- •Opuntia ficus-indica , a cactus widely cultivated for fruits and forage/fodder, has shoots composed of flattened stem segments (cladodes) that are relatively sensitive to freezing temperatures below −6°C but extremely tolerant of high temperatures up to 65°C. Based on the uptake of the vital strain neutral red, fruits and roots were damaged by 60 min below −7°C or above 55°C.
- •Young (6 wk old) and mature (1-yr-old) cladodes had 1.2°C greater low-temperature tolerance at day/night air temperatures of 20 : 10°C compared with 30 : 20°C and 2.8°C lower high-temperature tolerance. Fruits and roots (both 6 wk old) showed no such low-temperature acclimation; roots had high-temperature acclimation similar to that of cladodes, but fruits showed no high-temperature acclimation.
- •High-temperature tolerance did not change with age for cladodes and fruits up to 10 wk old nor did low-temperature tolerance for cladodes, but fruit low-temperature tolerance decreased by 2.6°C from 4.5 to 10 wk of age, a time when sugars, which can act as cryoprotectants, were increasing.
- •Cladodes showed 2.0°C greater tolerance of low temperatures with age up to 10 yr and 6.5°C greater high-temperature tolerance, which helps prevent the death of plants, especially during episodic freezing events.