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Indian mustard (Brassica junceaLinn., Czern and Coss) plants were inoculated withAgrobacterium tumefaciensstrain A208 harbouring either plasmid pTiT37 or pTiT37.14a/a. The latter carries an insertion at the ‘rooty’ locus (gene 4 orcyt) of the T-DNA governing cytokinin biosynthesis. The tumours induced by pTiT37.14a/a were small and formed many roots. Forin vitroculture, these transformed cells required supplementation of the basal medium with IAA and kinetin in the initial stages though after six sub-cultures they were also hormone autotrophic.In vitrocultures showed profuse rooting like the inplantatumours. Unlike transformed tobacco and carrot cells,Brassica junceacells transformed by pTiT37.14a/a could not be induced to differentiate into shoots. In contrast, the cells transformed by the wild type pTiT37 were hormone autotrophic and occasionally differentiated into shoots but could not be induced to produce roots. These results demonstrate how a single gene mutation affecting cytokinin biosynthesis can alter the inplantaas well as thein vitroresponse of a transformed cell of the same genotype.