Protection of plasma membrane of onion epidermal cells by glycinebetaine and proline against NaCl stress

Abstract

To test the hypothesis that glycinebetaine (GB) or proline (Pro) may have a specific effect on the plasma membrane under salt stress, Allium cepa bulb scale inner epidermal cells were exposed for 3 h to 150 mM NaCl before or after GB or Pro treatments at different regimes. Two concentrations of GB or Pro were applied (50 or 100 mM). Plasma membrane permeability for individual intact cells and cell viability were measured to determine whether GB or Pro counteract the deleterious Na-induced alterations of the cell membrane. The NaCl treatment increased membrane permeability for urea and methylurea, and the number of cells with swollen protoplasm. It also enhanced cell death. GB or Pro added before, after, or simultaneously with NaCl significantly prevented Na-induced cellular alterations; exposure to GB or Pro prior to salt treatment had the greatest protective effect. GB was more effective as a membrane protectant than Pro. Both concentrations of GB or Pro had about the same effect suggesting high concentrations of GB or Pro are not required for the stabilization of the cell membrane. In conclusion, it is evident that cell membrane protection under salinity stress can be provided by GB or Pro thus leading to increased salt tolerance in plants.