Acid Invertase in Mycorrhizal and Non-Mycorrhizal Roots of Norway Spruce (Picea abies [L.] Karst.) Seedlings

Sucrolytic enyzme activities and concentrations of hexoses typically increase in plant/microbe symbioses. However, there is little information on ectomycorrhizal associations. We measured invertase activity and soluble sugar contents in roots of mycorrhizal and non-mycorrhizal Norway spruce [Picea abies (L.) Karst.] seedlings. We used two ectomycorrhizal fungi, a basidiomycete [Amanita muscaria (L. ex Fr.) Hooker] and an ascomycete (Cenococcum geophilum Fr.). Mycorrhizas and non-mycorrhizal short roots, as well as other parts of the root system, were investigated at different developmental stages by micro-analytical methods. Neither sucrose nor invertase could be detected in fungal mycelia. In vitro measurable invertase activity and the sucrose, glucose and fructose content were reduced in both types of mycorrhizas compared with the non-mycorrhizal short roots. Correction of data for the fungal component in the mycorrhizas, indicated that there were no differences in plant-specific amounts of sucrose and acid invertase activity in mycorrhizal and non-mycorrhizal roots. However, amounts of glucose and fructose, which are present in both partners, were clearly reduced in the mycorrhizas. As high fructose levels inhibit acid invertase, a reduction in the amount of fructose in the symbiotic tissue could favour in vivo acid invertase activity. Our results indicate that the situation in ectomycorrhizas may be different from those in other biotrophic interactions.