Hormones213-page5 - ATP requiring process For auxin...

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Plant Growth Regulators - 5 Chemically, auxin is indoleacetic acid (IAA), which is synthesized from indole or tryptophan. There are a number of synthetic “auxins” too. Auxins promote growth in molar concentrations of 10 -3 to 10 -8 . Auxin and Gene Activity The genes that control activities activated by auxin are normally repressed. Auxin binds to the repressor, which activates ubiquitin to bind to the auxin-repressor complex, dragging the complex to proteasomes for degradation. Once the repressor is removed, gene transcription for the appropriate activity occurs. Auxins are synthesized in shoot apical meristems, young leaves, seeds and fruits. Auxin always moves down the stem parenchyma cells towards roots by polar (charged) transport. Auxin becomes negatively charged, using proton pumps, an
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Unformatted text preview: ATP requiring process. For auxin transport to be successful, the following conditions are must be met: • Diffusion of a polar molecule across the plasma membrane • Carrier molecules for auxin located only at the basal (bottom) end of the cell • Proton pumps must be present to remove H + from the cell, altering the pH gradient • Weak acid ionization (Indole Acetic Acid, IAA, aka auxin (A), is a weak acid: A-+ H + = AH Auxin enters cells as IAAH passively, or as IAA-via active cotransport. IAAH dissociates within the cytosol and special auxin transport proteins in the basal end of the cell are needed to carry auxin through the plasma membrane to the top of the adjacent cell. Auxin destined for root tissue, however, moves through phloem sieve tubes....
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