Exogenous application of pipecolic acid induces stomatal closure in Arabidopsis thaliana L.

Abstract

Objective: The major objectives of this study were (i) to determine whether exogenous Pipecolic acid treatment triggers the stomatal closure; (ii) to assess how the stomatal response is influenced by the method and concentrations of Pipecolic acid treatment; (iii) to investigate the response of Pipecolic acid-primed plants to the foliar bacterial pathogen Pseudomonas syringae pv. tomato DC3000 that invades plants through stomata. Material and Methods: Freshly harvested Arabidopsis leaves were immersed in MES-KCl buffer supplemented with 1 mM of D,L-Pipecolic acid for 2 h. Stomatal aperture was measured in epidermal strips collected from the abaxial side of the leaves. Stomatal aperture in Pipecolic acid-treated plants was also directly quantified after Pseudomonas syringae pv. tomato DC3000 inoculation. Results: The treatment with D,L-Pipecolic acid resulted in increased stomatal closure in a concentration-dependent manner. Treatments with 0.1 mM and 1 mM of D,L-Pipecolic acid led to a reduction in stomatal aperture by 32.5% and 54.7%, respectively. Leaves treated with either 1 mM of D,L-Pipecolic acid or L-Pipecolic acid demonstrated similar stomatal apertures corresponding to 2.67 and 2.49 μm, respectively. The stomatal apertures did not exhibit a significant difference between the treatments following the Pseudomonas syringae pv. tomato DC3000 infection. Pipecolic acid-mediated enhanced defense is independent of stomatal immunity. Conclusion: Exogenous Pipecolic acid triggers preinvasion stomatal closure in Arabidopsis. There is no difference between pipecolic acid application methods (soil drenching or foliar spray) in terms of affecting stoma closure.