auxin-binding protein

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auxin-binding protein A protein found in plant cells that binds auxins and thus may act as the initial receptor of the signal transduction pathway for these plant growth substances. Likely candidates have been found in various plant tissue cultures, including pith cells of tobacco and coleoptile tissue of maize. Such binding proteins are thought to act in a manner analogous to hormone receptor proteins in animal cells. According to one model, auxin stimulates the cell by binding to an auxin-binding protein (ABP) on the exterior surface of the plasma membrane. The ABP is held in place by a membrane-spanning docking protein. This activated complex of auxin, ABP, and docking protein then triggers the auxin-stimulated response in the cell, for example cell expansion (see acid growth theory).