Salicylhydroxamic acid enhances the NADH-oxidase activity of peroxidase in pea mitochondrial and chloroplast suspensions

Salicylhydroxamic acid (SHAM), an alternative oxidase inhibitor of plant mitochondria, enhances the NADH-oxidase activity in mitochondrial and chloroplast suspensions obtained from pea roots or leaves, respectively. This reaction is inhibited by the washing of mitochondria or chloroplasts and is observed in supernatants after the removal of the organelles by centrifugation. The reaction is sensitive to CN– and to antioxidant propyl gallate. The NADH oxidation is also enhanced by 2,4-dichlorophenol or phenol, but not salicylic acid. The acceleration of NADH oxidation by phenolic compounds is observed with presence of commercial horseradish peroxidase and is connected with the involvement of these compounds in NADH-dependent peroxidase reaction. SHAM and 2,4-dichlorophenol significantly enhance the destruction of nuclei in guard cells of pea leaf epidermis caused by the generation of reactive oxygen species during the oxidation of exogenous NADH by apoplastic peroxidase.