ) carry hydroxylated side chains. Cytokinins exist in free-base, riboside, and ribotide forms, with varying degrees of biological activity. Cytokinins also may be modified in several ways. For example, the N7 and N9 positions of the adenine moiety of cytokinins may be glucosylated to form N-glucosides. Alternatively, the hydroxyl group of tZ and cZ may be glucosylated or xylosylated to form zeatin-O-glucosides or zeatin-O-xylosides. N-and O-glycosides are biologically inactive (3).Experimental evidence demonstrates that free-base cytokinins are biologically active. For example, iP (11) and t...

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Section: Discussionmentioning

confidence: 99%

Roles of Arabidopsis ATP/ADP isopentenyltransferases and tRNA isopentenyltransferases in cytokinin biosynthesis

Miyawaki

Tarkowski

Matsumoto-Kitano

et al. 2006

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

505

536

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“…For example, a cis-trans-isomerase similar to the one isolated from immature bean seeds (Bassil et al, 1993) could have changed the CK isomer ratio following disruption of tissue or cell compartmentation at extraction. In addition, nonenzymatic isomerization of Z or [9R]Z is known to occur in vitro in the presence of light (Bassil et al, 1993). These extraction artifacts are unlikely to have influenced our results.…”

Section: Discussionmentioning

confidence: 99%

“…Clearly, tissues such as those of developing chickpea seeds, which accumulate cis-CK, challenge this idea. The demonstration of an isomerase that would interconvert the isomers (Bassil et al, 1993) also indicates that the cis-configuration may not be an impediment to a tRNA source. In the case of chickpea seeds it might be argued that the level of isomerase is very low.…”

Section: Cis-isomers Of Cytokinin Predominate In Chickpea Seedsmentioning

confidence: 99%

“…Using an analytical procedure requiring no extraction step, Parker et al (1989) showed in wheat and oat that cis-CK are minor components of xylem. 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.…”

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confidence: 99%

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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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“…Zeatin reductase isolated from immature seeds of Phaseolus vulgaris is highly specific to trans-zeatin base and does not reduce the cis-form of zeatin or isopentenyladenine . The enzyme converting zeatin from the trans-to the cis-isoform was partially purified from Phaseolus (Bassil et al 1993). However, such conversion slowly proceeds in vitro and without any enzymatic activity, and no other works so far have been published that exploit the physiological significance of zeatin isomerisation.…”

Section: Ck Metabolismmentioning

confidence: 99%

Cytokinins - recent news and views of evolutionally old molecules

Spíchal¹

2012

Functional Plant Biol.

156

169

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Cytokinins (CKs) are evolutionally old and highly conserved low-mass molecules that have been identified in almost all known organisms. In plants, they evolved into an important group of plant hormones controlling many physiological and developmental processes throughout the whole lifespan of the plant. CKs and their functions are, however, not unique to plants. In this review, the strategies and mechanisms of plants – and phylogenetically distinct plant-interacting organisms such as bacteria, fungi, nematodes and insects employing CKs or regulation of CK status in plants – are described and put into their evolutionary context. The major breakthroughs made in the last decade in the fields of CK biosynthesis, degradation and signalling are also summarised.

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Partial Purification of a cis-trans-Isomerase of Zeatin from Immature Seed of Phaseolus vulgaris L

Cited by 99 publications

References 22 publications

Roles of Arabidopsis ATP/ADP isopentenyltransferases and tRNA isopentenyltransferases in cytokinin biosynthesis

Roles of Arabidopsis ATP/ADP isopentenyltransferases and tRNA isopentenyltransferases in cytokinin biosynthesis

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

Cytokinins - recent news and views of evolutionally old molecules

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