ABSTRACT
The legume family (Fabaceae) includes soybean, Glycine max L. Merr., and many other important crop species, such as bean, Phaseolus vulgaris L.; pea, Pisum sativum L.; alfalfa, Medicago sativa L.; and peanut, Arachis hypogaea L. Legumes are the third largest family of higher plants, second only to the Gramineae (grasses) in agricultural importance. Legumes range all the way from minute herbaceous plants to towering trees that dominate many tropical rainforests. Legumes form symbiotic relationships with Rhizobia bacteria (1), together producing biological nitrogen of immeasurable value to world agriculture and essential in global ecology. Legumes are a major source of organic fertilizer, especially in the developing world, and are an essential component of nearly all agricultural rotation schemes. Legumes also form symbiotic relationships with beneficial mycorrhizal fungi (as do many other plant families), though studies increasingly point to a common symbiotic pathway for both Rhizobium and mycorrhizae (2). This makes legumes an ideal system for studying the biology of symbiosis. In part because of their novel biological nitrogen metabolism, legumes are remarkably high in protein content, providing the largest single source of vegetable protein in human and livestock diets. Legumes also produce health-promoting secondary compounds, including chemicals effective in protecting against human cancers (3). Not surprisingly, legumes are one of the beststudied plant families in the world.
