The role of p-coumaric acid in oxidative and peroxidative cycle of the ionically bound peroxidase of the maize root cell wall

Cell wall ionically bound peroxidase isolated from 14-day-old maize roots (Zea mays L.) exhibited peroxidase activity, detected as the oxidation of p-coumaric, ferulic acids and coniferyl alcohol, naturally occurring phenolics of maize apoplast. Although p-coumaric acid was the least oxidised substrate with H2O2, only its phenoxy radical (derived as the oxidation product) was able to sustain NADH oxidation or linoleic acid peroxidation. Cell wall isolates generated H2O2 in the oxidative cycle of the peroxidases by using NADH as substrate and Mn2+ and p-coumaric acid as cofactors. In such a reaction, coniferyl alcohol and ferulic acid showed no catalytic effect; moreover, they inhibited the reaction when p-coumaric acid was used as cofactor. According to the result presented, only p-coumaric acid participates in both the peroxidative and oxidative cycles catalysed by the peroxidase. These results point to numerous physiological roles for p-coumaric acid catalysed peroxidase reactions through its multiple control mechanisms.