Organization of Monoterpene Biosynthesis in Mentha. Immunocytochemical Localizations of Geranyl Diphosphate Synthase, Limonene-6-Hydroxylase, Isopiperitenol Dehydrogenase, and Pulegone Reductase

Abstract

We present immunocytochemical localizations of four enzymes involved in p-menthane monoterpene biosynthesis in mint: the large and small subunits of peppermint (Mentha x piperita) geranyl diphosphate synthase, spearmint (Mentha spicata) (2)-(4S)-limonene-6-hydroxylase, peppermint (2)-trans-isopiperitenol dehydrogenase, and peppermint (1)-pulegone reductase. All were localized to the secretory cells of peltate glandular trichomes with abundant labeling corresponding to the secretory phase of gland development. Immunogold labeling of geranyl diphosphate synthase occurred within secretory cell leucoplasts, (2)-4S-limonene-6-hydroxylase labeling was associated with gland cell endoplasmic reticulum, (2)-trans-isopiperitenol dehydrogenase labeling was restricted to secretory cell mitochondria, while (1)-pulegone reductase labeling occurred only in secretory cell cytoplasm. We discuss this pathway compartmentalization in relation to possible mechanisms for the intracellular movement of monoterpene metabolites, and for monoterpene secretion into the extracellular essential oil storage cavity.Monoterpenes are a large and diverse class of volatile C 10 isoprenoids that are the major constituents of many plant essential oils and resins. These natural products play important chemoecological roles in the interactions of plants with their environments. Some monoterpenes have been implicated as allelopathic agents, and they often directly, or indirectly, protect plants from herbivores and pathogens (Pickett, 1991;Harborne, 1991;Langenheim, 1994;Wise and Croteau, 1999;Hallahan, 2000). As important constituents of floral scents, monoterpenes also function to attract pollinators (Dudareva and Pichersky, 2000). Some plants release volatile monoterpenes and sesquiterpenes in response to herbivore damage that function to attract predatory insects that in turn feed on, or parasitize, the herbivorous insects (Langenheim, 1994;Degenhardt et al., 2003). In conifer species, mechanical wounding, insect attack, or applications of methyl jasmonate can induce resin secretion and differentiation of traumatic resin ducts within wounded tissues, producing a protective barrier of resin at the site of wounding (Steele et al., 1995;Trapp and Croteau, 2001;Franceschi et al., 2002;Martin et al., 2002). Many plant species constitutively produce large quantities of terpenoid-rich resins and essential oils within specialized glandular tissues, such as glandular trichomes, secretory cavities, and secretory ducts (Fahn, 1979(Fahn, , 2000. These natural stores of plant terpenoids probably serve as deterrents to herbivorous insects, but they also provide commercially important sources of flavorings, fragrances, resins, and pharmaceuticals (Langenheim, 1994;Wise and Croteau, 1999). The glandular cells of these secretory tissues are of interest for their remarkable ability to rapidly generate substantial amounts of specific terpenoid products.Peppermint (Mentha x piperita) has been employed as a model system for the study of monoterpene biosynthesis (Wise an...

Biosynthesis of plant‐derived flavor compounds

“…The peltate glandular trichomes of peppermint produce copious amounts of a commercially valuable, menthol-rich essential oil, composed primarily of p-menthane monoterpenes (Turner and Croteau, 2004). The glandular trichomes of sweet basil (Ocimum basilicum) are rich in phenylpropenes as well as monoterpenes and sesquiterpenes (Iijima et al, 2004a).…”

“…While many terpene volatiles are direct products of terpene synthases, many others are formed through transformation of the initial products by oxidation, dehydrogenation, acylation and other reactions (Croteau and Karp, 1991;Croteau et al, 2000;Dudareva et al, 2004;Pichersky et al, 2006). For example, ())-(1R,2S,5R)-menthol, the principal monoterpene of commercial peppermint essential oil and the component responsible for the familiar cooling sensation of peppermint and its products, is formed by eight enzymatic steps involving monoterpene synthases, isomerases and reductases (Ringer et al, 2005;Turner and Croteau, 2004). The biosynthesis starts with the formation of 4S-limonene from GPP and ends with the reduction of ())-menthone to ())-menthol.…”

Isolation and functional expression of an animal geranyl diphosphate synthase and its role in bark beetle pheromone biosynthesis

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] C]IPP was purchased from American Radiochemicals (St. Louis). Unlabeled IPP, DMAPP, GPP, FPP, and GGPP were purchased from Sigma.…”

“…GPPS catalyzes a single condensation of dimethylallyl diphosphate (DMAPP) with IPP to produce GPP, the C 10 backbone component of monoterpenes (9). Monoterpene biosynthesis is primarily localized to plastids of plant cells (10)(11)(12), found in the essential oil and resin of plants they function in plant defenses, in allelopathic responses, and as attractants of pollination (1). Recently, the isolation of cDNAs encoding GPPS from Mentha piperita (13), Arabidopsis thaliana (14), Abies grandis (15), Antirrhimum majus, and Clarkia breweri (11) has allowed for its functional characterization.…”

Essential oil research: past, present and future

“…[13] The Mendelian segregation of Mentha spp. [14,15] was exhaustively studied in a fascinating way, followed by several other EO plants, including chamomile. [16] Such experiments contributed, for instance, to specifi c knowledge on the fi nal biosynthetic steps in the formation of thujones in sage (J. Novak, personal communication) or of sabinene hydrate acetate in marjoram.…”