auxin

(noun)

a class of plant growth hormones that is responsible for elongation in phototropism and gravitropism and for other growth processes in the plant life cycle

Related Terms

Examples of auxin in the following topics:

  • Auxins, Cytokinins, and Gibberellins

    • The term auxin is derived from the Greek word auxein, which means "to grow. " Auxins are the main hormones responsible for cell elongation in phototropism and gravitropism.
    • While many synthetic auxins are used as herbicides, indole acetic acid (IAA) is the only naturally-occurring auxin that shows physiological activity.
    • Auxins also act as a relay for the effects of the blue light and red/far-red responses.
    • Commercial use of auxins is widespread in plant nurseries and for crop production.
    • Applying synthetic auxins to tomato plants in greenhouses promotes normal fruit development.

  • Blue Light Response

    • Most activation occurs on the lit side, causing the plant hormones indole acetic acid (IAA) or auxin to accumulate on the shaded side.
    • When the sun is positioned almost directly over the plant, the hormone auxin (pink dots) in the plant stem is evenly distributed.
    • As the sun moves, the auxin is repositioned on the other side of the plant.
    • This overload of auxin next to these cells causes them to start to grow or elongate, tipping the growth of the stem toward the light.

  • Plant Responses to Wind and Touch

    • Tendrils of a redvine produce auxin in response to touching a support stick and then transfer the auxin to non-touching cells.

  • Abscisic Acid, Ethylene, and Nontraditional Hormones

    • In addition to the growth hormones auxins, cytokinins, gibberellins, there are two more major types of plant hormones, abscisic acid and ethylene, as well as several other less-studied compounds that control plant physiology.
    • Its activity counters many of the growth-promoting effects of GAs and auxins.
    • Strigolactones promote seed germination in some species and inhibit lateral apical development in the absence of auxins.
    • Signals between these compounds and other hormones, notably auxin and GAs, amplify their physiological effect.

  • Agrobacterium and Crown Gall Disease

    • It also carries genes for the biosynthesis of the plant hormones, auxin and cytokinins, and for the biosynthesis of opines, providing a carbon and nitrogen source for the bacteria.

  • Plant Pathogens

    • Phytohormones: example Agrobacterium changes the level of Auxin to cause tumours.