Rhizosphere flavonoids released by alfalfa

Abstract

Flavonoids released from seeds and roots of alfalfa (Medicago sativa L.) are important chemical components of the seedling rhizosphere. Some flavonoids induce transcription of nodulation (nod) genes in Rhizobium meliloti as a first step toward root nodule formation and symbiotic N2 fixation, but many others with unknown functions also are released from imbibing seeds. Three flavonoid nod inducers exuded by alfalfa roots and others released from imbibing seeds have been identified. Interactions among those compounds indicate that the chemical domains created by seed and roots govern expression of rhizobial nod genes and, perhaps, other microbial activities in the soil. As modern tools increase our knowledge of rhizosphere chemistry, the specific signals that control interactions between plant roots and microbes may become management tools for achieving agricultural objectives.