| The fresh water resouces is becoming more and more limited, but there are a great deal of saline soil and salt water resources in the western region of China. The exploiture of saline soil and salt water resources will be an important challenge in agriculture in Northwest China. Muskmelon is one of the important crops in the western region, and it is salinity tolerant. Therefore, investigation into the salinity tolerance mechanism is of great importance for enriching muskmelon physiology, developing crop irrigation strategy with salt water, and empoldering the saline soil and salt water resources. In addition, it has great significance to the progress of the society, the development of the economy and the maintenance of ecosystem healthy in western region. Two muskmelon cultivars (Huanghemi and Baishami) belonging to two varieties were treated with 6 concentration of NaCl. The effects of NaCl stress on seed germination and physiochemcial and biochcmcial properties of muskmelon were studied. The results are summarized below: 1. Lower concentration 50mmol/L promoted the germination and the growth of radicle. With the increase of NaCl concentration, germination process was delayed. Relative germination index, relative vitality index, relative a-amylase activity were all decreased as NaCl concentration increased. The results imply that inhibition of a-amylase activity and membrane restoration may be important reasons of postponed germination and declined germination energy under salt stress. 2. Under NaCl stress, the height growth, the area of total leaves, fresh weight of the part above the ground and dry matter accumulation of Muskmelon seedlings inhibited, and this inhibition lied on the NaCl concentration and stress days. Muskmelon seedlings have the adaptability under 0-100mmol/L NaCl stress condition. 3. Net photosynthetic rate (Pn) ,transpiration rate (Tr), stomatal conductance (Gs),and chlorophyll fluorescence kinetics parameters Fm, Fv, Fv/Fm , Fv/Fo of leaves decreased under NaCl stress, while the thermal energy dissipation rate and photosynthetic limitation increased. The intercellular CO2 concentration (Ci) showed at trend from decrease to increase, but stomatal limitation value and water use efficiency increased in origin and then decreased. Changes of the Ci and Ls showed that the decline of net photosynthetic rate of muskmelon under mild NaCl stress was mainly caused by temporary stomatal limitations, but it was caused by nonstomatal limitations under severe NaCl stress. 4. The membrane permeability and contents of MDA increased in both cultivars with the increase of NaCl concentration and prolonging of time. The activity of SOD in both two cultivars and the activity of POD in Huanghemi showed at trend from decrease to increase in shorter term, but it decreased in longer term under NaCl stress. The activity of POD was higher than the control in 10 days, while it was lower in 5 and 15 days in Baishami. The effect of salt stress on the activity of CAT was less in both cultivars. 5. Under NaCl stress, relative water content of leaves decreased. The contents of praline and soluble sugar increased in both cultivars with the increase of NaCl concentration. The degree of increase of praline and soluble sugar in Huanghemi leaves were slower than that of Baishami under NaCl stress. 6. Na+ and Cl-contents in different organs were increased quickly as the severity of NaCl stress increasing. However K+ content was decreased in different organs. Ca2+ content was also decreased in leaves, but it was increased in roots. Under NaCl stress, Na+/K+ ratio was enhanced in different organs and so did Na+/Ca2+ ratio in leaves. With NaCl concentration increase, SK,Na and SCa,Na were declined gradually. 7. Inhibition of salt stress on growth of Baishami seedlings is stronger than Huanghemi seedlings. The damage of NaCl to membrane of Baishami was stronger than that of huanghemi. The degree of increase of Na+ and Cl-and the degree of decrease of K+and Ca2+ in different organs of Huanghemi were lower than that of Baishami under NaCl stress. Effects of NaCl stress on ability of selection and transportation to K+ and Ca2+ of Huanghemi were less than that of Baishami.The salt tolerance of Huangheni is stronger than that of Baishami.
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