Defensive Chemicals

B. Clucas , in Encyclopedia of Animate being Behavior, 2010

Introduction and Definitions

Chemical defense is peradventure one of the about widespread antipredator strategies amongst living organisms, from plants and leaner to animals. Within the creature kingdom, defensive chemicals are found extensively in invertebrates (eastward.g., arthropods and molluscs, terrestrial and marine), but vertebrates also possess chemical defense strategies.

Defensive chemicals are substances utilized by prey to reduce predation risk. These chemicals include baneful , odiferous , boxy, toxic , or venomous substances that repel, deter, injure/harm, distract, or prevent detection by predators. These substances can touch on predator behavior by influencing the predators' olfactory, gustatory, or tactile sensory systems while they are searching, attacking, or consuming the casualty. In addition, chemicals that when released warn conspecifics of presence of a predator tin can be considered a defensive chemical.

Chemical substances can exist airborne, waterborne, or substrate spring. They can be released (east.g., sprayed) away from the animal creating an air- or waterborne substance, can be released externally and retained on the creature'south integument , injected directly into some other animal, or sequestered internally into the integument or internal organs. Depending on the medium they travel through or on (air, water, or substrate) and other physical characteristics (i.eastward., chemic limerick, volatility), they can too have varying active spaces and time until dissipation. Defensive chemicals tend to have pocket-size active spaces and brusque duration due to the necessity of a targeted, fast acting effect on the predator's beliefs. However, some chemic defense strategies, particularly waterborne chemicals, can accept large agile spaces, and sure defensive odorants tin accept a long duration.

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Chemic Defense

Murray S. Blum , in Encyclopedia of Insects (2d Edition), 2009

Publisher Summary

This chapter discusses chemical defense, which is the ability of insects to biosynthesize a big multifariousness of compounds for use as agents of chemical defense against their omnipresent enemies. Many of these compounds are unique products with diverse modes of toxicity against a variety of vertebrate and invertebrate predators. These defensive secretions oft originate from unlikely sources that announced to optimize the effectiveness of the chemical defensive systems. Ultimately, for countless species of insects, chemical defense and survival are synonymous. For example, the proteinaceous saliva of the hemipteran Vela capraii has been adapted to promote escape from potential predators in aquatic environments. This aquatic true bug will discharge its saliva onto the h2o surface, a reaction that results in lowering the surface tension of the h2o behind the bug and propelling it across the aquatic surface. At that place are other defensive techniques every bit well such every bit froths from various glands, nonsalivary entangling secretions, externalizing allomones by reflex haemorrhage, blood every bit part of a glandular secretion, and nonglandular discharges of institute origin.

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Defenses, Ecology of

Phyllis D. Coley , John A. Barone , in Encyclopedia of Biodiversity (Second Edition), 2001

Glossary

Chemic defenses

Compounds used by plants to deter or poisonous substance herbivores and pathogens.

Constitutive defenses

Defenses that are manufactured and maintained by a institute, regardless of whether it has been attacked past an herbivore or pathogen.

Endophyte

Mucus or other organisms residing or growing within constitute tissues.

Herbivory

Damage to plant tissues by herbivores or pathogens.

Induced defenses

Plant defenses, including both chemic and physical defenses, that are produced, at least in their final class, only after the institute has been damaged past herbivores or pathogens.

Mutualism

Interactions betwixt organisms of different species that increase the fitness of both participants.

Secondary compounds

A synonym for chemical defenses in plants; contrasts with chemical compounds used in primary metabolism, such every bit photosynthesis and cellular respiration.

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Susceptibility and Response of Forests to Disturbance

Richard H. Waring , Steven W. Running , in Forest Ecosystems (Third Edition), 2007

A Biochemical Defenses in Plants

Defensive chemicals present in plants are broadly classified into nitrogen- and non-nitrogen-containing compounds. Compounds that contain N include cyanogenic glucosides, alkaloids, and nonprotein amino acids. Defensive compounds without North include tannins, terpenes, phytoalexins, steroids, and phenolic acids. Each kind of chemical compound may serve in a diversity of ways against various organisms (Tabular array vi.1).

Tabular array 6.1. Major Groups of Secondary Constitute Metabolites Known to Contain Products Of import for Defence force a

Class Number known Contains N Protection against
Alkaloids 1000 Yes Mammals
Amino acids 250 Yep Insects
Ligans 50 No Insects
Lipids 100 No Fungi
Phenolic acids 100 No Plants
Phytoalexins 100 No Fungi
Quinones 200 No Plants
Terpenes 1100 No Insects
Steroids 600 No Insects
a
From Fellow (1977). With permission, from the Almanac Review of Establish Physiology, Volume 28, © 1977, past Annual Reviews Inc.

