Kinetics of N-(Delta-Isopentenyl)Adenosine Degradation in Tobacco Cells: EVIDENCE OF A REGULATORY MECHANISM UNDER THE CONTROL OF CYTOKININS.

Uptake and degradation of the cytokinin, N(6)-(Delta(2)-isopentenyl) adenosine, were studied in tobacco cells grown as cell suspensions. Degradation occurs by cleavage of the isopentenyl chain which gives adenylic products. Rate of N(6)(Delta(2)-isopentenyl)[8-(14)C]adenosine degradation increases several-fold after a 3- to 4-hour delay when cells have been exposed to a cytokinin. Consequently, only rates of N(6)-(Delta(2)-isopentenyl)adenosine degradation measured during the first 3 hours of incubation with [8-(14)C]-N-(6)(Delta(2)-isopentenyl)adenosine are representative of the intrinsic in vivo cytokinin degradative activity of tobacco cells. Within these limits, it appears that cytokinin degradative activity is high in cytokinin-autonomous tobacco cells, as indicated by the half life of the supplied N(6)(Delta(2) isopentenyl adenosine (about 3 hours) when it is supplied at the physiological concentration of 0.2 micromolar. This cytokinin degradative activity appears to be under the control of cytokinins themselves because N(6)-(Delta(2)-isopentenyl)adenosine degradative activity is increased several-fold following a 3- to 4-hour delay after these cells have been exposed to a cytokinin.