INFLUENCE OF EXOGENOUS HORMONES ON THE GROWTH AND SECONDARY METABOLITE FORMATION IN TRANSFORMED ROOT CULTURES

Transformed organ cultures formed following transformation of plant ti ssues with Agrobacterium species owe their phenotypes to alterations i n hormone metabolism. Exogenously supplied hormones have been used to probe the relationship between the growth and morphology of transforme d root cultures of a number of species and their ability to accumulate secondary products. Auxins in the presence of low levels of kinetin i nduce the rapid disorganisation of transformed roots of Nicotiana rust ica ultimately to form suspension cultures of transformed cells and th is process is associated with a decrease in nicotine content of the ce lls. This is related to cells in the culture losing competence in alka loid biosynthesis. In contrast, exogenously supplied GA(3) enhanced br anching in two transformed root clones of the tropane-alkaloid produci ng species, Brugmansia candida and so enhanced their typical ''hairy r oot'' phenotype. This growth substance had the effect of reducing the overall alkaloid accumulation but in one case significantly altered th e relative concentrations of different tropine esters. In transformed roots of Cucumis sativus, the phenotype of the roots is influenced by the expression of auxin synthesis genes on TR-DNA resulting in roots w ith two distinct morphologies. The pattern of expression of the enzyme ascorbate oxidase in populations of control roots of different morpho logies is described. The significance of these phenotypic variations o n the utility of transformed root cultures for the study of secondary metabolic pathways will be discussed.