178:) leaves chewed on by caterpillars than in leaves damaged mechanically. Distinct signal transduction pathway are activated in response either to insect damage or mechanical damage in plants. While chemicals released in wounding responses are the same in both cases, the pathway in which they accumulate are separate. Not all herbivore attack begins with feeding, but with insects laying eggs on the plant. The adults of butterflies and moths (order Lepidoptera), for example, do not feed on plants directly, but lay eggs on plants which are suitable food for their larva. In such cases, plants have been demonstrated to induce defences upon contact from the ovipositing of insects.
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genes, signalling pathway genes and rerouting genes. The transcription of defensive gene produces either proteins that are directly involved in plant defence such as proteinase inhibitors or are enzymes that are essential for the production of such proteins. Signalling pathway genes are involved in transmitting the stimulus from the wounded regions to organs where defence genes are transcribed. These genes are essential in plants due to the constraints in the vascular systems of the plants. Finally, rerouting gene are responsible in allocating resources for metabolism from primary metabolites involved in photosynthesis and survival to defence genes.
68:. In essence, defensive chemicals can be viewed as having a particular dosage-dependent effect on herbivores: it has little detrimental effect on herbivores when present at a low or moderate dose, but has dramatic effects at higher concentrations. Hence, a plant which produces variable levels of defensive chemicals is better defended than one that always produces the mean level of toxin.
40:. This may confer an advantage over constitutive defenses for multiple reasons. First, it may reduce the chance that attacking insects adapt to plant defenses. Simply, inducible defenses cause variations in the defense constituents of a plant, thereby making the plant a more unpredictable environment for insect herbivores. This variability has an important effect on the
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Not all up-regulated genes in induced defences are directly involved in the production of toxins. The genes encoding newly synthesised proteins after a herbivory attack can be categorised based on the function of their transcriptional products. There are three broad classification categories: defence
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Systemically induced defences are at least in some cases the result of changes in the transcription rates of genes in a plant. Genes involved in this process may differ between species, but common to all plants is that systemically induced defences occur as a result of changes in gene expression. The
122:
Central to the concept of induced defences is the cost involved when stimulating such defences in the absence of insect herbivores. After all, in the absence of cost, selection is expected to favour the most defended genotype. Accordingly, individual plants will only do so when there is a need to.
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Induced defences require plant sensing the nature of injury, such as wounding from herbivore attack as opposed to wounding from mechanical damage. Plants therefore use a variety of cues, including the sense of touch, and salivary enzymes of the attacking herbivore. For example, in a study to test
94:
significantly later than plants with lower levels of nicotine. This results suggest that there is a biosynthetic cost to constantly producing a high level of defensive chemicals. Inducible defences are advantageous as they reduce the metabolic load on the plant in conditions where such biological
155:) resulted in plants with fewer but larger fruits, longer ripening time, delayed fruit-set, fewer seeds per plant and fewer seeds per unit of fruit weight. All these features play a critical role in attracting seed dispersers. Due to the consequences of induced defences on fruit characteristics,
27:
many defense mechanisms against insect herbivory. Such defenses can be broadly classified into two categories: (1) permanent, constitutive defenses, and (2) temporary, inducible defenses. Both types are achieved through similar means but differ in that constitutive defenses are present before an
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Allocation cost is related to the channelling of a large quantity fitness-limited resources to form resistance traits in plants. Such resources might not be quickly recycled and thus, are unavailable for fitness-relevant process such as growth and reproduction. For instance, herbivory on the
191:) photosynthetic genes are down-regulated, while genes directly involved in defences are up-regulated in response to insect attack. This allows more resources to be allocated to producing proteins directly involved in the resistance response. A similar response was reported in
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Tamiru (2017). Bruce TJA, Richter A, Woodcock CM, Midega CAO, Degenhardt J, Kelemu S, Pickett JA, Khan ZRA (2017) A maize landrace that emits defense volatiles in response toherbivore eggs possesses a strongly inducible terpene synthase gene. Ecology and
Evolution 7:
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Ecological cost results from the disruption of the many symbiotic relationships that a plant has with the environment. For example, jasmonic acid can be used to simulate an herbivore attack on plants and thus, induce plant defences. The use of jasmonic acid on tomato
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The cost of induced defences to a plant can be quantified as the resource-based trade-off between resistance and fitness (allocation cost) or as the reduced fitness resulting from the interactions with other species or the environment (ecological cost).
