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Adirek Rugkong, Jocelyn K.C. Rose, and Chris B. Watkins

Tomato fruit (Solanum lycopersicum L.) can develop mealiness and enhanced softening when exposed to chilling temperatures during storage, but the involvement of cell wall-associated enzymes in chilling injury development is not well understood. To study this aspect of injury development, we have exposed breaker-stage `Trust' tomato fruit to a chilling temperature of 3 °C for 0, 7, 14, and 21 days followed by storage at 20 °C for 12 days. Ethylene production was not affected by storage except after 21 days where production was greater at 20 °C. Exposure of fruit to chilling temperatures delayed the ripening-related color change (chroma and hue) and initially increased compression values, but percent extractable juice was not affected consistently. Increased polygalacturonase (PG) activity during ripening was reduced by about 50% after 7 days at 3 °C, and further inhibited with increasing storage periods. In contrast, the activities of pectin methylesterase (PME) and α-galactosidase were not significantly affected by the cold treatments. β-Galactosidase activity was greater in all chilled fruit compared with fruit ripened at harvest, whereas endo-β-1,4-glucanase activity was lower after 21 days at 3 °C. In chilled fruits, transcript accumulations for PG, PME (PME1.9), and expansin (Expt.1) were lower during storage at 20 °C compared with those of nonchilled fruits. Transcript accumulation for β-galactosidase (TBG4) was affected only at 14 days of cold storage, when transcript accumulation decreased. Cold treatment increased transcript accumulation of endo-β-1,4-glucanase (Cel1) after 12 days at 20 °C and decreased transcript accumulation after 7 days and 21 days at 21 °C. Cell wall analyses to investigate relationships among enzyme activities and cell wall disassembly are ongoing.