CHITINASE ISOFORMS IN ROOTS OF VARIOUS PEA GENOTYPES INFECTED WITH ARBUSCULAR MYCORRHIZAL FUNGI

Chitinase activity has been investigated in mycorrhiza-resistant (myc( -)), non-nodulating (nod(-)) isogenic pea (Pisum sativum L.) mutants i n an attempt to understand the reasons for such resistance to symbioti c fungi. Activities from control and Glomus mosseae-inoculated roots o f myc(-) mutants were compared to the corresponding mycorrhizal (myc()), nodulating (nod(+)) wildtype pea genotype cv. Frisson. A pea mutan t only deficient for the nod(-) character [myc(+), nod(-)] was also st udied. Two acidic and two basic chitinase isoforms were detected in co ntrol roots of all peas tested after native polyacrylamide gel electro phoretic (PAGE) separation of proteins at pH 8.9 or pH 4.3. No differe nce in basic chitinase isoform patterns occurred in the various pea ge notypes in the presence of G. mosseae. However, as soon as 1 week afte r infection, an additional acidic chitinase isoform was observed in ex tracts of G. mosseae-colonized roots from the wildtype pea genotype an d the [myc(+), nod(-)] mutant. The isozyme had a molecular mass of app roximately 27 kDa, estimated by sodium dodecyl sulfate (SDS)-PAGE unde r non-reducing conditions, and exhibited a faint lysozyme activity det ermined by lysis of Micrococcus luteus cells. It was not detected in t he [myc(-), nod(-)] pea mutant, unless plants were grown under conditi ons which increased the number of appressoria. The host origin of the 27 kDa chitinase isoform was indicated by its presence after infection with another Glomus species, and from the fact that it was not detect ed in a mixture of germinated spores and mycelia of G. mosseae.