Karrikin1 mitigates salt stress in creeping bentgrass (Agrostis stolonifera) via physiological regulation and metabolite reprogramming

Salinity poses a globally prevalent environmental stressor impairing plant growth and production. Karrikins (KARs), a recently identified class of plant growth regulators, are butenolide compounds generated during plant materials combustion, and can promote seed germination and subsequent seedling establishment under various abiotic stresses. However, the role of KARs in mediating physiological and metabolic processes under salinity remains poorly understood. This study therefore aimed to elucidate the effects of KAR₁ on ionic homeostasis, redox regulation, and metabolic reprogramming in salt-stressed creeping bentgrass (Agrostis stolonifera). Creeping bentgrass plants received foliar applications of either 100 nM KAR₁ or distilled water and then were exposed to non-stress or 200 mM salt stress for a 21-day experimental period. Foliar KAR₁ application mitigated salt stress-induced negative effects by significantly increasing shoot biomass, leaf relative water content, total chlorophyll and chlorophyll a content, proline accumulation, and antioxidant enzyme activities, while concurrently diminishing electrolyte leakage and decreasing malondialdehyde and hydrogen peroxide content. Moreover, KAR₁ elevated K⁺ and Mg²⁺ content in creeping bentgrass leaves and decreased Na⁺/K⁺ ratio under salt stress. Metabolomic analysis revealed that enhanced salt tolerance by KAR₁ application could be associated with metabolic reprogramming of specific amino acids for osmotic adjustment, and metabolites involved in alpha-linolenic acid and phenylpropanoid biosynthesis pathways for membrane integrity and stabilization.