TEMPERATURE PRECONDITIONING AFFECTS GLUTATHIONE CONTENT AND GLUTATHIONE-REDUCTASE ACTIVITY IN CHILLED ZUCCHINI SQUASH

Preconditioning zucchini squash (Cucurbita pepo L., cv. Elite) at 15 degrees C for 2 d prior to storage at 5 degrees C reduced chilling injury and altered glutathione content and glutathione reductase activity. When squash without temperature preconditioning treatment was placed at 5 degrees C, the contents of total glutathione (TG), reduced form of glutathione (GSH), total non-protein thiol (NPSH), and glutathione reductase (GR) activity increased intially for a short period (2 to 4 d) then declined thereafter. In preconditioned squash, the contents of TG, GSH, and NPSH increased even more after the preconditioning treatment, and the amounts of these substances remained higher in the treated squash than in the control after transfer to 5 degrees DC. GR activity was also higher in the preconditioned squash than in the untreated squash. The oxidized forms of glutathione (GSSG) and non-glutathione thiol (RSH) contents were low in zucchini squash and changed only slightly throughout the storage. Consequently, a higher ratio of GSH to GSSG was found in the preconditioned squash than in the control squash. These results indicate that the protection of SH-containing enzymes against oxidation and the detoxification of reactive oxygen species may also be a factor contributing to the effectiveness of temperature preconditioning in reducing chilling injury.