Auxins

Definition

Auxins are a class of plant hormones that play a crucial role in regulating plant growth and development, particularly by influencing cell elongation, apical dominance, and responses to light and gravity. These hormones are essential for coordinating various physiological processes in plants, including growth patterns and developmental stages.

5 Must Know Facts For Your Next Test

1. Auxins are primarily produced in the shoot tips and young leaves, where they promote cell elongation and contribute to stem growth.
2. They play a significant role in root development by stimulating the formation of lateral roots and influencing root growth direction.
3. Auxins help regulate the processes of fruit development and maturation, making them key players in agricultural practices like fruit ripening.
4. These hormones are also involved in the process of phototropism, guiding plants to grow towards light by redistributing auxins to the shaded side of the plant.
5. Auxins can induce programmed cell death in certain tissues, contributing to senescence and influencing how plants respond to environmental stresses.

Review Questions

• How do auxins influence phototropism and what is their role in a plant's response to light?
  • Auxins influence phototropism by redistributing unevenly within the plant when it is exposed to directional light. The side of the plant that is shaded accumulates more auxins, which promotes greater cell elongation on that side. This differential growth causes the plant to bend towards the light source, allowing it to maximize photosynthesis by optimizing its exposure to sunlight.
• Discuss the role of auxins in apical dominance and how this affects branch development in plants.
  • Auxins are critical for establishing apical dominance, where the main central stem grows more vigorously than lateral branches. This is achieved because auxins produced at the apex inhibit the growth of lateral buds through a feedback mechanism. As long as auxin levels are high at the tip, lateral shoot development is suppressed. If the apex is removed, auxin production decreases, leading to increased lateral branching as these suppressed buds begin to grow.
• Evaluate how auxins interact with other plant hormones during processes like fruit ripening and senescence.
  • Auxins interact with other hormones such as ethylene during critical processes like fruit ripening and senescence. While auxins promote growth and delay senescence by maintaining cell division and elongation, ethylene acts to trigger ripening and accelerate senescence. The balance between these hormones influences how plants respond to environmental signals. For instance, as fruits mature, auxin levels may decrease while ethylene levels increase, signaling the transition from growth to ripening, thus affecting agricultural practices for harvesting fruits.

Related terms

Phototropism: The growth of a plant in response to light direction, which is influenced by auxins that promote elongation of cells on the side of the plant away from the light.

Apical Dominance: The phenomenon where the main stem of a plant grows more strongly than the lateral branches, regulated by auxins that suppress the growth of side shoots.

Ethylene: A plant hormone involved in the regulation of fruit ripening and senescence, which can interact with auxins to influence growth and developmental processes.