Biology 220 Lecture #18 - Plant Defenses - 11-14-07

Biology 220 Lecture #18 - Plant Defenses - 11-14-07 -...

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Biology 220 Lecture #18 - Plant Defenses, Herbivores, and Pathogens – 11/1/07 INTERACTIONS UNIT – (2) Plants are susceptible to attack by a variety of enemies HERBIVORY o Roots (nematode) o Leaf level o Surface level o Destruction of the plant does two things: 1.) Sometimes stimulates plants to make more 2.) Weaken plant – take what they need without destroying plant PLANT DEFENSES – 5 Pathogens o Viral o Bacterial o Protist o Fungal Plant diseases consist of one of the 4 above PATHOGENS – 6 Plant Viruses – Similar to those that affect animals Viruses are often air borne PATHOGENS – 7 Bacteria Spread through liquid films on the top of the plant Plants that are heavily watered are very susceptible to bacterial infections Bacteria like that water film to grow in (thrive) “Green bean spot” disease Spotting occurs
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PATHOGENS – 8 Grow from spores Travel through air, but need water to germinate Heavily watered plants are very susceptible to fungal infections Appressorium – germinating spore – sticks to the underside of the leaf Creates infection peg – Grows up into the plant between the cells and starts to extract food molecules excretes digestive enzymes PATHOGENS – 9 Chlorosis – The cells on the leaf actually turn yellow because the chlorophyll is being broken down – yellow spots Necrosis – Cells dying off Brown spots Bacteria Wilting – Sign of a Lack of water Sometimes a Symptom of disease – bacteria and fungi go into the xylem and plug it up Plant can get water to leaves Leaves wilt and die because of not enough water PATHOGENS – 10 How pathogens enter a plant: o 1.) Penetrate the epidermis of a leaf or the bark of a tree or the stem in someway Bacteria or fungi produces digestive enzymes that dissolve the waxy cuticle on the plant or the cellulose on the cell walls. o 2.) Entering through the stomata This happens when the stomata is open, so if you have a lot of water on your plant or there is a high level of humidity or you need to perform gas exchange, the plant will be more susceptible to having stomata open and getting this type of infection. o 3.) Wounding Wounds are holes that open up to the inside of the plant and viruses, bacteria, fungi, etc. can enter in through the hole. Aphids Major way viruses can enter into a plant – Aphids are sap suckers – use stillete to poke hole into the plant to suck out the phloem fluid hole due to stillete can allow viruses to enter.
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DEFENSE AGAINST PATHOGENS – 11 – (22:10) Preformed Defenses – Best defense is a good offense o Put up a good defense prior to infection Induced Defenses – Triggered by the infection Preformed defenses o Epidermis (Cellulose is hard to penetrate!) o Wax is hard to dig through versus a sugar o Change the shape of the stomata or the timing of the opening of the stomata to prevent infection (open stomates during the day versus night or vice versa)
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Biology 220 Lecture #18 - Plant Defenses - 11-14-07 -...

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