Analysis of flavonoids in pubescence of soybean near-isogenic lines for pubescence color loci.

T and Td loci control pubescence color of soybean with epistatic effects (TT TdTd, tawny; TT tdtd, light tawny or near-gray; tt TdTd or tt tdtd, gray). The objective of this study was to investigate the nature of flavonoids in the pubescence of near-isogenic lines (NILs) for these loci. Flavonoids were extracted with methanol from pubescence of cultivar Clark with tawny pubescence (TT TdTd) and its NILs; from Clark-t with gray pubescence (tt TdTd) and Clark-td with near-gray pubescence (TT tdtd); and from a pair of NILs, To7B with tawny (TT TdTd) and To7G with gray pubescence (tt TdTd). Primary flavonoids were flavone aglycones. Luteolin and apigenin were predominant in NILs with tawny and gray pubescence, respectively. Small amount of 7-O-glucosides of the 2 flavones were also detected. Alleles at T locus were associated with 3'-hydroxylation in the B-ring of the flavones. The primary flavonoids in Clark-td were luteolin similar to Clark, but its amount was halved. High performance liquid chromatography peaks probably corresponding to isoflavonoids were found only in Clark-td in 2003. However, the peaks were not observed in 2005. The above results suggest that Td may encode a structural or a regulatory gene controlling flavone biosynthesis. Pigments remained visible in pubescence after methanol extraction, suggesting that a major part of the pigments was polymerized. Surface rinsing experiments revealed that flavone aglycones exist outside the surface of cells.