Signalling in arbuscular mycorrhiza: facts and hypotheses.

Abstract

The arbuscular mycorrhizal symbiosis is an association between plant roots and fungi. Arbuscular mycorrhizal fungi (AMF) colonize roots improving plant nutrition mainly by transferring phosphate (P) from the soil to the plant, whereas plants provide the fungi with carbohydrates (Smith and Read, 1997). In contrast to the rhizobial symbiosis with a host range limited to the Leguminoseae, AMF form symbiotic associations with a wide range of plant species. Interestingly, there seem to be striking similarities between signalling in rhizobial and arbuscular mycorrhizal symbiosis (reviewed by Hirsch and Kapulnik, 1998). Apart from the effect of plant derived secondary plant compounds (SPC) on the bacterial and the fungal symbiont, SPC (e.g. flavonoids) are accumulated in the roots of the respective host plants during the establishment of both symbioses. Whereas there is some information on the role of SPC in the rhizobial symbiosis, the exact role of SPC during the establishment of the AM symbiosis still remains unclear.