Explain the function of plant hormones please give the correct answer
Answers
There are several Plant Hormones classes, namely, Auxin, Cytokinin, Gibberellin, Abscisic Acid, Ethylene.
Here are the functions of plant hormones in short.
Functions of Auxin : Cell enlargement, apical dominance, prevention from bending; promote xylem differentiation, healing of wounds of plants.
Applications of Auxin include - root initiation in callus during plant tissue culture, application of auxins to induce parthenocarpy etc.
Function of Cytokinin : promote cell division, apical dominance, delay in senescenes ( aging ), phloem transport, accumulation of salts in cells, production of female flowers, increase resistance to extreme temperatures and diseases.
Applications of Cytokinin include - stem initiation in callus during plant tissue culture, disease resistant varieties in genetically modified crops
Functions of Gibberellin : promote increase in fruit size, inter-nodal elongation, seed germination
Applications of Gibberellin include - dose of Giibberellin during parthenocarpy, production of male flowers on genetically female plants, breaking dormancy of seed, bud, tuber etc.
Functions of Abscisic Acid : abscission of leaves, reduce transpiration, inhibit cambium activity, bud dormancy in seed during winter, seed development and maturation, induce flowering in some SDPs, synthesis of carotenoids in green organs
Functions of Ethylene : inhibit stem elongation; promote fruit ripening, increase girth of stem, speed of senescence, abscission of leaves
Applications of Ethylene - artificial ripening of fruits, sprouting of storage organs.
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♦ There are five different types of plant growth regulators known to affect the life processes and functions of plants.
1) Auxin
Auxin is also referred as IAA- indole-3-acetic acid. It was the first phytohormones to be recognized. This plant growth regulator plays an important role in the growth and development of a plant. They play a vital role in:
♦ Functions of Auxins :
- Promote flowering in plants
- Used in the process of plant propagation.
- Used by gardeners to keep lawns free from weeds.
- Involved in the initiation of roots in stem cuttings.
- Prevent dropping of fruits and leaves at early stages.
- Control xylem differentiation and help in cell division.
- Auxins are widely used as herbicides to kill dicot weeds.
- Used for the production of fruit without preceding fertilization.
- Promote natural detachment (abscission) of older leaves and fruits.
- Apical dominance may occur in which the growth of lateral buds is inhibited by the growth of apical buds. In such cases, the shoot caps may be removed.
2) Cytokinins Cytokinins are involved in promoting cell division (cytokinesis) hence it is referred to as Cytokinins. Zeatin is a naturally occurring plant growth hormone, which is isolated from corn plant. Cytokinins are present in all cell division sites including root tips, leaves, fruits, and seeds.
♦ Functions of Cytokinins :
- Break bud and seed dormancy.
- Promotes the growth of the lateral bud.
- Promotes cell division and apical dominance.
- They are used to keep flowers fresh for a longer time.
- Used in tissue culture to induce cell division in mature tissues.
- Promote lateral shoot growth and adventitious shoot formation.
- Promote nutrient mobilization which in turn helps delay leaf senescence.
- Helps in delaying the process of aging (senescence) in fresh leaf crops like cabbage and lettuce.
- Involved in the formation of new leaves and chloroplast organelles within the plant cell.
- Used to induce development of shoot and roots along with auxin, depending on the ratio.
3) Gibberellins The plant hormone Gibberellin is the most abundant hormone in plants. There are more than 70 gibberellins isolated. They are GA1, GA2, GA3.. and so on. The GA3 Gibberellic acid is the most widely studied plant growth regulators.
♦ Functions of Gibberellin :
- Delay senescence in fruits.
- Involved in leaf expansion.
- Break bud and seed dormancy.
- Promote bolting in cabbages and beet.
- Help fruits like apples to elongate and improve their shape.
- Used by the brewing industry for increasing the speed on the malting process.
- Used as the spraying agent to increase sugarcane yield by lengthening of the stem.
- Used to fasten the maturity period in young conifers and promote early seed production
- Helps in increasing the crop yield by increasing the height in plants such as sugarcane and increase the axis length in plants such as grape stalks.
4) Ethylene
Ethylene is an organic compound and gaseous substance, which is produced from an amino acid. It is present in the large amount and is mainly produced by plants that are under stress.
♦ Functions of Ethylene :
- Induce flowering in the mango tree.
- Promotes sprouting of potato tubers.
- Breaks the dormancy of seeds and buds.
- Enhances respiration rate during ripening of fruits.
- Applied to rubber trees to stimulate the flow of latex.
- Promotes abscission and senescence of both leaves and flowers.
- Used to stimulate the ripening of fruits. For example, tomatoes and citrus fruits.
- Affects horizontal growth of seedlings and swelling of the axis in dicot seedlings.
- Increases root growth and root hair formation, therefore helping plants to increase their absorption surface area.
5) Abscisic acid It is a growth inhibitor which was discovered in the 1960s. It was initially called dormant. Later another compound abscisin-II was discovered and are commonly called as abscisic acid. This growth inhibitor is synthesized within the stem, leaves, fruits, and seeds of the plant. Abscisic acid mostly acts as an antagonist to Gibberellic acid. It is also known as the stress hormone as it helps by increasing the tolerance of plants to different kinds of stress.
♦ Functions of Abscisic acid :
- Stimulates closing of stomata in the epidermis.
- Helps in development and maturation of seeds.
- Inhibits plant metabolism and seed germination.
- It is involved in regulating abscission and dormancy.
- It is widely used as a spraying agent on trees to regulate dropping of fruits.
- Induces dormancy in seeds and helps in withstanding desiccation and other unfavorable growth factors.
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