Relationship between cam and succulence in some species of vitaceae and piperaceae

Crassulacean acid metabolism (CAM) and succulence were compared in two species of Peperomia (Piperaceae) and six species of Cissus and Cyphostenz ma (Vitaceae). The species include thin-leaved plants, leaf succulents, and stem succulents. Succulence at the organ or the cellular level mesophylll succulence [Sm]) does not appear to be causally related to CAM. Peperomia, with high Sm, shows low CAM activity, while Cypizostenima, with relatively low Sm, exhibits very high CAM activity. Overnight accumulation of malic acid as high as 332 µeq/g fresh weight was measured in the nonsucculent, thin leaves of Cissus sp., while only 50 µeq of malic acid per gram fresh weight accumulated in the succulent, photosynthesizing stem of the same plant. In the thin-leaved species of Cissus, CAM does not appear to be related to drought adaptation. Succulence in the CAM species Cissus may be a new acquisition that has allowed the genus to spread from the wet tropics to arid environments. We suggest that CAM and succulence are often associated in drought-adapted plants because both characters have been selected for in arid environments