Water into the Xylem
When water reaches the endodermis by apoplastic pathway, the casparian strip in the endodermal cells prevents it from going any further. This forces the water into the protoplast of the cell, where is joins with water that took the ssymplastic pathway.
Endodermal cells actively transport salts into the xylem and this is how water gets into the xylem. This takes place along carrier proteins in the cell-surface membrane. For water to access the cell, it must pass through the cytoplasm of the endodermal cells.
The water potential in the xylem is now lowered, so water is moved into the xylem by osmosis. Root pressure is a force that helps to move water up the plant. Root pressure makes a big contribution to water movement.
Evidence for root pressure:
- Pressure increases with a raise in temp and decreases in a drop in temp
- Metabolic inhibitors prevent most energy release by respiration so cease root pressure.
- Decrease in avaliability of oxygen causes a reduction in root pressure.