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Lecture 11

BIOA02 LECTURE 11: Plant Defense

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University of Toronto Scarborough
Biological Sciences
Mary Olaveson

BIOA02 Lecture 11 Plant DefenseFebruary 02 2012Plants Feed the World but dont want toplants are primary producers and at the base of the food chainherbivorymost widespread class of herbivores are insectsnumerous insects and also they have mechanism to overcome the defense systemlarge animals also feed on plants including dinosaurs and other reptiles small and large mammals feed on plantsthere are also intermediate mammals that dont like to feed on plantsPlant defense mechanismtwo main ways of defense mechanical defense and chemical defensemechanical defense is a structural defense weaponchemical defensetoxins plant secondary compounds incorporated into plant tissuesome plants combine both mechanical and chemical defensesprimary compounds are those that are totally essential for the life of plants products of metabolic pathways ie photosynthesissecondary compounds are those have no known direct function in lifescientists thought the secondary compounds were waste products that were stored away in cells and leaves in the 80s scientist realized these products were under strict control and so it was realized that they were chemical weaponsmeans to fend of herbivoresexpensive to producetight coevolutionplant produces a secondary compound in response to herbivores but some herbivores overcome these toxins with own chemicals to degrade the toxin and the plant has to tweak its biochemical pathway to change it a little so the herbivore cant feed on the plant againfour main classes of secondary compounds phenolics terpenoids glycosides alkaloidsphenolics flavenoids give vibrant colours and tastes to fruitstoxic to small animals oxidantsterpenoids found in Mediterranean spices mint rosemary thyme etccan be toxic to small animalsglycosides toxins in milkweed sap and pits of apples bitter taste alkaloids caffeine nicotine morphinedeterrent of feeding by herbivoresmany are potent drugsall toxins evolved against herbivorythe plants are green because thats unpalatable to herbivore
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