Emission of nitrous oxide (N2O) from transgenic tobacco expressing antisense NiR mRNA

The emission of N-2 and N2O from intact transgenic tobacco (clone 271) expressing antisense nitrite reductase (NiR) mRNA, and wild-type plants grown aseptically, on NO3-, NO2- or NH4+-containing medium was investigated. N-15 contents of gas sampled from gas-sealed pots, in which the plants were grown on N-15-containing medium, were analyzed by gas chromatography and mass spectrometry (GC-MS). No emission of NP was detected in either of the gas samples from plant clone 271 or the wild-type grown on NO3--containing medium. N2O emission from clone 271 grown on NO3--containing medium was detected, but not from the wild-type plants. The N2O emission rate of clone 271 was 106 ng N2O mg(-1) incorporated N week(-1) and the N2O emission was inhibited by tungstate (a nitrate reductase inhibitor). No emission of N2O was found from clone 271 or wild-type plants grown on medium containing NH4+. Emission of N2O also was detected from clone 271 grown on NO2--containing medium and its emission rate increased with increasing NO2- levels in plants. We speculate that NO3- is reduced to NO2- and that a part of NO2- is metabolized to N2O in clone 271.