~Four cereals, Hordeum vulgare (barley), Triticum aestivum (wheat), Secale cereale (rye), and Avena safiva (oat), were grown in a defined nutritional medium with and without the arbuscular mycorrhizal fungus Glomus intraradices. Levels of soluble and cell wall-bound secondary metabolites in the roots of mycorrhizal and nonmycorrhizal plants were determined by high-performance liquid chromatography during the first 6 to 8 weeks of plant development. Whereas there was no difference in the levels of the cell wall-bound hydroxycinnamic acids, 4-coumaric and ferulic acids, there was a fungus-induced change of the soluble secondary root metabolites. The most obvious effect observed in all four cereals was the induced accumulation of a terpenoid glycoside. This compound was isolated and identified by spectroscopic methods (nuclear magnetic resonance, mass spectrometry) to be a cyclohexenone derivative, i.e. blumenol C 9-0(2'-D~-glucuronosyl)-~-glucoside. The level of this compound was found to be directly correlated with the degree of root colonization.Arbuscular mycorrhizas are universally found symbiotic associations between plant roots and certain fungi, and there is ample evidence that these symbioses are of significant benefit for plants (reviewed by Powell and Bagyaraj, 1984; Gianinazzi and Schüepp, 1994). These benefits include enhanced nutrient supply (e.g. phosphate) and increased resistance to pathogen attack (e.g. root pathogenic fungi) or stress (e.g. drought). Despite increasing efforts in research on arbuscular mycorrhiza at the cellular and molecular levels within the last years Dixon, 1993, 1994;Dumas-Gaudot et al., 1994), very little is known about the basic biochemical interactions between the symbionts leading to formation of arbuscular mycorrhiza and maintenance of an active symbiotic relationship. This is in sharp contrast to our knowledge about pathogenic plantfungus interactions .There is increasing evidence that secondary compounds in particular play a significant role in the interactions occurring between plants and their natural environment (Harborne, 1988). In this respect, secondary metabolites of roots might play an important role in mycorrhizal symbiosis. It has been documented, for example, that flavonoids promote spore germination of arbuscular mycorrhizal 'This work was supported by the Fonds der Chemischen * Corresponding author; fax 49-345-5582-106.Industrie.fungi (Gianinazzi-Pearson et al., 1989;Tsai and Phillips, 1991). Colonization of plants with arbuscular mycorrhizal fungi may lead to marked systemic reactions in terpenoid metabolism. Thus, Glomus intraradices induces accumulation of significant amounts of leaf sesquiterpenoids in Citrus jambkiri (Nemec and Lund, 1990). The sesquiterpenoid ABA reaches considerably higher levels in Glomus-colonized maize than in control plants (Danneberg et al., 1993).As part of our studies of arbuscular mycorrhizal fungiinduced changes in secondary metabolism of cereals, we report here quantitative changes of root secondary products during form...

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The tissue-specific and development-dependent accumulation of secondary products in roots and mycorrhizas of larch (Larix decidua Mill.; Pinaceae) was studied using high-performance liquid chromatography and histochemical methods. The compounds identified were soluble catechin, epicatechin, quercetin 3-Ocr-rhamnoside, cyanidin-and peonidin 3-Op-glucoside, 4-OP-hydroxybenzoyl-OP-glucose, 4-hydroxybenzoate 4-OP-glucoside, maltol 3 -0 4 -glucoside, and the wall-bound 4-hydroxybenzaldehyde, vanillin, and ferulate. I n addition, we partially identified a tetrahydroxystilbene monoglycoside, a quercetin glycoside, and eight oligomeric proanthocyanidins. Comparison between the compounds accumulating in the apical tissue of fine roots, long roots, and in vitro grown mycorrhizas (L. decidua-Suillus tridentinus) showed elevated levels of the major compounds catechin and epicatechin as well as the minor compound 4-hydroxybenzoate 4-OP-glucoside specifically in the root apex of young mycorrhizas. l h e amounts of wall-bound 4-hydroxybenzaldehyde and vanillin were increased in all of the mycorrhizal sections examined. During the early stages of mycorrhization the concentrations of these compounds increased rapidly, perhaps induced by the mycorrhizal fungus. I n addition, studies of L. decidua-Boletinus cavipes mycorrhizas from a natural stand showed that the central part of the subapical cortex tissue and the endodermis both accumulate massive concentrations of catechin, epicatechin, and wall-bound ferulate compared with the outer part of the cortex, where the Hartig net is being formed.

In cultures of the basidiomycetes Heterobasidion annosum, Gloeophyllum abietinum or Armillaria ostoyae, the biosynthesis of some of their toxic secondary metabolites is enhanced up to 400-fold when they grow in the presence of an antagonist. This stimulation is induced before any cell contact occurs. The "inducing signals" are not macromolecules, polypeptides or constituents of the cell membranes, but the same toxins which are synthesized already in monocultures in very low concentrations. After excretion and diffusion into the media, the fungi thus recognize the proximity of the antagonist in dualcultures. As a consequence, the enormous stimulation of toxin synthesis takes place. The increasing toxin concentrations in the fungal dual cultures finally cause the formation of mycel-free growth inhibition zones between the fungi, or sometimes one of the contrahents is killed. This stimulation of toxin synthesis is achieved by an enhanced de novo synthesis of enzymes of the corresponding secondary pathways.

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