Regulation of nitrite reductase by light and nitrate in the cotyledons of hot pepper (Capsicum annuum L.).

Light and nitrate are the major factors regulating the nitrite reductase (NiR) amongst various environmental and metabolic cues in plants. Hot pepper was used to investigate this regulatory mechanism of the NiR gene expression and its dependency on light and nitrate. The major results from this study are: (I) the nir partial clone (581 bp) obtained from hot pepper genomic DNA by degenerative polymerase chain reaction exhibited an amino acid sequence that is highly homologous with other plants. (II) Genomic DNA blot analysis and the NiR electrophoretic assay revealed that a small multigene family encodes NiR, which exists at least in two isoforms. (III) The light-mediated increase of NiR activity is correlated with the nitrate concentration, showing saturation kinetics above 50 mM of nitrate. (IV) Exogenous nitrate was required for the appearance of nir transcripts, but not for the enzyme activity. These results suggest that the gene expression of NiR in hot pepper is determined by the presence of nitrate at the transcriptional level. Furthermore, light has a synergistic effect on the action of nitrate on NiR levels.