Dynamic effect of La on reactive oxygen metabolism of soybean seedlings under supplemental UV-B irradiation

The dynamic effect of lanthanum(La~(3+)) on reactive oxygen metabolism of soybean seedlings under elevated ultraviolet-B radiation(UV-B: 280~330nm) at 15μW/cm~2 and 45μW/cm~2 level was studied through hydroponics in laboratory.Our result showed that plasmolemma permeability,malonadialdehyde(MDA) content,the accumulation amount of hydrogen peroxide(H_2O_2) and proline content of soybean seedlings gradually increased during UV-B stress period and subsequently decreased during recovery period.The dynamic tendency of catalase(CAT) activity of UV-B treatment was similar to that of plasmolemma permeability,MDA content,the accumulation amount of H_2O_2 and proline content.The activity of peroxidase(POD) firstly increased,kept on a high level and finally declined steeply when soybean seedlings were exposed to low level of UV-B radiation.However,POD activity rose all the time and declined slightly on the eleventh day when soybean seedlings were exposed under high level of UV-B radiation.With the add of La,as for plasmolemma permeability,MDA,the accumulation amount of H_2O_2 and proline content,their ranges of time intervals during photorepair were all declined and the activities of CAT and POD were significantly higher than those without La(P0.05).It suggested that the regulative effect of La on antioxidant enzymes such as CAT and POD could relieve the damage of UV-B radiation to these enzymes' function,strengthen their capacities to scavenge reactive oxygen species(ROS),improve the metabolism of ROS,decrease the concentration of MDA and the content of proline and maintain normal plasmolemma permeability.Further,the protection potential of La was better under low UV-B radiation than under high UV-B radiation.Thus,the protective effect of La on soybean seedlings under UV-B stress was carried out at the level of defense.