Citramalic acid and salicylic acid in sugar beet root exudates solubilize soil phosphorus

• Main Authors: Karlovsky Petr, Steingrobe Bernd, Ratzinger Astrid, Hettwer Ursula, Khorassani Reza, Claassen Norbert
• Format: Article
• Language: English
• Published: BMC 2011-08-01
• Series: BMC Plant Biology
• Online Access: http://www.biomedcentral.com/1471-2229/11/121

<p>Abstract</p> <p>Background</p> <p>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.</p> <p>Results</p> <p>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.</p> <p>Conclusions</p> <p>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.</p>