title: White lupin has developed a complex strategy to limit microbial degradation of secreted citrate required for phosphate acquisition.
abstract: White lupins (Lupinus albus L.) respond to phosphate deficiency by producing special root structures called cluster roots. These cluster roots secrete large amounts of carboxylates into the rhizosphere, mostly citrate and malate, which act as phosphate solubilizers and enable the plant to grow in soils with sparingly available phosphate. The success and efficiency of such a P-acquisition strategy strongly depends on the persistence and stability of the carboxylates in the soil, a parameter that is influenced to a large extent by biodegradation through rhizosphere bacteria and fungi. In this study, we show that white lupin roots use several mechanisms to reduce microbial growth. The abundance of bacteria associated with cluster roots was decreased at the mature state of the cluster roots, where a burst of organic acid excretion and a drastic pH decrease is observed. Excretion of phenolic compounds, mainly isoflavonoids, induced fungal sporulation, indicating that vegetative growth, and thus potential citrate consumption, is reduced. In addition, the activity of two antifungal cell wall-degrading enzymes, chitinase and glucanase, were highest at the stage preceding the citrate excretion. Therefore, our results suggest that white lupin has developed a complex strategy to reduce microbial degradation of the phosphate-solubilizing agents.
authors.affiliation: Institute of Plant Biology, University of Zürich, Zollikerstrasse 107, 8008 Zürich, Switzerland.
authors.forename: Laure
authors.initials: L
authors.lastname: Weisskopf
authors.forename: Eliane
authors.initials: E
authors.lastname: Abou-Mansour
authors.forename: Nathalie
authors.initials: N
authors.lastname: Fromin
authors.forename: Nicola
authors.initials: N
authors.lastname: Tomasi
authors.forename: Diana
authors.initials: D
authors.lastname: Santelia
authors.forename: Iris
authors.initials: I
authors.lastname: Edelkott
authors.forename: Günter
authors.initials: G
authors.lastname: Neumann
authors.forename: Michel
authors.initials: M
authors.lastname: Aragno
authors.forename: Raffaele
authors.initials: R
authors.lastname: Tabacchi
authors.forename: Enrico
authors.initials: E
authors.lastname: Martinoia
mesh_terms: D000327:Adsorption; D001419:Bacteria / Q000254:growth & development / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D002951:Citrates / Q000378:metabolism*; D005419:Flavonoids / Q000378:metabolism; D005670:Fusarium / Q000378:metabolism / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D031297:Lupinus / Q000378:metabolism* / Q000382:microbiology; D010710:Phosphates / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism / Q000382:microbiology; D013172:Spores, Fungal
chemical_list: D002951:Citrates; D005419:Flavonoids; D010710:Phosphates