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

Abstract

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 cinnamyl 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.