Amino acid-proton symporter. Stereospecific transporter with a broad specificity for histidine, glutamate and neutral amino acids. Reduced affinities for asparagine and valine. Involved in amino acid uptake from the apoplastic cavity into the embryo cells for storage protein accumulation and in root amino acid uptake. Inhibited by carbonylcyanide m-chlorophenylhydrazone and diethylpyrocarbonate (DEPC). Optimum pH is acidic. Highly expressed in developing pods. Found in the endosperm and in the storage parenchyma and the outer epidermis cells of the developing embryo. Lower levels of expression in flowers, in the vascular system of the cotyledon and in the root epidermal cells, including root hairs and throughout the root tip. Expressed in endosperm during early stages of seed development. Strongly induced at heart stage of embryogenesis. No effect on plant growth or seed germination, but reduced seed weight and total seed yield. Resistant to toxic concentrations of amino acids in the growth medium. Belongs to the amino acid/polyamine transporter 2 family. Amino acid/auxin permease (AAAP) (TC 2.A.18.2) subfamily.