Genotypic Variation in Cytokinin Oxidase from <i>Phaseolus</i> Callus Cultures

Kamínek, M.; Armstrong, Donald J.

doi:10.1104/pp.93.4.1530

Cited by 75 publications

(51 citation statements)

References 25 publications

(68 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This indicates that the enzyme can be induced by its substrate(s). The effect of increased levels of endogenous cytokinins on cytokinin oxidase activity was similar to that reported for the application of exogenous cytokinin solutions to different callus tissues, including tobacco (Chatfield and Armstrong, 1986;Kamínek and Armstrong, 1990;Motyka and Kamínek, 1990). It is interesting that the increase in cytokinin oxidase activity in derepressed IPT tissues did not prevent the accumulation of zeatin.…”

Section: Dlscusslonsupporting

confidence: 59%

“…Despite this accumulation, the elevated contents of endogenous cytokinins in transgenic plant cells is controlled by various homeostatic mechanisms such as conjugation or oxidation, which keep the hormone concentration below a lethal level. Indications that these mechanisms might be regulated by the hormone come from reports of enhanced cytokinin oxidase activity in various undifferentiated tissues or cell cultures after exogenous addition of cytokinins (Chatfield and Armstrong, 1986;Kamínek and Armstrong, 1990;Motyka and Kamínek, 1990). In the present investigation we studied the behavior of cytokinin oxidase, the key cytokinin-degrading enzyme, during conditional overproduction of endogenous cytokinins, which was made possible via the regulated Tc-dependent expression of the ipt gene in transgenic tobacco tissues.…”

Section: Dlscusslonmentioning

confidence: 99%

“…The supply of exogenous cytokinins to cultured callus tissues of Pkaseolus spp. (Chatfield and Armstrong, 1986;Kamínek and Armstrong, 1990) and N. tabacum (Motyka and Kamínek, 1990) induced transient increases in cytokinin oxidase activity. Both the substrate and the nonsubstrate cytokinins were effective in inducing elevated levels of the enzyme (Chatfield and Armstrong, 1986;Kamínek and Armstrong, 1990;Motyka and Kamínek, 1990).…”

mentioning

confidence: 99%

See 2 more Smart Citations

Changes in Cytokinin Content and Cytokinin Oxidase Activity in Response to Derepression of ipt Gene Transcription in Transgenic Tobacco Calli and Plants

et al. 1996

View full text Add to dashboard Cite

Metabolic control of cytokinin oxidase by its substrate was investigated in planta using wild-type (WT) and conditionally ipt gene-expressing transgenic (IPT) tobacco (Nicotiana fabacum 1.) callus cultures and plants. The derepression of the tetracycline (Tc)-dependent ipt gene transcription was followed by a progressive, more than 100-fold increase in total cytokinin content in IPT calli. The activity of cytokinin oxidase extracted from these calli began to increase 16 t o 20 h after gene derepression, and after 13 d it was 10-fold higher than from Tc-treated WT calli. An increase in cytokinin oxidase activity, as a consequence of elevated cytokinin levels, was found in detached leaves (8-fold after 4 d) and i n roots of intact plants (4-fold after 3 d). The partially purified cytokinin oxidase from WT, repressed IPT, and Tc-derepressed IPT tobacco calli exhibited similar characteristics. It had the same broad pH optimum (pH 6.5-8.5), its activity in vitro was enhanced 4-fold in the presence of copper-imidazole, and the apparent K,,,(N6-[A2iso-pentenylladenine) values were in the range of 3.1 to 4.9 PM. The increase in cytokinin oxidase activity in cytokinin-overproducing tissue was associated with the accumulation of a glycosylated form of the enzyme. The present data indicate the substrate induction of cytokinin oxidase activity in different tobacco tissues, which may contribote t o hormone homeostasis.

show abstract

Section: Dlscusslonsupporting

confidence: 59%

Section: Dlscusslonmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Changes in Cytokinin Content and Cytokinin Oxidase Activity in Response to Derepression of ipt Gene Transcription in Transgenic Tobacco Calli and Plants

et al. 1996

View full text Add to dashboard Cite

show abstract

“…The CKX activity staining of the wheat enzyme on high resolution IEF gel provided three major bands that all corresponded to a protein of about 60 kDa, thus showing interesting microheterogeneity that deserves further study. Isoforms with variability in pH optimum were not observed contrary to the Phaseolus callus culture [28]. The molecular mass of 60 kDa determined by SDS/PAGE for wheat and barley enzyme corresponds well with the molecular mass of the maize enzyme [11,12], but differs from the molecular mass of 40 kDa for the wheat CKX determined earlier by gel permeation chromatography [17].…”

Section: Discussionmentioning

confidence: 85%

Cytokinin oxidase or dehydrogenase?. Mechanism of cytokinin degradation in cereals

Galuszka¹,

Frébort²,

Šebela³

et al. 2001

Eur J Biochem

View full text Add to dashboard Cite

An enzyme degrading cytokinins with isoprenoid side chain, previously named cytokinin oxidase, was purified to near homogeneity from wheat and barley grains. New techniques were developed for the enzyme activity assay and staining on native electrophoretic gels to identify the protein. The purified wheat enzyme is a monomer 60 kDa, its N-terminal amino-acid sequence shows similarity to hypothetical cytokinin oxidase genes from Arabidopsis thaliana, but not to the enzyme from maize. N 6 -isopentenyl-2-(2-hydroxyethylamino)-9-methyladenine is the best substrate from all the cytokinins tested. Interestingly, oxygen was not required and hydrogen peroxide not produced during the catalytic reaction, so the enzyme behaves as a dehydrogenase rather than an oxidase. This was confirmed by the ability of the enzyme to transfer electrons to artificial electron acceptors, such as phenazine methosulfate and 2,6-dichlorophenol-indophenol. 2,3-Dimethoxy-5-methyl-1,4-benzoquinone, a precursor of the naturally occurring electron acceptor ubiquinone, readily interacts with the enzyme in micromolar concentrations. Typical flavoenzyme inhibitors such as acriflavine and diphenyleneiodonium inhibited this enzyme activity. Presence of the flavin cofactor in the enzyme was confirmed by differential pulse polarography and by measuring the fluorescence emission spectrum. Possible existence of a second redox centre is discussed.

show abstract

“…It is expected that all secreted CKX enzymes are post-transcriptionaly modified by glycosylation (Galuszka et al 2008). Glycosylation most probably contributes to the enzyme localisation, and also to translocation and protein stability , as the glycosylated CKXs were shown to have different pH optima and higher activity compared with the nonglycosylated forms (Kamínek and Armstrong 1990;Motyka et al 2003).…”

Section: Ck Metabolismmentioning

confidence: 99%

Cytokinins - recent news and views of evolutionally old molecules

Spíchal¹

2012

Functional Plant Biol.

156

169

View full text Add to dashboard Cite

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.

show abstract

Genotypic Variation in Cytokinin Oxidase from Phaseolus Callus Cultures

Cited by 75 publications

References 25 publications

Changes in Cytokinin Content and Cytokinin Oxidase Activity in Response to Derepression of ipt Gene Transcription in Transgenic Tobacco Calli and Plants

Changes in Cytokinin Content and Cytokinin Oxidase Activity in Response to Derepression of ipt Gene Transcription in Transgenic Tobacco Calli and Plants

Cytokinin oxidase or dehydrogenase?. Mechanism of cytokinin degradation in cereals

Cytokinins - recent news and views of evolutionally old molecules

Contact Info

Product

Resources

About