Flavanone 3-hydroxylase (F3H) expression and flavonoid localization in nodules of three legume plants reveal distinct tissue specificities

A fusion of the promoter of the Medicago sativa flavanone-3-hydroxylase gene to the gus reporter gene was introduced into three leguminous plants, M. truncatula, M. sativa subsp, varia, and Vicia hirsuta, Expression of this fusion was detected in the parenchyma cells surrounding the vascular tissues in the nodules of the Medicago spp, plants, correlating with the presence of flavonoid compounds detected in situ in these cells. In V. hirsuta nodules, the fusion was expressed in the meristematic region, where high accumulation of flavonoids could also be detected. Our results indicate that flavonoids of the dihydroflavonol pathway are not found in the same tissues of the nodules in these three species, where they may play different roles. In light of these results, the possible roles of the F3H products in this organ are discussed.