Constitutive defense resistance

Toth G, Karlson M, Pavia H (2007) Mesoherbivores reduce net growth and induce chemical resistance in natural seaweed populations. Oecologia 152 245-255 Toth GB, Langhamer O, Pavia H (2005) Inducible and constitutive defenses of valuable seaweed tissues consequences for herbivore fitness. Ecology 86 612-618... 

Some components of resistance are present in healthy plants and therefore are part of a constitutive defense other components are induced and formed following contact between the pathogen (or its products) and the host and therefore are parts of an active defense. The total defense is the sum of constitutive and active components. Many groups of chemicals function in both constitutive and active... 

Cotton tissues also may contain 1-3% flavonoid glucosides, most of which contain ortho-dihydroxyphenolic groups ( ). Additional quantities of flavonoid glucosides are formed Tn response to infection. These compounds are important in constitutive defense against insects, but their importance in the resistance of cotton to... 

Increased resistance to necrotrophs also could result from changes that increase antibiotic efficiency. Other approaches for these pathogens should aim at increasing constitutive defenses. Such things as higher tannin and lignin concentration, thicker cuticle structure, and increased suberization would be expected to improve resistance. 

Toth et al. 2005), induced resistance was found only in the top blades of S.filipendula (Taylor et al. 2002). The authors concluded that valuable basal stipes are mechanically and constitutively defended, while the valuable meristematic tissues have inducible chemical defenses (Taylor et al. 2002). 

All these data support the idea that QA may function as chemical defense compounds. We also tested whether this chemical defense is relevant for the survival of a lupin plant. Lupins offer a unique chance to explore this question experimentally plant breeders have selected "sweet" varieties, which have a very low alkaloid content. These varieties can be compared to semi-bitter or bitter ones. We have grown Lupinus albus strains that differ in their alkaloid content in our experimental garden and greenhouse and have monitored their susceptibility to attack by plant pests. As can be seen from Figure 2, "sweet" lupins are preferentially eaten by rabbits (Cuniculus europaeus) or are infested by aphids (Aphidae) or leaf miners (Agromyzidae). Literature data also support the assumption that alkaloid-rich lupins are much more resistant to plant pests than "sweet" varieties (30-32). We conclude therefore, that QA are indeed important for the fitness of a lupin plant and that they constitute a major part of its chemical defense system, in which... 

In contrast to the above-mentioned constitutive types of resistance, plants also possess adaptive defense mechanisms to defend themselves against pathogen or insect attack. Following an appropriate stimulation, they are capable of developing an enhanced defensive capacity, commonly referred to as induced resistance [5,6,7,8]. 

Plants contain plant secondary metabolites (PSMs) that confer resistance against herbivores and pathogens. The largest classes of PSMs are phenolics, terpenoids, and alkaloids. We distinguish constitutive and induced chemical defenses. The first occur in an entire plant or some of its parts as normal constituents, the latter are formed in response to herbivory or some other trauma to the plant. In some cases mere clipping induces defenses, in others additional factors, such as those in saliva of a herbivore are essential. 

Wang, Y., Nowak, G., Gulley, D., Hadwiger, L.A. and Fristensky B. (1999) Constitutive expression of pea defense gene DRR206 confers resistance to blackleg Leptosphaeria maculans) disease in transgenic canola (Brassica napus). Mol. Plant Microbe Interact., 12, 410-8. 

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