A possible mechanism for the apocynin-induced nitric oxide accumulation in plants

Nitric oxide (NO) is a small, ubiquitous bioactive molecule, postulated as a broad spectrum anti-stress compound. The NADPH oxidase inhibitor apocynin induces the accumulation of endogenous NO in leaves of maize seedlings through a nitric oxide synthase (NOS)-like activity, and confers an augmented tolerance to UV-B-induced oxidative damage. Here we propose a mechanism for the apocynin-induced NO increase in plants. NOS catalyzes the oxidation of arginine to citrulline and NO. It is suggested that apocynin inhibit arginase, the enzyme that hydrolyzes L-arginine to urea and L-ornithine, increasing the arginine availability for arginine-dependent NO synthesis. Superoxide (O2-) is a strong NO scavenger due to its high reactivity with NO to give peroxynitrite (ONOO-). Superoxide is mainly produced by plant NADPH oxidase (pNOX). Inhibition of pNOX by apocynin at relatively high NO concentration, could reduces the formation of O2- and ONOO-, increasing the availability of a huge amount of NO. We consider apocynin as a very attractive compound for studying NO-regulated processes in plants since it can replace the use of NO donors and overcome the subsequent technical problems. Fil: Tossi, Vanesa Eleonora. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Biológicas. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Biológicas; Argentina Fil: Lamattina, Lorenzo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Biológicas. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Biológicas; Argentina