Activities of carboxylation enzymes were analyzed in the mycelium of the mycorrhizal fungus Amanita muscaria (L. ex Fr.) Hooker, in non-mycorrhizal short roots of Norway spruce ( Picea abies [L.] Karst.) and in mycorrhizas of these two partners. While pyruvate carboxylase (PC, EC 6.4.1.1) and phosphoenolpyruvate carboxykinase activities (PEPCK, EC 4.1.1.49) could be detected in the mycelium of A. muscaria , phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) was only active in root tissue. In A. muscaria , PC activity was generally low (around 10 nmol mg -1 protein min -1 ) but PEPCK activity was above 250 nmol mg -1 protein min -1 . Mycorrhizal development in short roots decreased PEPC activity by more than 75%, although dilution by the fungal biomass in mycorrhizas was only 35%. This reduction in activity was paralleled by a decreased content of PEPC protein. By means of micro-analytical methods it was shown that PEPC activity was lowest in the central zones of the mycorrhizas, whereas PEPC activity was highest in the corresponding central sections in non-mycorrhizal short roots. 14 CO 2 labelling, on the other hand, revealed that in vivo CO 2 fixation was higher in mycorrhizas compared to non-mycorrhizal short roots. It is concluded that fungal carboxylases (probably PEPCK) are important for anaplerotic CO 2 fixation during nitrogen assimilation in mycorrhizas of Norway spruce.
Amanita muscaria , ammonium assimilation, anaplerotic metabolism, carboxylation reactions, ectomycorrhizas, phosphoenolpyruvate carboxykinase, phosphoenolpyruvate carboxylase, Picea abies , pyruvate carboxylase.
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