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Plant Responses to the Environment

Plant Responses to the Environment. Stationary Life. Animal response to stimuli Move toward or away Plant response to stimuli Adjust patterns of growth Plasticity varied forms Chemicals. Signal Transduction Pathways. Reception  Transduction Response Ex. Potato greening

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Plant Responses to the Environment

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  1. Plant Responses to the Environment

  2. Stationary Life • Animal response to stimuli • Move toward or away • Plant response to stimuli • Adjust patterns of growth • Plasticity varied forms • Chemicals

  3. Signal Transduction Pathways • Reception Transduction Response • Ex. Potato greening • Ex. Seed germination

  4. Reception • Receptor proteins undergo conformational changes in response to stimuli • Transduction • Second messengers amplify signal • Turn on kinases phosphorylate enzymes • Response • Stimulates RNA production • Make new enzymes • Activates existing enzymes • phosphorylation

  5. Response

  6. Hormones • Coordinate growth, response • Specific receptor, specific response • Minute quantities cause large reactions

  7. Plant movement • Tropism- growth toward or away from stimuli • Light- phototropism • Gravity-gravitropism • Pressure-thigmotropism • Affect division, elongation and differentiation of cells

  8. phototropism • Auxin (hormone) is distributed asymmetrically • One side grows more quickly • Plant grows toward light

  9. Response to Mechanical stress • Triple response due to • Slowing of stem elongation • Thickening of stem • Horizontal growth • “feels” for obstacle • Seedlings respond the same way when ethylene is applied without an obstacle

  10. Apoptosis-programmed cell death • Vessel element formation • Leaf abscission • Nutrients are stored in stem parenchyma • Abscission layer has weak cell walls, sensitive to ethylene

  11. Fruit ripening • Ethylene triggers cell wall breakdown • Starch converted to sugar • Chain reaction: ethylene triggers ripening ripening triggers more ethylene • Fruit ripens at the same time • Commercial use • GMO tomatoes lack ethylene

  12. Delayed germination • Abscisic Acid prevents germination • Removal/inactivation of ABA allows germination • Cold • Light • Water

  13. Gravity • Gravitropism • Controlled by Auxin • Statoliths=starch grains in cytoplasm • High concentration of starch attracts Auxin • High concentration of Auxin in roots slows down cell growth root bends down • High concentration of Auxin in stem speeds up stem growth

  14. Touch • Thigmotropism-move toward solid object • React to touch –open ion transport chanels • Cells deflate, leaves collapse

  15. Defense mechanisms • Secondary compounds • Tannins • Jasmonic acid= messenger • Symbiosis • Damaged leaves release volatile molecules • Attract parasitic wasps • Wasps kill caterpillars

  16. In a diseased state known as witches broom branches grow and proliferate excessively. Suggest a hypothesis to explain how a pathogen might induce this growth pattern?

  17. Responses to light • Photosynthesis • Development • photomorphogenesis • Timing • germination • Flowering • Fruit

  18. Light receptors • Blue light photoreceptors • Phototropism • Opening stoma • Slowing of cotyledon growth • Phytochromes (red and far red light) • Seed germination (break dormancy) • Shade avoidance (primary vs. apical growth)

  19. Red-Far Red phytochrome switch • Protein has two shapes: Pr and Pfr • Phytochromes “see” red and far red light • Pr absorbs red light  turns into Pfr • Pfr absorbs far red turns in to Pr

  20. Germination and shade avoidance • Germination • Sunlight contains red light, Pr turns into Pfr • Pfr (exposure to sunlight )promotes germination • Shade avoidance • Canopy filters out more red light, leaves far red light • Pfr more resources to growing taller • Pr branching, more leaves

  21. Circadian rhythms • Growth chamber experiments • Photosynthetic enzymes • Stomata • Leaf position Pfr is made during the day, reverts at night Dawn resets biological clock by putting more Pfr into the system when the sun comes out

  22. Photoperiodism • Germination, budding, flowering, etc. correspond to the season • Seasons have different relative day/night • Day/Night length determine timing of events (temperature is irrelevant) • Fall leaves

  23. Flowering • Short day (long night)- need longer period of continuous darkness • Long day (short night)- requires shorter period of continuous darkness • Leaves detect period of darkness, transmit signal to flower buds,

  24. Red light can interrupt night • Far red light cancels red light interruption • Manipulate plants to flower • Chrysanthymums long night plant, interrupt each night w/light, delay flowering until mother’s day

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