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Many plants indigenous to subtropical and tropical regions suffer physiological injury when subjected to low (1 to 100 C) but non-freezing temperatures (6,14). The injury, manifested by discoloration, susceptibility to decay, and failure to ripen, is generally progressive with time indicating a gradual de-,generation of physiological processes. There is also some evidence (7,16) (6,14) there have been few metabolic and physiological studies of this phenomenon. It therefore seemed desirable to investigate biochemical aspects concerned with chilling injury. The emphasis in such a study should be to detect changes occurring at the cellular and subcellular level during exposure of sensitive tissues to low temperatures.We recently studied cytoplasmic particles from sweetpotato roots (a tissue sensitive to low temperature) and had established a system for assaying their mitochondria (8, 9). It was therefore possible to investigate the effect of chilling on mitochondria, the organelles intimately concerned with energy metabolism in the cell. Our purpose was to compare mitochondrial activity from chilled and non-chilled tissues and also to study some metabolic differences between tissue slices from chilled and non-chilled tissues. It is hoped that this approach will yield clues to the mechanisms concerned in chilling injury.MATERIALS Beltsville, MIaryland, were used in these experiments. The roots were harvested early to insure that no chilling occurred in the field. Immediately after harvest, the roots were held for 10 days at 290 C and approximately 95 % relative humidity to promote healing of surface injuries. After this curing period the sweetpotatoes were divided into two lots. One lot was transferred to a constant temperature room held at 15°C, a recommended storage temperature, and the second lot was transferred to a room held at 7.50 C, the chilling temperature used in these experiments. Both rooms were equipped with humidistats set to maintain a relative humidity of 80 to 85 %. The roots were sampled after curing and at predetermined intervals during storage at the two temperatures. The chilled and non-chilled roots were compared with respect to ion leakage from tissue slices and with respect to oxidation and phosphorylation exhibited by isolated mitochondria.The leakage from tissue slices was determined by conductivity measurements of solutions surrounding slices which were approximately 2 mm thick and 1 cm in diameter. Duplicate 10-g samples from chilled and non-chilled roots, previously washed in distilled water for one hour, were placed in 120-ml flasks containing 15 ml of either distilled water or 0.5 M sucrose. The flasks were shaken in a constant temperature bath at 25°C for two hours at a shaking speed of 120 strokes per minute. Conductivity measurements were made with a Serfass Conductivity Bridge using a cell with a constant of 0.1. The tissue was sampled at harvest and at intervals as specified during a 10-week storage period.In the 2nd year the solutions were frozen and held until the end of the exp...

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