US - Czech Collaboration on the Role of Cytokinin Conjugation in Leaf Senescence

Oregon State University, Corvallis OR

Investigators

Abstract

This is an international collaborative research project between Oregon State University and the Institute of Experimental Botany of the Czech Republic focusing on the regulation of senescence by a plant hormone (cytokinin). The research will lead to a better understanding of the processes leading to cessation of growth in annual plants at the end of the season. The collaboration is a continuation of a previous COBASE project between Machteld Mok/David Mok and Radomira Vankova and the research is an extension of a NSF-funded project to the Mok lab (9981974). The collaboration combines research expertise of the two labs to address a classical topic in plant physiology with molecular tools. Cytokinins are hormones promoting cell division and regulating many phases of whole plant development. Zeatin is the most common and active natural cytokinin. Of the wide spectrum of zeatin metabolites, those derived from modifications of the N6-isoprenoid side-chain are of particular interest since biological activity is largely dependent on side-chain configuration. O-Glucosides of zeatin and ribosylzeatin occur in most plant species examined and are particularly abundant at the onset of leaf senescence. By virtue of their resistance to cytokinin oxidase attack and ready conversion to zeatin via b-glucosidase hydrolysis, O-glucosides are considered to be storage and transport forms of active cytokinins. However, their precise function has not been defined. Molecular tools, genes encoding the zeatin O-glucosyltransferase (ZOG1) and a b-glucosidase (Bgl4), are now available to examine this question. Gene expression, enzyme activity and distribution of zeatin, ribosylzeatin, and their O-glucosides will be determined in tobacco at specific stages of leaf development. The effects of modifying O-glucosylation and sugar hydrolysis on maturation and senescence will be examined by generating transgenic plants harboring the ZOG1 and Bgl4 genes in sense and anti-sense orientations. As few cytokinin-related genes have been isolated, the proposed study offers a unique approach to examine the control of a specific metabolic step on a single developmental process, and should bring new perspective to the hormonal regulation of leaf senescence.