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Chapter 39: Plant Communication

Chapter 39: Plant Communication. Plants and their Environments. Plants are living and respond to envir. They detect light and gravity especially. Plants respond by altering growth. Receptors receive signals and initiate a cellular response. Signal Transduction Pathway

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Chapter 39: Plant Communication

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  1. Chapter 39: Plant Communication

  2. Plants and their Environments • Plants are living and respond to envir. • They detect light and gravity especially. • Plants respond by altering growth. • Receptors receive signals and initiate a cellular response. • Signal Transduction Pathway • Ex: Potatoes bud in dark not light • b/c they grow in absence of light (underground)

  3. Hormones Chemical Signals • Sent by one cell to initiate responses in others • Can be introduced to soil or water to affect plant • Minimal concentrations needed for big effect • Triggers a cascade response • Relative, not absolute levels of hormones regulate plant responses

  4. Tropisms • Whole body response of plant to stimuli. • Phototropism – Plant grows towards light. • Coleoptile tip must be exposed to light. If removed or covered, no response. • Detection at coleoptile, but growth occurs further down shoot. • Chemical response sent from tip to shoot. • Gravi-. Photo- and thigmo-tropism • Gravity, light, touch

  5. Phototropism • Plants detect the intensity, direction, and wavelength of light. • They will bend towards the area with the best light (intensity/quality) • Phytochromes = receptors

  6. Phototropism is a Hormonal Response

  7. Auxins – Plant Growth Hormone • Responsible for tropisms. • 2 Theories: • Auxin concentrated on dark side of plant  traditional theory • An auxin inhibitor concentrated on light side of plant  more recent research

  8. Auxins • Main function is to promote shoot elongation at low concentrations • Loosen cell wall and allow increase H2O uptake (elongation) • Also induce division in cambium • Too high of a [auxin] will cause production of ethylene which inhibits elongation • Causes rapid translation of proteins • Gene regulation

  9. Cytokinins • Induce cytokinesis (cell division) • Operate in balance with auxins • Equal: No differentiation, just division • More cytokinin: Shoot buds form • More auxin: roots form • Auxins inhibit auxiliary growth, cytokinins promote it • Slow aging

  10. Gibberellins • Produced in roots and leaves • Stimulate growth of leaves and stems • Elongation and division • Works in cooperation with auxin to loosen cell walls (more H2O in = elongation) Effect of Gibberellins

  11. Seed Dormancy and Gibberellins • When conditions are appropriate, the release of gibberellins signals the seed to germinate • May stimulate digestive enzymes to mobilize stored nutrients

  12. Abscisic Acid (ABA) • Slows growth • Works antagonistically against the other growth hormones (gibberellins, auxins, cytokinins) • Ratio b/t ABA and others • Seed dormancy • Allows plants to withstand droughts (close stomata)

  13. Ethylene • Leaf abscission (fall off) • Fruit ripening • Programmed cell death • High [auxins] stimulate production • Involved in thigmotropism (touch) • Apoptosis

  14. Apoptosis • Systematic, preprogrammed (DNA) cell death. • Enzymes break down organics (DNA, chlorophyll, RNA, proteins) • Bursts of ethylene during autumn cause plants to lose their leaves and prepare for winter. First, they break down the organic molecules. • Stored in stem parenchyma cells (reused by new spring leaves)

  15. Seed Dispersal  Fruits • When a bear eats a piece of fruit, he eats the seeds. • He doesn’t digest the seeds. • He poops the seeds. • The poop is fertilizer for the seeds. • Thanks Fozzy.

  16. Ripening of Fruit • Ethylene production causes ripening • Storing fruits in a paper bag accelerates ripening (traps ethylene) • Storing orange juice in the cabinet accelerates ripening

  17. Circadian Rhythms • Plants go through processes in a 24-hour (approx.) cycle • When isolated, they lose sync with the external ques and regain when replaced • Think Jetlag

  18. Photoperiodism • Plant leaves monitor the relative length of day and night • Allows seasonal changes in plants (ie: flowering) • Short-day plants require light period shorter than a critical length to flower. • Long-day plants flower when the light period is longer than a critical number of hours • Day-neutral plants flower at maturity, regardless of day length

  19. Short/Long Day Plants • Short day = long night • Long Day = short night • Many plants require uninterrupted darkness hours to flower

  20. Water Deficit • Bright, sunny days  plants can lose more H2O than they take in • As H2O dec. the guard cells close stomata • Inc. ABA production (close stomata) • Inhibit growth of young leaves • Leaves roll to dec. surface area • All designed to decrease transpiration

  21. Heat/Cold Stress • Denatures plant enzymes • Transpiration = evaporative cooling • Heat shock protein = produced when temp. is raised beyond threshold • Often bind to enzymes to prevent denaturization • Extreme cold also freezes plants • Many plants collect solutes (dec. fp)

  22. Defense • Some “call” other species to fight predators off • Plants release signal chemicals to alert other plants of an infestation of herbivores

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