Physiological and Biochemical Changes in Lettuce under High Temperature Stress after Exogenous Salicylic Acid Treatments

Exogenous salicylic acid (SA) of different concentrations (Ommol L-1, 0.1mmol L-1, 0.2mmol L-1, 0.4mmol"L-1 and0.6mmol L-1) was applied to lettuce seedlings before submitting to high temperature stress. Results showed that the activities of catalase (CAT) and peroxidase (POD) were enhanced; the contents of soluble proteins and proline increased, while malondialdehyde (MDA) content and relative electric conductivity decreased by pretreatments of SA. The optimal effects resulted from the SA concentrations of 0.2mmol L-1 and 0.4 mmol L-1