Transmembrane Electron Transport in Plasma Membrane Vesicles Loaded with an NADH-Generating System or Ascorbate.

Area of Science:

• Plant Physiology
• Biochemistry
• Membrane Transport

Background:

• Plasma membrane electron transport plays a role in nutrient uptake and cellular signaling.
• Understanding the specific electron donors and acceptors involved is crucial for elucidating these processes.

Purpose of the Study:

• To investigate the capacity of sugar beet (Beta vulgaris L.) leaf plasma membrane vesicles to perform transplasma membrane electron transport.
• To identify potential electron donors and characterize the electron transport chains involved.

Main Methods:

• Preparation of right-side-out plasma membrane vesicles from sugar beet leaves.
• Loading vesicles with either an NADH-generating system (alcohol dehydrogenase plus NAD+) or ascorbate.
• Spectrophotometric assay of electron acceptor reduction (DCIP-sulfonate, ferric citrate, ferricyanide, cytochrome c).
• Assessment of the effect of ionophores (valinomycin) on electron transport.

Main Results:

• NADH-generating system reduced 2,6-dichlorophenolindophenol-3'-sulfonate (DCIP-sulfonate), with reduction stimulated by valinomycin.
• Ascorbate supported the reduction of both ferric citrate and DCIP-sulfonate.
• Fe(3+)-chelates and cytochrome c were not reduced by the NADH system.
• Distinct substrate specificities and inhibitor sensitivities suggest separate electron transport chains for NADH and ascorbate.

Conclusions:

• Sugar beet plasma membranes possess transplasma membrane electron transport capabilities utilizing both NADH and ascorbate as electron donors.
• These two electron donors appear to feed into different electron transport pathways.
• While a minor component of total activity, transplasma membrane electron transport is likely physiologically significant for processes like iron reduction for uptake.