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

这是俄勒冈州州立大学和捷克共和国实验植物研究所之间的一个国际合作研究项目，重点是植物激素（细胞分裂素）对衰老的调节。这项研究将有助于更好地了解导致一年生植物在季末停止生长的过程。这项合作是Machteld Mok/大卫Mok和Radomira Vankova之间以前的COBASE项目的延续，这项研究是NSF资助的Mok实验室项目（9981974）的延伸。该合作结合了两个实验室的研究专长，以分子工具解决植物生理学的一个经典课题。细胞分裂素是促进细胞分裂和调节整个植物发育的许多阶段的激素。玉米素是最常见、最具活性的天然细胞分裂素。在玉米素代谢物的广谱中，源自N6-类异戊二烯侧链修饰的那些代谢物特别令人感兴趣，因为生物活性在很大程度上取决于侧链构型。玉米素的O-葡萄糖苷和玉米素核糖基存在于大多数植物物种中，并且在叶片衰老开始时特别丰富。由于O-葡萄糖苷能抵抗细胞分裂素氧化酶的攻击，并能通过β-葡萄糖苷酶水解迅速转化为玉米素，因此被认为是活性细胞分裂素的储存和转运形式。然而，它们的确切功能尚未确定。分子工具，编码玉米素O-葡糖基转移酶（ZOG 1）和β-葡糖苷酶（Bgl 4）的基因，现在可以用来研究这个问题。玉米素、核糖基玉米素及其O-葡萄糖苷的基因表达、酶活性和分布将在烟草叶片发育的特定阶段确定。修饰O-葡萄糖基化和糖水解对成熟和衰老的影响将通过产生以正义和反义方向携带ZOG 1和Bgl 4基因的转基因植物来检查。由于很少有细胞分裂素相关基因被分离出来，这项研究提供了一种独特的方法来研究单个发育过程中特定代谢步骤的控制，并为叶片衰老的激素调控带来新的视角。

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.