CAM-Like Traits in C3 Plants: Biochemistry and Stomatal Behavior

Abstract

Although it is generally accepted that Crassulacean Acid Metabolism (CAM) originated from C3 ancestors through a co-option process, this is rarely discussed in terms of specific characteristics and putative mechanisms behind this event. Here we discuss the available data concerning the biochemical and stomatal traits that are present in C3 plants and could have been enrolled in the CAM cycle. In summary, the biochemical machinery of CAM seems to have originated from a potential stress-driven recruitment of key non-photosynthetic enzymes of the C3 background which have entrained circadian rhythm. CAM stomatal behavior could be either a direct consequence of an upregulation of the biochemical machinery or it might require additional changes in the signaling/perception pathways controlling stomatal aperture. Considering that CAM has multiple origins, it is likely that each plant group developed it through different combinations of biochemical/stomatal changes, resulting in various degrees of plasticity of this photosynthetic pathway.