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Hanling Yu and Claude Willemot

We examined the relationship between reduced galactolipid content in tomato fruit at 4C and chilling injury. Galactolipid biosynthesis from 14C-acetate was compared in pericarp discs of cold-tolerant `New York 280' (`NY') and -sensitive `Early Cherry' (`EC') at 4C and 20C. Labeled lipids were separated by 2D-TLC. Labeled monogalactosyldiglyceride (MGDG) molecular species were hydrolyzed using a position-specific lipase; the fatty acids released were hydrogenated and separated according to chain length by reverse-phase TLC. At 4C, the relative amount of radioactivity was reduced in MGDG and enhanced in phosphatidylcholine (PC) in both cultivars, in comparison with labeling at 20C. In discs from fruit chilled for 6 h, labeling was similar in `NY' and `EC'. In fruit held at 4C for 8 days, labeling of MGDG was reduced and that in PC was enhanced to a greater extent in chilling-sensitive `EC' than in `NY'. The proportion of the MGDG label in eukaryotic species (i.e., the ratio in C18/C16 fatty acids in position sn-2), was less in `EC' at 4C than at 20C, even for fruit held at 4C for only 6 h. The ratio was little affected in `NY'. The data indicate that biosynthesis of eukaryotic MGDG was inhibited in tomato fruit at chilling injury-inducing temperatures.

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Han-Ling Yu, Claude Willemot, Serge Yelle, Yves Castonguay, and Paul Nadeau

Translatable mRNAs from two tomato (Lycopersicon esculentum Mill.) cultivars differing in chilling tolerance were compared after 16 days of chilling at 4C and after return to 20C for 1 and 5 days. Before chilling, the translation products, resolved by 2D NEPHGE, showed significant differences between more tolerant `New York 280' (NY) and less tolerant `Early Cherry' (EC). In NY, chilling reduced the level of five to 10 mRNAs and enhanced or induced that of several other mRNAs. After transfer to 20C, the trend was progressively reversed. Changes in the levels of two low-molecular-weight basic peptides were most noticeable. One, absent in NY before chilling, was strongly expressed after chilling and 24 h after transfer to 20C, but disappeared 5 days after transfer. The level of this peptide increased slightly in EC at low temperature and was maintained after transfer to 20C. The level of the other, high in NY before chilling, was sharply reduced after chilling. In contrast, the level of this polypeptide was low in EC under all treatments.