Some plants produce fungistatic and bacteriostatic compounds that prevent colonization by pathogens. Other compounds act as concrete barriers, such as waxes on the leafage surface or resins or lignin in cell walls. Increasing fiber and lowering water content decrease digestibility of establish tissue and reduce herbivore growth rates and survival (Scriber and Slansky, 1981). Tannins precipitate protein, which inhibits most enzyme reactions and makes protein present in plant tissue nutritionally unavailable to most animals and microbes (Zucker, 1983). Phytoalexins are lipid-soluble compounds, which are activated following an attack by pathogens, and exhibit antibiotic properties (Harborne, 1982). The alkaloids constitute in many angiosperms are specially toxic to a variety of mammals (Young man, 1977).

Changes in host biochemistry may also affect the colonization of organisms helpful to the host establish. These include protective ant colonies, macroorganisms that graze on bacteria, and symbiotic associations of N-fixing leaner and mycorrhizal root fungi. These benign organisms may directly infect or prey on attacking organisms, release antibiotics, or provide essential nutrients. Many of the compounds released equally exudates, which include a variety of polysaccharides, organic acids, and amino acids, are essential to beneficial assembly, merely when these organisms are absent they tin as well exist assimilated by herbivores and pathogens.

In full general, defensive compounds that lack North reach rather loftier concentrations in cells, often 10–15% by weight, whereas N-containing compounds are commonly at concentrations below 1%. Plants expend less full free energy in the synthesis of minor amounts of N-containing defensive compounds than when producing large amounts of C-rich compounds, but variations in the turnover rates of defensive compounds and differences in relative growth rates must be considered in assessing relative costs (Bryant et al., 1991). Nitrogen-containing compounds are most frequently found in deciduous, fast-growing vegetation, whereas defensive compounds without Northward are more characteristic of slow-growing plants, peculiarly evergreens with long leaf life spans (Bryant et al., 1986; Coley, 1988). Regardless of the defensive chemical compound synthesized, no constitute is completely allowed to assault. Specialized insects and pathogens have evolved that not only detoxify toxic compounds, but really require them for optimal growth (Bernays and Woodhead, 1982). These highly evolved specialists are restricted to a few host species, but they may assault vigorous as well as weak individuals (McLaughlin and Shriner, 1980). Other less specialized organisms adjust a wider range of biochemical challenges and attack a wider diversity of plants.

Plants that depend on defensive compounds rich in N are at a competitive disadvantage where Due north is in short supply. On the other hand, plants producing C-rich defensive compounds are at a disadvantage when growing in shade with an arable supply of Northward. Those plants adapted to more fertile soils may be expected to build a diverseness of defensive compounds from North. Thus, alkaloids predominate in the foliage of trees in many lowland tropical forests where N is relatively abundant (McKey et al., 1978). Plants growing in areas where N is scarce mostly produce only tannins and related C-based compounds. Foliage is and so unpalatable in some tropical forests growing on sterile sands that primates survive mainly by eating fruits (Gartlan et al., 1980). A similar pattern in distribution of vegetation with N-based or C-based defensive compounds to that observed in tropical forests has been observed in boreal and temperate forests (Rhoades and Cates, 1976; Bryant et al., 1991). At the time of foliage elongation, when N is relatively available, even plants growing in nutrient-poor habitats may produce a few N-based defensive compounds (Dement and Mooney, 1974; Prudhomme, 1983).

Insects differ from other animals in the way they locate host plants. Birds and larger animals depend on sight to recognize flowers and fruits. Insects rely much more on odors of compounds volatilized or exuded by plants. Adult insects seeking to lay eggs on a suitable host may apply their antennae to sense volatile compounds at levels as depression as ten−12 g cm−3. By direct tasting, insects may discriminate nonvolatile compounds at concentrations of 1 mg per 1000 cm3 in tissue, which is far beneath toxic levels (Fellow, 1977). To run across the challenge of insects, many plants are able to produce toxic compounds quickly and to construct barriers that consist of dead or resin- or gum-filled tissue almost immediately post-obit assault (Schultz and Baldwin, 1982; Raffa and Berryman, 1983). In response to localized insect activity, foliage throughout an entire tree may get less palatable (Haukioja and Niemelä, 1979; Karban and Myers, 1989). Morphological responses such as stiffer thorns on Acacia trees may also exist induced past grazing (Seif el Din and Obeid, 1971). Bark sloughing is a response to attack by the woolly aphid (Adelges piceae) that only reaches epidemic populations when balsam fir (Abies balsamea) replaces native forest species (Kloft, 1957). The implication is that the woolly aphid is at a low-level equilibrium with its native host equally a outcome of long-term evolutionary adaptations simply reaches epidemic populations on the relatively defenseless introduced balsam fir.

