Effect of ammonium on anion uptake and trans-root potential in sunflower roots

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Abstract
Summary: Studies were made on detopped sunflower plants to see whether the depolarizing effect of NH4on the trans-root potential is the result of increasing H2PO4uptake and to determine the effect of NH4on the flux of NO3and SO4in xylem exudate. Increasing the NH4in the medium increased the H2PO4flux in the exudate, but decreased NO3and SO4fluxes. Ammonium and NO3influenced the uptake of each other but NH4had the greater effect. These NH4effects were attributed wholly or in part to blockage of the root metabolism which may have affected the permeability of root cell membranes. Therefore, the stimulation of H2PO4flux by NH4was probably not attributable to any specific effect of NH4on H2PO4uptake. Enhanced H2PO4and decreased uptake of NO3and SO4reflects toxic effects of NH4on the root metabolism.