Week 4 Lecture 1(7)

Week 4 Lecture 1(7) - Class Notes Week 4 Lecture 1 Plant Physical Defences continued Digestibility reducers tannins are a common form CHEMICAL

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Class Notes: Week 4 Lecture 1 Plant Physical Defences continued; Digestibility reducers – tannins are a common form CHEMICAL DEFENCES Plants usually contain a cocktail blend of chemicals, making it more difficult for herbivores to counterattack. Toxins are found in most parts of a plant, especially vulnerable tissues not fortified with lignin or silica, such as buds, young leaves, and unripe fruit Chemicals often play dual roles in the plant, primary function metabolic Other chemicals are produced solely for non-metabolic functions such as for pollination or defence; those are secondary metabolites . There are between 200,000 and 300,000 different secondary metabolites, many for defence only! If a chemical defence is always present, even when a plant is not under attack, it is called a constitutive defence . There are several major groups of constitutive toxins defined presence or absence of the element nitrogen (N). TYPES: 1. Do not contain Nitrogen a) Terpenoids , whose name reflects their initial discovery in turpentine. There are approximately 40,000 types of terpenoids and than 100,000 species of plants. While some secondary metabolites play non- defensive as growth stimulation and pollinator attraction, others serve only to protect. Many terpenoids are bitter tasting and defend through repulsion rather than by poisoning the animal that ingests them. A few, however, can be deadly. cardiac glycosides (specifically the cardenolides ) are a major group of terpenoids. Milkweeds white latex that oozes out is loaded with cardenolides If you have ever sat on a conifer log or stump the gummy exudate is oleoresin (resin for short), a chemical defence that is full of terpenoids. Many coniferous trees store resin special ducts or canals, and a few including firs store special blisters on bark . Bark Beetle chews a resin canal, its contents forced out through the wound, overwhelming the insect and encasing and killing it. When turpentine component evaporates, the resin thickens and effectively seals off wound. Some coniferous trees such as firs also manufacture oleoresin under attack. Induced resin differs slightly in its chemical composition from the plant’s constitutive resin, and it often accumulates in newly formed compartments called traumatic resin ducts that lie in wait, ready to defend the tree against the next attack The most famous (or infamous!) of all resins is likely the one found in Poison Ivy. All parts of the plant except pollen contain the resin and its active ingredient urushiol . 1
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Terpenoids include the menthol in mints, which advertise with distinctive smells, and saponins, which have been found to be an especially effective deterrent for slugs and snails (but especially microfungi). 2)
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This note was uploaded on 10/20/2011 for the course BIOL 1902 taught by Professor Runtz during the Fall '08 term at Carleton CA.

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Week 4 Lecture 1(7) - Class Notes Week 4 Lecture 1 Plant Physical Defences continued Digestibility reducers tannins are a common form CHEMICAL

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