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The relationship between the expression of crassulacean acid metabolism (CAM) and the electrophoretic transport of malate 2− into isolated tonoplast vesicles was investigated for leaves of three orchid species. The thick-leaved orchid species Epidendrum ibaguense exhibited a diel rhythm in both cell-sap titratable acidity and cell-sap malate concentration, characteristic of CAM, whereas the thin-leaved C3 species Coelogyne cristata and Coelogyne fimbriata did not. Tonoplast vesicles were prepared from leaf mesophyll homogenates of these three species by a combination of differential and sucrose density gradient centrifugation and were used to study the effects of anions on ATP- and PPi-dependent H+ transport. In tonoplast vesicles from C. cristata and C. fimbriata, chloride stimulated H+ transport (measured as quinacrine-fluorescence quenching) more effectively than malate. But in tonoplast vesicles from E. ibaguense, malate was as effective as chloride in stimulating H+ transport, reflecting the greater fluxes of malate across the tonoplast in this species. A number of other 1,4-dicarboxylates stimulated H+ transport in tonoplast vesicles from E. ibaguense, their order of effectiveness being fumarate > oxalacetate ≥ malate ≥ 2-mercaptosuccinate ≥ succinate > tartrate. The stimulation of H+ transport was not stereospecific, but required the 1,4-dicarboxylate to adopt the trans-carboxyl geometric configuration. Neither shorter-chain (oxalate, malonate) nor longer-chain (glutarate, adipate) dicarboxylates supported H+ transport. The specificity of organic-acid anion transport at the tonoplast of E. ibaguense was similar to that of Kalanchoë daigremontiana and thus appears to be a characteristic of the malate-influx system in CAM plants. © 1992, Gustav Fischer Verlag, Stuttgart. All rights reserved.

Original publication




Journal article


Journal of Plant Physiology

Publication Date





533 - 538