An Analysis of the Seed Coat Pigments in Eight Different Genotypes of Phaseolus vulgaris L.

in HortScience
Authors:
Clifford W. Beninger1USDA/ARS, Michigan State Univ., East Lansing, MI 48824

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George L. Hosfield1USDA/ARS, Michigan State Univ., East Lansing, MI 48824

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Muraleedharan Nair2Dept. of Horticulture, Michigan State Univ., East Lansing, MI 48824

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Dry bean (Phaseolus vulgaris L.) seed coat color is determined by the presence and relative amounts of phenolics, flavonoids, and anthocyanins present in the lumen of epidermal cells. Some of these chemicals may interact with proteins of the cotyledon to form complexes that render beans hard to cook and digest. Eight genetic loci control seed pigment chemistry. When all eight loci are dominant, a shiny black seed coat results, but recessive substitutions at one or more loci yield colors ranging from white, yellow, and brown to dark violet. In order to relate Mendelian genes for seed coat color to the pigments formed, we studied eight genetic stocks that had recessive substitutions at one or more color-determining loci in an otherwise all-dominant genetic background. Seed coat from each genotype was extracted exhaustively with hexane, EtOAc, MeOH, MeOH:H2O 1:1, and H2O 100%. Silica gel thin-layer chromatography (TLC) (solvent system CHCl3:MeOH 4:1) analysis of the MeOH fraction showed that one genotype had no phenolic compounds and two had only simple phenols. Once flavonol glycoside was present in relatively large amounts in four of the genotypes, but absent in genotypes with anthocyanins. Cellulose TLC (2-dimensional, Butanol:Acetic Acid:H2O 4:1:5 first dimension, 1% HCl second dimension) of the anthocyanin-containing genotypes showed that the presence of one flavonol and three anthocyanidin-3-glycosides (UV spot color and color shift with NH3). The relative importance of the seed coat chemicals in digestibility and their antioxidant will also be discussed.

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