Resins ducts

Fig. 1. Schematic section, where AR = annual ring, BP = bordered pits, F = wood fiber, FWR = fusiform wood ray, HRD = horizontal resin ducts,...

Wood also contains 3—10% of extraceUulat, low molecular weight constituents, many of which can be extracted from the wood using neutral solvents and therefore ate commonly caUed extractives. These include the food reserves, the fats and their esters in parenchyma ceUs, the terpenes and resin acids in epitheUal ceUs and resin ducts, and phenoUc materials in the heartwood. Resin materials occur in the vessels of some hardwood heartwood. 

Harz-galle,/ resin deposit (in wood), resin gall, -gang, m. (Bot.) resin duct, -gas, n. resin gas. 

Harz-reserve,/. (Calico) resin resist. -r3hre,/. resin duct, -saft, m. resinous j uice. -aalbe, /. (Pharm.) rosin cerate, -salz, n. resinate. harzsauer, a. of or combined with a resinic acid, resinate of. 

OCM images of resin ducts in in Picea and Pinus silvestris L. are shown in Fig. 3. The ducts appear as light spots located near the needle surface. Resin if not crystallized, is in a liquid form and is not registered as a dense material. 

Fig. 3 OCM Images of resin ducts (shown by arrows) in the needles of Conifer plants a -Picea sp. b - Pinus sylvestris L.

Martin D., Tholl D., Gershenzon J. and Bohlmann J. (2002) Methyl jasmonate induces traumatic resin ducts, terpenoid resin biosynthesis and terpenoid accumulation in developing xylem of Norway spruce stems. Plant Physiol. 129, 100-1018. 

Plants not only evolved allelochemicals with broad activities (see Section 1.3.1) but also some that can interfere vdth a particular target [3,6,17-19,25]. Targets that are present in animals but not in plants are nerve cells, neuronal signal transduction, and the endocrinal hormone system. Compounds that interfere with these targets are usually not toxic for the plants producing them. Plants have had to develop special precautions (compartmentation resin ducts, trichomes, laticifers) in order to store the allelochemicals with broad activities that could also harm the producer. 

Paraffin followed by candelilla wax and microcrystalline waxes, and eventually by beeswax, are considered as the most effective moisture barriers derived from edible waxes (Morillon et al. 2002). There is no satisfactory chemical definition for the term wax which is used for a variety of products of mineral, botanical and animal origin that contain various kinds of fatty materials (Table 23.4). The term resins or lacs can also be used for plant or insect secretions that take place along resins ducts, often in response to injury or infection, and result in more acidic substances (Hernandez 1994). However, all waxes tend to contain wax esters as major components, that is, esters of long-chain fatty alcohols with long chain fatty acids. Depending on their source, they may additionally include hydrocarbons, sterol esters, aliphatic aldehydes, primary and secondary alcohols, diols, ketones, triacylglycerols, and so on. 

Water soluble compounds are usually stored in the vacuole (Matile, 1978, 1984 Boiler and Wiemken, 1986 Wink, 1993, 1997 Terasaka et al, 2003 Kutchan, 2005 Yazaki, 2005, 2006) (Table 1.2), whereas lipophilic substances are sequestered in resin ducts, laticifers, glandular hairs, trichomes, thylakoid membranes or on the cuticle (Wiermann, 1981 Kutchan, 2005) (Fig. 1.5). 

Lipophilic compounds will interfere not only with the biomembranes of microbes and herbivores, but also with those of the producing plant. In order to avoid autotoxicity, plants cannot store these compounds in the vacuole but usually sequester them on the cuticle, in dead resin ducts or cells, which are lined not by a biomembrane but by an impermeable solid barrier (Fig. 1.5). In some cases, the compounds are combined with a polar molecule, so that they can be stored as more hydrophilic chemicals in the vacuole. 

Formation of speciaiized storage compartments (resin ducts, iaticifers, trichomes)... 

