Effects of CQ10-LPSp on antioxidative enzymes and defense enzymes of alfalfa seedlings

To clarify the effect of CQ10-LPSp (Pantoea agglomerans CQ10 Lipopolysaccharide, CQ10-LPSp) on antioxidant and defense enzymes of alfalfa seedlings, Medicago sativa ‘Juneng 551’ was used as the test material. Two seed treatments (disinfection and non-sterilization) and five concentrations (0, 0.067, 0.134, 0.200, and 0.267 EU·mL⁻¹) of CQ10-LPSp were interacted with alfalfa to explore the interaction of CQ10-LPSp with alfalfa. Antioxidant activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and malondialdehyde (MDA) and defense enzyme activities of phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and lipoxygenase (LOX) of CQ10-LPSp in alfalfa seedlings were investigated. With increasing CQ10-LPSp concentration, SOD, POD, PPO, and PAL activities of alfalfa seedlings in the non-sterilized and disinfected groups increased initially and then decreased. With increasing CQ10-LPSp concentration, the MDA content decreased, increased, and decreased again. All activities were significantly lower than that of the control, while CAT activity continued to decrease. When the concentration of CQ10-LPSp was low, activities of CAT, MDA, PAL, and LOX in the non-sterilized seedlings were higher than those in the disinfection group, whereas POD, SOD, and PPO were lower than those in the disinfection group. When the concentration of CQ10-LPSp was high, the non-sterilization CAT and MDA of the seedlings were lower than those in the disinfection group, the POD, SOD, and PAL of the seedlings were higher than those in the disinfection group. A concentration threshold effect on the tolerance of alfalfa seedlings to CQ10-LPSp was demonstrated, and the tolerance of alfalfa seedlings decreased with increasing CQ10-LPSp concentration, with a tolerance threshold of 0.200 EU·mL⁻¹. Treatment with lower concentration of CQ10-LPSp resulted in higher activities of antioxidant and defense enzymes of alfalfa seedlings in the non-sterilization group compared to the disinfection group. These results provide a scientific basis for the development of lipopolysaccharides and the study of innate immunity induced in alfalfa.