Does mycorrhization influence herbivore-induced volatile emission in Medicago truncatula?

Symbiosis with mycorrhizal fungi substantially impacts secondary metabolism and defensive traits of colonised plants. In the present study, we investigated the influence of mycorrhization (Glomus intraradices) on inducible indirect defences against herbivores using the model legume Medicago truncatula. Volatile emission by mycorrhizal and non-mycorrhizal plants was measured in reaction to damage inflicted by Spodoptera spp. and compared to the basal levels of volatile emission by plants of two different cultivars. Emitted volatiles were recorded using closed-loop stripping and gas chromatography/mass spectrometry. The documented volatile patterns were evaluated using multidimensional scaling to visualise patterns and stepwise linear discriminant analysis to distinguish volatile blends of plants with distinct physiological status and genetic background. Volatile blends emitted by different cultivars of M. truncatula prove to be clearly distinct, whereas mycorrhization only slightly influenced herbivore-induced volatile emissions. Still, the observed differences were sufficient to create classification rules to distinguish mycorrhizal and non-mycorrhizal plants by the volatiles emitted. Moreover, the effect of mycorrhization turned out to be opposed in the two cultivars examined. Root symbionts thus seem to alter indirect inducible defences of M. truncatula against insect herbivores. The impact of this effect strongly depends on the genetic background of the plant and, hence, in part explains the highly contradictory results on tripartite interactions gathered to date

Soluble proteins and polypeptide profiles of spores of arbuscular mycorrhizal fungi. Interspecific variability and effects of host (myc+) and non-host (myc -

Les protéines solubles totales des spores de quatre espèces de champignons mycorhizogènes arbusculaires (Gigaspora rosea, Scutellospora castanea, Acaulospora laevis et Glomus mosseae) appartenant à l'ordre des glomales ont été analysées par électrophorèse bidimensionnelle. Les profils polypeptidiques ont été comparés à celui de G rosea, choisi arbitrairement comme référence. Les modifications les plus importantes se caractérisent par la disparition de quelques polypeptides par rapport à G rosea. Plusieurs polypeptides ont été détectés seulement dans G rosea, S castanea et A laevis. L'analyse de profils polypeptidiques de spores de G mosseae, germées dans l'eau ou dans les exudats de deux génotypes hôtes (myc⁺) (cv Frisson et le mutant non nodulant P56) et d'un génotype non-hôte (P2) de P sativum a aussi été effectuée. Bien que de faibles stimulations dans la croissance des hyphes aient été obtenues dans les exudats racinaires par rapport à l'eau, aucune différence dans le profil polypeptidique n'a été observée

Expression of the PR-b1" gene in the roots of two Nicotiana species and their amphidiploid hybrid infected with virulent and avirulent races of Chalara elegans

The expression levels of PR-b1'' gene coding for PR-b1'' protein (a PR-I group protein) were investigated in the roots of two Nicotiana species and their amphidiploid hybrid in response to infection by virulent (84-1) or avirulent (85-26) races of black root rot fungus Chalara elegans. Nicotiana glutinosa is susceptible to C. elegans, while Nicotiana debneyi and the amphidiploid hybrid N. glutinosa x N. debneyi are highly resistant. The results showed that irrespective of whether the plant is susceptible or resistant, and the fungal race virulent or avirulent, low infection rates induce low levels of PR-b1'' mRNA, and high infection rates result in high production of PR-b1'' mRNA. The amphidiploid hybrid, which expresses the protein PR-b1'' constitutively, showed similar PR-b1'' mRNA levels with both races of C. elegans. At maximal levels of accumulation, PR-b1'' mRNA is quantitatively similar in the two Nicotiana species, and the amphidiploid hybrid, whatever the nature of the inoculum

Chitinase isoforms in roots of various pea genotypes infected with arbuscular mycorrhizal fungi

Chitinase activity has been investigated in mycorrhiza-resistant (myc⁻), non-nodulating (nod⁻) isogenic pea (Pisum sativum L.) mutants in an attempt to understand the reasons for such resistance to symbiotic fungi. Activities from control and Glomus mossease-inoculated roots of myc⁻ mutants were compared to the corresponding mycorrhizal (myc⁺), nodulating (nod⁺) wildtype pea genotype cv. Frisson. A pea mutant only deficient for the nod⁻ character [myc⁺, nod⁻] was also studied. Two acidic and two basic chitinase isoforms were detected in control roots of all peas tested after native polyacrylamide gel electrophoretic (PAGE) separation of proteins at pH 8.9 or pH 4.3. No difference in basic chitinase isoforms patterns occurred in the various pea genotypes in the presence of G. mosseae. However, as soon as 1 week after infection, an additional acidic chitinase isoform was observed in extracts of G. mosseae-colonized roots from the wildtype pea genotype and the [myc⁺, nod⁻] mutant. The isozyme had a molecular mass of approximately 27 kDa, estimated by sodium dodecyl sulfate (SDS)-PAGE under non-reducing conditions, and exhibited a faint lysozyme activity by lysis of Micrococcus luteus cells. It was not detected in the [myc⁻, nod⁻] pea mutant, unless plants were grown under conditions which increased the number of appressoria. The host origin of the 27 kDa chitinase isoform was indicated by its presence after infection with another Glomus species, and from the fact that it was not detected in a mixture of germinated spores and mycelia of G. mosseae