Long Distance Transport

Once in the xylem vessels, the transport of the mineral elements from the root to the shoot is driven by the gradient of hydrostatic pressure (root pressure) and by the gradient of water potential. The gradient of water potential between roots and shoots is usually quite steep during the day when the stomata are open. It follows the pattern: atmosphere << leaf cells << xylem sap < root cells < external solution (soil). Transport in xylem vessels is mainly unidirectional. An increase in the transpiration rate enhances both the uptake and the translocation of mineral elements in the xylem.