Blackwell Publishing Journal Backfiles 1879-2005
Five-week-old wheat plants were exposed, under controlled environmental conditions, to 60 nl 1−115NO2 or to purified air. After 48 and 96 h of exposure, leaves, stalks and roots were analysed for 15N-enrichment in α-amino nitrogen of soluble, free amino acids. In addition, the in vitro nitrate reductase (NR, EC 220.127.116.11) and nitrite reductase (NIR, EC 18.104.22.168) activities were determined in the leaves. NR activity in the leaves decreased continously during the 96-h exposure to purified air. In the leaves exposed to 15NO2, NR activity increased within the first 24 h, then decreased, and reached the level of controls after 96 h. NiR activity in leaves exposed to purified air was almost constant during the 96-h exposure. In leaves exposed to 15NO2, NiR activity increased within the first 48 h, then decreased, and reached the level of controls after 72 h, Exposure to 15NO2 enhanced the total content of soluble, free amino acids in all tissues analysed. Most of this increase was attributed to Glu in the leaves and to Asn plus Gln the α-amino group of soluble, free amino acids was observed in the leaves, the lowest enrichment in the roots. The main labelled amino compounds were Glu (with 8.0%15N enrichment compared to the control), γ-aminobutyric acid (GABA; 7.9%), Ala (7.2%). Ser (6.8%), Asp (5.5%) and Gln (4.6%). Appreciable incorporation of 15 into Asn was not found. After 96 h exposure to 15NO2 the 15N enrichment in the α-amino group of soluble, free amino acids in the leaves declined as compared to the values obtained after 48 h fumigation. The possible pathway and the time course of 15N incorporation into soluble, free amino acids from the 15NO2 absorbed are discussed.
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