Abstract: This invention relates to plants and plant cells which express heterologous D-amino acid metabolizing enzymes and may therefore employ D-amino acids as a source of nitrogen. Methods and means are provided for selectively modulating the growth and stress tolerance of such plants using D-amino acids. The methods can be used either for detoxification of phytotoxic D-amino acids such as D-alanine and D-serine, thereby allowing for selection of plants comprising said D-amino acid metabolizing enzymes, or for enhancing toxicity of lesser phytotoxic D-amino acids such as D-isoleucine, thereby allowing for selection of plants not comprising said D-amino acid metabolizing enzymes.