THE MECHANISM OF STOMATAL MOVEMENT

Abstract

Ketellapper, H. J. (California Inst. Tech., Pasadena.) The mechanism of stomatal movement. Amer. Jour. Bot. 46(3) : 225‐231. IIlus. 1959.—A review of the pertinent literature reveals that fairly exact knowledge is available about the effects of light, CO2, and water content of the leaf on stomatal movement. Two distinct types of light action can be distinguished: an indirect effect, mediated through photosynthesis and the resulting lower CO2 concentration within the leaf, and a direct effect which occurs even when the intercellular spaces are washed out with CO2‐free air. The CO2 concentration occupies a very central position in the regulation of stomatal movement. The action of CO2 and light will be influenced, or even counteracted, by the value of the water deficit in the leaf. A large number of changes in the guard cells, accompanying stomatal movement, has been described in the literature and some of these have been discussed in the present review: for example, the changes in osmotic value, in starch content, and in permeability. These observations led to the formulation of the classical theories of stomatal movement. It has been concluded that the classical theories are not adequate to explain stomatal movement. At present one can choose between 2 alternatives: an osmotic theory incorporating the pathways of the classical theories and bringing these together in one general scheme hinging on the sugar‐starch conversion, or else a theory incorporating non‐osmotic processes for the removal of water or osmotic active material. These alternatives have been discussed in some detail. It has been concluded that more experimental evidence is required before a valid theory of stomatal movement can be brought forward.