Adaptive changes of ROS/RNS redox and melatonin synthesis under salt and waterlogging stresses in Pittosporum tobira

Abstract

Plants have evolved a variety of complex mechanisms to resist the environmental factors including salt and waterlogging stresses. In this study, we described adaptive changes of Pittosporum tobira toward salt and/or waterlogging stresses by mediating ROS (reactive oxygen species)/RNS (reactive nitrogen species) redox and melatonin synthesis. When the P. tobira seedlings were subjected to salt stress, waterlogging stress, and salt-waterlogging stress, both the photosynthetic capacity and antioxidant capacity were significantly inhibited, accompanying with the alterations of MDA, H2O2, O2− and NO levels and melatonin metabolism. These observations were correlated with the changes in the activities of antioxidant enzymes (SOD, CAT, POD and APX) and melatonin biosynthetic enzymes (MEL, TDC, SNAT, SER, and 5-MT) as wells as in the expression of their encoding genes. Lower melatonin content was found in the seedlings treated by salt-waterlogging stress than in those treated by salt or waterlogging stress. Furthermore, the tolerances of the seedlings grown at Zhejiang province to salt and waterlogging stress were stronger than those grown at Fujian province. Our findings suggested that the MEL/ROS/RNS redox network induced by salt stress, waterlogging stress, salt-waterlogging stress may be a crucial mechanism for coping with adverse conditions in P. tobira.