Ethylene biosynthesis and signaling elements involved in chilling injury and other postharvest quality traits in the non-climacteric fruit of zucchini (Cucurbita pepo)

• 1-MCP improves postharvest quality parameters in zucchini: PCI, weight loss and firmness.
• The response to 1-MCP in zucchini squash is genotype dependent.
• Zucchini fruit induces the expression of ethylene biosynthesis and signaling genes in response to cold storage.
• 1-MCP reduces the respiration rate and the production of ethylene in the refrigerated fruit of zucchini.
• 1-MCP downregulates the expression of genes involved in ethylene biosynthesis, perception and signaling.

The immature non-climacteric fruit of zucchini is very sensitive to postharvest chilling injury (PCI). Although the fruit produces very low ethylene at harvest, cold storage induces an increase in ethylene production in the refrigerated fruit, and upon rewarming up to room temperature. The production of ethylene after rewarming was proportional to cold damage and found to be higher in the fruit of the cultivars most susceptible to chilling. The effects of the ethylene inhibitor 1-methycyclopropene (1-MCP) has been analyzed using the postharvest quality parameters of nine zucchini cultivars stored at 20 °C and 4 °C for 14 days. We have also determined the evolution of ethylene production in the fruit of these cultivars, and assessed the expression profiles of twelve ethylene biosynthesis and signaling genes in both control fruit and in 1-MCP treated fruit, of two cultivars that responded to 1-MCP. The 1-MCP treatment reduced the rate and delayed the onset of PCI symptoms and reduced fruit weight loss, although only in the fruit of the most chilling-susceptible cultivars, and concomitantly we found a reduction in the respiration rate and in the level of cold-induced ethylene. This data suggests that ethylene is not only a response of the fruit to cold damage, as occurs upon rewarming, but could also play a regulation role in the onset of PCI in this non-climacteric fruit. The genes CpACO1 and CpACS1 were found to be involved in the biosynthesis of the cold-induced ethylene, but the role played by CpACO1 was found to be the key function, since it was induced higher than CpACS1 in response to cold storage. More over CpACO1 was the only ethylene biosynthesis gene that was downregulated by the 1-MCP treatment. Some of the ethylene perception and signaling genes, including CpETR1, CpCTR1 and CpEIN3.1 were also induced in response to cold storage, and were downregulated in response to 1-MCP, indicating that the positive effect of 1-MCP in the fruit of certain zucchini cultivars is also associated with a downregulation of genes involved in ethylene perception and signal transduction pathways.