SALT-INDUCED CHANGES IN PROTEIN-COMPOSITION IN LIGHT-GROWN CALLUS OF MESEMBRYANTHEMURN CRYSTALLINUM

The halophyte Mesembryanthemum crystallinum (ice plant) has been sugge sted as a model for salt-tolerance in higher plants. To investigate sa lt-induced changes in polypeptide patterns at the cellular level, a li ght-grown callus of M. crystallinum with substantial chlorophyll conte nt, was established and the effect of NaCl on the composition of pheno l-extracted protein was examined by SDS-and 2D-polyacrylamide gel elec trophoresis (PAGE). SDS-PAGE showed the accumulation of five polypepti des with estimated molecular masses of 40, 34, 32, 29 and 14 kDa was e nhanced by the addition of 200 mM NaCl to the culture media. The addit ion of ABA (10 mu M) or mannitol (400 mM) did not elicit the same degr ee of accumulation of these salt-specific proteins. These polypeptides were classified into two groups according to their course of inductio n: early responsive (40, 34, 29 kDa) and late-responsive (32, 14 kDa) proteins. In addition, two polypeptides (20, 18 kDa) were transiently accumulated during salt treatment. Further separation of soluble prote ins by 2-D gel electrophoresis, either isoelectric focusing (IEF) or n on-equilibrium pH-gradient electrophoresis (NEPHGE) followed by SDS-PA GE, showed more alterations in accumulation of polypeptides by NaCl th an 1-D gel electrophoresis. Overall, levels of more than 30% of basic polypeptides, detected by NEPHGE/SDS-PAGE, were altered by 200 mM NaCl treatment, while only 10% of neutral and acidic polypeptides, detecte d by IEF/SDS-PAGE, were changed. The enhanced expression of these prot eins by salt in cultured cells is most likely related to the cellular responses to salinity, and not to the mechanism of CAM induction in th is facultative halophyte.