Mannose inhibition of nitrate uptake by wheat roots

The effect of mannose on nitrate uptake was investigated by a new non-invasive technique. Under normal condition, nitrate uptake by wheat (<em>Triticum aestivum</em> L.) roots was about 1-7 µmol gfwt^-1 h^-1. After the addition of 10 mM mannose, net nitrate influx by wheat roots started to decrease and reached a new steady state at -40 ±50% of the control value after 73 min. After mannose supplied for 2 h, its removal caused net nitrate influx to be recovered to an original rate. Therefore, the inhibition of mannose on nitrate uptake is not due to the onset of programmed cell death because it starts too rapidly and it is reversible, however, it is probably due to Pi and consequent ATP depletion.