Machteld C. Mok

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Cytokinins are structurally diverse and biologically versatile. The chemistry and physiology of cytokinin have been studied extensively, but the regulation of cytokinin biosynthesis, metabolism, and signal transduction is still largely undefined. Recent advances in cloning metabolic genes and identifying putative receptors portend more rapid progress based(More)
Zeatin is the most active and ubiquitous form of the naturally occurring cytokinins. Glycosyl conjugates of zeatin are found in many plant tissues and are considered important for storage and protection against degradative enzymes. Two enzymes catalyzing the formation of O-glycosyl derivatives of zeatin have been characterized, O-glucosyltransferase and(More)
Zeatin is the most active and ubiquitous of the naturally occurring cytokinins. The O-glucoside of zeatin, found in all plants examined, is considered to be important in cytokinin transport, storage, and protection against cytokinin oxidases. The enzyme UDPglucose:zeatin O-glucosyltransferase (EC 2.4.1.203) was previously isolated from Phaseolus lunatus(More)
trans-Zeatin is a major and ubiquitous cytokinin in higher plants. cis-Zeatin has traditionally been viewed as an adjunct with low activity and rare occurrence. Recent reports of cis-zeatin and its derivatives as the predominant cytokinin components in some plant tissues may call for a different perspective on cis-isomers. The existence of a maize (Zea(More)
Investigation of the conversion of exogenous cis-zeatin to trans-zeatin in immature seeds of Phaseolus vulgaris L. led to the isolation of a cis-trans-isomerase from the endosperm. The enzyme was purified more than 2000-fold by chromatography on a series of fast protein liquid chromatography (anion exchange, gel filtration, and hydrophobic interaction) and(More)
The effects of a highly cytokinin-active urea derivative, N-phenyl-N'-1,2,3-thiadiazol-5-ylurea (Thidiazuron), and zeatin on cytokinin-autonomous growth and the metabolism of N(6)-(Delta(2)-isopentenyl)[8-(14)C]adenosine ([(14)C]i(6) Ado) were examined in callus tissues of two Phaseolus lunatus genotypes, cv Jackson Wonder and P.I. 260415. Tissues of cv(More)
An enzyme catalyzing the formation of a cytokinin metabolite, an O-pentosyl derivative of zeatin [Lee, Y. H., Mok, M. C., Mok, D. W. S., Griffin, D. A. & Shaw, G. (1985) Plant Physiol. 77, 635-641], was isolated from Phaseolus vulgaris embryos. Of all the potential pentose donors tested, UDP-xylose was the only substrate recognized by the enzyme. This(More)
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(More)
The activities of eight cytokinins in promoting callus growth were tested in two Phaseolus genotypes, P. vulgaris L. var. Great Northern, and P. lunatus L. var. Kingston. The structural feature which contributes to the major genotypic difference in cytokinin structure-activity relationships is the presence or absence of a double bond at the 2,3-position of(More)
Adventitious shoots of Cydonia oblonga Quince A were obtained from leaves cultured on MS-N6 medium containing thidiazuron (TDZ) and α-naphthaleneacetic acid (NAA). The frequency of regeneration was high (78% of the cultured leaves with 3.2 shoots per regenerating leaf) at 32 μM TDZ plus 0.3 μM NAA on young leaves obtained from micropropagated shoots. Shoots(More)