Proton and malate fluxes in cells of Bryophyllum daigremontianum leaf slices in relation to potential osmotic pressure of the medium

Abstract

Summary Leaf slices obtained from the CAM plant Bryophyllum daigremontianum at the end of the dark phase were used to study proton und malate fluxes. Increasing potential osmotic pressure (π*) of the medium decreases loss of H + and malate from the leaf cells to the medium and increases the amounts of H+ and malate retained in the cells. As compared to the initial H + and malic acid levels, after the efflux experiments a certain amount of H+ and malate is not accounted for by efflux and retainment in the tissue. This amount is thought to be due to metabolic utilization of malic acid, it is smaller in the dark than in the light, and it is not clearly correlated to π * of the medium. Changes in potential osmotic pressure of extracts (Δπ * ) of the leaf slices are highly correlated to changes in malate content of the extracts. Malic acid accounts for about 55% of Δπ * of the extracts. It is suggested that net efflux of malic acid from the vacuoles of B. daigremontianum depends on turgor of the cells and that this mechanism plays a role in regulation of crassulacean acid metabolism (CAM) in vivo .