Variable Photosynthetic Metabolism in Leaves and Stems of Cissus quadrangularis L.

By measuring titratable acidity, gas exchange parameters, mesophyll succulence, and (13)C/(12)C ratios, we have shown that Cissus quadrangularis L. has C(3)-like leaves and stems with Crassulacean acid metabolism (CAM). In addition, the nonsucculent leaves show the diurnal fluctuations in organic acids termed recycling despite the fact that all CO(2) uptake and stomatal opening occurs during the day. Young succulent stems have more C(3) photosynthesis than older stems, but both have characteristics of CAM. The genus Cissus will be a fruitful group to study the physiology, ecology, and evolution of C(3) and CAM since species occur that exhibit characteristics of both photosynthetic pathways.