Induction of cytokinin autonomy by N,N'-diphenylurea in tissue cultures of Phaseolus lunatus L

The ability of N,N'-diphenylurea (Ph(2)urea) to substitute for cytokinin-active adenine derivatives in promoting callus growth of Phaseolus lunatus has been examined. In general, Ph(2)urea stimulated callus growth at high concentrations, although the growth of most callus tissues was irregular. Variability in the sensitivity and uniformity of the growth response to Ph(2)urea was found among different genotypes of P. lunatus. Most importantly, tissues cultured on Ph(2)urea-containing medium for one passage had acquired the ability to proliferate in subsequent passages in the absence of either Ph(2)urea or cytokinin-active adenine derivatives. Corresponding tissues maintained on kinetin-containing medium remained cytokinin-dependent. It appears that the effect of Ph(2)urea in promoting the growth of P. lunatus callus tissue resides in its ability to induce Cytokinin autonomy. This result suggests that the Cytokinin activity of Ph(2)urea may be due to promotion of endogenous Cytokinin biosynthesis in the bioassay systems in which it is active.