Fatty Acid Metabolism in Shading-Induced Tolerance of Star Ruby Grapefruit to Postharvest Chilling Injury

Chilling injury (CI) is a major postharvest disorder in citrus fruit, and fatty acid (FA) metabolism has been proposed as a key determinant of cold tolerance. We have investigated this relationship in the fruit of the Star Ruby grapefruit and found that preharvest fruit shading induces lycopene accumulation in the peel and tolerance to CI during subsequent cold storage in comparison with uncovered fruits, which were sensitive to CI. Then, FA profiling and the expression of FA desaturation (FADs) genes were examined in the flavedo of covered (C) and non-covered (NC) grapefruits during 8 weeks of storage at 2 °C. Linoleic acid was the predominant unsaturated FA in the flavedo of Star Ruby grapefruit, which accumulated more highly in the CI-sensitive than in the CI-tolerant fruit at harvest and during the whole storage period. Interestingly, C and NC fruit also exhibited distinct FAD transcriptional signatures at harvest, suggesting the influence of preharvest factors. Cold storage stimulated FA desaturation in both C and NC fruit and differentially affected the expression of FADs genes during cold storage. These results demonstrate that FA metabolism and regulation of FADs expression are tightly connected with preharvest factors that may modulate the response of grapefruits to postharvest cold storage.