What Are Plant Hormones?

Study Notes

Plants produce hormones, which are chemicals that promote and regulate functions in other parts of the plant, playing a crucial role in growth, repair, and protection.
Hormones are chemical messengers that tell different parts of the plant to do different things, depending on the type of hormone.

Hormones are synthesized in many parts of the plant, including roots, stems, and leaves
Hormones are then transported to the part of the plant that needs a specific hormone through vascular tissues, such as phloem and xylem

Five types of hormones: auxins, cytokinins, gibberellins (GAs), ethylene, and abscisic acid (ABA)
Each type of hormone has a specific function, with several secondary functions that help the plant in its life

Three plant hormones promote growth: auxins, cytokinins, and gibberellins
Auxins:
- Responsible for cell elongation in response to phototropism and gravitropism
- Produced in stems, buds, and root tips of the plant
- Regulate dormancy of lateral buds
Cytokinins:
- Responsible for cell division
- Most abundant in areas of the plant that produce cells, such as the seed embryo, fruit, and root and shoot tips
- Help differentiate between root and shoot cells
Gibberellins:
- Responsible for stem, fruit, and seed growth
- Produced in the roots of plants and move upward from the roots using the xylem tissue
- Stimulate shoot elongation and flower and fruit maturation

Two plant hormones inhibit growth: ethylene and abscisic acid (ABA)
Ethylene:
- Responsible for aging in plants
- Produced in aging leaves and ripening fruit and released as a gas
- Stimulates the conversion of starches and acids into sugars within the fruit of plants
- Causes mature leaves and flowers to age, fade, and drop
ABA:
- Responsible for the dormancy of different organs within the plant
- Causes leaves to drop
- Causes dormancy in seeds, which is important in assuring seed germination does not happen in the cold months
- Deteriorates over the winter, and its dissipation is part of what causes seed germination in the spring

Plant hormones used for protection from pathogens that cause diseases in plants
Plant hormones used as medicine, such as salicylic acid, which is used as an anti-inflammatory and is a primary ingredient in painkillers like aspirin