HETEROGENEITY OF FUNGAL AND PLANT ENZYME EXPRESSION IN INTACT SCOTS PINE SUILLUS-BOVINUS AND PAXILLUS-INVOLUTUS MYCORRHIZOSPHERES DEVELOPEDIN NATURAL FOREST HUMUS

Isozyme expression of nutrient-mobilizing and defence-related enzymes were examined in different functional components of intact Scots pine (Pinus sylvestris L.) ectomycorrhizal root systems developed in natura l unsterilized forest humus. Scots pine seedlings colonized by Suillus bovinus (L. ex Fr.) O. Kuntze or Paxillus involutus (Batsch ex Fr.) s trains were grown on humus in two-dimensional Perspex(R) microcosms to allow development of complete ectomycorrhizal root systems. Soluble p roteins from uncolonized short roots, whole mycorrhizal root tips or d issected mantle and core fractions, fungal strands and the outermost s oil colonizing fine hyphae were subjected to native polyacrylamide gel electrophoresis and stained to detect esterase, acid phosphatase, per oxidase and different polyphenoloxidase isozyme activities. Tissue-spe cific esterase isozymes were detected in all components and most, incl uding unique Hartig net isozymes, were of fungal origin. High fungal a cid phosphatase activities were detected in mycorrhiza and fine hyphae of S. bovinus, supporting earlier findings of active phosphatase acti vity at the fungal interface in the Hartig net region and in the fine hyphal margins of extramatrical mycelium actively colonizing the humus . All compartments in the P. involutus mycorrhizosphere had weaker aci d-phosphatase activities. Peroxidases formed a large part of the solub le-protein content in non-mycorrhizal short roots. The amount of perox idases, on a tissue f. wt basis, was similar in mycorrhizal and non-my corrhizal roots, but differential isozyme expression was detected, ind icating a change in root peroxidase activities following mycorrhiza fo rmation. The expression of DL-3,4-dihydroxyphenylalanine metabolizing polyphenol oxidase enzymes was reduced in mycorrhizas compared with no n-mycorrhizal short roots. In the extramatrical mycelial components, f ine hyphae expressed the highest polyphenoloxidase activity. P. involu tus displayed some polyphenol-oxidizing isoenzymes not detected in S. bovinus systems. Laccase activity was not detected in the plant and fu ngal components examined. It is concluded that enzyme activities and i sozyme expression are differentially regulated in the different functi onal components of Scots pine mycorrhizospheres.