Carbohydrate and Amino Acid Metabolism in the Eucalyptus globulus-Pisolithus tinctorius Ectomycorrhiza during Glucose Utilization

The metabolism of [1-(13)C]glucose in Pisolithus tinctorius cv Coker & Couch, in uninoculated seedlings of Eucalyptus globulus bicostata ex Maiden cv Kirkp., and in the E. globulus-P. tinctorius ectomycorrhiza was studied using nuclear magnetic resonance spectroscopy. In roots of uninoculated seedlings, the (13)C label was mainly incorporated into sucrose and glutamine. The ratio ((13)C3 + (13)C2)/(13)C4 of glutamine was approximately 1.0 during the time-course experiment, indicating equivalent contributions of phosphoenolpyruvate carboxylase and pyruvate dehydrogenase to the production of α-ketoglutarate used for synthesis of this amino acid. In free-living P. tinctorius, most of the (13)C 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 (13)C (43%), and anaplerotic CO(2) 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 (13)C 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.