Hydrogen peroxide generation and lignification by peroxidases from Acacia eburnea infected with Ravenelia esculenta

Ravenelia esculenta Naras. and Thirum. is a rust fungus which infects Acacia eburnea Willd. producing hypertrophy in the infected organs. We analysed the changes in the reaction patterns of peroxidase from the tissues at progressive disease stages. Peroxidases (POX) from the tissues were analysed for oxidation of reduced nicotinamine adenine dinucleotide (NADH), NADH-dependent hydrogen peroxide (H2O2) generation and polymerization of cin-namyl alcohol, a lignin precursor in plants. The effect of cofactors like Mn2+ and dichlorophenol (DCP) was also studied. Effect of externally added H2O2 on NADH oxidation and cinnamyl alcohol polymerization was analyzed. NADH oxidation and H2O2 generation are accelerated by supplement of cofactors. The cofactor requirements of the two reactions are different. The amount of H2O2 generated varies with disease stages, but the rate of NADH oxidation is comparable. Externally added H2O2 has an accelerating effect on NADH oxidation. Cinnamyl alcohol polymerizing activity of POX increased with disease progression and was strongly inhibited by H2O2. Stimulation of these reactions by cofactors has a physiological significance in terms of susceptibility of the host.