Chapter 14 - Plant responses

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  • Chapter 14 - Plant responses
    • Plant hormones
      • Unlike animal hormones, they are not made in glands, do not travel very far.
      • Same as animal hormones in that they bind to receptors, and starts a cascade, which brings about a response
      • Also known as 'plant growth substances' and ' plant growth regulators'
      • Commercial uses
        • Ethene
          • Can promote ripening, meaning fruits can be transported long distances while unripe, to prevent spoilage
        • Auxin
          • Prevents abscission of young fruits, initiates formation of fruits, even if unpollinated, vegetative propagation, selective herbicides
        • Gibberellin
          • Can produce seedless fruits, allows fruit to stay longer on trees, increased sucrose yield in sugar cane and stimulates seed germination
    • Nastic movements and tropisms
      • A nastic movement is a fairly rapid movement by a plant, normally caused by turgidity of certain cells. An example is a flower closing its petals at night
      • A tropism is a growth response to a stimulus, where the direction of the plant's growth is related to the direction of the stimulus. An example is plants growing towards light (phototropism)
    • Phototropism
      • Growth response towards light (positive phototropism shown by shoots) or away from it (negative phototropism, shown by roots)
      • Uses auxin, mechanism is not fully understood but thought it involves blue light, phototropins and transporter protein to get auxin to the shady side and cause permanent cell elongation
    • Apical dominance
      • Apical meristem inhibits growth of lateral buds using auxin, which travels down the plant using diffusion
      • Remove the apical meristem, and the plant becomes more bushy
    • Leaf abscission
      • Involves auxin, ethene and abscisic acid
      • Change in balance in auxin and ethene causes abscission layer, which is hydrolysed by enzymes until the petiole breaks off
    • Gibberellin and stem elongation
      • Dwarf plants lack the gene
      • Put GA on the stem of dwarf plants, and internodal growth increases

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