PHENOTYPIC ALTERATIONS AND COMPONENT ANALYSIS OF SEED YIELD IN TRANSGENIC BRASSICA-NAPUS PLANTS EXPRESSING THE TZS GENE

Cytokinins play an important role in plant development. We investigate d the possibility that the nopaline Ti plasmid gene (tzs) from Agrobac terium tumefaciens could encode a protein able to participate in plant cytokinin production and lead to alterations in plant phenotype as a result of the expression of endogenous tzs. tzs was placed under the c ontrol of a heat-inducible promoter from the Zea mays hsp 70 gene. The expression of this fused gene was examined in transgenic Brassica nap us plants. The tzs gene, which encodes the enzyme dimethylallyl transf erase, was used as a cytokinin biosynthetic gene. The expression of th e tzs gene was monitored by RNA hybridization and analysis of cytokini n. content. Overproduction of cytokinin was observed even when the pla nts had not been heat-shocked, and the plants displayed a reduced root system, increased height and branching, and delayed flowering. In add ition, a significant increase in seed yield was observed in the transg enic plants, accounted for by increased number of seeds per silique an d seed weight. The results suggest that increased levels of cytokinins , through the expression of tzs, are correlated with growth rather tha n with differentiation processes.