May 20 , 1983 Title : The Effects of Thidiazuron on Cytokinin Autonomy and the Metabolism of N-( A-isopentenyl ) [ 8-Cjadenosine in Callus Tissues of Phaseolus lunatus

approved: Dr. Machteld C. Mok The effects of a highly cytokinin-active urea derivative, Nphenyl-N'-l,2,3-thiadiazol-5-ylurea (Thidiazuron), and zeatin on cytokinin-autonomous growth and the metabolism of N -(A -isopentenyl) [8Cjadenosine ([ C]i Ado) were examined in callus tissues of two Phaseolus lunatus genotypes, cv. Jackson Wonder and P.I. 260415. Tissues of cv. Jackson Wonder maintained on any concentration of Thidiazuron became cytokinin-autonomous, whereas only tissues exposed to suboptimal concentrations of zeatin displayed cytokinin-autonomous growth. Tissues of P.I. 260415 remained cytokinin-dependent under all these conditions. 14 6 The metabolism of [ C]i Ado was similar for the two geno14 6 types, but differed with the medium used. [ C]i Ado was rapidly converted to N-(A-isopentenyl)[8-C]adenosine S'-P ([C]iAMP) by tissues grown on zeatin-containing medium, whereas only traces of the nucleotide were formed in tissues grown on medium with 14 6 Thidiazuron. Incubation with [ C]i AMP of tissues grown in the 14 6 presence of Thidiazuron resulted in rapid conversion to [ C]i Ado, 14 6 while [ C]i AMP persisted in tissues maintained on zeatin. Thus, Thidiazuron appears to stimulate enzyme activity converting the ribonucleotide to the ribonucleoside. 14 6 The [ C]i Ado metabolism was also examined in cv. Jackson Wonder tissues grown in the simultaneous presence of Thidiazuron and zeatin. Regardless of the zeatin concentration present, at 14 6 suboptimal Thidiazuron concentration, the [ C]i Ado metabolism resembled that of tissues grown on zeatin alone; while at optimal concentration of Thidiazuron, nucleotide formation was inhibited. Cytokinin-autonomous growth was observed in tissues transferred from medium containing optimal Thidiazuron concentrations (and any concentration of zeatin), as well as suboptimal concentrations of the two compounds. Moreover, uptake of Thidiazuron and zeatin was found to be independent. Thus, although the cytokinin-active phenylureas and adenine derivatives differ in their effects on cytokinin autonomy as well as nucleotide formation, the two effects do not seem to be related. The Effects of Thidiazuron on Cytokinin Autonomy fi 2 and the Metabolism of N (A -isopentenyl) 14 [8C]adenosine in Callus Tissues of Phaseolus lunatus L.