Effects of salt stress and salt leaching on the physiological characteristics of Chaenomeles speciosa

To evaluate salt tolerance of Chaenomeles speciosa, salt injury index, chlorophyll content, relative conductivity, MDA content, antioxidant enzyme activities and soluble protein content were measured during the potcultured 3\|yearold seedlings exposed to 50, 100 and 150 mmol/L NaCl for 14 days and following salt leaching for 37 days. The results showed that, the salt injury index, relative conductivity and MDA content increased with the increase of NaCl concentration and exposure periods, while chlorophyll content and soluble protein content decreased, indicating that C. speciosa suffered serious salt injury during salt exposure, even in 50 mmol/L NaCl treatment. So C. speciosa was one of saltsensitive shrubs. During the early stage of salt stress, the superoxide dismutase (SOD) activity was enhanced in a salt concentration and exposure duration dependent manner, and reached the maximum on the 7th day, then turned to sharply decrease on the 14th day. In 50 mmol/L treatment, the catalase (CAT) activity was higher than that of control, and rose with salt exposure extension, and maximized on the 14th day. While in 100 and 150 mmol/L NaCl treatment, the maximum of CAT activity shifted to the 7th day, and the activity decreased rapidly on the 14th day. The ascorbic acid peroxidase (APX) and peroxidase (POD) had the similar variation trend with the CAT activity. The results demonstrated that the antioxidant enzymes played important role in C. speciosa resisting to salt stress. After salt leaching for 37 days, the physiological indexes of 50 mmol/L NaCl treatment recovered to the control level. C. speciosa in 100 and 150 mmol/L NaCl treatments also apparently recovered from salt injury during salt leaching, but with lower speeds and less degrees compared with that of 50 mmol/L treatment. The results indicate that the recovering ability from salt injury has a close relation with salt injury degree, which might be used as a physiological index to evaluate plant salt tolerance.