Increased ethylene synthesis enhances chilling tolerance in tomato

Abstract

Exposure to chilling temperatures (0–10°C) increases ethylene synthesis in several species, but it is not clear whether this increase in ethylene synthesis is involved in the development of chilling tolerance. To determine this relationship, chilling tolerance development of the ethylene‐insensitive Never‐ripe (Nr) tomato (Lycopersicon esculentum Mill. cv. Pearson) mutant was compared to that of a normal isogenic line. Plants were grown for 3 weeks at 25/20°C day/night, and then half the plants of each genotype were chill‐hardened at 25/5°C day/night for 10 days, while the other half remained at 25/20°C. All plants were then exposed to a severe chill (5/5°C day/night) for 7 days, and a recovery period (25/20°C day/night) of 4 days. Chill hardening increased ethylene synthesis in both genotypes, but increased the rate of leaf development and dry weight accumulation during the recovery period only for the normal plants. Hardening also caused a greater decrease in lesion development in the normal plants following the severe chill. Therefore, chill hardening was more effective in the ethylene‐sensitive normal plants than in the ethylene‐insensitive mutants, indicating that a response to ethylene is involved in chilling tolerance development. However, chill hardening was effective for both genotypes in maintaining chlorophyll a fluorescence levels (Fv/Fm), suggesting that ethylene does not control all aspects of chilling tolerance. In a separate experiment, application of a 500 ppm ethephon solution to normal ‘Pearson’ plants led to higher rates of ethylene synthesis and a higher rate of leaf development following a 6 day severe chill (5/5°C day/night). These results further indicate that ethylene is involved in the development of chilling tolerance.