Modification of competence for in vitro response to Fusarium oxysporum in tomato cells. III. PR-protein gene expression and ethylene evolution in tomato cell lines transgenic for phytohormone-related bacterial genes.

Previous work carried out in our laboratory has shown that, in tomato, the alteration of endogenous phytohormone equilibria through the integration of Agrobacterium tumefaciens genes for auxin and cytokinin synthesis can modify the active defense response to Fusarium oxysporum f. sp. lycopersici. The susceptible cv Red River acquires a stable competence for active defense, particularly when the phytohormone equilibrium is altered in favour of cytokinins. Here, we analyse the expression of genes involved in the defense response against pathogens, i.e. pathogenesis-related (PR)-protein genes, in the susceptible Red River and resistant Davis cultivars transgenic for the aforementioned genes. Fungal cell-wall components, glutathione, salicylic acid and the ethylene-forming ethephon are used as probes for the induction of defense processes, including ethylene production. The data obtained show that the extracellular PR-proteins (acidic chitinase and PR-1 protein) that were inducible in the control tissue of the resistant Davis cultivar and not expressed in the susceptible Red River cultivar became constitutive in the transgenic tissues of both. On the other hand, expression of the intracellular PR proteins (basic chitinase and b-1,3-glucanase) was found to be constitutive in all cases, both in the control and in the transgenic cell lines of the resistant and the susceptible tomato cultivars. Ethylene production was higher in Davis than in Red River, and signiÞcantly increased in the transgenic cell lines, particularly when cytokinin synthesis was altered.