Effects of Glufosinate on Anion Uptake in Lemna gibba

G udrun D. Trogisch*, H elm ut Köcher**, and W olfram R. Ullrich* * Institut für Botanik, Technische Hochschule, Schnittspahnstraße 3. D-6100 Darmstadt, Bundesrepublik Deutschland ** Hoechst AG, D-6230 Frankfurt 80. Bundesrepublik Deutschland Z. Naturforsch. 44c, 33 — 38 (1989); received July 13/November 11, 1988 Dedicated to Professor Wilhelm Simonis on the occasion o f his 80th birthday Ammonium Accumulation, Nitrate Reductase Activity, Nitrate Uptake, Phosphate Uptake, Phosphinothricin. Photosynthesis, Respiration The duckweed Lemna gibba G 1 was used as a model to study inhibitory sites with the herbicide and glutamate analogue glufosinate (PPT). Growth and chlorophyll formation were partly inhib­ ited by 25 n-M, completely suppressed by 250 (im PPT. Photosynthesis showed partial inhibition within few hours, dark respiration ( 0 2 consumption) increased already within one hour. In the presence of 1 mM PPT in the light, the ammonium pool of Lemna increased to 600% within few hours, later to 1000%. The overall amino acid pool exhibited a slower increase to 300%, the nitrate pool only a slight increase, while total phosphate remained almost unchanged. In the dark all these effects were less pronounced than in the light. Nitrate, nitrite and phosphate uptake were partially inhibited by PPT, especially after 19 h PPT pretreatment. Nitrate reductase activity in vitro, after PPT treatment in vivo, showed an inhibition similar to that of nitrate uptake. Ammo­ nium was not taken up but released under the same conditions. The data are explained by a combined effect of PPT, by inhibition of glutamine synthetase leading to accumulation of ammonium from photorespiration and proteolysis, by membrane depolarization and inhibition of anion/proton cotransport, by secondary uncoupling of phosphory­ lation, and by secondary inhibition of nitrate reductase activity.