A surrogate measure of stomatal aperture

Abstract

It is proposed that a measurement of the peristomatal groove distance (PGD) of guard cells on surface impressions of leaf epidermis can act as a surrogate measure of stomatal aperture. To test this idea, investigations were carried out on two species, one in which it is possible to make direct measurements of pore width with relative ease (Commelina communis L.) and one whose stomata are so small that this is difficult (Phaseolus vulgaris L.). Leaf water vapour conductance measurements were first taken with a porometer, then, without delay, a silicone rubber impression of the leaf was made of the area directly under the porometer cup. From a positive replica of this impression, stomatal aperture, PGD and pore length were measured. The correlations between stomatal aperture and PGD and between PGD and stomatal conductance were positive and highly significant. Because a causal relationship between stomatal aperture and PGD is expected, linear regression was used to obtain equations for converting PGD measurements into estimates of stomatal aperture. These account for 91.7% of the variation of aperture in the case of C. communis and 70.7% in P. vulgaris, suggesting that PGD measurements have potential as an alternative measure of pore width in cases where direct measurements would be both difficult and subject to excessive measurement error or bias.