Kinetics of N6-(Δ2-Isopentenyl)Adenosine Degradation in Tobacco Cells

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Abstract
Uptake and degradation of the cytokinin, N6-(Δ2-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 N6(Δ2-isopentenyl)[8-14C]adenosine degradation increases several-fold after a 3- to 4-hour delay when cells have been exposed to a cytokinin. Consequently, only rates of N6-(Δ2-isopentenyl)adenosine degradation measured during the first 3 hours of incubation with [8-14C]-N-6(Δ2-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 N6(Δ2 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 N6-(Δ2-isopentenyl)adenosine degradative activity is increased several-fold following a 3- to 4-hour delay after these cells have been exposed to a cytokinin.
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