Exogenous arginine treatment additively enhances growth and tolerance of Salicornia europaea seedlings under salinity

The effects of foliar application of 5 mM arginine (Arg) on the growth and control of salinity-induced osmotic and oxidative stresses (0, 200, 400 and 600 mM NaCl) in Salicornia europaea seedlings were investigated. Despite higher levels of lipid peroxidation, lower membrane stability index (MSI), decreased pigment content and phenolic compounds, and reduced activity of antioxidant enzymes observed under salinity, seedling growth indices, including plant height and biomass, increased significantly, and some protective and antioxidant molecules such as proline and flavonoids accumulated. Soluble protein level increased at the low salt concentration (200 mM) but decreased at other doses. Exogenous Arg treatment alone had less or no effect on plant biomass and other metabolites, but in combination with salt, further enhanced growth parameters, MSI and accumulation of soluble protein, phenolic compounds and proline. Arg-induced changes under salinity were associated with decreased lipid peroxidation, flavonoids content and antioxidant enzymes activity. These results show that S. europaea seedlings are well tolerant to applied salt doses. The treatment with exogenous Arg alone affects plant growth slightly, but in combination with salt, synergistically increases growth and salt tolerance of these plants by enhancing the accumulation of proline and antioxidant molecules instead of enzymatic antioxidant.