Microorganisms and nematodes increase levels of secondary metabolites in roots and root exudates of Plantago lanceolata
Plant secondary metabolites play an important role in constitutive and inducible direct defense of plants against their natural enemies. While induction of defense by aboveground pathogens and herbivores is well-studied, induction by belowground organisms is less explored. Here, we examine whether soil microorganisms and nematodes can induce changes in levels of the secondary metabolites aucubin and catalpol (iridoid glycosides, IG) in roots and root exudates of two full-sib families of Plantago lanceolata originating from lines selected for low and high constitutive levels of IG in leaves. Addition of soil microorganisms enhanced the shoot and root biomass, and the concentration of aucubin in roots of both Plantago lines without affecting IG levels in the rhizosphere. By contrast, nematode addition tended to reduce the root biomass and enhanced the stalk biomass, and increased the levels of aucubin and catalpol in root exudates of both Plantago lines, without affecting root IG concentrations. The Plantago lines did not differ in constitutive levels of aucubin and total IG in roots, while the concentration of catalpol was slightly higher in roots of plants originally selected for low constitutive levels of IG in leaves. Root exudates of “high IG line” plants contained significantly higher levels of aucubin, which might be explained by their higher root biomass. We conclude that soil microorganisms can induce an increase of aucubin concentrations in the roots, whereas nematodes (probably plant feeders) lead to an enhancement of aucubin and catalpol levels in root exudates of P. lanceolata. A potential involvement of secondary metabolites in belowground interactions between plants and soil organisms is discussed.
KeywordsBelowground defense Iridoid glycosides Root exudates Nematodes Soil microorganisms
This study was financed by the EU funded Marie-Curie training network BIORHIZ (Biotic interactions in the rhizosphere as structuring forces for plant communities MRTN-CT-2003-505090). Publication 4602 Netherlands Institute of Ecology (NIOO-KNAW).
- Badri DV, Loyola-Vargas VM, Broeckling CD, De la Pena C, Jasinski M, Santelia D, Martinoia E, Sumner LW, Banta LM, Stermitz F, Vivanco JM (2008) Altered profile of secondary metabolites in the root exudates of arabidopsis ATP-binding cassette transporter mutants. Plant Physiol 146:762–771CrossRefPubMedGoogle Scholar
- Karban R, Baldwin IT (1997) Induced Responses to Herbivory. The University of Chicago Press, ChicagoGoogle Scholar
- Oostenbrink M (1960) Estimating nematode populations by some selected methods. In: Sasser JN, Jenkins WR (eds) Nematology. Chapel Hill, The University of North Carolina Press, pp 85–102Google Scholar