Auxiinid

Auxiinid are a class of plant hormones that regulate many aspects of growth and development. The most important natural auxin is indole-3-acetic acid (IAA). Auxiinid are produced mainly in young leaves and shoot apical meristems and can also be synthesized in seeds. They move through plant tissues by polar (directional) transport, predominantly from the shoot toward the base, a process driven by specific transporter proteins such as PIN and AUX/LAX family members. This polar transport establishes auxin gradients that guide development.

Functions of auxiinid are diverse. They promote cell elongation and are essential for phototropism and gravitropism, helping shoots grow toward light and roots grow in the correct direction. They regulate apical dominance, where the main shoot suppresses the growth of lateral buds. Auxiinid influence root initiation and formation, vascular differentiation, leaf and fruit development, and responses to wounding. They interact with other hormones, including cytokinins, gibberellins, ethylene, and abscisic acid, to balance growth and stress responses.

Synthesis and metabolism involve conjugation and degradation pathways that modulate activity. In agriculture, synthetic auxins such as 2,4-D and NAA are used as herbicides or growth regulators, while indole-3-butyric acid (IBA) is commonly used as a rooting hormone to promote root development in cuttings.

In summary, auxiinid are central regulators of plant morphology, coordinating growth, patterning, and adaptive responses through regulated production, transport, and interaction with other hormonal signals.