Polar auxin transport
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Polar auxin transport is the regulated transport of the plant hormone, auxin, in plants.
It is suggested that it involves the components of the cytoskeleton, plasma membrane, and cell wall.[1]
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[edit] Chemiosmotic Model
The model is to explain the basipetal transport of auxin in the living plant cells.
Influx carrier protein, located on the top side of the cells, uptake auxin into the plant cell by both passive and active transport while the efflux carrier protein, located on the base, transport auxin out of the cell.
In the plant cells, the proton pump continously pump the hydrogen ion (H+) from the cytoplasm. The pH value of the cytoplasm is maintained at about 5; the IAA is deionized in the pH condition. As the cell membrane is not peameable to IAA, the transport of IAA required the efflux carriter protein.
Some experiments suggest that the asymmetrical developement of efflux carrier protein requires the localized targeting of vesicles and the interaction with actin on cytoskeleton.
[edit] Polarity
Polarity is set up in the cell as the efflux carriers are only located on the base of the plant cells.
Pin-formed (PIN) auxin efflux facilitator is linked to the polarity of the transport.[2]
The polarity change due to the environmental stimuli, for example, directional light source and perceived gravity vector .[3].
[edit] Inhibitors of the transport
Quercetin(a flavonol) and Genistein are nuture-occurring transport inhibitors.
NPA and 2,3,5-triiodobenzoic acid are efflux protein inhibitors.
[edit] Regulation
[edit] Phosphorylation
Polor auxin transport can be regulated by reversible protein phosphorylation; protein kinases and protein phosphatases mediate the phosphorylation and dephosphorylation respectively. A study suggests that phosphatase inhibition can alter the activities of acropetal and basipetal auxin transport. [3].
[edit] Effects of auxin polar transport
Roots bend in response to gravity due to the regulated movement of the plant hormone auxin. In roots, an increase in the concentration of auxin will inhibit cell expansion, therefore, the redistribution of auxin in the root can initiate differential growth in the elongation zone resulting in root curvature.
[edit] References
- ^ Exploring the Cellular Basis of Polar Auxin Transport
- ^ [1]
- ^ a b Gloria K Muday, Alison DeLong. (2001)Polar auxin transport:controlling where and how much. Trend in Plant Science 6(11):535-542
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