Cytolocalization of zeatin O-xylosyltransferase in Phaseolus.

Zeatin O-xylosyltransferase (EC 2.4.2.-) mediates the formation of O-xylosylzeatin from trans-zeatin and UDP-xylose in immature seeds of Phaseolus vulgaris. Tissue printing with a monoclonal antibody specific for the enzyme and a cDNA probe demonstrated that the enzyme was primarily localized and synthesized in the endosperm. Immunolocalization performed on monolayer endosperm at the free-nuclei stage and on EM sections demonstrated that the enzyme was associated with the nucleus as well as with the cytoplasm. Immunoanalysis of nuclear fractions revealed that the enzyme was retained in the nuclear pellet. Western analysis also showed that the enzyme was present in the nuclei of cotyledons and endosperm callus. The findings suggest that the enzyme may be involved in the nuclear-cytoplasmic transport of cytokinins and related molecules or, possibly, with chromatin of rapidly dividing cells.