How does auxin affect plant cell enlargement and division?

Auxins are a group of plant hormones that play a critical role in regulating growth and development.12

Cell Enlargement

Auxins, most notably indolylacetic acid (IAA), stimulate cell elongation in stems. They achieve this by acting on the chemical bonds of the carbohydrates that make up plant cell walls. This action allows the cell walls to be irreversibly deformed, a process accompanied by the entry of water into the cell and the synthesis of new cell-wall material. This mechanism is fundamental to phenomena such as phototropism and geotropism, where differential auxin distribution causes specific sides of a stem to elongate more than others.12

Cell Division

Beyond elongation, auxins are essential for cell division and cell differentiation. While their specific role in division is distinct from their elongation effects, they are integral to overall plant growth, including fruit development and the formation of roots from cuttings.12