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Plant Hormones and their Functions

Plant Hormones and their Functions

Plant hormones regularize the growth of plants. They occur in very small proportions within the plant. The following article explains the five different types of these secretions and their functions.
Batul Nafisa Baxamusa
Plant hormones are known as phytohormonesin botanical terms. They are chemicals just like animal hormones that help in the growth, development, and functioning of plants. Like animals, plants too are living organisms that function as a unit. They carry out vital biochemical reactions that are required to survive. These biochemical reactions require hormones also known as 'plant growth substances'. These hormones help in the formation of leaves, flowers, stems, fruit, etc. They also help in determining the sex of the flowers, the color of the fruits, and leaves. They help in formation of tissues, respiration, energy production, and even plant longevity and death. Just as hormones are necessary for an animal body to function without any glitches, they too help the green living beings to survive normally. In this article, we shall cover some information related to these secretions and their functions.
What Are the Functions of Plant Hormones?
These hormones help in regulation of the plant body by responding to the various signals from the plant and environment. The hormones are regulated in different tissues during the different development stages. There are five major hormones which are auxin, cytokinin, gibberellin, abscisic acid, and ethylene. Each hormone differs in its effects. The auxins, gibberellins, and cytokinins act as growth stimulators, whereas, abscisic acid and ethylene act as growth inhibitors. Plant hormones are simple in their structure as compared to those of animals or humans. There are no specific or specialized glands that produce these hormones. In fact, they are synthesized anywhere in the plant and act on any part as their target. Besides the hormones, there are many plant growth factors that affect the function and growth of plants.
List of Plant Hormones
This hormone is present in the seed embryo, young leaves, and apical buds' meristem.

Functions of Auxins
  • Stimulation of cell elongation, cell division in cambium, differentiation of phloem and xylem, root initiation on stem cuttings, lateral root development in tissue culture
  • Delaying leaf senescence
  • Suppression of lateral bud growth when supplied from apical buds
  • Inhibition or promotion of fruit and leaf abscission through ethylene stimulation
  • Fruit setting and growth induced through auxin in some plants
  • Auxin can delay fruit ripening
  • In Bromeliads, the auxin hormone promotes flowering
  • Stimulation of flower parts, femaleness of dioecious flowers, and production of high concentration of ethylene in flowering plants
They are synthesized in roots and then transported to other parts of the plant.

Functions of Cytokinins
  • Stimulation of cell division, growth of lateral buds, and apical dominance
  • Stimulation of shoot initiation and bud formation in tissue culture
  • Leaf cell enlargement that stimulates leaf expansion
  • Enhancement of stomatal opening in some plant species
  • Etioplasts converted into chloroplasts through stimulation of chlorophyll synthesis.
Ethylene is present in the tissues of ripening fruits, nodes of stems, senescent leaves, and flowers.

Functions of Ethylene
  • Leads to release of dormancy state
  • Stimulates shoot and root growth along with differentiation
  • Leaf and fruit abscission
  • Flower induction in Bromeliad
  • Stimulation of femaleness of dioecious flowers
  • Flower opening is stimulated
  • Flower and leaf senescence stimulation
  • Stimulation of Fruit ripening
Abscisic Acid
Abscisic acid is found mostly near leaves, stems, and unripe fruit.

Functions of Abscisic Acid
  • Stimulation of closing of stomata
  • Inhibition of shoot growth
  • Inducing seeds for synthesizing storage of proteins
Gibberellins are present in the meristems of apical buds and roots, young leaves, and embryo.

Functions of Gibberellins
  • Stimulates stem elongation
  • Leads to development of seedless fruits
  • Delays senescence in leaves and citrus fruits
  • Ends seed dormancy in plants that require light for induction of germination