Water Flow in Wheat Seedlings after Small Water Deficits

Abstract

AbstractTranspiration and water uptake were measured simultaneously using a micro‐wave hygrometer and a recording potometer. Wheat seedlings (Triticum aestivum L. cv. Weibulls Starke) were kept with the roots at +1°C in nutrient solution and with the shoots in air at 20°C for 24 h, a treatment which induced a decrease of about 2% in relative water content of the leaves. The induced deficit rapidly disappeared after returning to normal root temperatures (20°C).The treatment produced after‐effects on steady rates of water absorption and transpiration in light, whereas the times taken for transient changes in transpiration brought about by changes in light conditions were not affected. The after‐effects were not completely eliminated 24 h after removal of stress. The magnitude of the after‐effects varied with the leaf water content, though some contribution of root cooling to the after‐effects cannot be excluded. The decreased water flow through the plant after removal of stress can be attributed mainly to increased stomatal resistance and not to effects on root conductivity. The increased stomatal resistance appears linked to increased membrane permeability rather than to a decrease in the active mechanism for ion uptake.