WRITE NOTES ON TYPES OF PLANT HORMONES FOR CLASS 10
Answers
Types of Phytohormones.
The major types of plant hormones which are involved in the control and coordination in plants are as follows:
(i) Auxins are the group of plant hormones synthesised at the shoot-tip of the plant body .
• It promotes cell elongation, root formation, cell division, respiration and other physiological processes like protein synthesis, water uptake and protoplasmic permeability.
• Auxins also play an important role in the development of seedless fruits.
(ii) Gibberellins stimulate stem elongation, seed gennination and flowering.
• The maximum concentration of gibberellins is found in fruits and seeds.
(iii) Cytokinins are produced in dividing cells throughout the plant
• In mature plants, cytokinins are produced in the root tips and are transported to the shoots.
• Cytokinins promote cell division and also helps in breaking the dormacy of seeds and buds and regulate the phloem transport.
• Cytokinins delay the ageing in leaves and promote the opening of stomata.
(iv) Abscisic Acid (ABA) : It is a growth inhibitor which reverses the growth-promoting effects of auxins and gibberellins.
Its effect include wilting of leaves.
• It causes dormancy of seeds, tubers and bulbs.
• It promotes the closing of stomata and is responsible for the loss of RNA, proteins and chlorophylls.
Heya,
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.
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.
List of Plant Hormones
- Auxin
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
- 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
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
- Gibberellin
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.