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Plant Hormones and Tropisms

  • Auxins are produced in the apical meristem of plants and stimulate stem elongation and phototropism as well as fruit development. Indoleacetic acid (IAA), an auxin, occurs naturally in plants.
  • Cytokinins are produced in the roots of plants and stimulate cell division and differentiation and play a role in apical dominance.
  • Gibberellins promote the elongation of plant stems and are responsible for the rapid growth of a floral stalk, which is known as bolting.
  • Ethylene is a hormone that is a gas. It stimulates fruit ripening, leaf abscission and promotes apoptosis of plant cells.
  • Abscisic Acid (ABA) promotes seed dormancy, preventing seeds from germinating until conditions are favorable. ABA also stimulates the closure of stomata in leaves when conditions are dry.
  • A tropism is a response in which a plant turns toward or away from a stimulus. Types of tropism include phototropism, gravitropism and thigmotropism.

Plant Hormones and Tropisms

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AP Biology Intro