Plant DefensesPlants are a source of nutrition for many other organisms - bacteria, fungi, protists, animals, and virusesPlants are not defenseless - dermal tissues are waxy and helpprevent entry of parasites, silica can be incorporated into tissues todeter grazers, irritating trichomes and thorns can also stopgrazing,Many plants produce chemicals that can deter attacks - a plantsecondary compound is a chemical produced by the plant thatfulfills no metabolic requirement but deters attack by otherorganisms. Include: alkaloids - caffeine, nicotine, cocainetanninsoils - peppermint, sageToxins are not toxic to the plant because• sequestered in membrane-bound compartments and only released when tissue is damaged (e.g. many quinones)• produced as a nontoxic chemical that becomes toxic when metabolized by predators (e.g. cyanogenic glycosides)Some plants can have defenses against competition from otherplantsAllelopathy occurs when a chemical signal secreted by the roots ofone plant blocks germination of nearby seeds or inhibits thegrowth of a neighboring plant. Black walnut is allelopathicSome plants have mutualistic interactions with animals thatprovide defenses for the plantAcacia trees and antstrees provide ants with sugar innectaries, ants provide predatorprotectionParasitoid wasps, caterpillars,and leaveswound response releases volatilecompound attracting
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