What is Auxin?

Definition of Auxin: Auxin is a class of plant hormones that regulate various aspects of plant growth and development.

The word auxin means “to rise”. It is a plant hormone important for growth regulation, mainly in the apical meristem and stem elongation. It controls various physiological processes like cell elongation, tropisms, and apical dominance. Auxin also influences root development, fruit development, and vascular tissue differentiation. The hormone’s distribution within plant tissues is tightly regulated, often moving in a polar manner. Synthetic auxins like indole-3-acetic acid (IAA) are used in agriculture for weed control, rooting hormones, and tissue culture.

Chemical Structure

Auxins are primarily indole derivatives. IAA is the most abundant natural auxin in plants. It has an indole ring and a carboxylic acid group. Other synthetic auxins, like 2,4-dichlorophenoxyacetic acid (2,4-D) and naphthaleneacetic acid (NAA), have similar structures but differ in their substitutions.

Biosynthesis

Auxins are synthesized in various plant tissues, including young leaves, apical buds, and developing seeds. The primary biosynthetic pathway of IAA involves the amino acid tryptophan, which undergoes several enzymatic steps to form IAA. Other pathways also contribute to auxin biosynthesis, especially under stress conditions.

Transport

Auxins can move within plants in a polar manner, from the apical meristems (where they’re synthesized) towards the basal parts. This polar transport occurs through cell-to-cell movement facilitated by specialized carrier proteins and can be both acropetal (upward) and basipetal (downward). This transport mechanism helps coordinate growth and developmental processes throughout the plant.

Also Read: Difference Between Auxin and Gibberellin

Auxin is a plant hormone. Auxin hormone function is to control growth and developmental processes in plants, including cell expansion, root initiation, and bud and flower growth. Auxin, discovered by Charles Darwin and his son Francis, was first isolated from human urine.

Auxin plays a key role in plant adaptation to the environment, and its functions are associated with signal transduction, transport, homeostasis, and biosynthesis pathways. In this article, we will study the auxin, its types, mechanism of action, and functions in detail.