Nitrogen (N) is an essential macronutrient for plant growth and development. Plant N nutrition generally relies on inorganic forms of N, nitrate NO3- and ammonia NH4+, which are readily available for plant uptake. However, it is now well established that plants can also take up N directly in the form of organic molecules such as amino acids and peptides (Norg). In this uptake, the proton motive force generated by electrogenic H+ transport is used for the secondary active transport of Norg. In Arabidopsis thaliana, root amino acid uptake systems belong to different families: Amino Acid Permeases (AAPs), Lysine/Histidine-like Transporters (LHTs) and Proline and Glycine Betaine Transporters (ProTs). Transporters and related genes for urea are also known. In general, substrate specificity and affinity vary between and within the different transporter families. Similar mechanisms are involved in allocation of Norg within the plant. The ability to utilize organic N allows plants to access a wide range of N sources in different environments. In cropping systems where inorganic N nutrition is predominant, the availability of organic molecules needs to be considered in fertilization planning. Moreover, the use of organic fertilizers, including amino acid, proteins as a N source, could be the answer to development od environmental- riendly methods of plant cultivation.
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