Tropospheric ozone has been found to have detrimental effects on plant life, in part due to the degradation of epicuticular and cuticular waxes that protect leaves and fruit skins from water loss, ultraviolet radiation, pathogens, and insects. A number of studies have explored the morphological changes and broad changes in functional group composition in waxes due to ozone exposure. However, little work has been done on direct reactions between molecular components in wax and ozone. Our research focuses on investigating the reactions between ozone and oleanolic acid, which is an important component of plant waxes in samples such as olive leaves and grape berry skins. We exposed pure oleanolic acid to ozone in PTFE bottles, separated the products using flash chromatography, and identified the products using various NMR techniques and HPLC-QToF-MS. We determined that the primary ozonolysis product of oleanolic acid is a lactone. We extracted waxes from the leaves of a dwarf olive tree (Olea europea) and the skins of red and green table grapes and analyzed the waxes via HPLC-QToF-MS. We ozonized waxes in PTFE bottles under humid and dry conditions and then analyzed the products via HPLC-QToF-MS. We determined that oleanolic acid reacted with ozone to form a lactone product in waxes from both Olea europa leaves and grape berry skins. Leaves harvested from the dwarf olive plant in January of 2018 showed significant levels of oleanolic acid and very little lactone. Leaves harvested from the same plant in September of 2018 and later showed very little oleanolic acid and very high levels of the lactone. This suggests that exposure to ambient conditions was sufficient to convert much of the oleanolic acid to the lactone. We are currently investigating the ability of ozone at ambient conditions to oxidize oleanolic acid using pure oleanolic acid standards and extracted plant waxes. These results have implications for understanding how ozone can affect wax structure and how ozone can deposit onto plants.

Evidence of direct reaction between ozone and oleanolic acid in plant cuticular waxes under laboratory and ambient conditions

2019 Fall National Meeting

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