Effect of sink size on photosynthesis and carbohydrate content of leaves of three spring wheat varieties

Effects of CO₂ on stomatal movements of Commelina communis L. were studied with plants, epidermal strips and guard cell protoplasts. With plants, the stomatal response induced by a blue light pulse was studied for different ambient CO₂ concentration ranging from CO₂-deprived air to 100 Pa in darkness or under red light. It was observed that the blue light response could be obtained not only under a red light background but also in darkness and CO₂-free air, the two responses being quite similar.
With epidermal strips, the effect of CO₂ on ferricyanide reductase activity at the guard cell plasmalemma was studied by transmission electron microscopy. In the presence of ferric ions, reduced ferricyanide gives an electron dense precipitate of Prussian Blue. In darkness and air, no precipitate was observed. In darkness and CO₂-free air as well as under light and normal air, a precipitate was found along the plasmalemma of the guard cells, indicating a ferricyanide reductase activity. With guard cell protoplasts suspended in a medium either in equilibrium with air or in a CO₂-free medium the H⁺ extrusion induced by a blue light pulse added to a red light background was measured. A low CO₂ content was obtained by adding photosynthetic algae to the suspension of guard cell protoplasts. In a CO₂-free medium the rate of H⁺ extrusion was enhanced.
The results are discussed on the basis of a possible competition for reducing power between CO₂ fixation and a putative blue light dependent redox chain located on the plasma membrane.