Dynamic response of antioxidant enzymes and osmotic adjustment substances to drought and enhanced UV-B radiation in three Lespedezas

The present work studied the effects of drought and enhanced UV-B radiation as well as their combined stress on antioxidant enzymes and osmotic adjustment substances in three Lespedezas species.Superoxide dismutase(SOD) activity decreased firstly and then increased under all kinds of stress in all three species,and the combined stress of drought and enhanced UV-B radiation increased SOD activity more substantially than the single factor stress does in L.potaninii and L.bicolor.In all three species,peroxidase(POD) activity firstly increased,and then decreased under enhanced UV-B radiation and its combination with drought stress.Catalase(CAT) activity of three species increased under both the drought and the combined stress,but decreased under enhanced UV-B radiation,compared with their controls value.In addition,the content of osmotic adjustment substances(soluble protein,soluble sugar,soluble proline) in three Lespedezas increased first,and then decreased compared with their controls value,but significant inter-species differences were observed.Generally,a significant increase of malondialdehyde(MDA) content was observed under stress conditions,and it increased more in L.potaninii than in L.bicolor and L.formosa when compared with their control values.These results suggested that the damage caused by the combined stress of enhanced UV-B radiation and drought was less than that caused by UV-B radiation or drought alone stress,which means there existed a cross adaptive phenomenon between draught stress and enhanced UV-B radiation in Lespedezas.Finally,a comprehensive evaluation on antioxidant defense capacity of different species was given according to subordinate function values analysis.L.formosa and L.bicolor with higher antioxidant capacity were more tolerant than L.potaninii to the stresses provided in this experiment.