Physiological Response to Chilling Temperatures of Intermittently Warmed Cucumber Fruit

Abstract

Symptoms of chilling injury were reduced by intermittently warming cucumber fruit (Cucumis sativus L. cv. Poinsett 76) from 2.5 to 12.5C for 18 hr every 3 days. Fruit continuously held at 2.5C for 13 days developed severe pitting and decay after 6 days at 20C, while fruit continuously held at 12.5C or intermittently warmed showed no pitting or decay during subsequent holding at 20C. The increased rate of C2H4 production during the first warming period, from 12 nl·(kg·hr)-1 at 2.5C to 201 nl·(kg·hr)-1 at 12.5C, was significantly greater than that during the second or third warming periods, i.e., 53 to 98 and 53 to 55 nl C2H4/(kg·hr), respectively. Respiration increased 3-fold during the initial warming period, but only 2-fold during subsequent warming periods. Leakage of cellular ions from excised disks of mesocarp tissue was around 6% and 10% of the total ion content of the tissue for control and intermittently warmed fruit, respectively, but increased to 17% for fruit that were continuously held at 2.5C for 10 days. After 320 hr (three cycles) of chilling and warming, chilled fruit showed significantIy lower ethylene-forming enzyme activity than the control or intermittently warmed fruit. Fruit held at 12.5C contained 0.09 to 0.34 nmol·g-1 of ACC. ACC levels were 6.23 nmol·g-1 in fruit exposed to 2.5C for 320 hr. In contrast, intermittently warmed fruit only showed 30% and 27% increases in ACC content during the first and second warming periods, respectively. Periodic warming appears to allow chilled fruit to acclimate to subsequent periods of chilling. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC).