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Auxin and differential growth in roots and shoots

Homeostasis and response • Plant hormones (biology only)

Key concepts

What you'll likely be quizzed about

  • Auxin is a plant hormone that regulates cell elongation and directional growth.
  • The primary sites of auxin production are the meristematic regions near the tips of shoots and roots.
  • Auxin molecules diffuse away from the tip into adjacent tissues, moving asymmetrically in response to environmental stimuli such as light or gravity.

Flashcards

Test your knowledge with interactive flashcards

What experimental evidence shows auxin production occurs in the shoot tip?

Click to reveal answer

Removing the shoot tip stops phototropic bending, indicating that the tip produces auxin or regulates its distribution.

Key notes

Important points to keep in mind

Auxin is produced at the tips of shoots and roots and moves via diffusion and polar transport.

Higher auxin concentrations promote cell elongation in shoots but inhibit elongation in roots.

Light causes auxin to gather on the shaded side of a shoot, leading to bending toward the light.

Gravity causes auxin to collect on the lower side of a root, inhibiting growth there and causing downward curvature.

Barrier experiments show that auxin diffusion from the tip is essential for curvature responses.

Auxin effects are concentration-dependent; excessive auxin can inhibit growth or lead to abnormal plant development.

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