Anticytokinin activity of substituted pyrrolo[2,3-d]pyrimidines

Ten substituted pyrrolo[2,3-d]pyrimidines were tested as cytokinins and anticytokinins in the tobacco bioassay. Eight new anticytokinins were identified and two were found to be highly active. The most potent species were 4-cyclohexylamino- and 4-cyclopentylamino-2-methylthiopyrrolo[2,3-d]pyrimidine, of which 0.05 and 0.009 muM concentrations, respectively, were required to produce detectable inhibition of the growth of tobacco callus cultured on a medium containing 0.003 muM 6-(3-methyl-2-butenylamino)purine. The inhibition of growth by moderate (