In over 40 years of research on the cellular uptake of auxin it is somewhat chastening that we have elaborated so little on the original kinetic descriptions of auxin uptake by plant cells made by Rubery and Sheldrake in 1974. Every aspect of that seminal work has been investigated in detail, and the uptake activity they measured is now known to be attributed to the AUX1/LAX family of permeases. Recent pharmacological studies have defined the substrate specificity of AUX1, biochemical studies have evaluated its permeability to auxin in plant cell membranes, and rigourous kinetic studies have confirmed the affinity of AUX1 for IAA and synthetic auxins. Advances in genome sequencing have provided a rich resource for informatic analysis of the ancestry of AUX1 and the LAX proteins and, along with models of topology, suggest mechanistic links to families of eukaryotic proton co-transporters for which crystal structures have been presented. The insights gained from all the accumulated research reflect the brilliance of Rubery and Sheldrake's early work, but recent biochemical analyses are starting to advance further our understanding of this vitally important family of auxin transport proteins.

• Keywords
• auxin transport, development, hormone, kinetics, permeability, structure,
• MeSH
• Biological Transport, Active physiology   MeSH
• Cell Membrane * genetics   metabolism   MeSH
• Indoleacetic Acids metabolism   MeSH
• Membrane Transport Proteins * genetics   metabolism   MeSH
• Plants * genetics   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Indoleacetic Acids MeSH
• Membrane Transport Proteins * 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

The molecular basis of cellular auxin transport is still not fully understood. Although a number of carriers have been identified and proved to be involved in auxin transport, their regulation and possible activity of as yet unknown transporters remain unclear. Nevertheless, using single-cell-based systems it is possible to track the course of auxin accumulation inside cells and to specify and quantify some auxin transport parameters. The synthetic auxins 2,4-dichlorophenoxyacetic acid (2,4-D) and naphthalene-1-acetic acid (NAA) are generally considered to be suitable tools for auxin transport studies because they are transported specifically via either auxin influx or efflux carriers, respectively. Our results indicate that NAA can be metabolized rapidly in tobacco BY-2 cells. The predominant metabolite has been identified as NAA glucosyl ester and it is shown that all NAA metabolites were retained inside the cells. This implies that the transport efficiency of auxin efflux transporters is higher than previously assumed. By contrast, the metabolism of 2,4-D remained fairly weak. Moreover, using data on the accumulation of 2,4-D measured in the presence of auxin transport inhibitors, it is shown that 2,4-D is also transported by efflux carriers. These results suggest that 2,4-D is a promising tool for determining both auxin influx and efflux activities. Based on the accumulation data, a mathematical model of 2,4-D transport at a single-cell level is proposed. Optimization of the model provides estimates of crucial transport parameters and, together with its validation by successfully predicting the course of 2,4-D accumulation, it confirms the consistency of the present concept of cellular auxin transport.

• MeSH
• Biological Transport MeSH
• Cells, Cultured MeSH
• 2,4-Dichlorophenoxyacetic Acid chemistry   metabolism   MeSH
• Indoleacetic Acids chemistry   metabolism   MeSH
• Naphthalenes chemistry   metabolism   MeSH
• Plant Growth Regulators chemistry   metabolism   MeSH
• Nicotiana chemistry   cytology   metabolism   MeSH
• Models, Theoretical MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• 2,4-Dichlorophenoxyacetic Acid MeSH
• Indoleacetic Acids MeSH
• Naphthalenes MeSH
• naphthalene MeSH Browser
• Plant Growth Regulators MeSH