Abstract:The location of GUS gene expression under control of T-cyt gene (gene 4 of T- DNA coding isopenteryl transferase) 5′ region in transgenic tobacco (Nicotiana tabacum cv. W38) and potato (Solanum tuberosum L, cv. Desiree) plants was examined with biochemical assays. The results showed differential distribution in various organs and different cell types. The highest levels of GUS activity were found in tobacco stem where axillary bud was initiated and potato buds on tubers. Moreover, the expression of T-cyt promoter/GUS was found to be inducible in transgenic tobacco stem with cytokinin rather than auxin treatment. Additionally, the level of expression was high in the wounded leaf of transgenic potato. It was suggested that T-cyt promoter may be selectively induced by some exogenous plant hormones.