Temperature-Induced Leakage from Chilling-Sensitive and Chilling-Resistant Plants

Abstract

Leakage rates were determined from leaf cells loaded with rubidium and I'Hlleucine. There was a differential response between leucine and rubid-ium leakage depending upon the species used. The rate of leucine leakage shows a small decline below 5 C for two altitudinal variants of Lycopersicon hirsutum Humb. and Bonpl., whereas Lycopersicon escudentum L. showed a marked increase below 5 C. Rubidium showed a marked increase in leakage rate below 10 C with the altitudinal variants, with only a slight increase for the L escuientum species. A rough relationship existed between rubidium leakage rate at 1 C and the altitude of origin of the L hirsutum race, the low altitudinal forms having higher leakage rates than the higher altitudinal variants. The L esculentum lines show a rubidium leakage response similar to that of the high altitude L. hirsutum variants. Higher leakage rates were obtained if the calcium concentration in the medium was less than 1 millimolar and upon addition of metabolic poisons and detergents. The results are consistent with the view that chilling injury causes changes in the membrane and that cell leakage is an early symptom of this change in some species. Some chilling-sensitive species have increased leakage within 1 hour of exposure to chilling temperature. Changes in the physical state of membranes at chilling temperatures are thought to be responsible for the increased leakage of cell electrolytes from the tissue of chilling-sensitive plants (8, 9). Liebermann et aL (7) found 5 times as much potassium leakage from sweet potato roots after 10 weeks storage at chilling temperatures. There was also enhanced leakage of electrolytes from leaf tissue (3, 11, 19) and fruit tissue (16) at chilling temperatures. The results of Tatsumi and Murata (16) showed that fruit pitting, a symptom of chilling injury, was visible after 5 days whereas leakage did not increase until the 7th day. This indicated that the injury was localized and the assay not sensitive enough to detect the earlier leakage changes that were visually apparent. Using narrow (1 x 3 mm) leaf strips which would avoid this problem, Patterson et al. (11) found two phases of ion leakage at 0 C: a relatively slow initial phase, followed by a rapid loss of most of the electrolyte. In the most chilling-sensitive Passiflora species used, the two phases could not be separated.