Stomatal patchiness of grapevine leaves .1. Estimation of non-uniform stomatal apertures by a new infiltration technique

Abstract

Non-uniform stomatal behaviour of vine leaves is associated with a heterobaric leaf structure. A microscopical analysis of cross sections of glasshouse- and in vitro-grown Silvaner leaves indicates single airspaces which are pneumatically isolated by vessels, bundle sheath extensions and the abaxial and adaxial epidermes. A pressure-regulated infiltration technique is presented by which the infiltration process and the infiltration capacity (percentage of the surface area of infiltrated airspaces) can be estimated and photographed using a light microscope. The average surface area of airspaces ranged from 0.10 mm² (Regent) to 0.14 mm² (Silvaner), the number of stomata per airspace from 35 (Regent) to 42 (Silvaner). The infiltration capacity of turgid leaves is shown to be negatively correlated with the surface tension of the infiltrated liquid and positively with stomatal conductance and with infiltration pressure, except for very low stomatal conductances (e.g. 12 mmol H₂O m^-2 s^-1). The latter relationship follows a saturation curve confirming heterogenous stomatal aperture over the leaf blade. The distribution of stomatal apertures does not appear to be bimodal but to follow a bell-shaped curve. There is some evidence for the stomata of an airspace to behave heterogenously as well.