Peculiarities of Root Exudation in the Absence of Water Uptake

摘要

It is commonly known that roots not only absorb water required for plant life from ambient medium but also pump it into shoots. The pressure developed is called root pressure. In detached roots, this pressure is manifested in exudation. With accumulation of experimental results, it becomes increasingly clear that root pressure is composed of two constituents, osmotic and metabolic, differing in their nature. Osmotic constituent provides for root functioning like an osmometer (along the gradient of osmotic pressure between the xylem sap and external solution); the metabolic constituent functions with the involvement of the energy-dependent intracellular contractile systems that induce rhythmic microoscillations of hydrostatic pressure. The latter creates the gradient of water potential and directs water along it. Pulsation of exudation arises due to these microoscillations [1].