Environment or Development? Lifetime Net CO2 Exchange and Control of the Expression of Crassulacean Acid Metabolism inMesembryanthemum crystallinum 

Abstract

(J.A.M.H.) The relative influence of plant age and environmental stress signals in triggering a shift from C 3 photosynthesis to Crassulacean acid metabolism (CAM) in the annual halophytic C 3 -CAM species Mesembryanthemum crystallinum was explored by continuously monitoring net CO 2 exchange of whole shoots from the seedling stage 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 CO 2 uptake involving CAM. In contrast, plants grown under nonsaline, well-watered conditions were capable of completing their life cycle by operating in the C 3 mode without ever exhibiting net CO 2 uptake at night. These observations are not consistent with the widely expressed view that the induction of CAM by high salinity in M. crystallinum represents an acceleration of preprogrammed developmental processes. Rather, our study demonstrates that the induction of the CAM pathway for carbon acquisition in M. crystallinum is under environmental control.

Evolution along the crassulacean acid metabolism continuum

“…The expression of CAM in such C 3 -CAM species varies dynamically with experimentally manipulated conditions, such as photoperiod (Brulfert and Queiroz 1982), water status, light, temperature, nutritional status, salinity, anoxia, or atmospheric CO 2 concentration (Winter 1985;Lüttge 1987;Griffiths 1988;Roberts et al 1997). The common ice plant, Mesembryanthemum crystallinum L., a member of the Aizoaceae, is a well studied example of inducible CAM under strict environmental control (Winter 1985;Winter and Holtum 2007;Cushman et al 2008aCushman et al , 2008b.…”

Pathogen-induced changes in malate content and NADP-dependent malic enzyme activity in C3 or CAM performing Mesembryanthemum crystallinum L. plants

“…Mesembryanthemum crystallinum L. (ice plant) is an annual halophytic plant that in its natural habitat shows seasonal shift from C 3 type of photosynthesis to Crassulacean Acid Metabolism (CAM) (Winter and Holtum 2007) During CAM cycle, malic acid is accumulated in the vacuole as a central intermediary in the process of carbon assimilation during the dark and then it is metabolized in the following light period (Cheffings et al 1997). One of the important malate metabolizing enzyme is NADP-malic enzyme (NADP-ME, L-malate: NADP oxidoreductase [oxaloacetate decarboxylating], EC 1.1.1.40) which produces after malate decarboxylation apart from pyruvate also CO 2 to be used in carbon fixation by ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco).…”

Crassulacean Acid Metabolism May Alleviate Production of Reactive Oxygen Species in a Facultative CAM Plant, the Common Ice PlantMesembryanthemum crystallinumL.

“…This halophytic species shift its photosynthetic carbon fixation pathway from C 3 to CAM under salt-stress and other abiotic stress factors (Winter and Holtum, 2007;Cushman et al, 2008b). Recently, the function of ROS as key signals for up-regulating the major genes and proteins required for the operation of CAM has been investigated in the common ice plant (Borland et al, 2006;Ślesak et al, 2008).…”