Regulatory effect of pipecolic acid (Pip) on the antioxidant system activity of Mesembryanthemum crystallinum plants exposed to bacterial treatment

Abstract The presented study aims to elucidate the regulatory role of Pipecolic acid (Pip) in modulating the antioxidant system activity of Mesembryanthemum crystallinum plants exposed to Pseudomonas syringae infestation. M. crystallinum , known for its semi‐halophytic nature, can transition its metabolism from C 3 to CAM under salt stress conditions. The research encompasses the antioxidant system of the plants, covering both enzymatic and low molecular weight components. The findings indicate that Pip supplementation confers a beneficial effect on certain elements of the antioxidant system when the plants are subjected to stress induced by bacteria. Notably, during critical periods, particularly in the initial days post‐bacterial treatment, M. crystallinum plants supplemented with Pip and exhibiting C 3 metabolism display heightened total antioxidant capacity. This enhancement includes increased superoxide dismutase activity and elevated levels of glutathione and proline. However, in plants with salinity‐induced CAM, where these parameters are naturally higher, the supplementation of Pip does not yield significant effects. These results validate the hypothesis that the regulatory influence of Pip on defence mechanisms against biotic stress is contingent upon the metabolic state of the plant. Furthermore, this regulatory effect is more pronounced in C 3 plants of M. crystallinum than those undergoing CAM metabolism induced by salinity stress.