Effect of Water Movement on Ion Movement into the Xylem of Tomato Roots

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Abstract
Water was moved through detopped tomato root systems by increasing the hydrostatic pressure of the solution surrounding the roots. Comparisons were made of amounts of ions moved into the root xylem when water was moved under pressure with amounts moved by active transport in the absence of external pressure. Application of pressure increased the amount of P32, Ca45, and total salts moved into the root xylem, but not in proportion to the increased rates of water movement. At 30 lb./sq. inch, the amount of ions moved into the root xylem was 2.0-2.4 times the amount moved by active transport in the absence of pressure. Treatment of roots with 10-3 [image] sodium azide initially reduced the rate of both water and P32 movement, but longer exposure to azide resulted in increased rates. It is suggested that application of pressure and the resulting increased water flow through the roots caused increased ion movement into the root xylem indirectly by creating a steeper ion concentration gradient from the cortex to xylem, and by increasing the permeability of the root cells to ions.