Auxin Efflux Carriers: Maintaining Concentration Gradients of Phytohormones
- Auxin is a crucial phytohormone that regulates plant growth and development.
- It can freely diffuse into plant cells but cannot exit them without specialized proteins.
How Auxin Moves Through Plant Cells
Passive Diffusion: The First Step
- Auxin enters plant cells by passive diffusion.
- In the acidic environment of the cell wall, auxin exists in an uncharged form, allowing it to cross the plasma membrane easily.
The cytoplasm of plant cells is slightly alkaline, causing auxin to lose a proton and become negatively charged. This traps auxin inside the cell, preventing it from diffusing back out.
Active Transport: The Role of Auxin Efflux Carriers
- Once inside the cell, auxin becomes charged (ionized) in the cytoplasm, preventing it from diffusing out.
- To move auxin out of the cell, plants rely on auxin efflux carriers.
- These are specialized membrane proteins that actively transport charged auxin molecules across the plasma membrane into the cell wall.
Remember, active transport requires energy because it moves molecules against their concentration gradient.
Creating a Concentration Gradient
- Auxin efflux carriers are strategically positioned on one side of the cell.
- This ensures that auxin is pumped out in a specific direction, creating a concentration gradient across the tissue.
In a growing shoot, auxin efflux carriers may be concentrated on the lower side of cells, causing auxin to accumulate on that side and promote cell elongation.
- Think of auxin efflux carriers as a conveyor belt in a factory.
- Just like items move along the belt in a specific direction to be assembled, auxin moves in a directed manner from one cell to the next.
- The active transport system ensures that auxin is placed where it is needed, much like items are delivered to the right assembly line.
