Quantification of the Product of the Direct Reaction Between Ozone and Oleanolic Acid in Cuticular Waxes of Grapes Under Ambient Conditions

Abstract:

Tropospheric ozone has detrimental effects on plant life, in part due to the degradation of epicuticular and cuticular waxes that protect leaves and fruit skins. Most agricultural regions in California also have very high levels of ozone, so ozone damage has real financial implications. 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 the direct reactions between molecular components in wax and ozone. In addition to implications for plant health, such reactions could constitute a significant source of non-stomatal ozone flux and influence ozone deposition onto plants. Our research focuses on investigating the reactions between ozone and oleanolic acid, which is a significant component of many plant waxes, especially those in grape skins. We have determined that the primary ozonolysis product of oleanolic acid in the pure solid state and in a wax matrix extracted from grape skins is a lactone that is known to form upon ozonolysis of oleanolic acid in solution. We have also observed qualitatively that plant waxes exposed to ambient air over the course of the summer in Redlands, CA show a significant amount of lactone by detecting the lactone signature using LC/Q-ToF MS. We are currently quantifying the amount of lactone produced in pure oleanolic acid and in waxes extracted from grape skins exposed to ambient air both indoors and outdoors over the course of the summer. This will provide an indication of the contribution of oleanolic acid in plant waxes to non-stomatal ozone flux over the course of several months.