Abstract
Nitrate reduction to ammonia is consisted of two consecutive redox reactions with different cellular compartments: nitrate reduction in cytosol and nitrite reduction in chloroplast. Loading of nitrite to chloroplast may be the most important process that determines the overall rate of nitrate assimilation. We evidenced nitrite uptake by chloroplast as an proton-coupled active transport, cloned a nitrite transporter cDNA, CsNitr1, from cucumber cotyledons, and found anNitr1 in chloroplast envelopes.
In early stage of germination and greening, there are two CsNitr1 isoforms: CsNitr1-L with N-terminal extension and CsNitr1-S with the N-terminal extension missing. We report here the expression of CsNitr1 isoforms in de-etiolating cucumber seedlings and subcellular localization of Nitr1 isoforms in transgenic tobacco leaves that expressed CsNitr1 isoform-GFP fusion proteins. A function of Nitr1-S on plasma membranes is presented from the phenotypes of antisense CsNitr1-S lines of tobacco.
