Terpene response

Many plants release chemicals that inhibit the germination and growth of other plants. Included among them are some of the terpenes responsible for the fragrance of many plants. They may travel from the leaves of plants to the soil as the leaves decompose. Many allelopathic substances are released from the roots of plants and have important effects on soil bacteria and fungi. The role that they play in organizing plant communities in nature is still controversial. 

Phytoalexins are low molecular weight compounds produced in plants as a defense mechanism against microorganisms. They do, however, exhibit toxicity to humans and other animals in addition to microbes (30). Coumarins, glycoalkaloids, isocoumarins, isoflavonoids, linear furanocoumarins, stilbenes, and terpenes aU. fall into the category of phytoalexins (31). Because phytoalexins are natural components of plants, and because their concentration may increase as a response to production and management stimuli, it is useful to recogni2e the possible effects of phytoalexins in the human diet. 

Polyterpenes. Polyterpenes is one of the first classes of non-polar tack-ifiers to be developed. Terpene monomers are a by-product in the extraction of rosin from wood stumps or tree sap, and from the extraction of oils from citrus fruits. The latter is the dominant source. As such, polyterpene prices generally mirror those of citrus fruits, which fluctuate substantially from one growing season to the next. Terpenes like rosin are cyclic, see Fig. 6, which is partly responsible for their excellent solvent properties. 

Plants produce a vast array of terpenes, alkenes built in multiples of five carbon atoms. Many terpenes have characteristic fragrances. For example, the fresh odor of a pine forest is due to pinene, a ten-carbon molecule with a ring structure and one double bond. The fragrances of terpenes make them important in the flavor and fragrance industry. Limonene, another ten-carbon molecule with a ring and two double bonds, is the principal component of lemon oil. Geraniol, a chainlike molecule with two double bonds, is one of the molecules that is responsible for the fragrance of roses and is used in many perfumes. Many other terpenes have important medicinal properties. 

Rycroft et al. (1999) identihed the major components of plants from six locations in western Scotland and four from the Azores using nuclear magnetic resonance (NMR) fingerprinting and GC-MS. The terpene P-phellandrene [129], which may be responsible for the aroma of material crushed in the held, was detected in all specimens. The major components, which appear in Fig. 5.6, were shown to be methyl eveminate [444], the four methyl orcellinate derivatives [445 8], the two 9,10-dihydrophenanthrene derivatives [449] and [450], the newly described phthalide killamiensolide [451], and the bibenzyl [453]. Methyl eveminate was the major compound in all 10 specimens other compounds were more varied in their occurrence. Killamiensolide was not isolated as such but was detected when extracts were acetylated yielding, among other compounds, [452]. The presence of the bibenzyl compound [453] in more than trace amounts in P. killarniensis raises the possibility that it represents contamination from P. spinulosa with which it was growing at the one site. 

A recent example demonstrates that corals rely on induced biosynthesis of terpenes as a dynamic defense strategy as well. The induction of terpenoid secondary metabolites was observed in the sea whip Pseudopterogorgia elisabethae [162]. Levels of pseudopterosins 89-92, a group of diterpene glycosides with anti-inflammatory and analgesic properties (Scheme 23) [163-165], are increased in response predation by the mollusk Cyphoma gibbosum. First bioassays indicate that these natural products are involved in the chemical defense. 

The analytical technique of choice for the identification of low molecular weight terpenes and terpenoids is GC/MS, assisted by off-line methylation or silylation reactions. However, comparable results in terms of sensitivity and response specificity... 

Chen F, Ro DK, Petri J, Gershenzon J, Bohhnann J, Pichersky E, Tholl D (2004) Characterization of a root-specific Arabidopsis terpene synthase responsible for the formation of the volatile monoterpene 1,8-cineole. Plant Physiol 135 1956-1966... 

Pine oil is a by-product of the pulp industry. This oily liquid contains a mixture of terpene alcohols and monoterpenes and is available under the trade name Norpine-65. Snowshoe hare, L. americanus, and voles,M. townsendii, consume less laboratory chow, apples, or carrots if they are treated with pine oil. This response did not habituate within the time of the experiment. When considering the use of pine oil as a herbivore repellent, we have to keep in mind that it is phytotoxic to seedlings if applied topically (Bell and Harestad, 1987). Red deer, C. 

Kohnle U, Francke W, Bakke A, Polygraphuspoligraphus (L.) Response to enantiomers of beetle specific terpene alcohols and a bicyclic ketal, Z Angew Entomol... 

Prenylation, the key step in terpene biosynthesis, is catalyzed by prenyltransferases. These enzymes are responsible for the condensation of isopentenyl pyrophosphate (IPP) with an allyl pyrophosphate, thus yielding isoprenoids. Numerous studies have been performed with fluorinated substrates in order to determine the mechanism of the reactions that involve these enzymes prenyltransferases, farnesyl diphosphate synthase (FDPSase), famesyltransferase (PFTase), and IPP isomerase. These studies are based on the potential ability of fluorine atoms to destabilize cationic intermediates, and then slow down S l type processes in these reactions. 

Within the domain of medicinal plants, preparations of Ginkgo biloba (Ginkgoaceae) are the most widely sold phytomedicines, with sales of over US 1 billion in 1998. " These principally involve special extracts of the leaves. Flavonoids are, at least in part, responsible for the beneficial effects of Ginkgo extracts. Generally, enriched ginkgo extracts for the preparation of ginkgo products are standardized to contain 24% flavonoids and 6% terpene... 

Historically, terpenes have enjoyed a role as symptom-relieving therapeutics. Camphor and carvone (spearmint oil) have been used as soothing agents in the past history of pharmaceutical compounds. More recently, the role of terpenes in biochemistry has been more fully appreciated. P-Carotene, for example, may be cleaved into two units of vitamin A. Other terpenes, such as geraniol, are now recognized as pheromones (a chemical secreted by one individual of a given species in order to elicit a response in another individual of the same species). Pheromones are of interest in medicinal chemistry for a variety of indications for instance, attractant pheromones can be used for the control of insects known to spread human disease. 

Ergosterol, the predominant sterol in yeast cells, plays an important role in membrane fluidity, permeability and the activity of many membrane-bound enzymes. In terpene-treated cells, ergosterol synthesis was strongly inhibited, and a global upregulation of genes associated with the ergosterol biosynthesis pathway was described in response to terpene toxicity [80, 121]. 

Figs. 7.1-7.4), which are responsible for a spicy, floral and fruity characteristic of stone fruits [17, 64, 71, 72]. Ca compounds are the major volatiles in immature, green fruits but the levels of these compounds decrease drastically during maturation, and lactones (lactonic note), aldehydes (benzaldehyde with an almond, nutty and stone fruit note), terpenes (linalool with a floral note) and esters become prominent [14,15, 65, 66, 68, 70]. 

The modern distinction between vegetable and fruit has been applied and therefore those plants or plant parts that are usually consumed with the main course of a meal will be regarded as vegetables thus, cucumber, tomato and pumpkin that botanically are classified as fruits are included in this section. The flavour compounds found in vegetables are diverse and include fatty acid derivatives, terpenes, sulfur compounds as well as alkaloids. This diversity is partially responsible for the unique flavours found in different species of vegetables. 

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