RESPONSES OF AN ARBUSCULAR MYCORRHIZAL FUNGUS, GIGASPORA-MARGARITA, TO EXUDATES AND VOLATILES FROM THE RI T-DNA-TRANSFORMED ROOTS OF NONMYCORRHIZAL AND MYCORRHIZAL MUTANTS OF PISUM-SATIVUM L SPARKLE

Transformed root cultures were established from the nonmycorrhizal (My c(-)) acid mycorrhizal (Myc(+)) Pisum sativum L Sparkle mutants to stu dy the biochemical factors necessary for initiating and maintaining th e arbuscular mycorrhizal (AM) symbiosis. Root exudates produced by bot h the Myc(-) and the Myc(+) mutants inhibited the hyphal growth of Gig aspora margarita, whereas root volatiles from these mutants stimulated the hyphal growth significantly in the precolonization stage. Carbon dioxide is the principal volatile compound necessary for the elongatio n of hyphae from both the Myc(-) and the Myc(+) transformed roots. The addition of quercetin, a flavonol compound, to the medium with a Myc( -) mutant enriched with an optimal CO2 improved hyphal elongation and spreading as previously reported but did not cause Myc(-) roots to bec ome mycorrhizal. These results suggest that the root factors may stimu late or inhibit AM fungal growth and that they do not determine the my corrhizal nature of P. sativum Sparkle mutants. (C) 1995 Academic Pres s, Inc.