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Lecture six Plant Hormones 22/10/2013

Lecture six Plant Hormones 22/10/2013. Auxins. Plants dont grow randomly, hormones make sure they grow in the right direction Auxins – are plant hormones which control growth at the tips of shoots and roots Auxins move through the plant in solution

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Lecture six Plant Hormones 22/10/2013

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  1. Lecture sixPlant Hormones22/10/2013

  2. Auxins • Plants dont grow randomly, hormones make sure they grow in the right direction • Auxins – are plant hormones which control growth at the tips of shoots and roots • Auxins move through the plant in solution • Auxins are produced in the tips and diffuses backwards to stimulate the cell elongation process which occurs in the cells behind the tips

  3. Auxins • Auxins promote growth in the shoot but also inhibits growth in the root • Auxins are involved in the growth responses of plants to light (phototropism) and gravity (geotropism)

  4. Shoots • Shoots are positively phototropic (grow towards light) • When a shoot is exposed to light, it accumulates more auxins on the side that`s in the shade than the side that`s in the light • This makes the cells grow faster on the ahded side, so the shoot bends towards the light

  5. Shoots • Shoots are negatively geotropic (grow away from gravity) • When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxins on the lower side • This causes the lower side to grow faster, bending the shoot upwards

  6. Roots • Roots are positively geotropic (grows towards gravity) • A root growing sideways will also have more auxin on its lower side • But in a root the extra auxin inhibits growth, this means the cells on top grow faster, and the root bends downwards

  7. Roots • Roots are negatively phototropic (grow away from light) • If a root starts being exposed to some light, more auxin accumulates on the shaded side • The auxin inhibits cell growth on the shaded side, so the root bends downwards, back into the ground • Basically, shoots grow towards light, roots grow towards gravity

  8. Example

  9. Quiz time !! How do plants grow in the right direction? What are Auxins? Where are Auxins produced? Explain how shoots are positively phototropic and negatively geotropic. Explain how roots are positively phototropic and negatively geotropic.

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