The effects of salinity, crassulacean acid metabolism and plant age on the carbon isotope composition of Mesembryanthemum crystallinum L., a halophytic C3-CAM species

Abstract

The carbon isotope composition of the halophyte Mesembryanthemum crystallinum L. (Aizoaceae) changes when plants are exposed to environmental stress and when they shift from C 3 to crassulacean acid metabolism (CAM). We examined the coupling between carbon isotope composition and photosynthetic pathway by subjecting plants of different ages to salinity and humidity treatments. Whole shoot d 13 C values became less negative in plants that were exposed to 400 mM NaCl in the hydroponic solution. The isotopic change had two components: a direct NaCl effect that was greatest in plants still operating in the C 3 mode and decreased proportionally with increasing levels of dark fixation, and a second component related to the degree of CAM expression. Ignoring the presumably diffusionrelated NaCl effect on carbon isotope ratios results in an overestimation of nocturnal CO 2 gain in comparison to an isotope versus nocturnal CO 2 gain calibration established previously for C 3 and CAM species grown under well-watered conditions. It is widely taken for granted that the shift to CAM in M. crystallinum is partially under developmental control and that CAM is inevitably expressed in mature plants. Plants, cultivated under non-saline conditions and high relative humidity (RH) for up to 63 days, maintained diel CO 2 gas-exchange patterns and d 13 C values typical of C 3 plants. However, a weak CAM gas-exchange pattern and an increase in d 13 C value were observed in non-salt-treated plants grown at reduced RH. These observations are consistent with environmental control rather than developmental control of the induction of CAM in mature M. crystallinum under non-saline conditions.

Stable carbon and nitrogen isotope compositions change with leaf age in two mangrove ferns

“…Salinity increases Na concentration in the leaf, which has been shown to be associated with physiological drought inducing stomatal closure and low c i /c a ratios and thus leading to 13 C enrichment of the leaf (Farquhar et al, 1989;Handley et al, 1997;Pakniyat et al, 1997;Poss et al, 2000;Winter and Holtum, 2005). In both Acrostichum species, however, Na accumulated with leaf age and concentration was highest in the oldest leaves but these were depleted in 13 C (Table 1).…”

Responses of chlorophyll fluorescence parameters of the facultative halophyte and C3–CAM intermediate species Mesembryanthemum crystallinum to salinity and high irradiance stress

“…Measurements of chlorophyll fluorescence, like effective quantum yield of PSII (DF/F m 0 ), make it possible to evaluate the plant's photosynthetic performance and the extent of its tolerance to environmental stress (Maxwell and Johnson, 2000). Effects of environmental stress factors have frequently been studied in M. crystallinum individually, as again recently salt stress alone (Barker et al, 2004), where the induction of CAM reduced the adverse effect of salt (Winter and Holtum, 2005). Conversely, there are few reports in the literature showing the effects of a combination of high irradiance with salinity on stimulation of CAM induction (Broetto et al, 2002).…”

Oxidative stress and fluctuations of free and conjugated polyamines in the halophyte Mesembryanthemum crystallinum L. under NaCl salinity

“…The halophytic C 3 -CAM species Mesembryanthemum crystallinum L. (the common ice plant) was used as a model system (Adams et al 1998;Winter and Holtum 2005).The aim of this investigation was to study: (1) the ability M. crystallinum plants to accumulate free and conjugated forms of PAs in leaves and roots in response to NaCl salinity; and (2) the prooxidant properties of free PAs and H 2 O 2 generation during accumulation of conjugated PAs in the plant cell.…”