For synthesis of IAA in plants, . . . . . . . . mineral is essential.

For the synthesis of IAA in plants, Zinc is essential.
IAA is indole acetic acid (Auxin) that can be synthesized through the precursor tryptophan known as the TRP-dependent IAA biosynthetic pathway.
Zinc is an essential plant micronutrient and soil availability is of great importance in many crops. Many enzymes include zinc as a cofactor, like acholol dehydrogenase, and carbonic anhydrase. And deficiency of zinc deficiency inhibits protein synthesis.
Plants require zinc for the synthesis of tryptophan, a key amino acid in the synthesis of auxin indole acetic acid. Its control of plant development through action on auxins.