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The contention that nocturnal malic-acid accumulation in the vacuoles of crassulacean acid metabolism (CAM) plants is an energy-dependent process was confirmed by experiments on excised phyllodia of Kalanchoë tubiflora with the inhibitors 2,4-dinitrophenol (DNP), m-chlorocarbonylcyanide phenylhydrazone (CCCP) and diethylstilbestrol (DES). Levels of ATP, ADP and Pi were also measured in bulk-tissue extracts of phyllodia during the normal CAM rhythm. ATP levels increased during the dark period and decreased during the light period, whereas ADP and Pi levels did not show any significant changes. In some plants the ATP levels started to decrease before the end of the dark period. It is suggested that the changes in ATP levels are a reflection of the changing flux through glycolysis towards malate in the dark period. The results were used to estimate the free energy available from ATP hydrolysis (ΔGATP), which was compared with the H+-electrochemical potential difference (ΔμH+) across the tonoplast. This permitted consideration of the stoichiometry of the H+-ATPase that is postulated to be responsible for malic-acid accumulation in the vacuole. © 1982.

Original publication




Journal article


Plant Science Letters

Publication Date





13 - 21