Indole acetic acid (IAA) is a plant hormone belonging to the class of auxins. It is the most abundant and well-studied auxin and is involved in various plant growth and development processes, including cell elongation, division, differentiation, and tropisms.IAA is synthesized in young plant tissues, primarily in the apical meristem and young leaves, and transported downwards through the plant. It is also synthesized by certain bacteria and fungi, which can influence plant growth and development.