The efects of exogenous salicylic acid(SA) on inducing the chilling tolerance of tomato seedlings(Solanum lycopersicum) was investigated and the results showed that SA mainly existed in conjugated form in tomato leaves under normal conditions.Under chilling conditions,tomato leaves contained relatively high SA levels,which should be attributed to the large accumulation of free SA.After foliar application of diferent concentrations of SA for 24 h,both free SA and conjugated SA largely accumulated,and the accumulation magnitude was positively correlated with the concentration of SA applied.Although the antioxidant capacity of tomato leaves was substantially enhanced under chilling conditions,the oxidative injury caused by low temperature was not alleviated.Among all the SA concentrations tested,0.5 mmol/L SA pretreatment was found to be able to alleviate oxidative injury caused by low temperature.After pretreatment with 0.5 mmol/L SA for 24 h,both the value of electrolyte leakage and the concentration of MDA decreased significantly,while the concentration of H2 O2 and the activities of CAT,POD,APX,GR increased remarkably in tomato leaves.Furthermore,c(AsA)/c(DHA) and c(GSH)/c(GSSG) remained stable when the seedlings were exposed to chilling conditions.Therefore,it was speculated that pretreatment with exogenous SA could enhance the endogenous SA level to some extent,which subsequently induced the accumulation of H2 O2.Then,the up-regulated antioxidant capacity of plant cell triggered by H2 O2 accumulation would be helpful in maintaining cellular redox balance under chilling conditions.Hence,SA pre-treatment could alleviate the oxidative damage caused by low temperature and enhance the chilling tolerance of tomato plants.

Lycium ruthenicum seedlings were chosen as test material,effect of different concentration of NaCl(0,200,400 mM)on seedling growth and physiological property of Lycium ruthenicum were studied.The results showed that the values of relative electrolyte leakage in roots increased significantly during the period of NaCl treatment;After NaCl treatment for 14 days,the contents of H2O2 and MDA did not change much as compared with the control;The content of soluble sugars decreased significantly in roots after 7 days of NaCl treatment,while the content of soluble protein declined after 14 days of NaCl exposure;Under different concentrations of NaCl treatment,POD activity in both leaves and stems declined dramatically after 7 and 14 days of treatment.According to the results obtained,the leaves and the stems posses relatively higher salt tolerance,while the root was relatively sensitive to salt stress.