| Terpenoids are produced by glandular trichomes of leaves of the mountain big sagebrush, Artemisia tridentata vaseyana (Rydb.) Beetle. Sagebrush possesses two types of leaves, summer ephemeral and winter persistent. I hypothesized that the peltate glandular trichomes of the two types of leaves were different and have a different pattern of producing terpenoids. Scanning electron microscopy and transmission electron microscopy were used to show the different types of trichomes of sagebrush leaves. Gas chromatography and mass spectroscopy were used for qualitative and quantitative analysis of the terpenoids in ephemeral leaves. Attempts to extract a fragment of the cyclase gene for study of the differential expression of cyclase mRNA in clipped versus control ephemeral leaves did not give satisfactory results.; Sagebrush has three types of trichomes: (1) “T”-shaped cover trichomes which blanket the leaves, giving them a silvery look. (2) Ten-cell peltate glandular trichomes on ephemeral leaves which are oblong in shape, and consist of one pair of stalk cells, one pair of secreting-support cells, and three pairs of secreting cells. This gland produces highly pressurized volatile terpenoids in the secretory head of the mature trichome and has four times the surface area as the round shaped trichome found on the persistent leaf. (3) Round trichomes on persistent leaves which have six pairs of cells consisting of one pair of stalk cells, one pair of support cells, and four pairs of secretory cells. These glands secrete volatile and non-volatile terpenoid compounds and are susceptible to shedding in extreme environmental conditions.; In three months, trichomes of the summer leaves reach their optimum production of volatiles, which makes this leaf type suitable for studies of alternatives for methyl bromide. The major terpenoid constituents of ephemeral leaves are camphor, eucarvone, eucalyptol (1, 8-cineole), and camphene. Camphor and eucarvone are natural pesticides, herbicides and fungicides. The increase of camphor (70%), eucarvone (66%), and α- and β-pinene 15 days after pruning, shows that A. t. vaseyana reacts to pruning of its branches. A mixture of camphor, eucarvone, eucalyptol, and α-pinene may be effective in controlling insect pests. |
