Chilling Stress Protection in Cucumber: A Role for Antioxidants?

Abstract

To examine the role of endogenous antioxidants in providing chilling stress protection, field-grown cucumber (Cucumis sativus L. cv. Eureka) fruit were stored in the dark and evaluated throughout storage. Storage treatments included continuous chilling (C) (5°C), continuous tempering (T) (12°C), intermittent warming (IW) (1 day at 12°C every 4 days) for 1, 2, 3, or 4 cycles, and preconditioning (PC) (12°C for 4 or 8 days) before chilling. Fruit exposed to in-field chilling (FC) were also stored under continuous chilling at 5°C. Samples were evaluated visually for tissue damage (lack of exudate, water-soaked appearance), and ascorbic acid (Asc) and reduced (GSH) and oxidized (GSSG) glutathione levels and glutathione reductase (GtR) and ascorbate free radical reductase (AFRR) activities were determined. Each 4 days of PC extended storage life by 7 days relative to C. FC or 1–2 IW cycles also extended storage life relative to C. With all treatments, Asc depletion preceded visual tissue damage, whereas GSH, GtR, and AFRR were not depleted before such damage. GSSG levels remained low throughout storage. GtR activity was elevated by FC and IW. AFRR activity was elevated by all treatments. Asc levels were elevated initially by all treatments, with this elevation lasting longer with PC and T. These results suggest that Asc levels decline during stress in the absence of an obvious lesion in the Asc regeneration scheme.