Systemically suppressed isoflavonoids and their stimulating effects on nodulation and mycorrhization in alfalfa split-root systems

Abstract

In split-root systems of alfalfa (Medicago sativa L.), already existing nodules or arbuscular mycorrhizal roots suppress further establishment of symbiosis in other root parts, a phenomenon named autoregulation. Roots treated with rhizobial nodulation signals (Nod factors) induce a similar systemic suppression of symbiosis.In order to test the hypothesis that flavonoids play a role in this systemic suppression, split-root systems of alfalfa plants were inoculated on one side of the split-root system with Sinorhizobium meliloti or Glomus mosseae or were treated with Nod factor. HPLC-analysis of alfalfa root extracts from both sides of the splitroot system revealed a persistent local and systemic accumulation pattern of some flavonoids associated with the different treatments. The two flavonoids, formononetin and ononin, could be identified to be similarily altered after rhizobial or mycorrhizal inoculation or when treated with Nod factor.Exogenous application of formononetin and ononin partially restored nodulation and mycorrhization pointing towards the involvement of these two secondary compounds in the autoregulation of both symbioses.

Plant-borne flavonoids released into the rhizosphere: impact on soil bio-activities related to plant nutrition. A review

“…Apigenin but not its glycosylated conjugate, 5,7,4′-hydroxy flavone glycoside, stimulated hyphal length, hyphal branching, and root colonization by G. mosseae and G. intraradices, and G. margarita and G. rosea (Scervino et al 2006). Interestingly, Catford et al (2006) used a split-root system to study the effect of external addition of flavonoids to already colonized (so-called "autoregulated") roots of M. sativa L. They showed that ononin (formonetin 7′-O-glucoside), but not the aglycone formonetin, stimulated root colonization in auto-regulated roots (Catford et al 2006).…”

“…However, little is known about their effects on the enzyme activities when they enter the rhizosphere soil as a result of root exudation and senescence; this knowledge is essential to better understand the flavonoids role in the rhizosphere soil. Recently, Shawa and Hooker (2008) examined the adsorption, biodegradation, and toxic impact of the flavonoids naringenin and formononetin (Catford et al 2006;Tsao et al 2006), on soil dehydrogenase activity. Naringenin and formononetin were characterized by different lag phases (4 and 24 h, respectively) prior to the beginning of their rapid biodegradation, suggesting the requirement of different catabolic enzymes.…”

Response of PGPR and AM Fungi Toward Growth and Secondary Metabolite Production in Medicinal and Aromatic Plants

“…This improved yield of oil is said to be associated with increased number of glandular trichomes present in the zones of basal and central leaves. Catford et al ( 2006 ) studied the suppression of isofl avonoids and their effects on stimulating nodule formation and mycorrhizal association in split root systems in Medicago sativa . They found that inoculation with Sinorhizobium meliloti or G. mosseae or nod factor altered the secretion of fl avonoids (formononetin and ononin).…”

The Biocontrol Effect of Mycorrhization on Soilborne Fungal Pathogens and the Autoregulation of the AM Symbiosis: One Mechanism, Two Effects?

“…Split-root systems of plants were inoculated on one side with an AMF and, when the symbiosis was well established, the other side was inoculated with the same or another AMF. In these experiments with different AM host plants, such as barley (Vierheilig et al 2000a(Vierheilig et al , 2000b, alfalfa (Catford et al 2003(Catford et al , 2006 and soybean (Meixner et al 2005(Meixner et al , 2007, it could be clearly shown that AM precolonization on one side of a split-root system systemically suppresses AM root colonization on the other side of the root system. The mechanisms which are actually controlling this autoregulatory effect are still unknown.…”