All organisms need iron, zinc, and copper as nutrients. They contribute to the essential catalytic functions within the cell. Because plants are at the beginning of the food chain, sufficient content of these minerals in them is essential for the human diet. These metals are chemically very similar, making it difficult for organisms to distinguish between them. The metal–binding molecule nicotianamine is important for iron transport in plants. In her time at the universities of Heidelberg and Bochum, Krämer has demonstrated that it also makes a major contribution to the zinc balance.