Nitric Oxide and Nitrous Oxide Production by Soybean and Winged Bean during the in Vivo Nitrate Reductase Assay 1

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This study was conducted to determine by gas chromatography (GC) and mass spectrometry (MS) the identity and the quantity of volatile N products produced during the helium-purged in vivo NR assay of soybean (Glycine max [L.] Merr. cv Williams) and winged bean (Psophocarpus tetragonolobus [L.] DC. cv Lunita) leaflets. Gaseous material for identification and quantitation was collected by cryogenic trapping of volatile compounds carried in the He-purge gas stream. As opposed to an earlier report, acetaldehyde oxime production was not detected by our GC method, and acetaldehyde oxime was shown to be much more soluble in water than the compound(s) evolved from soybean leaflets. Nitric oxide (NO) and nitrous oxide (N2O) were identified by GC and GC/MS as the main N products formed. NO and N2O produced from soybean leaflets were both labeled with 15N when 15N-nitrate was used in the assay medium, demonstrating that both were produced from nitrate during nitrate reduction. Other compounds co-trapped with NO and N2O were identified as air (N2, O2), CO2, methanol, acetaldehyde, and ethanol. Leaves of winged bean, subjected to the purged in vivo NR assay, evolved greater quantities of NO and N2O (13.9 and 0.37 micromole per gram fresh weight per 30 minutes, respectively) than did the soybean cv Williams (1.67 and 0.09 micromole per gram fresh weight per 30 minutes, respectively). In both species NO production was dominant. In contrast, with similar assays, NO and N2O were not evolved from leaves of the nr1 soybean mutant which lacks the constitutive NR enzymes. In addition to soybean cv Williams, six other Glycine sp. examined evolved significant quantities of NO(x) (NO and NO2). Other species including Neonotonia wightii (Arn.) Lackey comb. nov., Pueraria montana (Lour.) Merr., and Pueraria thunbergiana Benth. evolved lower levels of NO(x).

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