The Functions of Plant Hormones

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A Complete Guide on the Functions of Plant Hormones

You must have noticed that plants’ lifecycle starts from seeds, and years of development helps it reach maturity. Other than sunlight, oxygen, water, and minerals, there are some influencers in plants responsible for this development and growth. 

A German botanist named Julius von Sachs first identified organic substances in plants that transport and perceive by their tissues. These substances help plants to form and develop different body parts.

These molecules that influence all the physiological processes and activities in plants are known as plant hormones or phytohormones. From the following content, you can learn what are phytohormones and what their functions are.


Plant Hormones

Similar to animals, hormones in plants also act as chemical messengers transmitting signals throughout the body. In a plant, these molecules are present in low concentration and elicit only as response of various cells that have proper hormone receptors. 

Hormones help in regulating different behaviours of plants in terms of responding to environmental conditions and external stimuli. Every process of plants such as flowering, fruit maturation and setting, leaf falling, phototropism, etc. are regulated by hormones.


The major types of plant hormones and their derivatives found in plant body are given in a tabular format

Types of Plant Hormones

Hormones

Derivatives

Auxins

Indole

Gibberellins or GA

Terpenes

Cytokinin or CK

Adenine

Abscisic acids

Carotenoids

Ethylene or ET

Gases


Characteristics of Phytohormones

  • Unlike animals, plants do not have any specific hormonal glands. Plant hormones can be produced from any part of the body.

  • These molecules transmit through all parts of the vascular tissues called phloem and xylem and by plasmodesmata from cell to cell.

  • These hormones can act both individually or synergistically. Moreover, their roles can also be either antagonistic or complementary.

  • Every life process of plants, along with external factors, is controlled by these chemical messengers.

  • Synthetic phytohormones are used exogenously for customised crop production.


Primary Functions of Plant Hormones

Now, as you learned what are plant hormones, it is important to know their functions as well.

Phytohormones primarily control forming and developmental activities such as enlargement, cell division, the formation of seeds, dormancy, flowering, abscission, etc. Depending on these actions, plant hormones can be classified into two categories -

1. Growth Promoters of Plants

Some common example of growth promoters are- Auxins, Gibberellins, and Cytokinin.

2. Growth Inhibitors of Plants

A growth inhibitor example is an Abscisic acid.

3. Growth Promoters and Inhibitors of Plants

Ethylene is a prime example of growth promoters and inhibitors.


Auxins

The meaning of Auxin is “to grow”. These carbocyclic growth promoters are correlated with the growth regions distribution of plants and promote lengthwise growth in them. Primarily, Auxins are seen in developing apices of stems and roots and then transmit to different body parts to act. Synthetic Auxins are utilised in horticulture and agricultural practices.

  • Molecular formula: C18H32O5

  • Natural derivatives: Indole butyric acid or IBA, Indole-3-acetic acid or IAA.

  • Synthetic derivatives: Naphthalene acetic acid or NAA, 2,4-dichlorophenoxy acetic acid or 2,4-D.


Functions

Here are some Auxin functions-

  • This type of phytohormone helps in the elongation of root and stem cells.

  • The growth suppression of lateral buds is controlled by IAA that presents in apical buds.

  • Auxin also prevents early falling of fruits, flowers, and leaves.

  • This hormone also helps in initiating the rooting process by grafting and cutting stems.

  • In plants like pineapple, flowering is also promoted by Auxin.

  • 2,4-D also acts as an herbicide that eliminates unwanted weeds of dicot plants without causing any harm to monocot plants.

  • It promotes cell division and helps in xylem differentiation.


Gibberellins

Gibberellins can be found as more than 100 derivatives. These acidic phytohormones are mostly seen in fungi and higher plants.

  • Molecular formula: C19H22O6

  • Natural derivatives: Terpenes in different forms.


Functions

  • Gibberellins regulate sudden elongation of internodes while flowering, which is called bolting in plants like beet, cabbage, etc.

  • The delay of senescence is also controlled by these hormones.

  • It promotes stem elongation that works against dwarfism.

  • This also helps in inducing male characteristics in specific plants such as cannabis.

  • It regulates the creation of hydrolytic enzymes like amylase, lipase, etc. within the endosperm of cereals that germinate.

  • Gibberellins control parthenocarpy and the breaking of seed dormancy.


Cytokinin

Cytokinin majorly regulate cytokinesis process. The synthesising of these hormones happens in such cells that divide rapidly, like young fruits, root apices, shoot buds, etc. These hormones move in a polar and basipetal direction.

  • Molecular formula: C10H13N5O

  • Natural derivatives: Zeatin, isopentenyladenine.

  • Synthetic derivatives: Diphenylurea, Kinetin, Thidiazuron, and Benzyladenine.


Functions

  • Cytokinin promote the lateral growth of shoots.

  • This hormone works to overcome the apical dominancy regulated by Auxins.

  • It helps in stimulating chloroplast formation in leaves.

  • Cytokinin also help in transmitting nutrients and delaying senescence of leaves.


Abscisic acid

This growth-inhibiting hormone works against the effect of GAs. It hinders the metabolism of plants and controls dormancy and abscission. Also, this hormone increases the tolerance threshold of plans, and hence it is known as “stress hormone”.

  • Molecular formula: C15H20O4


Functions

  • Abscisic acids speed up dormancy in seeds.

  • It can stimulate the closing of stomata to stop transpiration in idler stretches.

  • These hormones hinder seed germination and induce leaf senescence and abscission.


Ethylene

This hormone acts as both inhibitor and promoter and widely utilised in agriculture.


Functions

  • It accelerates fruit ripening.

  • By inducing root hair formation and entire root growth, this hormone helps plants in absorption.

  • It controls leaf epinasty and promotes internodes and petiole elongation.

To learn more about this chapter, you can also refer to plant hormones class 10 books as well. You should try to practice online mock-tests for better performance in NEET. This chapter, Plant hormones, is relatively easy to memorise and score.

Thus, revise this chapter with your entire syllabus and solve previous years’ question papers. Also, you should remember that staying fit and healthy is important during your examination. So, avoid late-night studying, junk food, and maintain a healthy routine.

FAQ (Frequently Asked Questions)

1. What is the Source of Plant Hormones?

Ans. A plant does not have any hormone glands. Phytohormones can be produced in any part of plants. However, they are mostly created in the buds, root tips, and stem cells.

2. Which Plant Hormone is the Most Important One?

Ans. Auxin is an essential hormone in plants. These hormones are secreted at the elongation region and help in growth.

3. What is the Prime Role of Phytohormones?

Ans. The prime role of phytohormones is to regulate all physiological activities like germination, flowering, maturation of fruits, etc. of plants.