Effect of salicylic acid on the activities of anti-oxidant enzymes and phenylalanine ammonia-lyase in cucumber fruit in relation to chilling injury

The effect of salicylic acid (SA) on chilling injury (CI) in cucumber fruit, and its ability to induce biochemical defense responses were assessed. To explore the optimum concentration of SA to induce chilling tolerance, cucumber fruit were treated with 0.1, 0.5, or 1.0 mM SA then stored for 18 d at 1 degrees C. The results showed that the application of SA at 0.5 mM was most effective in reducing CI in cucumber fruit. SA at 0.5 mM maintained significantly higher fruit firmness and a lower CI index and malondialdehyde (MDA) content compared with untreated controls. Meanwhile, treatment with 0.5 mM SA delayed decreases in skin chlorophyll and vitamin C contents. The activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and phenylalanine ammonia-lyase (PAL) were increased in SA-pretreated cucumbers stored under chilling stress. These results suggested that pre-treatment with 0.5 mM SA could alleviate CI symptoms effectively and maintain fruit quality in cucumber. The enhanced chilling tolerance of cucumber fruit was due mainly to the increased activities of the anti-oxidant enzymes and PAL induced by SA. Post-harvest application of SA could be used commercially to control CI in cucumber fruit during cold storage.