McKay, S.A., Hunter, W.L., Godard, K.A., Wang, S.X., Martin, D.M., Bohlmann, J. and Plant, A.L. (2003) Insect attack and wounding induce traumatic resin duct development and gene expression of (—)-pinene synthase in Sitka spruce. Plant Physiol, 133, 368-78. 

Diterpene resin acids are abundantly produced in conifers of the pine family (Pinaceae) and in other plant species (Fig. 6). They are produced in the epithelial cells that surround the resin ducts that are found constitutively, or they are induced in the xylem upon wounding and are important for the physical and chemical plant defenses against herbivores and pathogens (18, 40). Industrially, diterpene resin acids are important chemicals for the naval stores industry, in printing inks, as potential antimicrobials and pharmaceuticals, and are byproducts of wood pulping processes. 

When guayule is in an active growth phase, it produces little or no rubber, but if the plants are stressed, such as in cool weather or because of reduced moisture supply, biomass growth slows and the photosynthetic products are diverted to rubber production. The rubbers are not metabolized by the plant, even when it is deprived of all carbohydrates and other energy sources, and continue to accumulate for at least 10 years. The resins, which include terpenes, sesquiterpenes, diterpenes, glycerides, and low-molecular-weight polyiso-prenes, are found in resin ducts throughout the plant they constitute 10-15 dry wt % of the plant. 

Pig. 56.—Resin duct (secretion reservoir) in leaf of Pinus sUveslris, in cross section at A, and in longitudinal section at A, cavity surrounded by the secreting cellssclerenchyma fibers surrounding and protecting the duct. (Stevens, after Haberlandt. 

Figure 9. Light micrograph of the earlywood-to-latewood transition within softwood growth increments as viewed in cross section. Key A, abrupt transition in eastern larch, with thick-walled latewood fibers (D = resin duct) and B, gradual transition in eastern white pine, with relatively thin-walled latewood fibers.

Surround normal resin ducts in pines, spruces, larches, and Douglas-fir, and trau matic resin ducts (formed as a result of tree injury) in these and other softwoods (2). 

Resin ducts or resin canals are tubelike voids that are both longitudinally and radially oriented throughout the xylem of some softwoods see Figure 9). These ducts are lined with specialized parenchyma, called epithelial cells, that secrete into the duct a substance called oleoresin (Figure 14A) (3). 

Vertical and horizontal resin ducts are natural and constant features of four domestic genera pines Finns), spruces Picea), larches Larix), and Douglas-fir Pseudotsuga). Resin ducts also develop as a response to injury or trauma in other genera, as well as in the four listed above (2). Horizontal resin ducts are contained in special multiseriate rays, called fusiform rays because of their spindle shape in tangential view (Figure 14B). 

Figure 13. Light micrograph of tangential section of redwood showing uniseriate rays (UR), the most common type of ray in softwoods, together with multiseriate rays (MR). The latter, if not containing a horizontal resin duct, are rare in softwoods.

Figure 14, SEM resin ducts in spruce wood. (A) Vertical duct with exuded resin droplets. (Reproduced from Ref. 39. C( yright 1982, American Chemical Society.) (d) Horizontal ducts contained in fusiform rays (FR) of the wood tangential surface.

Fir woods closely resemble the pines in being needleleaf or toft woods but have no resin ducts. The variety mostly favoured is the white or silver fir. 

Spruce woods resemble the soft pines. They grow extensively in North America and Europe . The common varieties are the Norway spruce Picecs exulsd) and the Douglas spruce or fir (pseudofsuga douglasii). The Norway spruce resembles silver fir but the resin ducts arc visible though few in number. 

The plant must be considered for example, the amount of compound in the tissues must be sufficient to produce a biological effect on the test insect. In the evaluation of this, it should be remembered that many plants have specialized tissues which contain high levels of secondary metabolites. For example, many conifer species contain specialized secretory structures, such as resin ducts, which contain high localized concentrations of terpenoids [82]. There may also be dynamic variations in the amounts of these compounds in the plant, resulting from seasonal fluxes or synthesis induced upon stress. 

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