Specificity of the Electron Donor for Transmembrane Redox Systems in Bean (Phaseolus vulgaris L.) Roots

Summary Plasma membrane (PM) vesicles from roots of french bean ( Phaseolus vulgaris L. cv. Prelude) grown in the presence (iron-sufficient) and absence (iron-deficient) of iron were isolated by aquaeous two-phase partitioning. PM-bound redox reactions were investigated using NADH and NADPH as electron donors, and ferricyanide and Fe 3+ -EDTA as electron acceptors. In PM preparations from iron-deficient plants, the activity of NADH: Fe 3+ -EDTA reductase was enhanced by 157%, whereas the NADPH-dependent activity was less affected by the iron nutritional status. NADH-dependent redox activity was stimulated by the addition of detergent (0.02% (w/v) Triton X 100) by about 2-fold for both electron acceptors. Transmembrane redox activity with NADPH as a source for electrons occurred only with ferricyanide but not with Fe 3+ -EDTA as an electron acceptor. The results provide evidence for multiple electron transport activities on PM from roots of Phaseolus vulgaris L. and also suggest that NADPH is not involved in extracellular ferric chelate reduction.