Colonization of barley (Hordeum vulgare cv Salome) roots by an arbuscular mycorrhizal fungus, Glomus intraradices Schenck & Smith, leads to elevated levels of endogenous jasmonic acid (JA) and its amino acid conjugate JA-isoleucine, whereas the level of the JA precursor, oxophytodienoic acid, remains constant. The rise in jasmonates is accompanied by the expression of genes coding for an enzyme of JA biosynthesis (allene oxide synthase) and of a jasmonate-induced protein (JIP23). In situ hybridization and immunocytochemical analysis revealed that expression of these genes occurred cell specifically within arbuscule-containing root cortex cells. The concomitant gene expression indicates that jasmonates are generated and act within arbuscule-containing cells. By use of a near-synchronous mycorrhization, analysis of temporal expression patterns showed the occurrence of transcript accumulation 4 to 6 d after the appearance of the first arbuscules. This suggests that the endogenous rise in jasmonates might be related to the fully established symbiosis rather than to the recognition of interacting partners or to the onset of interaction. Because the plant supplies the fungus with carbohydrates, a model is proposed in which the induction of JA biosynthesis in colonized roots is linked to the stronger sink function of mycorrhizal roots compared with nonmycorrhizal roots.

~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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Cell suspension cultures of Ruta graveolens L. produce a variety of acridone alkaloids, and the accumulation can be stimulated by the addition of fungal elicitors. Acridone synthase, the enzyme catalyzing the synthesis of 1,3-dihydroxy-N-methylacridone from N-methylanthraniloyl-CoA and malonyl-CoA, had been isolated from these cells, and the partial enzyme polypeptide sequence, elucidated from six tryptic fragments, revealed homology to heterologous chalcone synthases. Poly(A)+ RNA was isolated from Ruta cells that had been treated for 6 h with a crude cell wall elicitor from Phytophthora megasperma f. sp. glycinea, and a cDNA library was constructed in lambda 2AP. Clones harboring acridone synthase cDNA were isolated from the library by screening with a synthetic oligonucleotide probe complementary to a short stretch of sequence of the enzyme peptide with negligible homology to chalcone synthases. The identity of the clones was substantiated by DNA sequencing and by recognition of five additional peptides, determined previously from tryptic acridone synthase digests, in the translated sequence. An insert of roughly 1.4 kb encoded the complete acridone synthase, and alignments at both DNA and protein levels corroborated the high degree of homology to chalcone synthases. Expression of the enzyme in vector pET-11c in the Escherichia coli pLysS host strain proved the identity of the cloned cDNA. The heterologous enzyme in the crude E. coli extract exhibit high acridone but no chalcone synthase activity. The results were fully supported by northern blot hybridizations which revealed that the specific transcript abundance did not increase but rather decreased upon white light irradiation of cultured Ruta graveolens L. cells, a condition that commonly induces the abundance of chalcone synthase transcripts.