title: Quantification and enzyme targets of fatty acid amides from duckweed root exudates involved in the stimulation of denitrification.
abstract: Fatty acid amides from plant root exudates, such as oleamide and erucamide, have the ability to participate in strong plant-microbe interactions, stimulating nitrogen metabolism in rhizospheric bacteria. However, mechanisms of secretion of such fatty acid amides, and the nature of their stimulatory activities on microbial metabolism, have not been examined. In the present study, collection, pre-treatment, and determination methods of oleamide and erucamide in duckweed root exudates are compared. The detection limits of oleamide and erucamide by gas chromatography (GC) (10.3ngmL(-1) and 16.1ngmL(-1), respectively) are shown to be much lower than those by liquid chromatography (LC) (1.7 and 5.0μgmL(-1), respectively). Quantitative GC analysis yielded five times larger amounts of oleamide and erucamide in root exudates of Spirodela polyrrhiza when using a continuous collection method (50.20±4.32 and 76.79±13.92μgkg(-1) FW day(-1)), compared to static collection (10.88±0.66 and 15.27±0.58μgkg(-1) FW day(-1)). Furthermore, fatty acid amide secretion was significantly enhanced under elevated nitrogen conditions (>300mgL(-1)), and was negatively correlated with the relative growth rate of duckweed. Mechanistic assays were conducted to show that erucamide stimulates nitrogen removal by enhancing denitrification, targeting two key denitrifying enzymes, nitrate and nitrite reductases, in bacteria. Our findings significantly contribute to our understanding of the regulation of nitrogen dynamics by plant root exudates in natural ecosystems.
authors.affiliation: State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Li
authors.initials: L
authors.lastname: Sun
authors.affiliation: State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
authors.forename: Yufang
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Department of Biological Sciences & Canadian Centre for World Hunger Research (CCWHR), University of Toronto, 1265 Military Trail, Toronto, ON, M1C 1A4, Canada.
authors.forename: Herbert J
authors.initials: HJ
authors.lastname: Kronzucker
authors.affiliation: State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China. Electronic address: wmshi@issas.ac.cn.
authors.forename: Weiming
authors.initials: W
authors.lastname: Shi
mesh_terms: D000577:Amides / Q000378:metabolism*; D029064:Araceae / Q000187:drug effects / Q000201:enzymology*; D001419:Bacteria / Q000187:drug effects / Q000378:metabolism; D001673:Biodegradation, Environmental / Q000187:drug effects; D002849:Chromatography, Gas; D002853:Chromatography, Liquid; D058440:Denitrification / Q000187:drug effects*; D004883:Erucic Acids / Q000032:analysis; D005227:Fatty Acids / Q000378:metabolism*; D050901:Nitrate Reductase / Q000378:metabolism; D009572:Nitrite Reductases / Q000378:metabolism; D009584:Nitrogen / Q000494:pharmacology; D009829:Oleic Acids / Q000032:analysis; D053147:Plant Exudates / Q000494:pharmacology*; D018517:Plant Roots / Q000737:chemistry* / Q000187:drug effects
chemical_list: D000577:Amides; D004883:Erucic Acids; D005227:Fatty Acids; D009829:Oleic Acids; D053147:Plant Exudates; C049508:erucyl amide; C029407:oleylamide; D009572:Nitrite Reductases; D050901:Nitrate Reductase; D009584:Nitrogen
keywords: Continuous collection; Duckweed root exudates; Eutrophication; Fatty acid amides; Nitrogen-removal stimulation; Plant-microbe interactions