Scientists Examine Role of Cytokinin in Root to Shoot Signaling of Transgenic Tobacco

Cytokinin is a plant hormone involved in several developmental processes of plants. One of these processes is the root to shoot signaling. If there are low concentrations of cytokinin transported from the roots to the shoots, then there would be an adaptive response on the shoot. However, abscisic acid (ABA) has been widely accepted as an effective root to shoot signaling hormone. Lydia Vysotskaya of the Russian Academy of Sciences, together with other scientists conducted a study to re-examine the function of cytokinins in root to shoot interaction by using transgenic tobacco plants with gene coding for isopentenyltransferase (ipt) and root-targeted expression of the ipt gene. To induce local expression of ipt in the root system of Nicotiana tabaccum, heat shock (HS) promoter at 40 ^oC was applied for 1 hour.

HS was also applied to wild type (WT) tobacco plants and it was observed that the effect was smaller in WT, concentrated only in the upper leaves. Zeatin riboside, the main transportable form of cytokinin, was also  increased in the roots. This could be the reason for the increased concentration of cytokinin in the leaves through transpiration. HS treatment in the roots of both WT and transgenic plants also elevated the transpiration and stomatal conductivity or the speed at which water evaporates from pores in a plant. Elevated transpiration caused depressed leaf relative water content, which further raised the concentration of ABA causing closure of the stomata. With the observed effects of cytokinin in the stomatal opening and transpiration, it is confirmed that cytokinin has a role in root and shoot communication.

The abstract of this study is available at http://jxb.oxfordjournals.org/cgi/content/abstract/61/13/3709.