308 IMMUNOLOCALIZATION AND GENE CLONING OF ZEATIN OXYLOSYLTRANSFERASE

Abstract

Cytokinins are widely used in tissue culture and transformation systems; however, little is known of their mode of action or the mechanisms regulating their levels in plant tissues. We are studying enzymes responsible for the metabolism of zeatin in immature seeds of Phaseolus. Selective expression of genes encoding such enzymes may regulate the level of active cytokinins during seed development as well as in in vitro systems. A zeatin O-xylosyltransferase, which mediates the formation of O-xylosylzeatin from trans-zeatin and UDP-xylose, has been isolated and monoclonal antibodies specific to the enzyme have been produced. Tissue print analyses demonstrated that the enzyme is primarily localized in the endosperm. ln situ localization and EM studies indicated that the enzyme is present in the cytoplasm and the nucleus. cDNA libraries were constructed from immature seed mRNA and immunopositive clones were selected. The products of these clones are being analyzed in E. coli and baculovirus expression systems.