CHILLING-INDUCED OXIDATIVE STRESS IN CUCUMBER (CUCUMIS-SATIVUS L CV CALYPSO) SEEDLINGS

One-week old cucumber (Cucumis sativus L. cv. Calypso) seedlings were chilled at 4-degrees-C in the dark for up to 6 days, after which they were rewarmed at 13-degrees-C in the light (16-h photoperiod) for 2 d to allow for recovery. Responses of these seedlings were compared to unchilled controls (13-degrees-C) held in the dark or in the light with a 16-h photoperiod. Loss of viability in dark-chilled seedlings required more than 1 d of chilling and progressed to the point where it was complete after 4 d of chilling. Irreversible increases in cotyledon tissue electrolyte leakage of dark-chilled seedlings did not occur until after seedling collapse, indicating that increases in passive permeability are secondary responses to chilling injury. There were only minor differences in the temporal changes in the tissue antioxidants reduced glutathione, ascorbic acid, alpha-tocopherol, and beta-carotene between chilled, unchilled, and chilled/rewarmed seedlings, with the exception that slightly lower levels of beta-carotene and alpha-tocopherol may have been induced by dark-chilling. Peroxidation of thylakoid lipids was induced during the rewarming period, after only 1 to 2 d of chilling, as indicated by the accumulation of lipid fluorescent pigments (LFPs). LFPs accumulated in both the phospholipid and glycolipid fractions of thylakoid lipids extracted from rewarmed seedlings, whereas little evidence for lipid peroxidation was obtained for the unchilled controls. Our results indicate that chilling-induced oxidative stress may have a role in transducing chilling injury in cucumber seedlings.