Assay of Chilling Injury in Wild and Domestic Tomatoes Based on Photosystem Activity of the Chilled Leaves

Abstract

Tomato leaves were detached and stored at 0.degree. C for various periods of time. Chloroplasts were isolated from the leaves and their photoreductive activities were determined. Comparisons were made between 2 altitudinal forms of the wild tomato L. hirsutum Humb. and Bonpl. (a tropical lowlands form and a highlands form adapted to growth at 3100 m), and 2 cv. of the domestic tomato L. esculentum Mill. In each case the capacity of the isolated chloroplasts to photoreduce ferricyanide declined linearly with time of storage of the leaves at 0.degree. C, but not at 10.degree. C. This injury developed more slowly in the high altitudinal form of the wild tomato compared with the low altitudinal form and the 2 domestic cv. indicating an enhanced resistance toward chilling injury in the tomato from 3100 m. Chloroplast activity declined in green tomato fruit held at 0.degree. C, at about the same rate as in the chilled leaves. Measurements of photochemical activities in the isolated chloroplasts and in vivo measurements of cytochrome-554 photooxidation in chilled leaves showed that the site of action of the chilling effect was water donation to photosystem II. The chilling-induced impairment of photoreductive activity in chloroplasts provides a useful assay for detecting and measuring differences in the susceptibility of plants to chilling injury.