Micronutrients, such as iron, copper, and zinc are essential for a variety of functions in the living cell. They are essential in different redox systems such as the electron transport chains of cells, organelles, and membranes, but also play an important role in DNA- and RNA-protein interaction. Deprivation of these elements is causing symptoms of deficiency, whereas excess can be toxic due to the production of reactive oxygen species and an imbalance of the cellular redox state. Both deficiency and toxicity are the cause of reduced growth and crop yields. Proteomic approaches revealed alterations of several proteins of different functional classes due to adaptation to nutrient deficiency or toxicity. General and specific responses to micronutrient deficiency and toxicity will be discussed with respect to transporters, signaling, and adaptation mechanisms.