Changes in pathways for carbon and nitrogen assimilation in spruce roots under mycorrhization

Abstract

The metabolism of carbohydrate break- down appeared to be deeply perturbed during mycorrhization. Mitochondrial respi- ration became cyanide-resistant, whereas only the cytochrome pathway existed in uninfected roots. Moreover, the changes in the enzymatic capacities of glycolysis, the Krebs cycle and the pentose phosphate pathway indicated that mycorrhization caused a rearrangement of the carbohy- drate metabolic sequences. If an in- creased respiration rate due to mycor- rhization were to be confirmed, the functioning of the alternative pathway could allow both sufficient ATP synthesis and carbon skeletons needed for the production of compounds by NADPH- using pathways. Nitrogen metabolism appeared to be classical in both mycor- rhizal fungus, where GDH predominates (Marzluf, 1981 and roots, where GS is the major route of ammonium assimilation (Oaks and Hirel, 1985). Our findings also show that both pathways might be opera- tive in mycorrhizal tissues. The further transfer to an amino group or to other car- bon skeletons might occur through amino- transferases, since both AAT and GPT were detected in the mycorrhizal tissues.