STRUCTURE AND FUNCTION OF THE ECTOMYCORRHIZAL ASSOCIATION BETWEEN PAXILLUS-INVOLUTUS AND BETULA-PENDULA - II - METABOLIC CHANGES DURING MYCORRHIZA FORMATION

Seedlings of Betula pendula Roth. were grown in the presence of Paxill us involutus (Batsch) Fr., and metabolic changes during mycorrhiza for mation were examined by measuring organic acid and amino acid pools an d related enzyme activities, following sequential harvests. Glutamine, aspartate and asparagine pools were always lower in infected roots th an in non-infected roots, especially during Hartig net initiation and formation. Glutamate concentration was similar in both tissues. Citrat e and malate were the two major organic acids detected and their conce ntrations were equal in infected and non-infected roots. Aspartate ami notransferase, glutamine synthetase, NAD-dependent malate dehydrogenas e and glucose-6-phosphate dehydrogenase activities were higher in infe cted roots than non-infected roots. For all enzymes revealed on polyac rylamide gels, both root and fungal isoforms were present in infected roots. Quantitative changes in enzyme capacities and metabolite pools indicated that mycorrhiza formation caused a re-arrangement of the mai n metabolic pathways during the very early stages following contact, w hich might be related to the structural changes.