Induced responses to attack can only exist constructive if sufficient resources can be rapidly mobilized. The rate at which stored carbohydrates or protein can be converted to mobile forms (sugars and amino acids) and transported to sites of attack may limit the capacity of copse to respond (McLaughlin and Shriner, 1980), although this may not affect canopy responses to partial confusion if photosynthetic rates are high. Changes in the allocation of electric current photosynthate to remote organs, such as the lower bole or roots, still, cannot be accomplished rapidly because of the altitude involved and limitations imposed by phloem transport (Chapter 3). For this reason, concentrations of stored reserves in roots, stems, and twigs are a good indicator of a tree'southward potential to survive localized attack by insects or pathogens (Ostrofsky and Shigo, 1984). Wargo et al. (1972) demonstrated that defoliation of saccharide maple (Acer saccharum) greatly reduced starch content in roots at the end of the growing flavor. Low starch reserves in the roots predisposed trees to attack past root pathogens (Wargo, 1972).

Tropical forests are rarely heavily defoliated because the insects and pathogens are highly specialized and their host copse are few and widely separated. In temperate and boreal forests, on the other manus, but a few species of trees may be nowadays. Even with genetic diversity within a population, major outbreaks of insects are common in higher latitude forests. Population outbreaks of insects tin can completely defoliate a large fraction of trees in a wood within a unmarried year, simply, depending on the physiological status of the trees, mortality may be low, equally shown in 2 photographs taken during and 5 years afterward an outbreak of tussock moth in northeastern Oregon (Fig. 6.2). It is critical to understand whether a forest is resistant or susceptible to defoliating insects or other biotic agents earlier making management decisions. In the following sections we draw on ecosystem-level experiments to examination the reliability of various stress indices and follow changes in susceptibility and response to changing environmental conditions created by biotic disturbance.

Effigy 6.ii. (a) Outbreaks of defoliating insects occur more frequently in the western United States where fire protection has enabled large expanses of fir trees (Abies grandis) to replace much of the original pino. (b) Mortality from insect outbreaks varies, depending on the length of the outbreak and physiological condition of host trees. This scene records nearly full recovery 5 years after the first photograph was taken. Whatever bloodshed improved bore growth of surviving copse (Wickman, 1978). (Photograph from Boyd Wickman, La Grande, Oregon.)

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Brute Defense Strategies

D. Spiteller , in Encyclopedia of Ecology, 2008

Conclusions

The chemic defence of animals parallels in many aspects that of plants (see Constitute Defense Strategies). Often deterrents or toxins used are Michael acceptors that react with nucleophiles, inhibitors of the respiratory chain, or neurotoxins. Simple mechanisms such as bad taste or smell and extreme pH acquired by strong acids are also a very common strategy used past both types of organisms. In addition to these parallels, many animals of all classes use a unlike defense strategy. They take advantage from adaptation to their nutrient and reuse toxins from the food past sequestration.

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Jasmonates and Other Defense-Related Compounds

Lalit M. Srivastava , in Found Growth and Development: Hormones and Environment, 2002

Other defense chemicals include enzymes and products, which are harmful to invading organisms. For case, proteinase inhibitors (PINs) in white potato or tomato shoots, when ingested by the insect, inhibit the protein-digesting enzymes, trypsin and chymotrypsin, in the insect gut. α-Amylase inhibitors inhibit the activity of the starch-digesting enzyme, α-amylase. Patatin, the almost arable protein in potato tuber, is a nonspecific acyl hydrolase, which hydrolzyes a variety of lipids—phospholipids, glycolipids, and mono- and diacylglycerols, all except triacylglycerols. Many pathogenesis-related (PR) proteins are synthesized as defense against microbial pathogens. For example, chitinases and β-ane, 3-glucanases provide defense past digesting the cell walls of invading bacteria and fungi. Phytoalexins are a chemically heterogeneous group of secondary metabolites that accrue around the site of infection and are believed to exist toxic to the invading pathogen. Unlike institute families employ different types of secondary products as phvtoalexins. For case, isoflavonoids are mutual phytoalexins in the legume family unit, whereas in plants of the spud family (Solanaceae), various sesquiterpenes are produced as phytoalexins.

