INFLUENCE OF PHENOLIC-COMPOUNDS ON AGROBACTERIUM VIR GENE INDUCTION AND ONION GENE-TRANSFER

Eight chalcones and benzalacetones were tested for their virulence induction on Agrobacterium Tumefaciens. With one exception, they had a strong action, and in particular 4-(3,5-dimethoxy-4-hydroxy-phenyl)-but-3 en-2-one (10a) was very effective with a virulence induction about 1.5-2 times that of acetosyringone (AS). When applied to Agrobacterium-mediated gene transfer of onion, both 10a and AS at 250 mu M, led to increased gene transfer of between 25 and 35% when compared with the control. Many derivatives of AS were tested and the indispensable chemical functions required to induce vir genes were determined; for example, the presence of at least one methoxy group and a carbonyl group as in acetyl, aldehyde and acid functions. The most effective vir-inducing compound used was the original AS with two methoxy groups and an acetyl function. By testing the corresponding beta-glucosides and glucosyl esters (from acids), we established that a phenolic function was also essential for virulence induction. These glucosides led to a decreased toxicity to the bacteria in relation to the original product. However, the presence of a beta-glucosylated phenol function led to the total loss of vir induction while the corresponding esters, particularly the glucosyl sysingate ester, conserved a good vir induction.