A partial cDNA clone (PSnir) encoding the C-terminal region of nitrite reductase was isolated from a 2gtl 1 library of the gymnosperm Pimus sylvestris (L.). Nucleotide sequence analysis showed that PSnir contains a reading frame encoding 105 amino acid residues. The amino acid sequence revealed a homology to NiR of 63-68~o to dicotyledoneous and of 57-59~o to monocotyledoneous species. The protein region implicated to be involved in binding of the prosthetic group is highly conserved between the NiR of the gymnosperm and of angiosperms. In all organs (cotyledonary whorls, hypocotyls, roots) the pattern of NiR gene expression in response to nitrate and light is the same at the level of transcript accumulation and at the enzyme level. This suggests that regulation of NiR gene expression in the Scots pine seedling is predominantly at the level of transcript accumulation. The highest NiR appearance was observed in roots and hypocotyls. In the cotyledonary whorls only small amounts of NiR were found. In roots and hypocotyls the accumulation of NiR mRNA and the appearance of NiR protein is mainly controlled by nitrate, whereas the regulation of NiR gene expression in the whorls is strongly affected by light and the inducive effect of nitrate is only weak.