Abstract: Two different ecotypes cultivars cv.461 and 407 of cucumber were used under the cold stress ( ( 6 ±1) ℃, 72 h ) and spraying concentrations of salicylic acid( SA) were 0.25, 0.50, 1.00, 1.50, 2.00 mmol/L respectively, to study the effect of SA pretreatment on physiological characteristic and the expression of CATmRNA.The results were as follows: Spraying suitable SA can increased the activity of antioxidases( SOD,CAT and POD); The ratio of variable to maximal fluorescence( Fv/Fm) in the SA-pretreated plants was higher than those control.Northern hybridization blot analysis suggested the expression of the CAT gene in 1.0 mmol/L SA-pretreated plants was higher than control,which was the same as that of CAT activities.It is seen that SA pretreatment can increase chilling tolerance in cucumber seedling by regulating antioxidases activities and the ratio of variable to maximal fluorescence, 1.00 mmol/L SA pretreatment was more effective．

Key words: Chilling stress, Salicylic acid, Antioxidases, Fv/Fm, CATmRNA, Cucumber

CLC Number: 

• S642.2