Plant hormones (also known as plant growth regulators (PGRs) and phytohormones) are chemicals that regulate plant growth. Plant hormones are signal molecules produced at specific locations in the plant, and occur in extremely low concentrations. The hormones cause altered processes in target cells locally and at other locations.
Auxins are phytohormones, which help to coordinate growth and development in the plant body. Auxin stimulates cell elongation. Together with cytokinins, auxins stimulate cell division. Auxins shoot apical dominanace.They are responsible for causing phototropism, geotropism and hydrotropism.
Auxins and gibberellins help in growth of the stem and roots in appropriate concentrations. Gibberellins are plant growth hormones inflencing a range of developmental processes in higher plants.
Cytokinins promote cell division and hence they are present in larger amounts in areas of rapid cell division, such as in fruits and seeds.
Abscisic acid inhibits growth and causes wilting of leaves.
Ethylene helps in ripening of fruits.