Photoinactivation of Superoxide Synthases of the Plasma Membrane from Rose (Rosa damascena Mill.) Cells

Abstract

AbstractThe UVC‐induced synthesis of hydrogen peroxide (H2O2) by cultured rose (Rosa damascena Mill, cv Gloire de Guilan) cells is inhibited by broad‐band radiation containing UVA, UVB and blue wavelengths. In order to understand the basis for this inhibition, we tested the effects of broad‐band radiation and of monochromatic radiation on NADH‐ and NADPH‐dependent O2‐ synthases of purified plasma membranes. Both activities were inhibited by wavelengths from 254 to 435 nm, with the NADPH‐dependent enzyme being more sensitive than the NADH‐dependent enzyme. Incubation in the presence of flavin adenine dinucleotide had a small but significant ameliorative effect on the inhibition of the O2‐ synthase activities of plasma membranes by 300 nm radiation. The data support the hypothesis that the NADH‐ and NADPH‐dependent activities are catalyzed by different enzymes. The NADPH‐dependent activity, but not the NADH‐dependent activity, was sufficiently sensitive to account for the inhibition of H2O2 synthesis by the broad‐band radiation.