Leaf trichome types

During the 1970 s the USDA Nicotiana tabacum germplasm collection was evaluated in field plots at the Clemson University Pee Dee Research and Education Center, Rorence, SC for their resistance to the tobacco hornworm, Manduca sexta (L,) (1), and the tobacco budworm, Heliothis virescens (F.) (2). During this investigation a large variation in leaf trichome types and density was observed. Johnson et al. (3,4) classified the major trichome types from the various tobacco types as simple trichomes without exudates, glandular trichomes without exudates, glandular trichomes with exudates, and... 

Kamatou, G.P.P., R.L. van Zyl, S.F. van Vuuren, A.M. Viljoen. A.C. Figueiredo, J.G. Barroso, L.G. Pedro, and P.M. Tilney, 2006. Chemical composition, leaf trichome types and biological activities of the essential oils of four related salvia species indigenous to Southern Africa. J. Essent. Oil Res., 18(Special edition) 72-79. 

As is the case with many members of Lamiaceae, Satureja douglasii produces abundant essential oil from glandular trichomes on the leaves. Gas chromatographic analysis of the leaf oils from specimens collected throughout the species range revealed the presence of some dozen and a half well-known compounds. The major compounds identified were camphene [215], camphor [216], which, taken together, were considered to comprise the bicyclic type, carvone [217], pulegone [218], menthone [219], and isomenthone [220] (see Fig. 2.68 for structures 215-220). The predominance of each of these major components defined a terpene type. (All compounds were observed in each of the terpene types, most in comparatively small amounts, some only as traces.)... 

Polyphenol Oxidases. Plant trichomes and their exudates confer resistance to a variety of insects (54-56). In solanaceous plants, such as the tomato and potato, trichomes contain polyphenol oxidases and catecholic phenolics (e.g., caffeic and chlorogenic acids), which contribute to resistance to a variety of insect pests. In the potato plant, the polyphenol oxidases and phenolics are separated in different trichomes. When insects, such as aphids or leaf hoppers, walk across the surface of the plant they break the two types of trichomes. Trichomal fluids are liberated and, upon mixing, polymerize as a result of polyphenol oxidase activity on catechols, forming an often lethal adhesive trap for the insects (52,58) In tomato plants, the polyphenol oxidase and chlorogenic acid are separated by intracellular compartments, but upon breakage of trichomes by insects, polymerization and physical entrapment occurs (54). 

Fig. 86.—Transverse section through portion of dorsoventral leaf blade of horehound Marrubium vulgare). Upper epidermis devoid of stomata up.ep.) lower epidermis which possesses stomata (1. ep) palisade parenchyma (pal.) spongy parenchyma (sp, p) xylem ( ) and phloem ph) regions of fibrovascular tissue of stronger vein long-pointed non-glandular trichome (I), branched tri-chomes (/(, ft fP) several types of glandular trichomes (gt, gt, gt , gi ).

Several woody plant species will react to exposure of simulated acid rain by forming foliar lesions. While the pH level of simulated acid rain that produced these lesions varies from species to species, the lesions themselves are generally yellow to brown necrotic spots or regions (see Table 1). Additionally, on two clones of poplar, galls were formed in response to simulated acid rain. Surface characteristics such as stomatal presence and density, trichome density, type and amount of epicuticular wax, leaf surface wettability and buffering capacity have all been shown to influence foliar injury by simulated acid rain. However, it may be... 

The sesquiterpenes of j>. tuberosum foliage are not present in sufficient quantities at the leaf surface interface to discourage aphid settling. By contrast, the exudate of the Type B glandular trichomes on S. berthaultii foliage contains sesquiterpenes, thus enhancing the external level of these insect-repellent compounds. 

Terpenoids can be found in various plant organs. Concentrations of terpenoids in plant tissues are controlled by the availability of substrate and the activity and type of biosynthesis enzymes. Emission rates of volatile terpenoids from plant leaves are controlled by their synthesis rates and compound-specific physicochemical characteristics, mainly their solubility, volatility and diffusivity. These are affected by physicochemical constraints caused by temperature, stomatal conductance and leaf structure. Storage of terpenoids could be isolated from other plant tissues with specialized structures such as secretory cavities, resin canals (Fig. 94.1), latex canals (lactifers), and glandular trichomes. 

---