AGROBACTERIUM VIR-INDUCING ACTIVITIES OF GLYCOSYLATED ACETOSYRINGONE, ACETOVANILLONE, SYRINGALDEHYDE AND SYRINGIC ACID-DERIVATIVES

Expression of the Agrobacterium tumefaciens virulence (vir) gene is known to be dependent on host plant phenolic compounds. The A. tumefaciens strain A348 (pSM358) harbouring a virE::lacZ fusion plasmid was used to detect the ability of 13 synthetic acetosyringone, acetovanillone, syringaldehyde and syringic acid beta-glycosides to induce virulence. The activity of the reporter beta-galactosidase was detected by spectrofluorimetry using 4-methylumbelliferyl beta-galactopyranoside as substrate. Acetosyringonyl beta-L-fucopyranoside was the most active monoglycoside tested; even at high concentration this compound was devoid of toxic effects. However, monoglycosides were less active vir inducers than free acetosyringone. In contrast, the beta-maltoside of syringaldehyde showed higher activity than the free phenol at high concentration. The activity of such glycosylated inducers may be related to specific sugar receptors on the bacterial cell surface.