Response of the Fruit Antioxidant System to the Post-Chilling Period in Two Different Tomato Lines

Antioxidant systems play an important role in prevention of chilling injury, and chilling-tolerant fruit may initially contain more antioxidants or be able to maintain their antioxidant levels during stress. Tomato fruit are chilling sensitive and chilling symptoms generally appear after fruit are transferred to non chilling temperatures. The aim of this study was to characterise the events occurring at 20°C, immediately after a storage period at 4°C, and to establish the importance of tomato fruit ascorbic acid levels in the response to chilling. Two different tomato lines were used: a processing cultivar (M82) with low to average ascorbic acid levels and an introgression line (IL9.2.5) containing elevated ascorbic acid levels due to the introgression of wild Solanum pennellii alleles on chromosome 9. We show a rapid response (0.5 hours) of the antioxidant system in tomato to re-exposure to normal temperatures and light following chilling. The ascorbate redox state undergoes rapid changes and is followed by changes in the redox state of the glutathione pool. The response is different in the two tomato lines studied: fruits from IL9.2.5 have a higher ascorbic acid and glutathione redox state compared to the parent M82 where the pool of both antioxidants becomes oxidised. The redox state of the ascorbate pool is correlated with the activity of enzymes involved in ascorbate regeneration (monodehydroascorbate reductase and dehydroascorbate reductase) in the fruit. Furthermore the ability of IL9.2.5 to maintain reduced antioxidant levels is correlated with a decreased loss of fruit firmness when compared to M82. _____________________________________________________________________________________________________________