Immunohistochemical studies on localization of the extracellular polysaccharide produced by Xanthomonas oryzae pv. oryzae in infected rice leaves

An antibody reacting with extracellular polysaccharide from Xanthomonas oryzae pv. oryzae was used to detect the extracellular polysaccharide in infected leaf tissues of rice plants (Oryzae sativa cv. IR24) by immunofluorescence and immunoelectron microscopy. Using extracellular polysaccharide as a hapten and bovine serum albumin as a carrier, an extracellular polysaccharide – bovine serum albumin conjugate was prepared. After a rabbit was immunized against the conjugate, an antibody reacting with extracellular polysaccharide from X. oryzae pv. oryzae was isolated and purified. Using ELISA, the antibody was capable of detecting extracellular polysaccharide at concentrations above 0.1 μg/mL. Immunofluorescent antibody staining of infected rice leaves showed that extracellular polysaccharide produced by X. oryzae pv. oryzae was distributed in both xylem vessels and transverse veins but not in either sieve tubes or mesophyll tissues. This demonstrates that the distribution of extracellular polysaccharide coincided with that of bacteria in the infected leaf tissues. Immunoelectron microscopy showed that localization of extracellular polysaccharide was restricted to the area close to bacterial cells. The amount of extracellular polysaccharide may not be enough to plug xylem vessels of rice leaves infected with X. oryzae pv. oryzae.Key words: anti extracellular polysaccharide antibody, Xanthomonas oryzae pv. oryzae, immunofluorescent microscopy, immunoelectron microscopy, rice plant.