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Plant Hormones and Their Effect

Plant Hormones and Their Effect. 24.3. Hormones. A hormone is a chemical signal that affects growth, activity or development in a living organism A plant hormones control development, but also coordinate responses to environment. How do hormones work?.

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Plant Hormones and Their Effect

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  1. Plant Hormones and Their Effect 24.3

  2. Hormones • A hormone is a chemical signal that affects growth, activity or development in a living organism • A plant hormones control development, but also coordinate responses to environment.

  3. How do hormones work? • Specific target cell that have a receptor for the hormone • Response depends on the receptors

  4. Auxin • Auxin • Stimulate cell elongation • Promote growth of roots • Regulate division in meristem • Apical Dominance • Prevent growth of buds closer to the stem’s tip • Also play a role in phototropism • Bending towards a light source

  5. Cytokinins • Produced in growing roots and developing seeds and fruits • Stimulate cell division • Regeneration of damaged tissue • Delay aging of leaves • Usually have the opposite affect of Auxin • Auxin: made in shoots, sent to roots • Cytokinins: made in roots, sent to shoots • Helps to restore lost organs

  6. More Hormones • Gibberellins • Stimulate growth • Dramatic increase is size, specially in stems and fruits • Abscisic Acid • Controls seed dormancy until a shift in hormones brought on by environmental conditions • Inhibits the cellular division • There opposite affect helps to control homeostasis

  7. Ethylene • In the form of a gas • Stimulates fruits to ripen • Helps to “seal off” and drop organs that are no longer useful for the plant

  8. Tropisms • Tropism – a response to the environment • Phototropism • Gravitropism • Thigmotoropism

  9. Phototropism • Tendency to grow towards light • Auxin in responsible • Migrate towards shaded area • Seedlings can quickly change to grow in opposite directions

  10. Gravitropism • Shoots grow upward, roots grow downward • Auxin is also responsible for this • Still not understood why auxin migrates to the areas that cause this

  11. Thigmotoropism • Response to touch • Plant will wrap around an object to help support its growth • Vines and climbing plants • Tomato plants and wind

  12. Rapid Response • Some responses are extremely quick • Ex:Mimosa pudica • “sensitive plant” – fold together in seconds when touched • Ex: Venus flytrap • Close when an organism lands inside • Triggers sensory to close the leaves

  13. Response to Seasons • Plants flower according to photoperiod • Length of daylight • Photoperiodism • Major factors in the timing of seasonal activities • Flowering and growth • Phytochrome – absorb red light and different signaling pathways within the plant • Not completely undestood

  14. Photoperiodism Page: 713

  15. Winter Dormancy • Deciduous trees stop photosynthesis, transport important material to roots and seal leaves off from rest of plant • This is why leaves drop • Phytochrome absorbs less due to day length  less auxin produced  ethylene production increases

  16. Winter Dormancy • Because of the change in hormone levels • Chlorophyll breaks down and pigments that were there but were not displayed become more visible • Yellow and red pigments • This is why leaves change color. What hormone helps them fall off? • Ethylene

  17. Winter Dormancy • More effects: • Meristems produce protecting scale over buds • Waxy coating • Xylem and Phloem are occupied by many ions and organic compounds • Anti-freeze • Prevents sap from freezing

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