Abstract: | Previous papers have shown that abscisic acid can inhibit transportof ions across the root to the xylem vessels, resulting in reducedexudation from excised roots or inhibiting guttation from intactplants. However, it has not been established whether the inhibitionwas due to a reduction in salt transport (Js) or in permeabilityof the roots to water (Lp). This paper investigates the effectof ABA on Lp and Js separately. It is shown that Lp increasedin ABA and then fell, but was about the same as in control rootswhen transport was inhibited. The effect of ABA on exudationtherefore appeared to be mainly due to reduction in Js. Inhibitionof Js was also present in intact, transpiring plants and sowas not due to reduced water flow. The inhibition of ion releaseto the xylem affected Na+, Mg2+, Ca2+, and phosphate as wellas the major ion in the exudate, K+. It is concluded that ABAinhibits salt transport to the shoot by acting on ion transportinto the xylem, and not by reducing water flow coupled withsalt transport. |