Three amino acid permeases (AAP) and two oligopeptide transporters (OPT) were isolated from seed-specific libraries of Vicia faba. Functional characterization in a yeast mutant showed that VfAAP1 and VfAAP3 have high substrate affinity and transport a broad range of amino acids, whereas VfAAP1 showed a preference for cysteine and VfAAP3 for lysine and arginine. VfOPT1 functionally complemented the mutation in a peptide transporter gene of a mutant yeast strain by promoting growth in a medium supplemented with the di-peptide His-Ala. Specific expression profiles were seen for the AAPs and OPTs. VfAAP1 was highly expressed in cotyledons at early developmental stages and moderately in gynoecia. Its peak of expression in cotyledons corresponded to the appearance of storage protein transcripts, suggesting that this transporter fulfills an important role in providing amino acids to build up storage proteins, whereas VfAAP3 was expressed ubiquitously in maternal tissues and seemed to have a 'house-keeping' role. Expression of the OPTs in late cotyledon development may be correlated to periods of intensive proteolysis due to leaf senescence. In situ hybridization showed that VfAAP1 mRNA is distributed throughout the cotyledon parenchyma, but not in the epidermal cell layer. VfOPT1 transcripts were localized only in the epidermal cell layer of the cotyledons. Data showed that VfAAP1 is down regulated in the presence of amino acids, as opposed to storage protein genes, which were up-regulated by amino acids. Seeds from transgenic V. narbonensis plants overexpressing the VfAAP1 cDNA under control of the LegB4 promoter had altered contents of nitrogen, proteins, sulfur and starch, implicating that this permease can affect, at least to some extent, the accumulation of storage products in the seeds.