Cytokinin-like effect of a new phenylurea derivative.

We have synthesized 14 N-phenylurea derivatives, differing in the heterocyclic portion linked in N-position, and tested their cytokinin-like activity. Three different bioassays were used: the chlorophyll level determination test, the bioassay for the expression of hormone-induced chimeric Pg5-GUS gene and the tomato regeneration test, in which 1,2-benzisoxazole-3-acetic acid (BOAA) was utilized as auxin. The cytokinin-like activity showed by three of these compounds in the regeneration assay seems to be related to their different heterocyclic nature. Results obtained indicate that the N-phenyl-N-1,3,4-thiadiazol-2-ylurea (compound 4), an isomer of N-phenyl-N-1,2,3- thiadiazol-5-ylurea (thidiazuron, TDZ), in the absence of auxin induces shoot regeneration in the 34,2% of the explants cultured; the N-phenyl-N-(3-chloro-1,2-benzisothiazol-7-yl) urea (compound 10), structurally different from TDZ, in the absence of auxin induces shoot regeneration in the 25,9% of explants, significantly lower than that of TDZ (68,8%). N-phenyl-N-benzothiazol-6-ylurea (compound 13), structurally different from TDZ, in the absence of auxin induces the 99,5% of shoot regeneration, significantly different from that of the other substances. The addition of auxin in the cotyledon regeneration assay reduces the differences. The compound 13 could be considered a new phenylurea derivative with a highly specific cytokinin-like activity.