[Effect of verapamil on dark acidification in Bryophyllum tubiflorum]

Excised phyllodia of Bryophyllum tubiflorum standing in phosphate buffer to which verapamil is added undergo specific alterations in their gaseous exchange reactions as well as in the amount of malate accumulated in the dark period. Inhibition of accumulation of malate increases with increasing concentrations of verapamil. The effects caused by verapamil are reversible. During the dark period plasmalemma under the chloroplasts detaches itself from the cell wall, forming a vacuole-like space between plasmalemma and cell wall which disappears in the following light period. In the presence of verapamil this formation of a vacuole-like structure does not occur.Verapamil is thought to influence the permeability of plasma membranes, thus decreasing the capacity of the vacuole to accumulate malate in the dark. Our interpretation of the results seems to demonstrate that the occurence of crassulacean acid metabolism is dependent on the integrity of the plasma membranes. Further details are discussed.