Effects of exogenous 5 – aminolevulinic acid on physiological characteristics of alfalfa

This study was conducted to determine the effect of different concentrations (0, 5, 10, 15, 20, 25 mg·L^–1) of exogenous ALA (5 – aminolevulinic acid) on the antioxidant system and on photosynthesis in alfalfa (Medicago sativa). The results showed that foliar application of 10 mg·L^–1 ALA could significantly increase the photosynthetic pigment content of alfalfa seedlings (P < 0.05). In addition compared to the control, the chlorophyll a, chlorophyll b, carotenoids, and total chlorophyll contents in the leaves of " Nongmu 806” seedlings increased by 12.29%, 36.21%, 18.69%, and 11.46%, respectively. Finally, exogenous 10 mg·L^–1 ALA caused significant increases in the activities of various antioxidant enzymes (SOD, POD, CAT, APX) and in soluble protein (SP) content, but reduced the accumulation of malondialdehyde (MDA) and reactive oxygen species (ROS). These results indicate that the application of moderate amounts of ALA could increase the accumulation of photosynthetic pigments and could augment the activities of antioxidant enzymes in the leaves of alfalfa seedlings.