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Defenses, Ecology of

Phyllis D. Coley , John A. Barone , in Encyclopedia of Biodiversity, 2001

V.C. Induced Defenses

The chemical defenses described then far are usually constitutive—that is, they are produced and maintained regardless of whether herbivores or pathogens have damaged the institute. Many secondary compounds, nevertheless, are induced, with product (or at least the final stages of product) only occurring subsequently the plant has been attacked ( Karban and Baldwin, 1997). Usually, an aspect of impairment, such as partially eaten cell walls, leads to a transduction process that causes the cell, tissue, or whole plant to brainstorm synthesis of defensive compounds. This entire process tin can have place in less than i   hr. In field and laboratory conditions, plants that have been induced suffer less herbivory and take higher fitness than controls. However, almost species do non appear to have inducible defenses.

Plants should have induced defenses instead of constitutive ones if defenses are costly to plants, and free energy and nutrients that are allocated for secondary compounds or other compounds cannot exist used for growth or reproduction. Therefore, by producing defenses only when they are needed—during an attack by herbivores or pathogens—the plant is able to divert these resources to growth and reproduction. However, almost species do not appear to have inducible defenses, suggesting that plants may oft not be in the position to predict when it would be advantageous to induce defenses.

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Chemical Ecology

Mary J. Garson , in Comprehensive Natural Products 2, 2010

4.12.3.3 Other Algal Metabolites

Activated chemical defenses based on dimethylsulfoniopropionate (DMSP) 54 are widely distributed among many species of green, brown, and red algae. Withal feeding deterrency trials have given inconsistent results; neither DMSP nor the two conversion products dimethyl sulfide and acrylic acid deter feeding by the sea urchin E. lucunter, 50 although artificial foods containing dimethyl sulfide or acrylic acid are avoided by the sea urchin Strongylocentrotus droebachiensis. 72 DMS, acrylic acid and triethylamine are not deterrent to the amphipod A. longimana when tested individually, nonetheless in combination are deterrent at natural concentrations. 73

The Northeastern Pacific green algae Ulvaria obscura uses dopamine 55 equally a feeding deterrent. 74 Two simple aromatic compounds p-hydroxybenzaldehyde 56 and p-methoxyphenol 57 from the red algae Myriogramme smithii deter feeding past the sea stars Perknaster fuscus and Odontaster validus. 38

Brown algae are rich in phlorotannin components that play an of import role as a structural back up and every bit photoprotective agents. A range of herbivore responses to phlorotannins has been described, 75 most recently in Fucus vesiculosus 76 in which a bioassay-guided fractionation revealed that a polar galactolipid contributed to feeding deterrency. 77 Increased phlorotannin levels may be induced by environmental cues and by injury or predation. Several reviews cover this specialized topic in considerable detail. 7,ix,78,79 Some brown algae are chemically defended by the presence of sulfuric acid within prison cell vacuoles. 80

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Plant and fungal toxins as contaminants of feed and meat

B.J. Blaney , in Improving the Safety of Fresh Meat, 2005

4.3.1 Minimising toxin intake in foraging situations

The chemical defences in plants can reduce palatability, merely no plants are either completely repellent or totally acceptable to all herbivores, which larn preferences for the flavours of familiar foods that have been associated with the positive post-ingestive effects of nutrients (Provenza, 1996). Excesses or deficits of nutrients and excesses of toxins crusade food aversions by causing a subtract in liking for the flavour of the nutrient. These aversions cause animals to sample novel foods and eat varied diets.

Ruminants that are allowed liberty to forage in rangelands where institute density is balanced confronting grazing pressure will generally eat a range of establish species and avert intoxication. Moreover, animals that take spent sufficient time in given ranges acquire a body of information about furnishings of consumption of the plants in that range and transmit this information (learned behaviour) within the herd, by means not fully studied, but most apparently from mother to offspring (Malechek and Balph, 1987). Grazing animals also appear to take well adult spatial and temporal memories, enabling them to observe and safely swallow fodder that is only seasonally available over wide ranges. Fifty-fifty when introduced into a new range, animals volition usually approach foraging with considerable caution, attempting to eat just familiar plants until acclimatised. As described previously, plant poisonings usually crave consumption of a large amount of toxic found in a brusk time, on an empty tummy.

