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

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Abstract
The ability of N,N''-diphenylurea (Ph2urea) to substitute for cytokinin-active adenine derivatives in promoting callus growth of P. lunatus was examined. In general, Ph2urea stimulated callus growth at high concentrations, although the growth of most callus tissues was irregular. Variability in the sensitivity of uniformity of the growth response to Ph2urea was found among different genotypes of P. lunatus. Most important, tissues cultured on Ph2urea-containing medium for 1 passage acquired the ability to proliferate in subsequent passages in the absence of either Ph2urea or cytokinin-active adenine derivatives. Corresponding tissues maintained on kinetin-containing medium remained cytokinin-dependent. The effect of Ph2urea in promoting the growth of P. lunatus callus tissue resides in its ability to induce cytokinin autonomy. The cytokinin activity of Ph2urea may be due to promotion of endogenous cytokinin biosynthesis in the bioassay systems in which it is active.