Proton translocation in corn coleoptiles: ATPase or redox chain?

Area of Science:

• Plant Physiology
• Biochemistry

Background:

• Proton (H+) efflux is crucial for plant cell function.
• Oxygen (O2) levels can impact cellular metabolic processes and ion transport.

Purpose of the Study:

• Investigate the oxygen dependence of net proton efflux in maize coleoptiles.
• Characterize the relationship between oxygen concentration and proton transport.

Main Methods:

• Measurements of net proton efflux in young and old maize coleoptiles under varying oxygen concentrations.
• Treatment with fusicoccin to assess proton efflux.
• Analysis of CO2 production and proton efflux ratios.

Main Results:

• Net proton efflux decreased significantly in young coleoptiles below 100 μM O2, and in old coleoptiles below 10 μM O2.
• Fusicoccin treatment normalized proton efflux in old coleoptiles.
• Proton influx observed at low O2 (10 μM) if H+ concentration was below pH 6.5.
• A potential increase in efflux at very low O2 due to organic acid leaching, without significant CO2 change.

Conclusions:

• Maize coleoptile proton efflux is sensitive to oxygen concentration, with differential responses based on tissue age.
• Multiple systems likely mediate proton translocation across the plasmalemma.
• One proton transport system exhibits high sensitivity to low oxygen, correlating with the alternative oxidase pathway's Km.