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Unformatted text preview: PLANT DEFENSE RESPONSES CHAPTER 39 RAVEN,JOHNSON, ET AL Life on land is not all milk and honey. True, that plants coevolved with many species of animals to enhance the reproductive potential of plants, but the downside is the animals also use the plants as a source of food bummer like a bad boyfriend! Primary defenses include many physical barriers of dermal tissue such as waxes, hairs, thorns, and so forth. However, many attackers have found ways to breach these defenses. Figs. 39.4 (nematodes) and 39.5 (fungi). Defenses also include a suite of chemicals secondary plant compounds. These are in contrast to primary plant compounds such as glucose, sucrose, starch, proteins, DNA, etc that are needed for normal cell metabolism. Secondary plant compounds are produced primarily to ward off insect, fungal, and bacterial pests (also bird and mammals). Your book mentions the cyanide-containing compounds called cyanogenic glycosides . These are compounds that can release cyanide upon digestion. Cyanide is deadly because it blocks cellular respiration via the electron transport system. An example is Manihotoxin (Table 39.1) which is found in the outer layers of cells in the root of the Cassava plant. Cassava is eaten by many Africans (and people who visit Africa) but these layers must be cleaned off or the effects of cyanide poison can be deadly. Other SECONDARY PLANT COMPOUNDS include: Terpenes Phenols Alkaloids Terepenes are lipids. Example are Pyrethroids from Chrysanthemum, peppermint, lemon, basil, etc repels insects. used in many natural insect repellents.insects....
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