A STUDY OF STOMATAL MECHANICS USING THE CELL PRESSURE PROBE

The relationship between stomatal aperture (a) and guard cell pressure (P-g) was measured directly in four different species (Vicia faba, Tr adescantia virginiana, Ginkgo biloba and Nephrolepis exaltata) using a special cell pressure probe technique, The effect of epidermal turgor (P-ep) on this relationship was also measured in T. virginiana. The r elationship was sigmoidal for V. faba and T. virginiana, but entirely convex for G, biloba and N. exaltata, Epidermal turgor,vas found to ha ve a pronounced closing effect on stomata of T. virginiana. Maximum ap erture with full epidermal turgor (0.92 MPa) was about half that with zero epidermal turgor, Also, with full epidermal turgor stomata of I: virginiana did not begin to open until P-g was more than 1.25 MPa. The se characteristics were used to develop an expression for a as a funct ion of P-g and P-ep. Results for the different species are compared an d discussed in terms of possible advantages and limitations of water e conomy.