CYTOKININS IN PLANT SENESCENCE - FROM SPRAY AND PRAY TO CLONE AND PLAY

Three approaches have been used to investigate the inhibitory role of the cytokinin class of phytohormones in plant senescence: external app lication of cytokinins, measurement of endogenous cytokinin levels bef ore and during senescence, and manipulation of endogenous cytokinin pr oduction in transgenic plants. In transgenic plant studies, endogenous cytokinin levels are manipulated by expression of IPT, a gene encodin g isopentenyl transferase. Transgenic plants expressing IPT from a var iety of promoters exhibit developmental and morphological alterations and often display retarded leaf senescence. A recently developed autor egulatory senescence-inhibition system targets cytokinin production qu antitatively, spatially and temporally, and results in transgenic plan ts that exhibit significantly delayed senescence without abnormalities . These transgenic studies not only confirm the regulatory role of cyt okinins in plant senescence, but also provide a way to manipulate sene scence for potential agricultural applications.