Effect of Mannitol and Polyethylene Glycol on Phosphorus Uptake by Maize Plants

The effect of mannitol and polyethylene glycol 6000 (P.E.G.) on phosphorus absorption and translocation was studied with maize seedlings. Mannitol inhibited P absorption and translocation to the shoots at −10 bars while P.E.G. only affected translocation. Plants treated with P.E.G. recovered within 24 h after removal of the osmoticum, but mannitol-treated plants were impaired further. It is concluded that the primary effect of the osmoticum is a reduction in phosphorus translocation, inhibition of uptake by mannitol being a secondary effect. Polyethylene glycol treatments reduced transpiration in the dark, but plants recovered completely after 24 h, concomitant with return to normal translocation. Polyethylene glycol was detected in both roots and shoots after 24 h treatment, but root content decreased to about half after a 2-h wash, and to about 3 per cent of the initial content after 24 h. P.E.G. content of shoots also decreased upon washing of the roots, but at a slower rate.