How do auxins affect plant growth?

Auxins are plant hormones that regulate growth by promoting cell elongation, particularly in shoot tips and roots.

Auxins, primarily indole-3-acetic acid (IAA), are produced in the shoot tips and then transported down the plant in the vascular tissue. They play a crucial role in the growth and development of plants by promoting cell elongation. This process is particularly noticeable in the shoot tips and roots, where auxins stimulate the cells to elongate and divide, leading to overall plant growth.

Auxins also play a significant role in phototropism and gravitropism, the growth responses of plants to light and gravity respectively. In phototropism, when light shines on one side of a plant, auxins are distributed more on the shaded side, causing cells there to elongate more and the plant to bend towards the light. In gravitropism, auxins move to the lower side of the shoot or root, causing the cells there to elongate less in shoots and more in roots, resulting in the shoot growing upwards and the root downwards.

Furthermore, auxins are involved in apical dominance, the phenomenon where the main, central stem of the plant grows more dominantly than the side shoots. This is because the high concentration of auxins in the shoot tip inhibits the growth of side shoots, allowing the main stem to grow taller and stronger.

In addition to their natural occurrence, auxins are also used in agriculture and horticulture. They are used as rooting powders and sprays to promote root growth in cuttings, and as weed killers, as they cause rapid, uncontrolled growth in broad-leaved plants, which eventually kills them.

In summary, auxins are vital for plant growth and development, influencing cell elongation, phototropism, gravitropism, and apical dominance, and are also utilised in agricultural practices.