Plant World

Plant Structure and Function

What are the major classes of plant hormones?

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


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