Protective effect of bacterial lipopolysaccharides in the grapevine- Agrobacterium vitis interaction

Cell-associated lipopolysaccharides (LPS) were extracted by the phenol-chloroform-petroleum ether extraction method (PCP) from a nopaline strain of Agrobacterium vitis , purified by treatment with DNase/RNase, proteinase K and dialysis, characterized by polyacrylamide gel electrophoresis (SDS-PAGE), and bioassayed on grapevine shoot nodal segments. LPS preparation used for the experiments in planta was a mixture of rough-type LPS, obtained from precipitation with water after PCP-extraction, and some smooth- and rough-type LPS from the remaining phenol phase. Infiltration of an aqueous dispersion of the mixture in concentrations of 25-1000 µ g.ml -1 did not cause grapevine tissue necrosis, and callus formed within one month. When the LPS dispersions were infiltrated in the grapevine nodal segments, 24 h before challenge inoculation with A. vitis (5x10 2 cells per 5 µ l droplet), they prevented tumorgenesis and tissue necrosis; but, when the pathogen was inoculated at a higher concentration (5x10 5 cells per 5 CII droplet), these LS applications were active in protecting plant tissue from necrosis and did not prevent tumor induction. The potential role of LPS as candidate molecules in the protection of grapevine from A. vitis infection is discussed.