A Method for Separating Cuticular and Stomatal Components of Gas Exchange by Amphistomatous Leaves

Abstract

The apparent cuticular component of transpiration of stomata bearing leaf epidermis was estimated by restricting stomatal diffusion by mass flow of air in the opposite direction. This was achieved by applying an air pressure gradient across the amphistomatous leaf. Some assumptions of the previously suggested method (Šantrůcek and Slavík, 1990) were experimentally verified using maize leaves. The technique makes possible a quantitative estimation of cuticular water loss including that of the external peristomatal (i.e. vapour not passing through the pores) and the respective conductance when the stomata are partially open. In addition to the fact that the cuticular portion of the total leaf vapour loss (i.e. relative cuticular transpiration) depends on stomatal opening, even the absolute value of apparent cuticular transpiration was (1) increased by lower vapour pressure deficit and (2) decreased with closing stomata. These changes, induced by variations in a vapour pressure deficit of 2.45±0.35 kPa, ranged between 0.66±0.14μg cm −2 s−1. The absolute value of apparent cuticular transpiration changed on average by a factor of 2.3 due to stomata opening or closing which was induced by turning the light on or by exogenous ABA application. Possible interference by residual vapour diffusing through the stomatal pore was evaluated by the model application. An attempt was also made to assess the cuticular component of CO2-uptake rate. Experimental results are discussed in context with the feedforward response of stomata to air humidity.