Analysis of Parsley Arbuscular Endomycorrhiza: Infection Development and mRNA Levels of Defense-Related Genes. Philipp Franken. Max-Planck-lnstitut fur Zuchtungsforschung, Abteilung Biochemie. Carl von Linne-Weg 10, D-50829 Cologne, Germany. Friederike Gnadinger, Max-Planck-lnstitut fur Zuchtungsforschung, Abteilung Biochemie, Carl von Linne-Weg 10, D-50829 Cologne, Germany. MPMI 7:612-620. Accepted 25 May 1994. Copyright 1994 The American Phytopathological Society.

Molecular aspects of the symbiosis between plants and arbuscular endomycorrhizal fungi have been investigated in parsley (Petroselinum crispum). Time course of infection with the inoculum Glomus sp. T6 was determined by estimating the total living or metabolically active fungal biornass. This revealed that phosphate nutrition and low light conditions negatively influenced plant-fungal interactions in different ways. Northern blot analyses of RNA from roots infected with the mycorrhizal fungus or from nonmycorrhizal roots of plants grown with or without phosphate fertilization were conducted using fresh weight as a basis for calibration. At the stage of highest symbiotic fungal activity, no dramatic changes were observable in the amount of plant mRNA encoding enzymes of the phenylpropanoid pathway and the methyl group cycle or the pathogenesis-related protein PR1. In contrast, two genes involved in cell wall modifications showed important differences. A transcript which codes for a hydroxyproline rich glycoprotein was produced in much higher amounts in mycorrhizal roots than in the uninfected controls. mRNA of a second gene encoding an anionic peroxidase showed strong accumulation after phosphate fertilization compared with the phosphate-deficient control and the mycorrhizal roots. Thin-layer chromatography revealed no large changes in the pattern of phenolic substances in root extracts, confirming the results concerning the phenylpropanoid pathway genes. New compounds could, however, be detected in the root exudates of phosphate-deficient plants.