Plant Physiol.
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Plant Physiology 90:1630-1635 (1989)
© 1989 American Society of Plant Biologists

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Metabolism and Enzymology

An Enzyme Mediating the Conversion of Zeatin to Dihydrozeatin in Phaseolus Embryos 1

Ruth C. Martin, Machteld C. Mok, Gordon Shaw and David W. S. Mok

Department of Horticulture, Oregon State University, Corvallis, Oregon 97331, Department of Chemistry, University of Bradford, Yorkshire, BD7 1DP, United Kingdom

A reductase catalyzing the conversion of zeatin to dihydrozeatin was detected in soluble fractions of immature Phaseolus vulgaris embryos. The enzyme was partially purified by ammonium sulfate fractionation and affinity, gel filtration, and anion exchange chromatography. NADPH was the only cofactor required for enzyme activity, and the pH optimum was 7.5 to 8.0. The enzyme did not recognize compounds closely related to zeatin, such as ribosylzeatin, cls-zeatin, O-xylosylzeatin, N6-({Delta}2-isopentenyl)adenine, or N6-({Delta}2-isopentenyl)adenosine. No conversion of dihydrozeatin to zeatin by the enzyme was observed. Two forms of the reductase could be separated by either gel filtration or anion exchange high performance liquid chromatography. The high molecular weight isozyme (Mr 55,000 ± 5,000) eluted as the second peak from the anion exchange column, while the low molecular weight isozyme (Mr 25,000± 5000) was less negatively charged. The results suggest that side chain reduction occurs at the free base level. In addition, Phaseolus embryos are useful for the detection of zeatin-specific metabolic enzymes.

1 Research was supported by the Oregon Agricultural Experiment Station and by grants from National Science Foundation (DCB-8818620 and US-UK Cooperative Sciences INT-8513026). This is technical paper No. 8789 of the Oregon Agricultural Experiment Station.




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Copyright © 1989 by the American Society of Plant Biologists