Methyl jasmonate improves tolerance to high salt stress in the recretohalophyte Limonium bicolor

Limonium bicolor is a typical recretohalophyte with salt glands in the epidermis, which shows maximal growth at moderate salt concentrations (100 mM NaCl) but reduced growth in the presence of excess salt (more than 200 mM). Jasmonic acid (JA) alleviates the reduced growth of L. bicolor under salt stress; however, the underlying mechanism is unknown. In this study we investigated the effects of exogenous methyl jasmonate (MeJA) application on L. bicolor growth at high NaCl concentrations. We found that treatment with 300 mM NaCl led to dramatic inhibition of seedling growth that was significantly alleviated by the application of 0.03 mM MeJA, resulting in a biomass close to that of plants not subjected to salt stress. To determine the parameters that correlate with MeJA-induced salt tolerance (assessed as the biomass production in saline and control conditions), we measured 14 physiological parameters relating to ion contents, plasma membrane permeability, photosynthetic parameters, salt gland density, and salt secretion. We identified a correlation between individual indicators and salt tolerance: the most positively correlated indicator was net photosynthetic rate, and the most negatively correlated one was relative electrical conductivity. These findings provide insights into a possible mechanism underlying MeJA-mediated salt stress alleviation.