A New Porometer Based upon the Electrical Current Produced by Guard Cells

Stomatal guard cells extrude protons when the stomata open. This gives rise to an electrical current which is proportional to the degree of stomatal opening. An instrument has been developed to measure this leaf surface current which is, in effect, a new type of porometer. The performance of the new porometer has been compared with that of a commercially available diffusion porometer and a close relationship between leaf surface current and stomatal conductance was observed for all the species investigated. It is concluded that the instrument has several advantages over the diffusion porometer, in particular, its small size and simplicity of operation, making it especially suitable for use in the field.