Responses of corn root protoplasts to exogenous reduced nicotinamide adenine dinucleotide: Oxygen consumption, ion uptake, and membrane potential

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Abstract
Addition of 1.5 mM NADH tripled the O 2 consumption in corn root protoplasts. The stimulation was temperature and pH dependent, specific to NADH, and accompanied by a 2- to 3-fold increase in K + and P i uptake into protoplasts. The increase in ion uptake was not due to the accumulation of NADH into protoplasts. The effect of exogenous NADH on O 2 consumption and ion uptake was also evident in corn root segments but to a lesser extent. A 20-mV hyperpolarization of protoplast membrane potential occurred on addition of NADH and was abolished by the uncoupler carbonyl cyanide p -trifluoromethoxyphenylhydrazone. Increases in cell volume of 30% and 40% were detected in response to NADH/H + and NADH/H + /K + , respectively. The data are discussed in terms of a transmembrane redox reaction and the possibility that some part of the energy-linked ion transport may be driven by a NADH → O 2 electron-transport system in the plasmalemma.

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