Metabolism of reactive oxygen species and contents of osmotic substances in watermelon seedlings under salinity stress.

The experiment was carried out to study the effect of NaCl stress on the reactive oxygen species metabolism and osmoticum content of watermelon(Citrullus lanatus) seedlings in hydroponically.The results showed that NaCl stress inhibited obviously the growth of watermelon seedling,and the extent of inhibition for 'Xiuya' was less than that for 'Xiuli';With increasing NaCl concentration,O-·2 production rate,MDA content and membrane permeability in leaves of both cultivars significantly increased,and increased range of 'Xiuli' obviously exceeded 'Xiuya'.POD activity declined under the low concentration of NaCl and increased under the high concentration of NaCl.CAT and APX activities,and ascorbic acid content apparently increased with increasing NaCl concentration.SOD activity showed different regularity for two cultivars.Proline and soluble sugar contents significantly increased with increasing NaCl concentration.Soluble protein content increased under the low concentration of NaCl and decreased under the high concentration of NaCl.Besides soluble protein content,the activities of antioxidant enzymes,contents of ascorbic acid and osmotic substances in the leaves of 'Xiuya' were obviously higher than that in 'Xiuli' beyond 50 mmol·L-1 NaCl.The research revealed that salinity seriously inhibited the growth of watermelon seedlings,destroyed the structure of cell membrane,influenced normal metabolism of reactive oxygen species and osmoticum.The extent of growth inhibition and lipid peroxidation of 'Xiuya' seedling were lower than that of 'Xiuli',which was related with high activities of antioxidant enzymes and high content of osmotic substances.