DistinctCellular ndOrganismicResponses to Salt Stress

We have compared rnetabolic effects of high salinity between plants and cell suspension cultures frorn the facultative halophyte Mlesembt:yanthemum castallinum (common ice plant). This plant shows developrnentally-programmed inducibility for a switch from C3-photosynthesis to CAM (Crassulacean Acid Metabolism). The metabolic switch is enhanced by environrnental 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 RhysioL 98: 6as] 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 saltand 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 be ween cells and plants under stress. Particularly obvious is the distinction between cell types in the different composition of sugars and