IN-VITRO SALT TOLERANCE OF CELL-WALL ENZYMES FROM HALOPHYTES AND GLYCOPHYTES

The halophyte Suaeda maritima grows optimally in high concentrations ( 40-60% seawater) of salt, In these conditions the concentration of sal t in the apoplast of the leaves is at least 500 mM, a concentration wh ich severely inhibits the activity of cytoplasmic enzymes of both glyc ophytes and halophytes, The in vitro salt tolerance of a number of cel l wall enzymes was assayed in the presence of a range of concentration s of NaCl. There was no significant inhibition of the activity of gala ctosidase, glucosidase, peroxidase or xyloglucan endo-transglycosylase extracted from Suaeda maritima by in vitro concentrations of NaCl up to at least 1 M. in vitro salt tolerance of cell wall enzymes was not restricted to the halophyte, similar enzymes from the non-halophilic r elative Kochia tricophylla, and from the glycophytes Vigna radiata and Cicer arietinum, were inhibited little, or not at all, by the same co ncentrations of salt. Pectin esterase was somewhat less tolerant, but activity at 500 mM NaCl was still greater than at 0 mM NaCl in both Su aeda and Vigna. It is concluded that these enzymes of the cell wall co mpartment are much more salt-tolerant than cytoplasmic enzymes of high er plants. The results are discussed in relation to conditions thought to pertain in the apoplast.