EFFECTS OF SEED-SPECIFIC EXPRESSION OF A CYTOKININ BIOSYNTHETIC GENE ON CANOLA AND TOBACCO PHENOTYPES

The Agrobacterium tumefaciens isopentenyl transferase gene (ipt), a cy tokinin biosynthetic gene, was placed under the control of 1.9 kb of p romoter sequence from the 2S albumin AT2S1 gene isolated from an Arabi dopsis thaliana library. The construct was introduced into canola (Bra ssica napus) and tobacco (Nicotiana tabacum). ipt transcripts were fol lowed during embryo development of transgenic plants by northern hybri dizations. The phenotype of transformed plants from the T-1 generation was analysed and we observed an increased branching of inflorescences in tobacco and canola plants expressing the ipt gene. Comparing with controls, the average number of capsules and siliques in AT2S1-ipt pla nts was 82.6 and 24.8% higher, respectively. This result was correlate d with an increase in cytokinin levels in transgenic plants, as reveal ed by RIA. Indeed, cytokinin contents of T-1 AT2S1-ipt B. napus seeds were found 2.2-fold higher than cytokinin contents of control seeds, a nd T-1 AT2S1-ipt N. tabacum capsules contained 2.6-fold more cytokinin s than control capsules. In tobacco, the average seed weight per capsu le was lower in AT2S1-ipt plants while the seed number per silique and the average seed weight were not modified in canola carrying this con struct. The average seed yield per plant was not significantly increas ed in AT2S1-ipt tobacco or canola plants.