How do auxin, cytokinins, and gibberellins affect plant growth?

Plant growth is regulated by a complex interplay of hormones, including auxins, cytokinins, and gibberellins, which coordinate development across different plant tissues.

Auxins

Auxins, such as indoleacetic acid (IAA), are primarily responsible for promoting lengthwise growth by loosening plant cell walls, allowing for elongation. They are synthesized at the tips of shoots and move downward to growth regions. Auxins also mediate phototropism and geotropism by redistributing themselves within the plant, and they play key roles in fruit development, root formation, and apical dominance, where they inhibit the growth of lateral buds.12

Cytokinins

Cytokinins are synthesized in the roots and move upward through the xylem. Their primary function is to promote cell division in conjunction with auxins. They are also essential for delaying senescence (aging) in leaves by stabilizing protein and chlorophyll content. Additionally, cytokinins help regulate axillary bud activity, often counteracting the inhibitory effects of apical dominance.32

Gibberellins

Gibberellins are produced in young leaves, roots, and seeds. Unlike auxins, they promote the growth of main stems and are particularly involved in the elongation of rosette plants and dwarf varieties. They also play a critical role in seed germination by inducing the production of enzymes that break down food reserves. Like auxins, gibberellins stimulate the activity of the vascular cambium, contributing to secondary thickening in stems.452