Effects of proline on photosynthesis, root reactive oxygen species (ROS) metabolism in two melon cultivars (Cucumis melo L.) under NaCl stress

Effects of 0.2 mM proline applied to saline nutrient solution on biomass, chlorophyll content, photosynthetic parameters, reactive oxygen species and antioxidant enzymes activities of two melon cultivars (cv. Yuhuang and cv. Xuemei) were examined. Results indicate that exogenous proline increased the fresh and dry weights of both melon cultivars under NaCl stress, raised their chlorophyll content, net photosynthetic rate (Pn), actual efficiency of photosystem II (Phi PSII), enhanced the activity of SOD, POD, CAT, APX, DHAR and GR in their roots, lowered the superoxide anion radical level and reduced the hydrogen peroxide (H2O2) content and malondialdehyde (MDA) content. Exogenous proline also alleviate salinity-induced damage of membrane in both melon cultivars. In conclusion, proline treatment enhanced the salinity tolerance of both melon plants and alleviated their salinity-induced damage. However, all the above effects of proline were markedly more significant in cv. Xuemei than in cv. Yuhuang, suggesting that proline had different effects on different cultivars of melon plants.