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Chapter 39: Control Systems in Plants

Chapter 39: Control Systems in Plants. Question. Do plants sense and respond to their environment ? Yes - By adjusting their pattern of growth and development. In Dark. In Light. Comment. Plants can’t “move” away from a stimulus, but can change their growth response.

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Chapter 39: Control Systems in Plants

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  1. Chapter 39:Control Systems in Plants

  2. Question • Do plants sense and respond to their environment ? • Yes - By adjusting their pattern of growth and development. In Dark In Light

  3. Comment • Plants can’t “move” away from a stimulus, but can change their growth response. • Result – plant bodies are more “flexible” in morphology than animals.

  4. Classical Example • Phototropism - plant growth response to unilateral light. • Observation – plants bend or grow towards the light.

  5. Phototropism Experimenters • Darwins: late 1800's. • Boysen & Jenson: early 1900's. • F.W. Went: 1926

  6. Went Experiments

  7. Mechanism of Phototropism • Cells on the dark side elongate faster than the cells on the light side. • The uneven growth rate causes the bending of the stem toward the light.

  8. Question • What is the adaptive value of phototropism? • It tilts the leaves toward the light source for more efficient photosynthesis.

  9. Cause of Phototropism • Chemical messenger from the tip caused the growth response in the stem. • The distribution of the chemical changes in the unequal light, resulting in unequal cell elongation.

  10. Hormone • Chemical signal produced in one location, transported, has effect in another location. • Phototropism is caused by a plant hormone.

  11. Plant Hormones • Are produced in small quantities. • Effects may reflect balance between several hormones.

  12. Mechanism

  13. Plant Hormones 1. Auxins 2. Cytokinins 3. Gibberellins 4. Abscisic Acid 5. Ethylene

  14. Auxins • Named by Went in 1926. • First plant hormone described. • Ex: IAA (natural) 2,4-D (synthetic)

  15. Major Functions • Stimulates cell elongation. • Fruit development. • Apical Dominance. • Tropism responses.

  16. Apical Dominance

  17. Where Produced • Apical Meristems. • Young leaves. • Embryos.

  18. Cytokinins • Isolated from coconut "milk" (endosperm) in the 1940’s. • Named because they stimulate cell division. • Ex: Zeatin

  19. Major Effects • Stimulates cell division. • Delays senescence. • Root growth and differentiation. • Where Produced - roots

  20. Control shoot or root differentiation in tissue cultures. Auxin/Cytokinin Ratios

  21. Gibberellins • Found from the "Foolish Seedling" disease in rice. • Ex: GA3 70 types known

  22. Foolish Seedlings

  23. Internode elongation. Seed/Bud germination. Flowering (some species). Fruit development. Major Effects Extra GA3 No GA3

  24. Have GA3 Lack GA3

  25. Where Produced • Apical Meristems. • Young leaves. • Embryos.

  26. Abscisic Acid • Slows or inhibits plant growth. • "Stress" hormone produced under unfavorable conditions.

  27. Major Effects • Inhibits growth • Seed/Bud dormancy. • Stomata closure. • Leaf drop – produces abscission layer.

  28. Abscission Layer

  29. Where Produced • Leaves • Stems • Green fruit

  30. Ethylene • Gaseous hormone (fast diffusion rates). • Often interacts with Auxin.

  31. Major Effects • Fruit ripening. • Accelerates Senescence. • Stem/Root Elongation (+ or -).

  32. Where Produced • Ripening fruits. • Senescent tissue. • Nodes.

  33. New Hormones • Oligosaccharins – short chains of sugars released from the cell wall. • Function: • Pathogen responses • Cell differentiation • Flowering

  34. New Hormones • Brassinosteroids – steroid hormones similar to animal sex hormones. • Function: • Needed for normal growth and development.

  35. Commercial Applications of Plant Hormones • Weed killers • Seedless fruit • Rooting of cuttings • Tissue culture

  36. Plant Movements 1. Tropisms 2. Circadian Rhythms

  37. Tropisms • Growth responses in response to external stimuli. • + toward a stimulus • - away from stimulus

  38. Examples 1. Phototropism 2. Gravitropism

  39. Phototropism • Response to light (blue).

  40. Movie

  41. Gravitropism • Response to gravity. • Stems are – gravitropic and roots are + gravitropic.

  42. Statolith movement may be the receptor for the stimulus. Gravitropism - mechanism

  43. Thigmotropism • Response to touch. • A series of 5 genes are involved. • Ex: Tendrils Climbing stems Wind direction response of stems.

  44. Turgor Movements • Movement caused by turgor pressure differences in certain cells.

  45. 1. Rapid Leaf Movement Ex: Mimosa 2. Sleep Movements Ex: Bean Leaves Prayer Plant Types Sleep Movements Day Night

  46. Mimosa Rapid Leaf Movement

  47. Circadian Rhythms • A physiological cycle about 24 hours long. • Ex: Stomata opening Sleep movements

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