Flavonoids Released Naturally from Alfalfa Promote Development of Symbiotic Glomus Spores In Vitro

Abstract

Because flavonoids from legumes induce transcription of nodulation genes in symbiotic rhizobial bacteria, it is reasonable to test whether these compounds alter the development of vesicular-arbuscular mycorrhizal (VAM) fungi that infect those plants. Quercetin-3-O-galactoside, the dominant flavonoid released naturally from alfalfa (Medicago sativa L.) seeds, promoted spore germination of Glomus etunicatum and Glomus macrocarpum in vitro. Quercetin produced the maximum increases in spore germination, hyphal elongation, and hyphal branching in G. etunicatum at 1 to 2.5 ,iM concentrations. Two flavonoids exuded from alfalfa roots, 4',7-dihydroxyflavone and 4',7-dihydroxyflavanone, also enhanced spore germination of this fungal species. Formononetin, an isoflavone that is released from stressed alfalfa roots, inhibited germination of both Glomus species. These in vitro results suggest that plant flavonoids may facilitate or regulate the development of VAM symbioses and offer new hope for developing pure, plant-free cultures of VAM fungi.

Suppression of defence responses in mycorrhizal alfalfa and tobacco roots

“…The role of flavonoids as signal molecules in the establishment of the mycorrhizas is not clear, but some flavonoids enhance germination and hyphal growth of AM fungi (Gianinazzi-Pearson, Branzanti & Gianinazzi, 1989;Tsai & Phillips, 1991) and promote AM fungal colonization of white clover roots (Siqueira, Saflr & Nair, 1991). Likewise, both rhizobial nodulation factors and several of the flavonoids known to accumulate in response to the nodulation factor promoted AM colonization of soybean roots (Xie et al, 1995), suggesting a Bavonoid-mediated stimulation of mycorrhizal colonization.…”

“…In most cases plant resistance is associated with a multiple defence response which might include: (i) a hypersensitive response (HR), which is characterized by rapid, localized, chemical defences, and death of plant cells surrounding the infection site (Meier, Shaw & Slusarenko 1993 ;Uknes et al, 1996); (ii) the accumulation of secondary metabolites, such as antimicrobial phytoalexins (Dixon, Dey & Lamb, 1983); (iii) structural defensive barriers such as lignin, and hydroxyproline-rich cell wall proteins (Dixon & Harrison, 1990); and (iv) the production of several new enzymes (Van Loon, 1985), some with antifungal activities (Mauch, Mauch-Mani & Boiler, 1988).…”

Spatial patterns of expression of flavonoid/isoflavonoid pathway genes during interactions between roots of Medicago truncatula and the mycorrhizal fungus Glomus versiforme

“…Regulation of the mycorrhizal interaction may involve a combination of nutritional and non-nutritional factors (Koide and Schreiner, 1992;Schwab et a/., 1991). It has recently been reported that a variety of flavonoid derivatives stimulate germination of VA fungal spores, hyphal elongation in vitro and formation of full mycorrhizal interactions in vivo (B~card eta/., 1992; Gianinazzi-Pearson et aL, 1989;Nair eta/., 1991;Siqueira eta/., 1991;Tsai and Phillips, 1991). The effective concentrations of such compounds are, however, too low for nutrient effects, and by analogy to a number of other plant-microbe interactions it has been suggested that they might act as signal molecules.…”

Differential hyphal morphogenesis in arbuscular mycorrhizal fungi during pre‐infection stages

“…Some authors found that root exudates of host plants not only stimulated hyphal growth, but also exerted some morphogenetical effects on the fungus (Mosse & Hepper, 1974;Powell, 1976;Glenn, Chew & Williams, 1985;Gemma & Koske, 1988; Mosse, 1988). Recently, some fiavonoids like quercetin have been shown to promote spore germination, hyphal elongation and hyphal branching in Glomus etunicatum (Tsai & Phillips, 1991).…”