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What are the major classes of plant hormones?
Plant Structure and Function
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The discovery of the role of bees in pollination was discovered by Joseph Gottlieb Kölreuter (1733–1806) in 1761. He was the first to realize that plant fertilization occurs with the help of pollen-carrying insects.
The five major classes of plant hormones are auxins, gibberellins, cytokinins, ethylene, and abscisic acid.
| Hormone | Principal Action | Where Produced or Found in Plant |
| Auxins | Elongate cells in seedlings, shoot tips, embryos, leaves | Shoot apical meristem |
| Gibberellins | Elongate and divide cells in seeds, roots, shoots, young leaves | Apical portions of roots and shoots |
| Cytokinins | Stimulate cell division (cytokinesis) in seeds, roots, young leaves, fruits | Roots |
| Ethylene | Hastens fruit ripening | Leaves, stems, young fruits |
| Abscisic acid | Inhibits growth; closes stomata | Mature leaves, fruits, root caps |