Pipecolic acid priming promotes salt stress tolerance via regulating antioxidant defense system and sugar metabolism in barley plants

Pipecolic acid (Pip) is the product of L-lysine metabolism and plays a role in the systemic acquired resistance (SAR) response under biotic stress factors in plants while there is limited research on abiotic stress related to its effect. To illuminate this, in the present study, barley (Hordeum vulgare L.) B & uuml;lb & uuml;l89 seeds were primed with 2, 4 and 8 ppm pipecolic acid and distilled water as a control for 24 h. After germination, for salinity treatments, seedlings were treated with 300 mM NaCl for 48 h. The physiological (growth parameters, relative electrolyte leakage (REL), relative water content (RWC), chlorophyll content) along with stress markers (malondialdehyde (MDA), hydrogen peroxide (H2O2) and proline content) as well as antioxidant enzymes (SOD, CAT, POX, APX, GR) and sugar metabolism (glucose, fructose and maltose) and SEM analysis were used to determine the anatomical changes in the samples. In the results, all Pip doses maintained RWC and REL, and 8 ppm Pip was the most effective in reducing oxidative damage. Beside this, Pip priming treatment alleviated chlorophyll content under salinity, but only 8 ppm Pip reduced proline, glucose and fructose content. Only 2 and 4 ppm Pip induced SOD enzyme activity under salinity, whereas no change was observed in APX, POX and CAT enzyme activity. On the other hand, leaf area was increased by pipecolic acid with enlarged cells as supported by SEM observations. In summary, the present study firstly indicates that Pip (2, 4 and 8 ppm) could be used as an effective antioxidant molecule or ROS inhibitor to increase salt stress tolerance in barley plants.