Regulation of Electrogenic Pumping in Barley by pH and ATP

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Abstract
The relationship of the electrogenic pump to the ATP concentration in barley roots was examined. Excision, salt accumulation and changes in temperature produced changes in the ATP concentration which did not correlate with changes in membrane potential (ψm). Illumination of seedlings prior to excision of the root elevated the ATP level and caused ψm to hyperpolarize. Metabolic inhibition by sodium azide resulted in a fall in ATP concentration and membrane depolarization. With treatment in azide for longer than 10 min there was a linear relationship between ATP concentration and ψm. Time-courses of the effects of azide and carbon monoxide showed that this relationship did not hold at short treatment times because the ATP concentration fell more rapidly than the decay of ψm. Application of butyrate or fusicoccin produced little or no change in the ATP concentration but both caused significant changes in ψm. The effects on ψm of butyrate, fusicoccin, external pH and metabolic inhibitors were considered to be consistent with regulation of electrogenic pumping by cytoplasmic pH.