Artemisia tridentata vaseyana (Rybd.) Beetle has two types of leaves: 1) ephemeral leaves present only in summer and 2) persistent leaves fully developed by September of each year and lasting for 12-13 months before being shed. Transmission and scanning electron microscopes were used to study their trichomes. Three month-old leaves were extracted with methylene chloride and the extracts were analyzed using gas chromatograph mass spectroscopy (GC/MS).
Glandular trichomes of the two types of leaves have a different morphology and physiology.
Ephemeral leaves had oblong-shaped ten-celled glandular trichomes. Each trichome was composed (from bottom to top) of a pair of support cells and four pairs of secretory cells. Three pairs of the secretory cells contained numerous chloroplasts while the topmost pair of secretory cells contain numerous mitochondria and no chloroplasts. Persistent leaves possessed round-shaped twelve-celled trichomes. Each trichome had a pair of support cells, a pair of stalk cells, and four pairs of secretory cells. Three pairs of the secreting cells contained plastids while the topmost pair of cells contained no plastids. The major constitutive terpenoids produced by ephemeral leaves were camphor (26.78%), eucarvone (18.48%), eucalyptol (15.60%), berbenone (8.19%) and camphene (7.06%). These compounds have documented action as pesticides or pest repellents. The major terpenoids in persistent leaves were safranal (28.38%), camphor (13.63%), 7-oxabicyclo[4.1.0]heptane (13%) eucalyptol(9.50%). The gland of ephemeral leaves appeared to produce volatile terpenoids, while glands of persistent leaves appeared to produce both volatile and non-volatile terpenoids.
Species 1: Asterales Asteraceae Artemisia tridentata (big mountain sagebrush)
Keywords: glandular trichomes
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