Eukaryotic nitrate and nitrite transporters

Nitrate transport is the key step controlling the amount of nitrate incorpo rated by the cells and subsequent of storage, reduction or export. Molecula r, genetic and biochemical approaches to the study of eukaryotic nitrate/ni trite transporters allow an initial understanding of this step, which is mu ch more complex and structured than previously suspected, At the plasma mem brane level, two gene families, Nrt1 and Nrt7, account for high- and low-af finity nitrate transporters. Functionality of NRT1 from Arabidopsis and NRT 2 proteins from Aspergillus and Chlamydomonas has been demonstrated. Howeve r, redundancy of these systems makes it difficult to assign particular phys iological roles to each. Data on genes involved in the regulation of nitrat e transport and reduction are still scarce. Information on nitrite transpor ters to the chloroplast is biased by the belief that in vivo nitrous acid d iffuses freely to this organellum. The recent progress on these aspects is discussed in this review.