AMMONIUM INHIBITION OF NITRATE UPTAKE BY THE DIATOM, PHAEODACTYLUM-TRICORNUTUM

Cells of Phaeodactylum tricornutum have a mechanism for uptake of nitrate which leads to its accumulation. The uptake system was absent from ammonium-grown cells but became active during incubation for 2 h with 1.0 μM nitrate. Nitrate uptake into the cells was stopped by addition of 0.3 mM ammonium chloride; it recommenced as soon as the added ammonium had disappeared. It is concluded that ammonium (or a product of its assimilation) can inhibit nitrate metabolism by inhibiting uptake of nitrate. © 1979 Elsevier/North-Holland Scientific Publishers Ltd.