Despite not having a nervous system, plants have developed ingenious ways to regulate their growth and lifecycle. This is done entirely by chemical signals and organic compounds (hormones) that are synthesized in one part of the plant and translocated to another plant. Below are some of the most common and most understood plant hormones
Auxin are compounds affecting plant growth such as cell enlargement, bud formation, and root initiation. In large concentrations, auxins are toxic to plants and have been developed into synthetic herbicides for weed control. Many gardeners will be familiar with auxins if they are use hormone rooting powders.
Gibberellins, or GAs, are a large range of chemicals and are important in seed germination, flowering, cellular division and flowering.
Cutplomoms stimulate cell division and plant growth. There is a constant ratio of auxins and cytokinins as these chemicals work in a synergistic way affecting the major growth period of a plant’s lifetime.
This is probably the best known plant hormone as it plays are large role in stimulating the ripening of fruit. Ethylene is formed by the breakdown of mentionine, which is present in all cells. It does not build up within cells, but diffuses out of the cell and escapes out of the plant. Ethylene affects cell growth and shape and was discovered by the ancient Chinese who found bananas would ripen prematurely if stored with oranges.
Abscisic Acid (ABA) is an important plant regular and is named because large concentrations of this hormone was found if freshly fallen (abscissed) leaves. ABA helps protect plants from stresses such as lack of water, salty soil, and cold temperatures by closing the stomata.
These are the 5 most well understood hormones at the moment, and much more research is needed on these and a variety of other ones as well.