| Claim/finding | Evidence type/assay system | Quantitative result(s) | Biological implication | Citation with year + DOI URL |
|---|---|---|---|---|
| AUX1 is a high-affinity auxin influx carrier for IAA | Heterologous expression in *Xenopus laevis* oocytes; plasma-membrane localization of EYFP-AUX1; radiolabeled ^3H-IAA uptake | AUX1 increased ^3H-IAA uptake by >10-fold vs. water controls; uptake was saturable with **Km ~800 nM**; aux1-7 and aux1-117 abolished uptake, aux1-102 reduced uptake by ~60% | Establishes AUX1 as a bona fide carrier-mediated IAA importer with physiologically relevant high affinity | Yang et al. 2006, https://doi.org/10.1016/j.cub.2006.04.029 (pqac-00000006, pqac-00000013) |
| AUX1 shows selective pharmacology consistent with influx-carrier behavior | Same *Xenopus* oocyte uptake system plus Arabidopsis root elongation assays | AUX1-mediated uptake inhibited by **2,4-D** and **1-NOA**; not inhibited by **NAA** or **IBA** in the cited assay summary; in roots, 50 nM IAA reduced elongation up to ~80%, while 20 mM 1-NOA produced ~3-fold longer roots than IAA alone | Confirms substrate/inhibitor specificity and links transporter pharmacology to plant growth responses | Yang et al. 2006, https://doi.org/10.1016/j.cub.2006.04.029 (pqac-00000005, pqac-00000013) |
| AUX1 directly binds IAA with micromolar affinity | Radioligand binding to HA-AUX1 expressed in Sf9 insect-cell membranes; homologous displacement/saturation analysis | **Kd ~2.6 µM**; **Bmax ~11,800 fmol IAA/mg membrane protein**; specific binding in control membranes ~1% of HA-AUX1 membranes | Direct biochemical evidence that AUX1 physically recognizes auxin at affinities comparable to transport measurements | Carrier et al. 2008, https://doi.org/10.1104/pp.108.122044 (pqac-00000008, pqac-00000009, pqac-00000010, pqac-00000011) |
| AUX1–IAA interaction is pH dependent and consistent with transport of anionic auxin near apoplastic pH | Sf9 membrane binding assays across buffered pH range | Binding optimum between **pH 5.0 and 6.0**; rapid association reported, with binding half-life on the order of seconds in assay summaries; >90% specific binding retained after 60 min in dissociation conditions | Supports the proton-coupled import model and physiological relevance at the acidic cell wall/apoplastic interface | Carrier et al. 2008, https://doi.org/10.1104/pp.108.122044 (pqac-00000008, pqac-00000010, pqac-00000011) |
| Auxin analogs and influx inhibitors displace IAA from AUX1 | Competitive displacement of ^3H-IAA from AUX1-containing membranes | All tested auxins/inhibitors displaced >95% of bound IAA; reported IC50 values included approximately **39.7 µM, 53.6 µM, 70.8 µM, 3.6 µM, 32.4 µM**, with **2-NAA ~3.6 µM** among the strongest competitors in the reported table | Refines substrate-recognition and inhibitor-binding landscape of AUX1 | Carrier et al. 2008, https://doi.org/10.1104/pp.108.122044 (pqac-00000008, pqac-00000011, pqac-00000014) |
| AUX1 contributes quantitatively to lateral root development | Review synthesis of genetic and developmental studies in Arabidopsis | **aux1 mutants show ~50% reduction in emerged lateral roots** | Indicates AUX1-mediated auxin uptake is required for normal lateral root emergence/development | Swarup & Péret 2012, https://doi.org/10.3389/fpls.2012.00225 (pqac-00000024) |
| AUX1 in non-hair/epidermal cells sustains root-hair patterning and polarity | Review synthesis of expression, mutant, rescue, and modeling studies | aux1 mutants show **~30-fold higher frequency of double-hair formation**; exogenous auxin rescues shorter root hairs | Shows AUX1 helps establish auxin distribution needed for correct root-hair elongation and planar polarity | Swarup & Péret 2012, https://doi.org/10.3389/fpls.2012.00225 (pqac-00000024) |
| Modeling and tissue-expression data support AUX1-mediated auxin focusing in epidermal patterning | Review synthesis of computational and experimental studies | AUX1 expression in non-hair cells can drive **>10-fold auxin accumulation** relative to adjacent hair cells; elevated auxin in hair-cell files can be maintained up to **~500 µm** from the root apex | Explains how localized influx can shape spatial auxin gradients over multicellular distances | Swarup & Péret 2012, https://doi.org/10.3389/fpls.2012.00225 (pqac-00000024) |
| AUX1/LAX transport is proton-coupled and likely stoichiometric with two protons per IAA− | Mechanistic review integrating vesicle transport, topology, and biophysical work | Reported stoichiometry: **2 H+ per IAA−**; summarized AUX1 affinity for IAA **~0.5 µM** and influx permeability **~1.4 µm/s**; related measurements include **1.5 µm/s** IAA uptake permeability in Arabidopsis protoplasts | Supports the current model of AUX1 as an energized H+:IAA− symporter that dominates cellular auxin influx | Singh et al. 2018, https://doi.org/10.3390/ijms19113391 (pqac-00000023, pqac-00000025, pqac-00000029, pqac-00000015) |
| AXR4 is required for correct AUX1 plasma-membrane targeting | 2024 mechanistic study using Arabidopsis mutants, immunolocalization, heterologous expression, and biochemical interaction assays | In **axr4**, AUX1 accumulates in the **ER** rather than the plasma membrane; AXR4–AUX1 interaction detected biochemically; AXR4 reduced AUX1 aggregation in a **dose-dependent** manner | Identifies AXR4 as an ER accessory/chaperone-like factor that enables functional AUX1 deployment to the plasma membrane | Tidy et al. 2024, https://doi.org/10.1093/plphys/kiad506 (pqac-00000016, pqac-00000017, pqac-00000020) |
| AXR4 trafficking control extends beyond AUX1 and has applied significance | Same 2024 Plant Physiology study; localization and phenotype analyses | LAX2 also shows ER retention/mislocalization in **axr4**; mutated AXR4 transgenes largely restored AUX1 PM localization, with one allele showing partial rescue | Suggests that manipulating AXR4-dependent AUX/LAX trafficking could be used to engineer root system traits (“designer roots”) for nutrient/water acquisition | Tidy et al. 2024, https://doi.org/10.1093/plphys/kiad506 (pqac-00000017, pqac-00000018, pqac-00000019, pqac-00000021) |


*Table: This table compiles core experimental and review-supported evidence for Arabidopsis AUX1 function, kinetics, localization, and developmental roles. It highlights the most cited quantitative findings and the key 2024 mechanistic advance on AXR4-dependent trafficking.*