Physiological studies have shown that in many species
cytokinins can inhibit leaf senescence and that the endogenous
cytokinin level drops with the progression of leaf
senescence (reviewed by Gan and Amasino, 1996). One
obvious approach for manipulating senescence is to engineer
plants that will overproduce cytokinins. In the cytokinin
biosynthesis pathway, the first committed and controlling
step is catalyzed by IPT. Therefore, expression of
this enzyme will result in the production of cytokinins. The
native plant IPT has not been identified, but a bacterial
version is available. Many strategies (i.e. different promoters)
have been used to manipulate the expression of IPT in
transgenic plants, including heat-, wound-, and lightinducible
promoters, and tissue- or development-specific
promoters. Most of the transgenic plants containing such.