Cell wall metabolism in cold-stored tomato fruit

The effects of chilling on cell wall metabolism of tomato fruit (Solanum lycopersicum L. cv. Trust) have been investigated. Fruit were harvested at the breaker stage of maturity and ripened at 20 °C for 1–12 d, or stored at 3 °C for up to 3 weeks, and then ripened at 20 °C. The effects of cold storage on fruit ripening were small. Pericarp tissues from fruit stored for 2 weeks had only slightly reduced pectin solubilization and depolymerization. Polygalacturonase (PG) mRNA levels, PG protein accumulation and PG activity in the tissues were also reduced by chilling. A reduction of PG protein abundance and PG activity occurred to a greater extent than that of PG mRNA levels, suggesting that chilling affected post-transcriptional regulation. Expression of the expansin1 (LeEXP1) gene was also reduced by chilling, but LeExp1 protein accumulation levels were not affected by chilling. β-Galactosidase activity was highest in chilled fruit during cold storage and during early ripening, but expression of a β-galactosidase gene (TBG4) was unaffected. While chilling had no effect on pectin methylesterase (PME) activity, expression of PME1 in tissues from cold-stored fruit was lower. Endo-β-1,4-glucanase (EGase) activity and the expression of endo-β-1,4-glucanase (Cel1) were not affected by chilling. The predominant effect of chilling on the activity, protein accumulation, and gene expression of PG did not correlate with pectin solubilization and depolymerization.