GENE-EXPRESSION OF NITRITE REDUCTASE IN SCOTS PINE (PINUS-SYLVESTRIS L) AS AFFECTED BY LIGHT AND NITRATE

A partial cDNA clone (PSnir) encoding the C-terminal region of nitrite reductase was isolated from a lambda gt11 library of the gymnosperm P imus sylvestris (L.). Nucleotide sequence analysis showed that PSnir c ontains a reading frame encoding 105 amino acid residues. The amino ac id sequence revealed a homology to NiR of 63-68% to dicotyledoneous an d of 57-59% to monocotyledoneous species. The protein region implicate d to be involved in binding of the prosthetic group is highly conserve d between the NiR of the gymnosperm and of angiosperms. In all organs (cotyledonary whorls, hypocotyls, roots) the pattern of NiR gene expre ssion in response to nitrate and light is the same at the level of tra nscript accumulation and at the enzyme level. This suggests that regul ation of NIR gene expression in the Scots pine seedling is predominant ly 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 accumula tion of NiR mRNA and the appearance of NIR protein is mainly controlle d by nitrate, whereas the regulation of NiR gene expression in the who rls is strongly affected by light and the inducive effect of nitrate i s only weak.