Evidence for a CO2 Inhibited Proton Extrusion Pump in the Stomatal Cells of Tradescantia virginiana

The effect of CO₂ on the electrical potential difference (p.d.)of the cells of the stomatal complex of Tradescantia virginianahas been investigated. Enhanced levels of CO₂ affected all thecells equally by depolarizing the p.d. On removal of the CO₂there was an immediate hyperpolarization, the degree of whichwas linearly related to the length of time the CO₂ was given.Changes in the pH of the cytoplasm and the vacuolar sap wereobserved during and after treatment with CO₂. The metabolicinhibitor 2,4-DNP eliminated the effect of CO₂ on the p.d. Theseresults wuld be explained by postulating an electrogenic protonpump in the plasmalemma which is inhibited by CO₂. Key words: CO₂, Proton pump, Stomata