Plants can use protein as a nitrogen source without assistance from other organisms

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 105; no. 11; pp. 4524 - 4529
• Main Authors: Paungfoo-Lonhienne, Chanyarat, Lonhienne, Thierry G.A, Rentsch, Doris, Robinson, Nicole, Christie, Michael, Webb, Richard I, Gamage, Harshi K, Carroll, Bernard J, Schenk, Peer M, Schmidt, Susanne
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 18-03-2008; National Acad Sciences
• Subjects: Acid soils; Agrology; Amino acids; Arabidopsis - growth & development; Arabidopsis - metabolism; Arabidopsis thaliana; Biological Sciences; Botany; endocytosis; Forest soils; Fungi; Hakea; Hakea actites; Microscopy, Electron; Nitrogen; Nitrogen - metabolism; nutrient uptake; Organic soils; Plant growth; plant nutrition; Plant roots; Plant Roots - enzymology; Plant Roots - ultrastructure; Plants; Proteaceae - growth & development; Proteaceae - metabolism; Proteaceae - ultrastructure; protein uptake; proteinases; Proteins; Proteins - chemistry; Proteins - metabolism; proteolysis; root exudates; roots; Soil air; soil organic matter; soil protein; Soils
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0712078105

Nitrogen is quantitatively the most important nutrient that plants acquire from the soil. It is well established that plant roots take up nitrogen compounds of low molecular mass, including ammonium, nitrate, and amino acids. However, in the soil of natural ecosystems, nitrogen occurs predominantly as proteins. This complex organic form of nitrogen is considered to be not directly available to plants. We examined the long-held view that plants depend on specialized symbioses with fungi (mycorrhizas) to access soil protein and studied the woody heathland plant Hakea actites and the herbaceous model plant Arabidopsis thaliana, which do not form mycorrhizas. We show that both species can use protein as a nitrogen source for growth without assistance from other organisms. We identified two mechanisms by which roots access protein. Roots exude proteolytic enzymes that digest protein at the root surface and possibly in the apoplast of the root cortex. Intact protein also was taken up into root cells most likely via endocytosis. These findings change our view of the spectrum of nitrogen sources that plants can access and challenge the current paradigm that plants rely on microbes and soil fauna for the breakdown of organic matter.