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herbivore attacks, while induced defenses are activated only when attacks occur. In addition to constitutive defenses, initiation of specific defense responses to herbivory is an important strategy for plant persistence and survival.
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Second, synthesizing a continually high level of defensive chemicals renders a cost to the plant. This is particularly the case where the presence of herbivorous insects is not always predictable. For example, the production of
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Frost CJ, Appel HM, Carlson JE, Moraes CMD, Mescher MC, Schultz JC. Within-plant signalling via volatiles overcomes vascular constraints on systemic signalling and primes responses against herbivores. Ecology
Letters.
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whether plants can distinguish mechanical damage from insect herbivory attack, Korth and Dixon (1997) discovered that the accumulation of induce defence transcription products occurred more rapidly in potato (
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plants where there is an up-regulation of all genes that are involved in defence. Such changes in the transcription rates are essential in inducing a change in the level of defence upon herbivory attack.
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Ataide, Livia M. S.; Pappas, Maria L.; Schimmel, Bernardus C. J.; Lopez-Orenes, Antonio; Alba, Juan M.; Duarte, Marcus V. A.; Pallini, Angelo; Schuurink, Robert C.; Kant, Merijn R. (2016-11-01).
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Ryan CA. The systemin signaling pathway: differential activation of plant defensive genes. Biochimica et
Biophysica Acta-Protein Structure and Molecular Enzymology. 2000;1477(1-2):112-21.
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changes in transcription can involve genes which either do not encode products involved in insect resistance, or are involved in general response to stress. In cultivated tobacco (
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Huntzinger, P.M., R. Karban, T.P. Young and T.M. Palmer. 2004. Relaxation of induced indirect defenses of acacias following exclusion of mammalian herbivores. Ecology 85:609-614.
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Young, T.P., M.L. Stanton and C. Christian. 2003. Effects of natural and simulated herbivory on spine lengths of Acacia drepanolobium in Kenya. Oikos 101:171-179.
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Korth KL, Dixon RA. Evidence for chewing insect-specific molecular events distinct from a general wound response in leaves. Plant
Physiology. 1997;115:1299-305.
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Moor JP, Taylor JE, Paul ND, Whittaker JB. Reduced leaf expansion as a cost of systematic induced resistance to herbivory. Functional
Ecology. 2003;17:75-81.
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Dicke M, van Poecke RMP, de Boer JG. Inducible indirect defence of plants: from mechanisms to ecological functions. Basic and
Applied Ecology. 2003;4:27-42.
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In addition to chemical defenses, herbivory can induce physical defenses, such as longer thorns, or indirect defenses, such as rewards for symbiotic ants.
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Preisser EL, Gibson SE, Adler LS, Lewis EE. Underground herbivory and the costs of constitutive defense in tobacco. Acta Oecol-Int J Ecol. 2007;31:210-5.
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Heil M, Baldwin IT. Fitness costs of induced resistance: emerging experimental support for a slippery concept. Trends in Plant
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Strauss SY, Rudgers JA, Lau JA, Irwin RE. Direct and ecological costs of resistance to herbivory. Trends in
Ecology & Evolution. 2002;17:278-85.
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Shelton AL. Variation in chemical defenses of plants may improve the effectiveness of defense. Evolutionary
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Steppuhn A, Gase K, Krock B, Halitschke R, Baldwin IT. Nicotine's
Defensive Function in Nature. PLoS Biology. 2004 August 01, 2004;2(8):e217.
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Agrawal AA. Induced responses to herbivory in wild radish: effects on several herbivores and plant fitness. Ecology. 1999;80:1713-23.
