Apios

Abstract: American groundnut (Apios americana Medikus) is a nitrogen-fixing legume that produces edible tubers and seeds. Even though studies have been conducted on the quality of tuber storage compounds, very little is known about compounds that could have beneficial effects on human and animal health. The objective of this study was to investigate the presence of genistein in the tubers. The nodC gene of Rhizobium fredii Scholla and Elkan USDA191 that had been fused with β-galactosidase was used to detect the presence of genistein in A. americana tubers. The flavonoids from A. americana tubers were purified by C 18 reversed-phase HPLC. The HPLC profile revealed nine UV absorbing peaks. Among them, Peaks 6 and 8 activated the nodC-lacZ gene fusion about two fold, while the bulk of the inducing activity was associated with Peak 9. The compound in Peak 9 and authentic genistein standard had identical retention times. When A. americana tuber flavonoids were spiked with an authentic genistein standard, Peak 9 coeluted with genistein. In addition, a peak at m/z 271, corresponding to the protonated genistein, was found when the HPLC Peak 9 was analyzed by electrostaticspray mass spectrometry. The results of this present investigation indicate that A. americana tubers contain the isoflavone genistein. The discovery of genistein in A. americana tubers should rekindle interest in this legume as a food crop since genistein has been shown to reduce the incidence of various forms of cancer.

Abstract: Apios americana Medicus (Leguminosae; Phaseoleae), a tuberous, herbaceous vine, consists of diploid and triploid clones which are morphologically nearly identical. Although A. americana is widespread in eastern North America and flowers profusely throughout its range, fruit set is low. In part, this is because populations north of Connecticut consist almost exclusively of sterile triploid individuals. Although triploid populations occur south of this region, diploids predominate. Fruit set is also low in diploids. We attribute this to partial self-incompatibility and to a low rate of floral visits by leaf-cutter bees (Megachile spp.), the only legitimate pollinator. Visitation is easily measured because flowers have a nonrepetitive explosive tripping mechanism which must be triggered by insects. In two Connecticut populations only 10% of 299 flowers were tripped, and on average only about one-halfof these set fruit. We conclude that A. americana maintains populations by vegetative propagation, but expands its range and retains variability through sexual reproduction of diploids.