Abstract
Nitrate uptake activity was measured under various conditions using the protonemal cells of the moss Physcomitrella patens, which are amenable to nitrate uptake measurements in liquid medium. The activity was not detected in ammonium-grown cells and induced by transfer of the cells to nitrate-containing medium, suggesting that P. patens has only inducible transport system(s). Once induced, nitrate uptake activity was detected in the dark as well as in the light, indicating that light is not required for nitrate uptake. We previously reported quick and reversible inhibition of nitrate uptake by ammonium in P. patens. The inhibitory effect of ammonium was abolished by an inhibiter of glutamine synthetase, suggesting that ammonium is not the actual inhibitor. Glutamine or an inhibiter of glutamate synthase inhibited nitrate uptake activity, indicating that glutamine acts as the actual inhibitor of nitrate uptake.
