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

The emission of N₂ 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. ¹⁵N contents of gas sampled from gas-sealed pots, in which the plants were grown on ¹⁵N-containing medium, were analyzed by gas chromato- graphy and mass spectrometry (GC–MS). No emission of N₂ 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.