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550:. 1. Large-scale changes in the accumulation of growth- and defense-related plant mRNAs. Plant Physiology. 2001;125:1875-87.
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147:. In the absence of herbivory, inducing such a defence would be ultimately costly to the plant in terms of development.
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Milewski, A.V., T.P. Young and D. Madden. 1991. Thorns as induced defenses: experimental evidence. Oecologia 86:70-75.
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Mole S. Trade-offs and constraints in plant-herbivore defense theory: a life history perspective. Okios. 1994;71:3-12.
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Schenk JM, Kazan K, Wilson I, Anderson JP, Richmond T, Somerville SC, et al. Coordinated plant defence responses in
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Gatehouse JA. Plant resistance towards insect herbivores: a dynamic interaction. New Phytologist. 2002;156:145-69.
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Herms DA, Mattson WJ. The dilemma of plants: to grow or to defend. Quarterly Review of Biology. 1992;67:283-335.
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Karban R, Agrawal AA, Mangel M. The benefits of induced defenses against herbivores. Ecology. 1997;78:1351-5.
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Chen MS. Inducible direct plant defence against insect herbivores: a review. Insect Science. 2008;15:101-14.
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Walling LL. The myriad plant responses to herbivores. Journal of Plant Growth Regulation. 2000;19:195-216.
143:. The allocation of resources to this increased activity results in reduced leaf growth and expansion in
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revealed by microarray analysis. Proceedings of the National Academy of Sciences, USA. 2000;97:11655-60.
423:"Induced plant-defenses suppress herbivore reproduction but also constrain predation of their offspring"
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plants with a higher constitutive level of nicotine are less susceptible to insect herbivory. However,
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does not use nicotine as a nitrogen source under nitrogen-limited growth Oecologia. 1994;98:385-92.
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Giovannoni JJ. Genetic regulation of fruit development and ripening. Plant Cell. 2004;16:S170-S80.
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chemicals are not yet necessary. This is particularly the case for defensive chemicals containing
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Boyd, Jade (2012). "A bit touchy: Plants' insect defenses activated by touch". Rice University.
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Hermsmeier D, Schittko U, Baldwin IT. Molecular interactions between the specialist herbivore
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Redman AM, Cipollini DF, Schultz JC. Fitness cost of jasmonic acid-induced defense in tomato,
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Karban R, Baldwin IT. Induced responses to herbivory. Chicago: Chicago University Press; 1997.
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are less able to attract seed dispersers and this ultimately results in a reduced fitness.
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103:) as if the plant is not being attacked it is able to divert more nitrogen to producing
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and behaviour of herbivores. For example, the study of herbivory on radish (
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A mechanism of defence induction: changes in gene transcription rates
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and will therefore be able to grow faster and produce more
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plants that produce a continually high level of nicotine
389:Baldwin IT, Ohnmeiss TE. Swords into plowghshares?
139:) induces an increased activity in cell wall-bound
546:(Lepidoptera, Sphingidae) and its natural host
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23:together for 350 million years. Plants have
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36:Inducible defenses allow plants to be
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215:Plant defense against herbivory
200:Classification of induced genes
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169:Plant perception (physiology)
481:. Oecologia. 2001;126:380-5.
220:Plant tolerance to herbivory
133:) by the green dock beetle (
32:Benefits of induced defences
19:Plants and herbivores have
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603:Antipredator adaptations
163:Sensing herbivory attack
118:Cost of induced defences
479:Lycopersicon esculentum
153:Lycopersicon esculentum
76:in cultivated tobacco (
38:phenotypically plastic
167:Further information:
391:Nicotiana sylvestris
176:Solanum tuberosum L.
136:Gastrophysa viridula
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231:References
141:peroxidase
88:N. tabacum
84:N. tabacum
62:R. sativus
21:co-evolved
598:Herbivory
524:2835-2845
457:0168-9452
101:alkaloids
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209:See also
97:nitrogen
74:nicotine
435:Bibcode
105:rubisco
42:fitness
25:evolved
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99:(e.g.
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