Effects of various inhibitors on in vivo reduction by Plantago lanceolata L. roots

Abstract

Roots of Plantago lanceolata L. showed an iron stress-induced increase in the rates of electron transport to the extracytoplasmatic acceptors FeEDTA and ferricyanide. No significant changes in the reduction of hexachloroiridate were observed with respect to the iron-nutritional status of the plants. The reduction activity of iron-deficient roots was inhibited by the translation inhibitor cycloheximide (CHM) and the amino acid analog p-fluorophenylalanine (FPA). In both cases, the reduction of FeEDTA and ferricyanide was affected to a different extent, providing evidence for enzyme heterogeneity. Resupply of FeEDTA to iron-deficient plants resulted in a qualitatively similar pattern of decrease in FeEDTA and ferricyanide reduction rates, although a longer time period was required for the decrease of the redox activity by iron resupply compared to the effect of inhibitors of protein synthesis.

Inhibitors of the plasma membrane (PM)-bound H⁺-ATPase decreased the FeEDTA reduction activity of iron-deficient plants. In contrast, the reduction of ferricyanide and hexachloroiridate was not inhibited. Oxidation of ferrocyanide occurs in both iron-deficient and iron-sufficient plants at comparable rates. The reaction was decreased by the H⁺-ATPase inhibitor orthovanadate.

The results are interpreted in terms of a simultaneous action of distinct redox systems in iron-deficient roots. The role of proton extrusion in the regulation of iron stress-induced electron transport is discussed.