Connecting Environmental Stimuli and Crassulacean Acid Metabolism Expression: Phytohormones and Other Signaling Molecules

Abstract

Plasticity in Crassulacean acid metabolism (CAM) expression has long been recognized to occur both within and between species, and a range of environmental cues is implicated in both long- and short-term regulation of CAM operation. Important insights into the signal transduction chains between environmental stimuli and CAM expression are now available, and our discussion is focused on these recent findings. The role of plant hormones, nitric oxide, reactive oxygen species, intracellular calcium, protein phosphatases, and kinases in the signaling cascades leading to changes in CAM expression in response to water availability, salinity, light intensity, and photo- and thermoperiod is discussed. Whenever possible, differences and similarities among the signaling elements controlling CAM expression in distinct CAM plant models are highlighted. Conceivably, many other aspects of the signaling processes leading to CAM expression are still to be elucidated; therefore, some potential strategies to improve our knowledge in this field are briefly discussed.