What Are Plant Hormones?

Plant Hormones

• 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.

Functions of Plant Hormones

• Regulate growth, repair, and protection in plants
• Promote and inhibit growth in roots, stems, leaves, buds, and seeds
• Protect plants from pathogens
• Repair damage
• Ripen fruit
• Start or delay senescence (e.g., discoloration of leaves)

Where Are Hormones Synthesized in Plants?

• 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

Types of Plant Hormones

• 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

Growth Promoters

• 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

Growth Inhibitors

• 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

Other Uses of Plant Hormones

• 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