Ingress of Gaseous 1-Methylcyclopropene in Tomato Fruit, Poster Board #016

Recommended doses of gaseous 1-Methylcyclopropene (1-MCP, SmartFresh^TM Quality System) for harvested fruits and other plant tissues have been based on analyses of external levels required to attain desired responses; however, no information is available regarding the extent and rate of 1-MCP ingress. This study addressed ingress of gaseous 1-MCP in tomato fruit exposed to 20 µL·L^-1 1-MCP followed by sampling of internal atmosphere from fruit immersed in water. Harvested, unwaxed tomato fruit accumulated 1-MCP rapidly, reaching maximum values of approximately 6 to 8 µL·L^-1 within 3 h at 20 °C. Internal gaseous [1-MCP] declined approximately 60% to 70% within 1 h of removal and was nearly depleted within 3 h.  1-MCP ingress was similar among fruit of all ripening stages and reduced 45% in fruit coated with commercial wax. Diffusion of gaseous 1-MCP through inert matrices (e.g., glass microfibre filters) positioned between double-flask chambers occurred rapidly (< 30 min) through dry filter paper but was completely prevented through hydrated filter paper, providing evidence that water constitutes an effective barrier to 1-MCP diffusion.  Blocking 1-MCP ingress through peduncle and style scars by application of a water barrier resulted in a 50% to 60% reduction in accumulation of internal 1-MCP, indicating that 1-MCP ingress also occurs through epidermal tissues. Fruit preloaded with 1-MCP and immersed in water for 2 h retained from 45% to 70% of 1-MCP levels measured immediately after removal from the gas, indicating that significant quantities of 1-MCP remain in gaseous form and are not rapidly sorbed or metabolized by tomato fruit tissue. Diffusion of gaseous 1-MCP occurred rapidly through baby spinach and bok choi leaves, but was nearly completely prevented in epidermal and peduncle-scar disks of tomato and other fruits. Recent work in our lab demonstrated that excised tissues of some fruits can metabolize 1-MCP through apparent wound-induced, free-radical chemistry and are not suitable models for estimating 1-MCP ingress properties. Rapid ingress of 1-MCP was also observed in tomato fruit exposed to aqueous 1-MCP.  Immersion in aqueous 1-MCP at 1 mg·L^-1 for 1 or 2 min resulted in internal [1-MCP] of around 4 and 5.8 µL·L^-1, respectively. Analysis of internal [1-MCP] provides another tool for investigating variable responses of different fruits/cultivars to the low levels of 1-MCP (≤1 µL·L^-1) employed commercially. 1-MCP ingress is likely influenced by epidermal morphology, composition and architecture of native and applied waxes, and tissue hydration.