EFFECTS OF HORMONES
There are five main groups of plant hormones.

1) Auxins function primarily in stem elongation by influencing cells to elongate. Auxins are implicated in tropism responses such as phototropism and gravitropism. Auxins are also involved in apical dominance, root initiation, and fruit development.

2) Gibberellins influence stem elongation, as well as flowering and fruit development. Gibberellins are also involved in the germination of seeds in many plants.

3) Cytokinins stimulate cell division and influence flower development, seed germination, and embryo development. Cytokinins delay the aging process, known as senescence, in plant cells. Auxins and cytokinins are antagonistic in the control of apical dominance: Auxins inhibit the growth of axillary buds, and cytokinins promote their growth.

4) The gas ethylene stimulates fruit ripening, inhibits cell elongation, and promotes seed germination. Ethylene is also involved in the plant's response to environmental stressors such as wind and hail.

5) Abscisic acid is produced by plants, often in response to environmental stressors such as drought. Abscisic acid interacts with gibberellins and cytokinins in controlling seed dormancy: Abscisic acid induces seed dormancy, and the other two hormones break dormancy.