Received August 30, 2006
Accepted October 9, 2006
Environment or Development? Life-Time Net CO2 Exchange and Control of the Expression of Crassulacean Acid Metabolism in Mesembryanthemum crystallinum
Klaus Winter * and Joseph A.M. Holtum
Smithsonian Tropical Research Institute, P.O. Box 0843-03092, Balboa, Ancon, Republic of Panama
Tropical Plant Sciences, James Cook University, Townsville, Australia
* Corresponding author; email: winterk{at}si.edu.
The relative influence of plant age and environmental stress signals in triggering a shift from C3 photosynthesis to crassulacean acid metabolism (CAM) in the annual halophytic C3-CAM species Mesembryanthemum crystallinum L. was explored by continuously monitoring net CO2 exchange of whole shoots from seedling until seed set. Plants exposed to high salinity (400 mM NaCl) in hydroponic culture solution or grown in saline, droughted soil acquired between 11 and 24 % of their carbon via net dark CO2 uptake involving CAM. In contrast, plants grown under non-saline, well-watered conditions were capable of completing their life cycle by operating in the C3 mode, without ever exhibiting net CO2 uptake at night. These observations are not consistent with the widely expressed view that the induction of CAM by high salinity in Mesembryanthemum crystallinum represents an acceleration of pre-programmed developmental processes. Rather, our study demonstrates that the induction of the CAM pathway for carbon acquisition in Mesembryanthemum crystallinum is under environmental control.
