EFFECT OF FUNGAL-ISOLATE AGGRESSIVITY ON THE BIOSYNTHESIS OF SYMBIOSIS-RELATED POLYPEPTIDES IN DIFFERENTIATING EUCALYPT ECTOMYCORRHIZAS

Changes in protein biosynthesis were examined during the early stages of differentiation of Eucalyptus grandis-Pisolithus tinctorius ectomyc orrhizas by two-dimensional polyacrylamide gel electrophoresis of S-35 -labelled proteins. Three distinct isolates of P. tinctorius Coker and Couch were chosen based on the rate of ectomycorrhizal formation (i.e . infectivity) with E. grandis W. Hill ex Maiden. The isolate H506 was not able to induce mycorrhiza, isolate 441 showed moderate infectivit y and isolate H2144 exhibited a very high infectivity. Mycorrhiza were produced in vitro in a system where seeds were germinated in the pres ence of fungal mycelium and exudates. The non-mycorrhizal isolate caus ed no changes in root protein biosynthesis as analyzed by two-dimensio nal polyacrylamide gel electrophoresis, whereas drastic alterations in protein biosynthesis were observed from initial contact with the aggr essive mycobionts. During mycorrhizal development, there was a marked inhibition of plant polypeptides synthesis, enhanced accumulation of s ome fungal polypeptides and the emergence of symbiosis-specific polype ptides, the so-called ectomycorrhizins. The major changes were observe d in a group of fungal acidic polypeptides (apparent molecular weight 28-32 kDa) including the ectomycorrhizin E(32). These polypeptides fir st appeared at contact and their synthesis increased during mycorrhiza l formation, suggesting a role in mycorrhizal development, most likely as structural proteins. Up-regulation of the synthesis of fungal symb iosis-related polypeptides was tightly correlated to the infectivity o f the strain.