My research concerns control of oxylipin formation. Oxylipins are a diverse class of oxygenated fatty acid derivatives with roles in plant growth and development, pest resistance and quality of food products. Some oxylipins are also high value industrial chemical feedstocks. Oxylipin formation is thought to be initiated by specific lipases which release free fatty acids (FFAs) from membrane lipids. FFAs are subsequently acted upon by lipoxygenases (LOXs) and then by hydroperoxide lyase (HPL), allene oxide synthase (AOS) and/or peroxygenase, generating volatile 6-carbon aldehydes, jasmonic acid (JA), and epoxy/hydroxy fatty acids, respectively.

6-carbon aldehydes and alcohols such as hexanal, trans-2-hexenal and cis-3-hexenol are associated with 'green odors' of leaves and are important components of the aroma and flavor of many food and beverage products. These volatile compounds are lost during the production process such as canning or drying. As a result, there is interest in the food industry for the natural production of these compounds so as to be used in food and beverage flavorings. These compounds are also associated with off-odor and off-flavor of soybean products. Thus, some of the 6-carbon aldehydes are thought to have antimicrobial properties. Normally, 6-carbon aldehydes and alcohols are undetectable in undamaged plant tissues except from fruits and flowers.

JA and its methyl ester, methyl-jasmonate (JAMe) are involved in signal transduction in response to wounding and pest attack. JA and/or JAMe can induce proteinase inhibitors in plants, which can be important in pest resistance.

Members of the Artemisia species are of economic use. Artemisia afra is a medicinal herb (it is used to treat coughs, colds and flu, as well as intestinal ailments) in South Africa. A. absinthium and A. camphorata are moth and insect repellents, respectively. In China, A. annua and A. vulgaris are used to treat malaria and asthma, respectively. A. dracunculus is used for maximizing food flavor.

Our research with these plants is not directly geared towards the understanding of their medicinal value, but rather the oxylipin pathway which is thought to give flavor and aroma to food, as well as conferring resistance to pests.

Our preliminary data have shown that species of Artemisia produce a high level of JA and JAMe, as well as 6-carbon aldehydes from crushed leaves. In addition, these plant species seem to have comparable level of esterified and free fatty acids. JA/JAMe, 6-carbon aldehydes and fatty acids were analyzed by Gas Chromatography (GC-FID detector), and their identity confirmed by Gas Chromatography-Mass Spectrometry (GC-MS).

The overall goal of this research project is to understand the regulation of JA/JAME and 6-carbon aldehyde formation in Artemisia species. This will be achieved by:

1. feeding [U-¹⁴C] linolenic acid (18:3) to plant tissues and monitor its conversion to JA and 6-carbon aldehydes, and
2. examine step(s) representing key regulatory points in the formation of JA and 6-carbon aldehydes

Cited References

Farmer, E. E. and Ryan, C. A.  (1990)  Interplant communication:  Airborne methyl jasmonate induces synthesis of proteinase inhibitors in plant leaves.  PNAS 87:  7713-7716

Gardner, H. W.  (1989)  How lipoxygenase pathway affects the organoleptic properties of fresh fruit and vegetables.  In D. B. Min and T. H. Smouse, eds.  Flavor Chemistry of Lipid Foods.  Am. Oil Chemists Soc., Champaign, IL, pp. 98-112

Hamberg, M. and Gardner, H. W.  (1992)  Oxylipin pathway to jasmonates:  Biochemistry and Biological Significance.  Biochem. Biophys. Acta 1165:  1-8

Hatanaka, A., Kajiwara, T. and Sekiya, J.  (1987)  Biosynthetic pathway for 6-carbon aldehyde formation from linolenic acid in green leaves.  Chem. Phys. Lipids 44:  341-361