The invention relates to a method for producing a transgenic plant in which the capability for incorporating undesired nitrogen compounds, especially amino acids, in the storage organs is reduced compared with the wild type, comprising the steps: introducing at least one DNA sequence and/or at least one RNA sequence corresponding to the DNA sequence and/or a mixed sequence composed of DNA and RNA nucleotides corresponding to the DNA sequence with the coding region for an amino acid transporter or parts thereof into a plant cell, wherein the DNA and/or RNA sequence and/or mixed sequence is used in sense or antisense orientation and the expression of an endogenous amino acid transporter gene is prevented or reduced, and regenerating a plant from this plant cell, wherein the DNA and/or RNA sequence is a sequence from Beta vulgaris.