Effects of Exogenous Melatonin on Alfalfa Growth and Plasma Membrane Permeability under Aluminum Stress

Purpose To explore the alleviating effect of different concentrations of melatonin on aluminum toxicity in alfalfa (Medicago sativa L.) seedlings, providing a theoretical basis for planting alfalfa and the application of melatonin on acid-aluminum soil.

Methods Two alfalfa varieties named WL525HQ (tolerant type) and Suntory (sensitive type) were used as materials, and the seedlings were cultivated using hydroponics at different concentrations (0, 5, 10, 20, 50, 100 µmol/L) melatonin pretreatment followed by aluminum stress, and the changes of aboveground and underground biomass, root elongation, root tip aluminum content and plasma membrane permeability of alfalfa seedlings were measured.

Results Under aluminum stress, the growth of both materials was severely inhibited, and the root elongation rate and the dry weight of aboveground and underground of materials decreased significantly (P<0.05); compared with the only aluminum stress treatment, the above-mentioned three indexes of the treatment with melatonin pretreated increased significantly (P<0.05), and showed a trend of first increasing and then decreasing with the increase of melatonin concentration, reaching the maximum at 20 µmol/L melatonin treatment, the relative root elongation rate of WL525HQ and Suntory increased by 55% and 59%, respectively; the aboveground dry weight increased by 14% and 33%, respectively; and the underground dry weight increased by 47% and 54%, respectively. Under aluminum stress, the root tip aluminum content, relative conductivity and MDA content of WL525HQ and Suntory increased significantly (P<0.05); with the increase of melatonin concentration, the above-mentioned three indexes decreased first and then increased, reaching the minimum with 20 µmol/L melatonin treatment. At this time, compared with the only aluminum stress treatment, the aluminum content in the root tips of WL525HQ and Suntory decreased by 20% and 24%, respectively; the relative conductivity decreased by 14% and 21%, respectively; the MDA content decreased by 30% and 40%, respectively, and the change trend of WL525HQ was more obvious than that of Suntory.

Conclusion Exogenous melatonin can effectively alleviate the damage of aluminum toxicity to alfalfa, and the melatonin concentration is 20 μmol/L with the best relief effect.