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The role of auxin transport in plant patterning mechanisms.

Smith RS - PLoS Biol. (2008)

View Article: PubMed Central - PubMed

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A slightly increased concentration of the activator in a cell due to random variation can lead to a small local increase in production of both the activator and the inhibitor in the cell... If the inhibitor diffuses to neighbor cells much more quickly than the activator, it will reduce the inhibitor's negative effect on local activator self-enhancement, and suppress the activation of cells nearby... Based on these results, Reinhardt et al. proposed a model for organ initiation in which the local activation of cells is not caused by local self-enhanced production, as is the case in reaction–diffusion models, but rather by the directed transport of auxin to organ initiation sites (Figure 3)... Longer-range inhibition does not require a second substance; it is due to the removal of auxin from surrounding tissue... But this in itself does not provide a complete mechanism for patterning, as it does not answer the question as to what controls the orientation of the PIN1 transport proteins... A possible answer to this question came from computer simulation studies in which it was hypothesized that PIN1 proteins are able to react to the concentration of auxin in neighbor cells, and orient preferentially toward cells with higher concentration... Similar in concept to reaction–diffusion, if one cell has a slightly higher auxin concentration, then this causes the PIN1 proteins in neighboring cells to orient preferentially toward it, causing a further increase in concentration... In a tissue of cells, this can result in a spacing mechanism similar to Meinhardt and Gierer's activator–inhibitor system... As with shoots, the root must also periodically create lateral organs to extend its structure, and the experimental data suggest that this process is also triggered by elevated auxin levels... In the root, however, lateral root primordium initiation does not appear to be accompanied by dramatic changes in PIN relocation, as is the case with the patterning in leaves and shoots... Instead, an article by Laskowski et al. in this issue of PLoS Biology suggests that it is the auxin import protein AUX1, combined with the geometry of the cells themselves, that is the crucial player in the patterning mechanism behind lateral root initiation... To start the process, Laskowski et al. suggest that it is not simply noise, or distance from previous lateral root primordia, that gives select cells that initial slight advantage, but that it is the result of the geometry of the cells themselves... The article by Laskowski et al. demonstrates the utility of a combined approach involving both experimental and computer simulation methods.

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Auxin Transport Proteins in Arabidopsis CellsExport (red) and import (green) proteins sit in the plasma membrane and transfer auxin between the cytosol and extracellular space. Often, the export proteins are polarly localized, resulting in a net flux of auxin through the cells.
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pbio-0060323-g002: Auxin Transport Proteins in Arabidopsis CellsExport (red) and import (green) proteins sit in the plasma membrane and transfer auxin between the cytosol and extracellular space. Often, the export proteins are polarly localized, resulting in a net flux of auxin through the cells.

Mentions: The plant hormone auxin is at the center of many key patterning events in plants. The selection of cells for organ initiation in the shoot apex, leaf venation, apical dominance, tropisms, and embryo axis formation are all under the control of auxin [9–12]. However, auxin is different from the morphogens considered by Turing. Instead of moving primarily via diffusion, it is actively pumped from cell to cell by the action of import and export proteins (Figure 2). Experimental evidence now starting to accumulate suggests that it is the control of auxin transport by these transport proteins that is central to many patterning processes involving auxin [13–15].


The role of auxin transport in plant patterning mechanisms.

Smith RS - PLoS Biol. (2008)

Auxin Transport Proteins in Arabidopsis CellsExport (red) and import (green) proteins sit in the plasma membrane and transfer auxin between the cytosol and extracellular space. Often, the export proteins are polarly localized, resulting in a net flux of auxin through the cells.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2602727&req=5

pbio-0060323-g002: Auxin Transport Proteins in Arabidopsis CellsExport (red) and import (green) proteins sit in the plasma membrane and transfer auxin between the cytosol and extracellular space. Often, the export proteins are polarly localized, resulting in a net flux of auxin through the cells.
Mentions: The plant hormone auxin is at the center of many key patterning events in plants. The selection of cells for organ initiation in the shoot apex, leaf venation, apical dominance, tropisms, and embryo axis formation are all under the control of auxin [9–12]. However, auxin is different from the morphogens considered by Turing. Instead of moving primarily via diffusion, it is actively pumped from cell to cell by the action of import and export proteins (Figure 2). Experimental evidence now starting to accumulate suggests that it is the control of auxin transport by these transport proteins that is central to many patterning processes involving auxin [13–15].

View Article: PubMed Central - PubMed

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

A slightly increased concentration of the activator in a cell due to random variation can lead to a small local increase in production of both the activator and the inhibitor in the cell... If the inhibitor diffuses to neighbor cells much more quickly than the activator, it will reduce the inhibitor's negative effect on local activator self-enhancement, and suppress the activation of cells nearby... Based on these results, Reinhardt et al. proposed a model for organ initiation in which the local activation of cells is not caused by local self-enhanced production, as is the case in reaction–diffusion models, but rather by the directed transport of auxin to organ initiation sites (Figure 3)... Longer-range inhibition does not require a second substance; it is due to the removal of auxin from surrounding tissue... But this in itself does not provide a complete mechanism for patterning, as it does not answer the question as to what controls the orientation of the PIN1 transport proteins... A possible answer to this question came from computer simulation studies in which it was hypothesized that PIN1 proteins are able to react to the concentration of auxin in neighbor cells, and orient preferentially toward cells with higher concentration... Similar in concept to reaction–diffusion, if one cell has a slightly higher auxin concentration, then this causes the PIN1 proteins in neighboring cells to orient preferentially toward it, causing a further increase in concentration... In a tissue of cells, this can result in a spacing mechanism similar to Meinhardt and Gierer's activator–inhibitor system... As with shoots, the root must also periodically create lateral organs to extend its structure, and the experimental data suggest that this process is also triggered by elevated auxin levels... In the root, however, lateral root primordium initiation does not appear to be accompanied by dramatic changes in PIN relocation, as is the case with the patterning in leaves and shoots... Instead, an article by Laskowski et al. in this issue of PLoS Biology suggests that it is the auxin import protein AUX1, combined with the geometry of the cells themselves, that is the crucial player in the patterning mechanism behind lateral root initiation... To start the process, Laskowski et al. suggest that it is not simply noise, or distance from previous lateral root primordia, that gives select cells that initial slight advantage, but that it is the result of the geometry of the cells themselves... The article by Laskowski et al. demonstrates the utility of a combined approach involving both experimental and computer simulation methods.

Show MeSH