The lipopolysaccharides of the phytopathogen Xanthomonas campestris pv. campestris induce an oxidative burst reaction in cell cultures of Nicotiana tabacum

Abstract.

The lipopolysaccharides (LPS_Xcc) of the phytopathogenic bacteria Xanthomonas campestris pv. campestris (X.c.c.) were purified from an exopolysaccharide-deficient mutant strain. The isolated LPS_Xcc induced an oxidative burst reaction in cell-suspension cultures of the non-host plant tobacco (Nicotiana tabacum L.) SR1. The oxidative burst elicited by LPS_Xcc differed from that induced by yeast elicitor (YE), a cell wall preparation of baker's yeast. The LPS_Xcc-induced oxidative burst was characterised by a slow increase in H₂O₂ production and an extended decline. Both the LPS_Xcc- and YE-induced oxidative bursts were completely blocked by the NAD(P)H-oxidase inhibitor diphenylene-iodonium. When LPS_Xcc and YE were applied in combination, a synergistic effect and the establishment of refractory states in the generation of H₂O₂ were observed. The amount of cytosolic calcium was measured in transgenic tobacco cell cultures carrying the apoaequorin gene by coelenterazine-derived chemiluminescence. Whereas YE induced a calcium peak within 1 min after application, LPS_Xcc induced a long-term calcium signal without transients. To our knowledge this is the first report on the elicitation of an oxidative burst in plant cell cultures by isolated LPS of a phytopathogenic bacterium.