Effects of Chemical Protectants against Chilling Injury of Young Cucumber Seedlings

Chilling of 8-day-old cucumber (Cucumis sativus L.) seedlings for 48 hours at 2°C caused reversible damage; chilled seedlings collapsed but regained turgor within 6 hours at 25°. Hypocotyl segments from chilled seedlings exhibited increased solute leakage, ethylene production, and O2 uptake after transfer to 25°. Pretreatment of seedlings with 10−4m abscisic acid generally reduced symptoms of damage but did not prevent chilling injury. Pretreatment with 10−3m CaCl2 was generally ineffective, and pretreatment with 10−3m ascorbate generally intensified symptoms of injury. Oxygen uptake increased during the first 6 hours at 25° but returned to the level of unchilled seedlings within 24 hours. Chilled tissue was sensitive to 2,4-dinitrophenol during this period, although sensitivity was less than in controls during the first 12 hours after chilling. Unchilled tissue was insensitive to SHAM, but O2 uptake was inhibited by SHAM during the respiratory burst following chilling. Tissue was no longer SHAM-sensitive after 24 hours at 25°, by which time the respiratory burst had subsided. Thus, the alternative respiratory pathway was apparently operating only during the time of the respiratory burst, when the seedlings were recovering from chilling injury.