Protection against biotic stress

Part IV includes applications of various biopolymers such as seed coating to protect against biotic stress, biosorbent for the organic pollutant, pharmaceutical technology, drug delivery, and gene therapy. 

An important role of PGR is their involvement in abiotic and biotic stress defense mechanisms. Triazoles like paclobutrazole, propiconazole and tetracona-zole are reported to be stress protectants [36]. Natural PGR are involved in indirect defense mechanisms of plants against herbivores [37]. Jasmonic acid, salicylic acid (Fig. 11.7) and ethylene are part of the signaling pathways of stress defense mechanisms. 

Conifer resin, which is a mixture of monoterpenes and diterpenes is an important protective compound against bark beetles and other conifer herbivores. The volatile monoterpenes emanating from a specific tree is often the cue for bark beetles to find a tree where the tree defenses could be compromised from abiotic or biotic stresses. The synchronized mass attack is the strategy bark beetles use to reduce the effects of resin-based defenses in conifers. Aggregation hormones released by bark beetles are oxidized monoterpenoids such as ipsdienol, ipsenol and verbenol. It is believed that these compounds can be oxidation products of host plant monoterpenes such as myrcene. Recently it has been observed that most of the monoterpenoid aggregation pheromone components are biosynthesized de novo in bark beetles [7]. 

Plants need to defend and protect themselves against attack from herbivores and microorganisms. Toward this goal, plants produce a vast array of natural products some of which mediate broad resistance toward herbivores and pests and some of which are highly specific. Accordingly, the ability of plants to produce natural products enhances plant fitness by efficiently counteracting otherwise damaging biotic and abiotic stresses. 

Pterocarpans are a group of modified isoflavonoids occurring in small amounts in legume plants (Fabaceae) and in several other families. They typically act as phytoalexins, protecting plants against pathogens. Unlike most of the isoflavones, pterocarpans are synthesised in response to biotic and abiotic stress factors. Their important precursors are the isoflavones daidzein and formononetin. 

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