Molecular and physiological aspects of nitrate uptake in plants

Nitrate is an important macronutrient and also acts as a signal for plant growth; however, its levels in the soil solution can vary by three to four orders of magnitude. Consequently, plants have evolved regulated, energy dependent systems for the uptake of nitrate using both high and low affinity transporters. Genes that encode representatives of each class of transport system have been identified and fall into two families: NRT1 and NRT2. Members of these families are induced in response to nitrate in the environment and are regulated by internal signals including nitrogen metabolites and shoot demand for nitrogen. The evidence to date indicates that the NRT2 transporters contribute specifically to the nitrate-inducible, high affinity nitrate uptake system while the NRT1 transporters contribute more broadly to nitrogen uptake and show both inducible and constitutive expression.