Nitrogen transport in plants, with an emphasis on the regulation of fluxesto match plant demand

Physiological methods, especially the use of isotopes of N, have allowed fo r the detailed characterizations of the several putative transport systems for nitrate and ammonium in roots of higher plants. Ln the last decade, the cloning of genes that appear to encode both high- and low-affinity transpo rters represent major advances, as well as substantiating the inferences ba sed on earlier physiological methods. Nevertheless, the unexpected plethora of genes that have been identified now presents even greater challenges, t o resolve their individual functions and to attempt to place these function s in a whole plant/environmental context.