using the acid hypothesis explain how auxins bring about cell enlargement in plants
The acid hypothesis suggests that auxins increase the acidity in the cell walls of plants, which leads to cell enlargement. Here's a step-by-step explanation of how this process occurs:
1. Auxins are a class of plant hormones responsible for various growth processes, including cell elongation. They are produced in the tips of shoots and roots and then transported to other parts of the plant.
2. When auxins are transported to the plant cells, they bind to specific receptors present on the plasma membrane of the cells.
3. This binding triggers a signaling pathway that ultimately leads to the activation of specific proton pumps called H+-ATPases present in the plasma membrane.
4. The activated H+-ATPases actively pump hydrogen ions (H+) from the cytoplasm into the cell wall space.
5. As more hydrogen ions are pumped into the cell wall, the pH of the cell wall becomes more acidic. This increased acidity is primarily due to the accumulation of these hydrogen ions.
6. The acidic environment in the cell wall activates enzymes called expansins. Expansins are proteins that break the bonds between cellulose microfibrils in the cell wall.
7. By breaking these bonds, expansins loosen the cell wall structure and allow for easier expansion and elongation of the cells.
8. The increased acidity and the action of expansins contribute to the cell wall becoming more flexible and expansible, resulting in cell enlargement.
In summary, the acid hypothesis suggests that auxins stimulate the transport of hydrogen ions into the cell wall, leading to increased acidity. This acidic environment activates expansins, which loosen the cell wall structure, allowing for cell enlargement and elongation.
The acid hypothesis is the theory that auxins, a class of plant hormones, promote cell enlargement by increasing the acidity (lowering the pH) of the cell wall.
Here's a step-by-step explanation of how auxins bring about cell enlargement in plants, according to the acid hypothesis:
Step 1: Auxin synthesis and transport
- Auxins are synthesized in the actively growing parts of the plant, primarily the apical meristems (tip of the stem or root).
- They are then transported in a polar manner from the apical meristem towards the base of the plant through a process called polar auxin transport.
Step 2: Activation of proton pumps
- When auxins reach their target cells, they trigger the activation of proton pumps in the cell membrane. Proton pumps use energy to expel H+ ions from the cytoplasm to the cell wall.
Step 3: Acidification of cell wall
- The action of the proton pumps results in the accumulation of H+ ions in the cell wall, making it more acidic. This acidification process lowers the pH of the cell wall.
Step 4: Activation of expansins
- The lowered pH in the cell wall activates enzymes called expansins. Expansins function to loosen the cross-linking between cellulose microfibrils in the cell wall, allowing for easier expansion of the cell.
Step 5: Cell wall loosening and water uptake
- With the action of expansins, the cell wall becomes more flexible and stretches easily.
- The flexible cell wall allows the cell to take up more water through osmosis.
- As water enters the cell, it exerts pressure on the cell wall, causing the cell to enlarge.
Step 6: Cell enlargement and growth
- The increased turgor pressure from water uptake, combined with the flexibility of the cell wall, leads to cell enlargement.
- This enlargement contributes to plant growth by elongating stems, roots, and other plant organs.
Overall, the acid hypothesis suggests that auxins promote cell enlargement by acidifying the cell wall, activating expansins, and allowing for increased water uptake and turgor pressure in the cell.