We have compared metabolic effects of high salinity between plants and cell suspension cultures from the facultative halophyteMesembryanthemum crystallinum(common ice plant). This plant shows developmentally-programmed inducibility for a switch from C3-photosynthesis to CAM (Crassulacean Acid Metabolism). The metabolic switch is enhanced by environmental factors such as drought, low temperature, and, most effectively, soil salinity. CAM induction is dependent on organized leaf tissue and cannot be elicited by salt stress in suspension culture cells. In contrast, the accumulation of proline [Thomas et al. (1992)Plant Physiol. 98: 626] is induced by NaCl in cultured cells as well as in plants and must be considered a cellular response to stress. We have extended our observations to include another trait of salt- and low-temperature-stress responses in the ice plant, the accumulation of putative osmoprotective sugars and sugar alcohols. In whole plants the cyclic sugar alcohol, pinitol, accumulates to amounts that approach 1 M during stress, while in suspension cells no increase in sugar alcohols is observed. The distribution of carbon to different sugars is markedly different between cells and plants under stress. Particularly obvious is the distinction between cell types in the different composition of sugars and polyols, as exemplified by the epidermal bladder cells of ice plants. Ion contents and the content of sugars and sugar alcohols of bladder cells indicate that Na+, Cl−, pinitol and an unknown carbohydrate compound provide osmotic pressure in these cells, while organic anion concentrations are low. With the ice plant, we conclude that cells in culture mimic only partly the stress response mechanisms of intact plants and we hypothesize that communication between different tissues is required to mount a complete environmental stress respons
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