Determination of H+-ATPase Activity in Arabidopsis Guard Cell Protoplasts through H+-pumping Measurement and H+-ATPase Quantification

The opening of stomata in plants in response to blue light is driven by the plasma membrane H+-ATPase in guard cells. To evaluate the activation of the H+-ATPase in vivo, we can use H+-pumping by guard cells in response to blue light and fusicoccin. To do this, it is required to prepare a large amount of guard cell protoplasts and measure H+-pumping in the protoplasts. It is also necessary to determine the protein amount of H+-ATPase. In this protocol, we describe the procedures required for these preparations and measurements.