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 degrees 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. (C) 2013 Elsevier B.V. All rights reserved.