Studies of Cytokinin Action and Metabolism Using Tobacco Plants Expressing either the ipt or the GUS Gene Controlled by a Chalcone Synthase Promoter. IIipt and GUS Gene Expression, Cytokinin Levels and Metabolism

Abstract

The expression of GUS and ipt genes under control of a chalcone synthase (chs) promoter (PCHS) has been determined in tobacco (Nicotiana tabacum L.) plants and related to the development of plants expressing the chimaeric PCHS -ipt gene. GUS gene expression, which served as a model for the expression of the ipt gene, was highest in the internal phloem tissue of stems, in mature leaf laminae and in the upper part of corollas when fully open. Expression of the PCHS -ipt gene was assessed by quantifying the cytokinins produced, by determining incorporation of [3H]adenine into cytokinins and by quantifying ipt mRNA. Results from these studies were in general agreement with those based on expression of the PCHS -GUS gene. The chs promoter controlled expression of the ipt gene with some degree of tissue and temporal specificity. Expression of the ipt gene markedly elevated the cytokinin level in mature leaf laminae and the upper stems of flowering plants. The former was associated with retardation of leaf senescence and increased rates of transpiration due to changes in number, size and aperture of stomata, while the latter was associated with development of lateral shoots. In shoot tip cultures, 2-fold elevations in endogenous cytokinin level caused clear changes in development and this is discussed in relation to current concepts concerning the hormonal control of plant development. Using the transgenic tobacco tissues, it was shown that cis-zeatin is a substrate for cytokinin oxidase, that cis-zeatin is not converted to trans-zeatin in these tissues and that the endogenous cytokinin level influences the level of cytokinin oxidase activity in tissue and the rate of degradation of exogenous zeatin riboside to adenosine.

giganteaSuppressesimmutansVariegation by Interactions with Cytokinin and Gibberellin Signaling Pathways

“…(2) Cytokinins delay the transition to flowering in our study (Fig. 3) and in other studies (Wang et al, 1997;McCabe et al, 2001). (3) Cytokinins positively influence chloroplast biogenesis, plastid gene expression, pigment contents, and rates of photosynthesis, although the molecular mechanisms are unclear (Figs.…”

Cytokinin-Dependent Photorespiration and the Protection of Photosynthesis during Water Deficit

“…are offset by CKs (Pospíšilová and Dodd, 2005). Moreover, the increase in endogenous CK content in transgenic plants expressing a bacterial ipt gene (Wang et al, 1997) or zmp, a gene coding a protein capable of cleaving CK glucosides, promoted increases in g s and plant E in vivo (Pospíšilová et al, 1998). Plants transformed with P SARK ::IPT were shown to overexpress the IPT gene during maturity and during water shortage, and the enhanced expression of IPT was correlated with the increase of CKs in the leaves (Rivero et al, 2007).…”

Improving low-temperature tolerance in sugarcane by expressing the ipt gene under a cold inducible promoter

“…As most of the transgenic plants with constitutively expressed ipt exhibit some delay in leaf senescence, as well as a variety of morphological and developmental abnormalities (Wang et al 1997), different promoters have been used to manipulate the expression of ipt, including heat, wound and light-inducible promoters, and tissue or development specific promoters. Using the senescence-specific SAG12 promoter (Gan and Amasino 1995), delayed yellowing was reported in lettuce and broccoli both before and after harvest (Chen et al 2001, McCabe et al 2001.…”