VARIATIONS IN THE LIPID-COMPOSITION OF ALFALFA ROOTS DURING COLONIZATION WITH THE ARBUSCULAR MYCORRHIZAL FUNGUS GLOMUS VERSIFORME

Lipids and their fatty acids were characterized and quantified during the development of the arbuscular mycorrhizal fungus Glomus versiforme in roots of alfalfa (Medicago sativa). A net increase in root total l ipids was observed and was proportional to the development of arbuscul ar mycorrhizal fungus colonization. Triacylglycerols were the main lip id class in colonized roots and appear to have been synthesized by fun gi. The increase of palmitoleic acid (characteristic of triacylglycero ls from arbuscular mycorrhizal fungus) in roots colonized with G. vers iforme reinforced this suggestion. Phosphatidylethanolamine and to a m inor extent phosphatidylcholine also increased during the endophyte gr owth. Variations in the lipid classes of external mycelia isolated fro m one-, two- and three-mo old colonized roots with G. versiforme were also analyzed. Despite the continuous increase of triacylglycerols and phosphatidylethanolamine observed, the polar lipid class predominated in the external mycelia isolated from one-mo old colonized roots and the neutral lipid class prevailed in the external mycelia obtained fro m three-mo old mycorrhizal roots. Biosynthesis of triacylglycerols in intra- and extramatrical mycelia as well as an induced synthesis of po lar lipids in roots are suggested as the consequence of fungi coloniza tion.