Induction of nitrate reductase in needles of Scots pine seedlings by NOX and NO3−

Abstract

The possibility to induce nitrate reductase (NR; EC 1.6.6.2) in needles of Scots pine (Pinus sylvestris L.) seedlings was studied. The NR activity was measured by an in vivo assay. Although increased NR activities were found in the roots after application of NO3−, no such increase could be detected in the needles. Detached seedlings placed in NO3− solution showed increasing NR activities with increasing NO3− concentrations. Exposure of seedlings to NOx (70–80 ppb NO2 and 8–12ppb NO) resulted in an increase of the NR activity from 10–20 nmol NO2− (g fresh weight)−1 h−1 to about 400 nmol NO2− (g fresh weight)−1 h−1. This level was reached after 2–4 days of exposure, thereafter the NR activity decreased to about 200 nmol NO2− (g fresh weight)−1 h−1. Analyses of free amino acids showed low concentrations of arginine and glutamine in NOx‐fumigated seedlings compared to corresponding controls.