UV-C effect on ethylene, polyamines and the regulation of tomato fruit ripening

Molecular responses of tomato fruit harvested at the breaker ripening stage treated with UV-C (3.7 kJ/m2) and 1-methylcyclopropene (1-MCP; 2 μL/L) both separately and in combination, were evaluated postharvest until fruit reached fully ripe stage. Metabolite content and transcript accumulation of selected genes were examined in both the exocarp and mesocarp tissues of tomato fruit. UV-C radiation induced ethylene production but delayed red color development. As expected, 1-MCP inhibited ethylene production, color development and loss of flesh firmness. UV-C treatment delayed degreening and carotenoid accumulation when compared to control fruit. In addition, polyamine content of UV-C treated fruit was higher than in untreated tomatoes. In general, the studied genes had increased transcript accumulation one day after UV-C treatment and the mesocarp showed higher gene expression than the exocarp. 1-MCP prevented transcript accumulation of almost all genes on either the exocarp or mesocarp one day after treatments. The 1-MCP + UV-C induction of total carotenoid accumulation suggested that UV-C induction of total carotenoid accumulation is a partially ethylene dependent event, since 1-MCP alone inhibited accumulation and UV-C alone induced accumulation. Chlorophyll degradation was also partially ethylene dependent. 1-MCP prevented degradation, but control and UV-C treated fruit had high chlorophyll degradation while 1-MCP + UV-C treated fruit showed chlorophyll degradation higher than in 1-MCP alone and lower than in UV-C alone. The results suggest that UV-C slows down ripening, despite ethylene production stimulation, with molecular changes more pronounced in the mesocarp than the exocarp, and changes limited to phytochemical content, which may be influenced by the increased polyamine content.