Induction of peroxidase by Fe2+ in detached rice leaves

Abstract

Peroxidase (POD) activity was significantly stimulated in detached rice leaves by Fe2+. By electric focusing with thin-layer scanning, three new bands were identified in Fe2+-treated leaves, and the activities of other isozymes were also drastically increased, of which a band with a pI of ca. 9.8 was enhanced from trace amount (invisible) in the control to a large band in the Fe2+-treated leaves. How Fe2+ induced POD activity was investigated. Cycloheximide completely blocked the stimulation of POD activity by Fe2+, but actinomycin D could not inhibit it effectively, indicating that the stimulated activity resulted from inducing de novo biosynthesis of the enzyme at translational level rather than at transcriptional level. When same molar concentration of H2O2 as Fe2+ and sublethal and lethal concentrations of paraquat were introduced to the rice leaves, no significant stimulation of POD activity was observed compared with Fe2+-induced activity, and scavengers of free radicals still could not inhibit the induction of POD by Fe2+. Several chemicals such as EGTA, LaCl3, CPZ, verapamil, which were known to interfere with the action of calcium/calmodulin, were not able to retard POD induction by Fe2+. From these results it appears that the process of Fe2+-induced POD may not be mediated by free radicals or calcium/calmodulin action.