Nitrate uptake and reduction in higher and lower plants

The nitrogen compounds nitrate and ammonium are the minerals that plants ne ed in large quantities and which limit their growth in temperate zones. The nitrate assimilation pathway starts with nitrate uptake followed by nitrat e reduction resulting in ammonium which is fixed into the amino acids gluta mine and glutamate in most plants. This review concentrates on nitrate upta ke and nitrate reduction with respect to higher and lower plants. The physi ology and the progress in molecular approaches of both processes are consid ered. For nitrate uptake the well-established uptake systems are discussed and special attention is drawn to nitrate sensing and the nitrate carrier. Knowledge, particularly on nitrate sensing is rare, but it seems to be the first step in a signal transduction chain triggered by nitrate. Therefore f urther work should consider this topic more frequently. For nitrate reducta se the focus is on the posttranslational modification as a regulatory tool for nitrate assimilation, on the intersections of carbon and nitrogen metab olism and on the molecular approaches. A few remarks on how environmental c onditions affect nitrate assimilation are also included. Further progress i s needed to understand the transduction of positive and negative signals fr om the environment affecting the expression of genes coding for the nitrate assimilating pathway.