Carbohydrate and amino acid metabolism in the Eucalyptus globulus Pisolithus tinctorius ectomycorrhiza during glucose utilization

The metabolism of [1-C-13]glucose in Pisolithus tinctorius cv Coker & Couch, in uninoculated seedlings of Eucalyptus globulos bicostata ex Maiden cv Kirkp., and in the E. globolus-P. tinctorius ectomycorrhiza was studied using nuclear magnetic resonance spectroscopy. In roots of uninoculated seedlings, the C-13 label was mainly incorporated into sucrose and glutamine. The ratio ((13)C3 + (13)C2)/(13)C4 of glutamine was approximately 1.0 during the timecourse experiment, indicating equivalent contributions of phosphoenolpyruvate carboxylase and pyruvate dehydrogenase to the production of a-ketoglutarate used for synthesis of this amino acid. In free-living P. tinctorius, most of the C-13 label was incorporated into mannitol, trehalose, glutamine, and alanine, whereas arabitol, erythritol, and glutamate were weakly labeled. Amino acid biosynthesis was an important sink of assimilated C-13 (43%), and anaplerotic CO2 fixation contributed 42% of the C flux entering the Krebs cycle. In ectomycorrhizae, sucrose accumulation was decreased in the colonized roots compared with uninoculated control plants, whereas C-13 incorporation into arabitol and erythritol was nearly 4-fold higher in the symbiotic mycelium than in the Free-living fungus. It appears that fungal utilization of glucose in the symbiotic state is altered and oriented toward the synthesis of short-chain polyols.