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Plant responses to internal and external signals

Plant responses to internal and external signals. Chapter 39. I) Plant responses to hormones * hormones are the major way plants can have a long term response to stimuli. A) detection of first hormone 1) experiments by Darwin and Darwin. 2) experiment by Boysen -Jenson. B) Auxins

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Plant responses to internal and external signals

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  1. Plant responses to internal and external signals Chapter 39

  2. I) Plant responses to hormones *hormones are the major way plants can have a long term response to stimuli. A) detection of first hormone 1) experiments by Darwin and Darwin

  3. 2) experiment by Boysen-Jenson

  4. B) Auxins 1) any hormone that causes elongation and growth a) mainly found in apical meristem of shoot or root tip

  5. b) moves by activetransport to dark side of plant. Those cells elongate and plant grows toward light( or inhibit growth in root)

  6. c) can be added to cuttings to promote adventitous root formation

  7. C) Cytokinins 1) made in the roots 2) promotes cell division, root growth, and germination

  8. 3) in equal amounts auxins and cytokinins cause cell growth but not differentiation

  9. 4) if cytokinin levels rise, cells turn into shoot buds, but if auxin levels rise roots form

  10. D) Gibberellins 1) Found in meristems of apical buds and roots, young leaves, embryo 2) seed/bud germination, stem and leaf growth

  11. 3) must be present for a fruit to set 4) when water is absorbed by seed gibberellins are released to break dormancy

  12. E) Abscisic Acid(ABA) 1) high levels of ABA in developing seeds prevent germination

  13. 2) if leaf begins to wilt from loss of water, ABA buildup closes stomata

  14. F) Ethylene ** 1) auxin levels fall, and ethylene triggers leaves to fall off in the fall

  15. 2) Allow fruit to ripen a) acts as positive feedback b) “one bad apple can spoil the whole bunch”

  16. 3) triple response a) if seed germinates under something the mechanical stress on the tip triggers ethylene production, which: a1) slows growth a2) thickens stem a3) causes it to bend

  17. II) Plant responses to light 1) photomorphogenesis: effects of light on plant morphology 2) action spectrum: graph that relates response to wavelenth

  18. A) Blue-light photoreceptors 1) cryptochromes: pigments that inhibit hypocotyl elongation

  19. 2) phototropin: pigment that allows phototropism

  20. B) Phytochromes and seed germination 1) phytochrome: a protein with a non-protein section that responds to light

  21. 2) some seeds germinate when provided with red light

  22. a) phytochrome response is reversible and is determined by the last flash of light received.

  23. b) Pr(P660) recognizes red light Pfr(P730) recognizes far red

  24. c) as Pr is hit by red light, it changes to Pfr. Seeds in the dark have just Pr, but the appearance of Pfr triggers germination.

  25. C) Shade avoidance 1) in full light amount of Pr and Pfr is equal. 2) in shady areas, more red light is absorbed during photosynthesis from the canopy, so the presence of more far red causes a shift to the production of Pr

  26. 3) the increase of Pr triggers growth of the stem to try and reach sunlight so the tree isn’t shaded out.

  27. III) Biological clocks and circadian rhythms. 1) circadian rhythm: an internal “clock” that keep time for an organism

  28. A) Light sets the clock 1) Pr is made by plants, and is converted to Pfr during the day, which is the active form. a) a flash of red light during the night resets the clock and shortens the night for the plant

  29. 2) Pr accumulates during the night as the plant makes it and it isn’t converted to Pfr because there is no red light.

  30. 3) this is what triggers flowering. a) long-day plants a1) flash of red during the night “shortens” the night and can trigger flowering

  31. a2) if you flash red-far red, the initial red flash is cancelled out.

  32. b) Short day plants b1) are also affected this way

  33. B) Photoperiodism 1) the response of plants to length of day and night

  34. 2) Control of flowering a) short-day plant: will only flower if day is shorter than a critical time( 14 hours, for example) a1) can also say they flower when day length is decreasing

  35. b) long-day: flower if day is longer than a critical period(14 hours for example) b11) flower when day length is increasing

  36. c) Day neutral: flower plants reaches a certain point of maturity, regardless of day length

  37. d) all of these trigger the hormone florigen in leaves, which then travels to shoot tips to make the flower

  38. e) night length is what controls this

  39. IV) Responses to things other than light A) Response to gravity 1) gravitropism a) gravity causes statoliths to settle at bottom of horizontal root. Auxins then congregate here and inhibit growth, so opposite side grows faster to turn root

  40. b) if stem is horizontal, same thing happen, but the auxins stimulate growth to turn stem up towards sun.

  41. 2) thigmotropism a) respond to touch to grow around an object

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