Pathogens inducible conifer defenses

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. 

Based on our current knowledge, the chemistry of induced defenses in P. abies and other woody plants is not materially different from that of herbaceous plants. Terpenes, phenolics, and chitinases are all common metabolites in herbs, and in many cases are inducible upon herbivory or pathogen infection. However, the presence of inducible terpene resins is a special feature of conifers. In the rest of the plant kingdom, mixtures of terpenes accumulate in resin ducts, cavities or glandular hairs of many taxa, but are usually not reported to be inducible. Moreover, the long induction time of conifer resin also sets it apart from other induced defenses. 

Mono- and sesquiterpenes are the main constituents of the essential oils, while the other terpenes are constituents of balsams, resins, waxes, and rubber. Oleoresin is a roughly equal mixture of turpentine (85 % Cio-monoterpenes and 15 % C15- sesquiterpenes) and rosin (C2o-diterpene) that acts in many conifer species as a toxic material to invading insects and their pathogenic fungi [12]. A number of angiosperm species have inducible terpenoid defensive compounds (phytoalexins) [13]. These include both sesquiterpenoid and diterpenoid t)pes. Isoprenoid units are also found within the framework of other natural molecules. Thus, indole alkaloids, several quinones (vitamin K), alcohols (vitamin E, vitamin A formed from p-carotene), phenols, and isoprenoid alcohols (also known as terpenols or polyprenols) also contain terpenoid fragments. The biogenesis. 

Fig. 94.3 Conifer tree defense against bark beetles with induced resin production, (a) Resin flow on Norway Spruce (Picea abies) bark after attack by bark beetles, (b) The European spruce bark beetle Ips typographus), the most serious bark beetle pest of Norway spruce, attacking spruce bark with phoretic mites, which are probably involved in the transmission of fungal tree pathogens...

Keeling Cl, Bohlmann J (2006) Genes, enzymes, and chemicals of terpenoid diversity in the constitutive and induced defense of conifers against insects and pathogens. New Phytol... 

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