Nickel (Ni) has only recently been added to the list of essential nutrients. While only very minor quantities are needed for growth cycles (200 nanograms), it does play an important role in seed germination. Nickel deficiencies have led to depressed seedling vigor, chlorosis, and necrotic legions in leaves.
The basis for a nickel requirement in plants is not clear, but it may be related to mobilization of nitrogen during seed germination. Nickel is known to be a component of two enzymes; urease and hydrogenase.