Salicylic acid-altering Arabidopsis mutants response to salt stress

The role of salicylic acid (SA) in plant responses to salinity is still a matter of controversy. To address the effect of endogenous SA variation in level and signaling on plant responses to salinity, biochemical and physiological analyses were performed on SA-altering Arabidopsis mutants including snc1 with high level of SA, transgenic line nahG with low SA, npr1-1 with SA signaling blockage, snc1/nahG plants (expression of nahG in the snc1 background), as well as wild type plants. Plants were cultured in 1 x Hoagland solution under controlled conditions. For salt exposure, NaCl at final concentrations of 100 mM, 200 mM, and 300 mM, respectively, was added to the culture solution after 25 d of seed germination. Except where mentioned, plant leaves were harvested after 14 d of salt stress, and used for physiological and chemical analyses. Salt stress caused all plants growth retardation with a dose-effect relationship relative to control. However, compared to wild type plants, a greater growth inhibition occurred in snc1, while a less inhibition was observed in nahG and npr1-1 plants, and a comparable extent was detected in snc1/nahG plants in which the SA level was near to that in wild type plants. The snc1 plants had lower net photosynthetic rate, variable to maximum fluorescence ratio, quantum efficiency of photosystem 2, reduced glutathione/oxidized glutathione ratio, proline levels, and higher malondiadehyde levels and electrolyte leakage rates as compared to wild type plants under salt stress. These values were effectively reversed by the expression of nahG gene in snc1 plants. The nahG and npr1-1 plants always exhibited more tolerance to salinity in above-mentioned indices than wild type plants. However, higher activities of superoxide dismutase and peroxidase in snc1 plants did not contribute to salt tolerance. These data showed that SA deficit or signaling blockage in Arabidopsis plants was favorable to salt adaptation, while a high accumulation of SA potentiated salt-induced damage to Arabidopsis plants.