Auxin regulates the transcription of auxin-responsive genes by the TIR1/AFBs-Aux/IAA-ARF signaling pathway, and in this way facilitates plant growth and development. However, rapid, nontranscriptional responses to auxin that cannot be explained by this pathway have been reported. In this review, we focus on several examples of rapid auxin responses: (1) the triggering of changes in plasma membrane potential in various plant species and tissues, (2) inhibition of root growth, which also correlates with membrane potential changes, cytosolic Ca2+ spikes, and a rise of apoplastic pH, (3) the influence on endomembrane trafficking of PIN proteins and other membrane cargoes, and (4) activation of ROPs (Rho of plants) and their downstream effectors such as the cytoskeleton or vesicle trafficking. In most cases, the signaling pathway triggering the response is poorly understood. A role for the TIR1/AFBs in rapid root growth regulation is emerging, as well as the involvement of transmembrane kinases (TMKs) in the activation of ROPs. We discuss similarities and differences among these rapid responses and focus on their physiological significance, which remains an enigma in most cases.

• MeSH
• Endocytosis MeSH
• Plant Roots growth & development   MeSH
• Indoleacetic Acids metabolism   MeSH
• Membrane Potentials MeSH
• GTP-Binding Proteins metabolism   MeSH
• Receptors, Cell Surface metabolism   MeSH
• Plant Proteins metabolism   MeSH
• Plants metabolism   MeSH
• Calcium metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• auxin receptor, plant MeSH Browser
• Indoleacetic Acids MeSH
• GTP-Binding Proteins MeSH
• Receptors, Cell Surface MeSH
• Plant Proteins MeSH
• Calcium MeSH

Here we present an overview of what is known about endogenous plant compounds that act as inhibitors of hormonal transport processes in plants, about their identity and mechanism of action. We have also summarized commonly and less commonly used compounds of non-plant origin and synthetic drugs that show at least partial 'specificity' to transport or transporters of particular phytohormones. Our main attention is focused on the inhibitors of auxin transport. The urgent need to understand precisely the molecular mechanism of action of these inhibitors is highlighted.

• Keywords
• Abscisic acid, Auxin, Cell biology, Cytokinins, Inhibitors, Plant hormones, Strigolactones, Transport,
• MeSH
• Models, Biological MeSH
• Biological Transport MeSH
• Plant Growth Regulators metabolism   MeSH
• Plant Proteins metabolism   MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Plant Growth Regulators MeSH
• Plant Proteins MeSH