RICE CATIONIC PEROXIDASE ACCUMULATES IN XYLEM VESSELS DURING INCOMPATIBLE INTERACTIONS WITH XANTHOMONAS-ORYZAE PV ORYZAE

A cationic peroxidase, PO-C1 (molecular mass 42 kD, isoelectric point 8.6), which is induced in incompatible interactions between the vascul ar pathogen Xanthomonas oryzae pv oryzae and rice (Oryza sativa L.), w as purified. Amino acid sequences from chemically cleaved fragments of PO-C1 exhibited a high percentage of identity with deduced sequences of peroxidases from rice, barley, and wheat. Polyclonal antibodies wer e raised to an 11-amino acid oligopeptide (POC1a) that was derived fro m a domain where the sequence of the cationic peroxidase diverged from other known peroxidases. The anti-POC1a antibodies reacted only with a protein of the same mobility as PO-C1 in extracellular and guttation fluids from plants undergoing incompatible responses collected at 24 h after infection. In the compatible responses, the antibodies did not detect PO-C1 until 48 h after infection. Immunoelectron microscopy wa s used to demonstrate that PO-C1 accumulated within the apoplast of me sophyll cells and within the cell walls and vessel lumen of xylem elem ents of plants undergoing incompatible interactions.