title: Citramalic acid and salicylic acid in sugar beet root exudates solubilize soil phosphorus.
abstract: BACKGROUND
  In soils with a low phosphorus (P) supply, sugar beet is known to intake more P than other species such as maize, wheat, or groundnut. We hypothesized that organic compounds exuded by sugar beet roots solubilize soil P and that this exudation is stimulated by P starvation.
  
  
  RESULTS
  Root exudates were collected from plants grown in hydroponics under low- and high-P availability. Exudate components were separated by HPLC, ionized by electrospray, and detected by mass spectrometry in the range of mass-to-charge ratio (m/z) from 100 to 1000. Eight mass spectrometric signals were enhanced at least 5-fold by low P availability at all harvest times. Among these signals, negative ions with an m/z of 137 and 147 were shown to originate from salicylic acid and citramalic acid. The ability of both compounds to mobilize soil P was demonstrated by incubation of pure substances with Oxisol soil fertilized with calcium phosphate.
  
  
  CONCLUSIONS
  Root exudates of sugar beet contain salicylic acid and citramalic acid, the latter of which has rarely been detected in plants so far. Both metabolites solubilize soil P and their exudation by roots is stimulated by P deficiency. These results provide the first assignment of a biological function to citramalic acid of plant origin.
authors.affiliation: Department of Crop Science, Plant Nutrition, Georg-August-University Göttingen, Carl-Sprengel-Weg 1, D-37075 Goettingen, Germany.
authors.forename: Reza
authors.initials: R
authors.lastname: Khorassani
authors.forename: Ursula
authors.initials: U
authors.lastname: Hettwer
authors.forename: Astrid
authors.initials: A
authors.lastname: Ratzinger
authors.forename: Bernd
authors.initials: B
authors.lastname: Steingrobe
authors.forename: Petr
authors.initials: P
authors.lastname: Karlovsky
authors.forename: Norbert
authors.initials: N
authors.lastname: Claassen
mesh_terms: D027461:Beta vulgaris / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D018527:Hydroponics; D008293:Malates / Q000378:metabolism*; D013058:Mass Spectrometry; D055442:Metabolome; D010758:Phosphorus / Q000378:metabolism*; D018517:Plant Roots / Q000737:chemistry*; D020156:Salicylic Acid / Q000378:metabolism*; D012987:Soil / Q000737:chemistry
chemical_list: D008293:Malates; D012987:Soil; D010758:Phosphorus; C011729:citramalate; D020156:Salicylic Acid