Expression Of Ipt Gene Controlled By Seed-specific Promoter In Transgenic Tobacco Influences Seed Development

Cytokinin is one of the five classes of phytohormone, which is involved in a wide range of physiological and metabolic processes. Cytokinin has many functions during the development of plants, such as promoting cell division, inducing the differentiation of bud, root and plytoplast, promoting seed and fruit development, the onset of senescence, the plant intimidation resistance , regulating some gene expression and directing flow of assimilates and transportation and nutrients. Cytokinin is also involved in plant signal transduction. Historically, the studies on the functions cytokinin are based on exogenous applications of cytokinins. Studies based on exogenous applications are complicated by problems of updating, transportation and catabolism of the supplied cytokinins; it is difficult to distinguish between the causes and the effects. With the development of molecular biology and plant transgenic technology, it has been popular to study the cytokinin's functions and it's mechanisms in plant growth by using genetic engineering. In the same time, it has provided a way of hereditary breeding by using phytohormone. In recent years, more and more promoters of eukaryotes have been cloned, which accelerates the development of cytokinin genetic engineering. Under the regulation of tissue-specific or development-specific promoters, we can control ipt gene expression in a certain tissue and development stage. We can regulate the site, time and level of cytokinin expression according to different study goals. Though some studied have been made on the physiological functions of cytokinin by using some tissue-specific promoters, which was attached to ipt gene, little is known about the cytological effects of ipt gene on embryo and seed development. In order to study the functions of cytokinin during seed and embryo development, we fused the seed-specific promoter-lectin of bean with ipt gene. This chimeric lectin-ipt gene was introduced into tobacco. We analyze the effects of ipt expression on seed and embryo development. Under the control of the promoter lectin, the expression of ipt gene promoted the cell division of embryo and endosperm, the cell numbers of embryo and endosperm were significantly increased, the layers of plerome cells and the diameter of the transgenic tobacco seeds were increased. Consequently, the embryo and endosperm were enlarged. The enlargement of embryo and endosperm may simulate meristematic activity and accumulation of nutrients. The soluble protein level was elevated, the dry weight of lectin-ipt seeds was increased 8%-15% compared with controls. Lectin-ipt seedlings also grew faster than controls during early seedling growth, this faster growth might be the result from stronger meristerrmatic activity, which was sustained by the availability of more storage compounds (such as seed protein) in lectin-ipt seeds.