Action of Abscisic Acid on Ion Transport as Affected by Root Temperature and Nutrient Status

Measurements were made of the transport of ions through excisedbarley roots. It is shown that addition of 10^–5 M abscisicacid (ABA) may lead to inhibition or stimulation of transport.The effect of ABA depended on the conditions in which the plantshad been grown and on the temperature at which the experimentwas carried out. It is suggested that stimulation of transportis a direct effect of ABA, but inhibition may be an indirecteffect due to disturbance of endogenous levels of plant hormones.The results are considered in relation to regulation of iontransport in the plant as a whole.