Developmental regulation of the H2O2-producing system and of a basic peroxidase isoenzyme in the Zinnia elegans lignifying xylem

The lignin content, H2O2 production and peroxidase (EC 1.11.1.7) isoenzyme patterns of the lignifying xylem of the first internode from Zinnia elegans L. stems were analyzed at three different developmental stages. The results showed that both H2O2 production and the catalytic activity of a basic peroxidase isoenzyme were strongly regulated developmental processes, which coincided temporally with the onset of lignification. H2O2 production by the lignifying xylem was stimulated by the sulfhydryl blockers, N-ethyl-maleimide (NEM) and N-pyrenyl-maleimide (NPM), and this sulfhydryl blocker-stimulated H2O2 production was inhibited by imidazole, suggesting that it was performed by an NADPH oxidase-like enzyme. These distinctive features of H2O2 production by the lignifying Z. elegans xylem open up the possibility of unambiguously identifying this enzymatic system responsible for the delivery of H2O2 to xylem peroxidases from the vast array of plasma membrane oxidoreductases present in plant cells.