Evidence for an up-regulation of the host and a down-regulation of the fungal phosphofructokinase activity in ectomycorrhizas of Norway spruce and fly agaric

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summary

For an understanding of metabolic interactions in ectomycorrhizal associations it is essential to distinguish enzyme activities of the symbionts. For the ATP-dependent phosphofructokinase (PFK) from ectomycorrhizas of fly agaric (Amanita muscaria (L. ex Fr.) Hooker) on Norway spruce (Picea abies (L.) Karst.) we were able to achieve a symbiont-specific differentiation by special assay conditions. Substrate concentrations, Mg2+: ATP ratio and pH values which were optimum for the fly agaric PFK completely suppressed the PFK activity of spruce roots. On the other hand, under the optimum assay conditions for the spruce root PFK, the fungal PFK activity was reduced by more than 90%. The most pronounced difference between the enzymes of both organisms was the response towards fructose-2,6-bisphosphate (F26BP); whereas F26BP had no influence on the spruce PFK activity, the fly agaric PFK activity was strongly enhanced by very low levels of F26BP.

The distinction of the partner-specific PFK activities illustrated that mycorrhiza formation exerted partner-specific effects. On the basis of host d. wt of the mycorrhizas, the host-specific PFK activity was more than doubled compared with that of the non-mycorrhizal short roots. By contrast, the fungal PFK activity, on a fungal d.wt basis, was reduced in the mycorrhizas to less than 1/4 of the activity of the free-living mycelium.

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