Postharvest UV-C irradiation inhibits the production of ethylene and the activity of cell wall-degrading enzymes during softening of tomato (Lycopersicon esculentum L.) fruit

Mature green cherry tomato fruit were harvested and treated with ultraviolet-C (UV-C) irradiation at a predetermined dose of 4.2   kJ   m −2 and stored at 18   °C for 35 days. The effects of UV-C treatment on firmness, cell wall compositions (pectin and cellulose), cell wall ultra-structure, levels of ethylene production, and activities of cell wall degrading enzymes in the fruit were investigated during storage. Major genes involved in cell wall degradation ( PME 2.1, Cel 1, PG cat and Exp 1) were also checked. Fruit firmness was better maintained in UV-C treated fruit corresponding with higher contents of cellulose and acid-soluble pectin. Transmission electron microscopy indicated that UV-C irradiation retarded cell wall disassembly in the pericarp. Ethylene production was significantly inhibited by UV-C treatment. The UV-C treatment also suppressed the transcriptional expression of PME2.1 , Cel1 , PGcat and Exp1 genes, and inhibited pectin methylesterase (PME; EC 3.1.1.11), polygalacturonase (PG; EC3.2.1.15) and cellulase (EC3.2.1.4) activities during storage. These results suggested that the inhibition of ethylene production, which in turn down-regulated expression of genes encoding cell wall degrading enzymes, might be one of the possible mechanisms of UV-C delaying tomato fruit softening.