Lecture 24- Guest Lecture on Plant Defenses•Plants are autotrophs and necessary organisms in the food chain because they provide energy for higher trophic levels. Plants are linked throughout the food web through herbivores (mostly insects)•Plants need to defend themselves because every plant will be attacked by an herbivore at some lifestage. Wide variety of herbivores- Including:•Chewers (Beetles, larvae, etc.)•Miners (Leave a “maze” like pattern with a dark line of waste in the center).•Suckers (Suck out Phloem which is where the carbohydrates are).•Gallers (On the stems and/or leaves of most plants).•Root feeders (Feed on the roots of plants).•Seed predators (Eat the embryo).•Seed predators eat the seeds-preventing new plants from growing. Only type of herbivore that kills the plant.•Co-evolution of plants and herbivores:1.Herbivores select for plant defensive traits2.Those defenses select for “offensive” traits in the herbivores (stronger mouthparts)3.Plants become better defended, and herbivores become better at overcoming defenses4.Co-evolution requiresspecificity—the evolution of each trait is due to the other5.Co-evolution requiresreciprocity—both traits must evolve.Note than evolution can occur without another organism, such as evolution within one species to develop flashier coloring.•Types of plant defenses:1.Physical-Trichomes, spines, latex (milky white sap substance) thick cuticle. Consider a flower that has derived spines. It is tough for insects to maneuver around them. They also fill the insect gut with useless crap and little nutrients.2.Chemical-Secondary metabolites not directly involved in growth, reproduction or development. Defense compounds that inhibit enzymes, disrupt protein synthesis and DNA repair, or weaken cell structure include codeine, morphine, cocaine, nicotine, strychnine, and more. Defense chemicals that inhibit cellular respiration include cyanide and digitalis. Essential oils may also act as repellants: citronella, menthol, and camphor.Those that inhibit digestion include tannis, cannabinoids, and more.3.Indirect-Attacked plants emit volatiles (airborne chemicals) that attract enemies of herbivores—like parasitoid wasps.Some plants house ant colonies that defend plants from herbivores—Like from elephants that eat acaciatrees.•The importance of plant-survival for humans :1) Agriculture- A large percentage of our crops are lost to herbivorous insects. US farms spend $7-8b annually on chemical pesticides. Alternatives to chemical pest control include:•-associational plants (planting a repellant crop in with the regular crop)•-natural enemies•-genetic engineering•Some bacteria genes encode a pesticidal protein•2).Medicine- Of the top 150 prescription drugs, 118 come from natural sources.•Ex: Periwinkle, Pacific Yew, etc- Produce anticancer drugs.•80% of the world's population relies on products of natural
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