page_title: Auxin
section_title: Effects
hierarchical_section_title: Auxin / Effects
caption_attribution_description: Wild type Arabidopsis thaliana (left), auxin signal-transduction mutant (axr2, right)
context_page_description: Auxins are a class of plant hormones with some morphogen-like characteristics. Auxins play a cardinal role in coordination of many growth and behavioral processes in plant life cycles and are essential for plant body development. The Dutch biologist Frits Warmolt Went first described auxins and their role in plant growth in the 1920s.Kenneth V. Thimann became the first to isolate one of these phytohormones and to determine its chemical structure as indole-3-acetic acid. Went and Thimann co-authored a book on plant hormones, Phytohormones, in 1937.
context_section_description: Auxin participates in phototropism, geotropism, hydrotropism and other developmental changes. The uneven distribution of auxin, due to environmental cues, such as unidirectional light or gravity force, results in uneven plant tissue growth, and generally, auxin governs the form and shape of the plant body, direction and strength of growth of all organs, and their mutual interaction.
  Auxin stimulates cell elongation by stimulating wall-loosening factors, such as elastins, to loosen cell walls. The effect is stronger if gibberellins are also present. Auxin also stimulates cell division if cytokinins are present. When auxin and cytokinin are applied to callus, rooting can be generated if the auxin concentration is higher than cytokinin concentration. Xylem tissues can be generated when the auxin concentration is equal to the cytokinins.
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  Auxin also induces sugar and mineral accumulation at the site of application.
caption: A healthy Arabidopsis thaliana plant (left) next to an auxin signal-transduction mutant with a repressed response to auxin.
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