Under certain weather, animals volition ignore these normal behavioural inhibitions, and these are the circumstances in which poisoning is most often observed. Hunger is naturally a powerful driving force, simply it needs to be combined with competitive grouping (mob) behaviour, usually past immature animals, and unremarkably outside the constraints of the native herd. However, once some individuals accept behaved in this manner, the herd inhibitions tin be disrupted, the rest of the herd can follow and big mortalities can outcome (Ralphs, 1994). The risks of poisoning can be greater with introduced plants than with native species (Welsh and James, 1994), because introduced plants can become dominant in the absence of natural constitute pathogens.

It can thus exist concluded that providing animals with a diverse mix of nutritive plants is one of the most of import means of reducing consumption of phytotoxins on rangelands and in pastures. Strategies to achieve this vary with the region, but normally include managing stock density, and sward composition through burning, selective clearing or slashing. Removal of toxic plants might be possible in limited situations, only generally is neither feasible nor desirable, particularly with native species. In summary, noesis of the toxic plants present on a farm or grazing property is essential knowledge for the manager, as is cognition of the seasons and circumstances in which the plants achieve maximum toxicity and bewitchery to livestock.

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Chemic Ecology and Phytochemistry of Wood Ecosystems

Diane Martin , Jörg Bohlmann , in Recent Advances in Phytochemistry, 2005

INTRODUCTION

Successful chemical defense of long-lived conifers against herbivores and pathogens is largely dependent on the formation, aggregating, and release of oleoresin monoterpenoids, sesquiterpenoids, and diterpenoids. In addition, conifers also produce a big assortment of phenolic and other defense compounds. The topic of terpenoid defenses in conifers has previously been reviewed. ane-7 Oleoresin terpenoids are stored in large quantities in resin canals, resin blisters, or resin cells in stems, roots, or leaf of many conifer species. The development of these specialized anatomical structures tin be induced with insect or fungal attack, mechanical wounding, and chemical elicitation. Terpenoids may also be released equally constitutive or induced volatiles from the leaf of conifers. These volatiles tin can human action as chemical signals past alluring natural enemies of herbivores. The terpene synthases (TPS) play a primal role in the formation of terpenoid chemical diversity, in maintaining phenotypic plasticity in conifer defense, and they are a major office of the genomic hardwiring of conifer resistance. 7,8 Recent work has revealed much of the multigenic nature of this successful conifer terpenoid defense system. Application of methyl jasmonate (MeJA) has enabled a detailed label of inducible terpenoid defenses in several conifer species, including Norway spruce (Picea abies), Sitka bandbox (P. sitchensis), and Douglas fir (Pseudotsuga menziesii). 9-15 For example, species of spruce produce copious amounts of oleoresin terpenoids, which are stored in constitutive resin ducts, mainly in the bark, or in inducible traumatic resin ducts (TD) in the xylem. Terpenoid aggregating in traumatic resin ducts is regulated, at to the lowest degree in office, by TPS gene expression and by TPS enzyme activities, which are induced upon MeJA treatment or in response to insect attack. TPS gene expression and TPS enzyme activities are also elevated in foliage following MeJA elicitation. The cDNA cloning, functional characterization, and gene expression assay of a large family of TPS genes from Norway bandbox and Sitka spruce enabled an clan of the biochemical function of these TPS genes with the aggregating of oleoresin terpenoids in stems or the release of terpenoid volatiles from needles. viii,12,sixteen Recent work in Sitka spruce compared the MeJA- and insect-induced terpenoid defenses at the molecular, biochemical, and anatomical levels. 15 The initial targeted gene characterization of the complex insect- and MeJA-induced terpenoid defence system in spruce has laid the foundation for new genome-scale label of insect-induced defenses in conifers (www.treenomix.com).

In this chapter, we emphasize recent research, published and unpublished, of the final v years that has established bandbox every bit one of the best characterized systems for molecular, biochemical, and genomic research of conifer defence force confronting insect pests. viii,10-12,15,16 The chapter touches on molecular and biochemical regulation of chemic variety of conifer defense and provides an outlook towards new genomics inquiry in a forest wellness context, specifically the genomics of copse interacting with insect pests and insect-associated fungal pathogens. Most of the chapter covers our recent research with two species of spruce, Norway bandbox and Sitka spruce, including terpenoid defense responses induced past MeJA and the white pine weevil (Pissodes strobi). Results from our enquiry with spruce terpenoid defenses are relevant to the larger field of secondary metabolite structural diversity in establish defense and the development of such defenses and their phenotypic plasticity in long-lived, sessile organisms. vii

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