Hormones-in-Plants

Hormones in Plants (Phytohormones)

Hormones in Plants

Plant hormones are signal particles, produced within plants, that take place in very low concentrations.

Plant hormones manage all aspects of plant development and growth, from embryogenesis, the regulation of organ size, pathogen defense, tension tolerance, and through to reproductive development.

Some of the unique substances produced by the plants which influence the development and plant response to various stimuli are given below.

(a) Auxins:

These are indole acetic acid (IAA) or its variants.

  • In the stem, promotes cell augmentation in the region behind the apex. Promote cellular division in the cambium.
  • In the root, promotes growth at very low concentrations. Prevent growth at higher concentrations, e.g., geotropism. Promote the growth of roots from cuttings and calluses.
  • Promote bud initiation in shoots however often antagonistic to cytokinin’s and is repressive.
  • Promote apical dominance and fruit growth. They can sometimes induce parthenocarpy.
  • Cause delay in leaf senescence (aging) in a couple of species.
  • Inhibit abscission.
Synthetic auxins

NAA (Naphthalene acetic acid) Indole propionic acid

  • Stimulates fruiting – help natural fruit set. In some cases, causes fruit setting in lack of pollination (parthenocarpy).

2,4 D (2,4 Dichloro phenoxy acetic acid)

  • Selective weed killer. Eliminates broad-leaved species (dicots). Utilized in cereal crops and grass to eliminate weeds. Prevents the growing of potatoes. Prevents early fruit drop (slows down abscission).
Commercial Applications

The Discovery of IAA resulted in the synthesis of a vast array of substances by chemists. The artificial auxins are more economical than IAA to produce and frequently more active because plants normally do not have the needed enzymes to break them down.

(b) Gibberellin:

These are produced commercially from fungal cultures.

  • Promote cell enhancement in the existence of auxins. Also, promote cell division in apical meristem and cambium.
  • Promote ‘bolting’ of some rosette plants.
  • Promote bud initiation in shoots of chrysanthemum callus.
  • Promote leaf growth and fruit growth. May induce parthenocarpy.
  • In apical supremacy, improve the action of auxins.
  • Break bud and seed dormancy.
  • Often might alternative to red light. For that reason, promotes lowering in long-day plants, while preventing in short-day plants.
  • Cause delay in leaf senescence in a few types.
Commercial Applications

A few of their industrial applications are as under.

  1. GA promotes fruit setting e.g., in tangerines and pears, and is used for growing seedless grapes (parthenocarpy) and likewise increases the berry size.
  2. GA3 is used in the brewing industry to promote a-amylase production in barley and this promotes malting.
  3. To delay ripening and enhance the storage life of bananas and grapefruits.
(c) Cytokinins
  • Promote stem growth by cell division in apical meristem and cambium.
  • Hinder primary root development.
  • Promote lateral root growth.
  • Promote bud initiation and leaf development.
  • Promote fruit development but can seldom cause parthenocarpy.
  • Promote lateral bud growth, also break bud dormancy.
  • Cause delay in leaf senescence.
  • Promote the stomatal opening.
Commercial Application

Cytokinins postpone the aging of fresh leaf crops, such as cabbage and lettuce (delay of senescence) along with keeping flowers fresh. They can also be used to break the dormancy of some seeds.

Further Reading:  Skeleton, Types of Skeleton and Functions
(d) Abscisic acid:
  • Inhibits stem and root growth notably during physiological stress, e.g., dry spells, and waterlogging.
  • Promotes bud and seed dormancy.
  • Promotes flowering in short-day plants, and inhibits in long-day plants (antagonistic to gibberellins).
  • Often promotes leaf senescence.
  • Promotes abscission.
  • Promotes the closing of stomata under conditions of water stress (wilting).
Commercial Application:

Abscisic acid can be sprayed on tree crops to regulate fruit drop at the end of the season. This removes the requirement for choosing over a large time-span.

(e) Ethene:
  • Inhibits stem growth, significantly during physiological stress.
  • Inhibits root growth.
  • Breaks dormancy of bud.
  • Promotes flowering in pineapple.
  • Promotes fruit ripening.
Commercial Application

Ethene induces flowering in pineapple. Promotes ripening of tomatoes and citrus fruit. The industrial substance ethephon breaks down to release ethene in plants and is applied to the rubber plant to promote the flow of latex.

MCQs

  • What are plant hormones?
    • A. Chemicals produced by animals
    • B. Signal particles produced within plants
    • C. Synthetic substances used for plant growth
    • D. Inorganic compounds in the soil
    • Answer: B
  • Which plant hormone promotes cell augmentation in the stem and inhibits abscission?
    • A. Gibberellin
    • B. Cytokinins
    • C. Ethene
    • D. Auxins
    • Answer: D
  • What is the commercial source of Gibberellin?
    • A. Animal tissues
    • B. Synthetic production
    • C. Fungal cultures
    • D. Root extracts
    • Answer: C
  • Which synthetic auxin is known for its selective weed-killing property?
    • A. NAA (Naphthalene acetic acid)
    • B. IAA (Indole acetic acid)
    • C. 2,4 D (2,4 Dichloro phenoxy acetic acid)
    • D. Indole propionic acid
    • Answer: C
  • What is the main commercial application of synthetic auxins like NAA and 2,4 D?
    • A. Delaying leaf senescence
    • B. Selective weed killing
    • C. Promoting fruit ripening
    • D. Enhancing root growth
    • Answer: B
  • Which plant hormone promotes fruit setting, delays ripening, and enhances the storage life of bananas and grapefruits?
    • A. Ethene
    • B. Cytokinins
    • C. Gibberellin
    • D. Abscisic acid
    • Answer: C
  • What effect does cytokinins have on primary root development?
    • A. Promotes
    • B. Inhibits
    • C. No effect
    • D. Causes senescence
    • Answer: B
  • Which hormone inhibits stem and root growth during physiological stress, promotes abscission, and induces flowering in pineapple?
    • A. Ethene
    • B. Abscisic acid
    • C. Gibberellin
    • D. Cytokinins
    • Answer: B
  • What is the main role of auxins in roots at low concentrations?
    • A. Inhibit growth
    • B. Promote growth
    • C. Induce senescence
    • D. Enhance abscission
    • Answer: B
  • Which plant hormone is antagonistic to gibberellins in terms of flowering regulation in short-day plants?
    • A. Cytokinins
    • B. Auxins
    • C. Ethene
    • D. Abscisic acid
    • Answer: D
  • What is the primary function of ethene during physiological stress?
    • A. Promotes stem growth
    • B. Inhibits root growth
    • C. Enhances fruit ripening
    • D. Breaks bud dormancy
    • Answer: B
  • Which synthetic auxin is commonly used as a selective weed killer?
    • A. NAA (Naphthalene acetic acid)
    • B. IAA (Indole acetic acid)
    • C. 2,4 D (2,4 Dichloro phenoxy acetic acid)
    • D. Indole propionic acid
    • Answer: C
  • What effect does abscisic acid have on stomata under conditions of water stress?
    • A. Opening
    • B. Closing
    • C. No effect
    • D. Promotes senescence
    • Answer: B
  • Which hormone is responsible for promoting the flow of latex in rubber plants when applied industrially?
    • A. Cytokinins
    • B. Gibberellin
    • C. Auxins
    • D. Ethene
    • Answer: D
  • What is the primary function of gibberellins in barley in the brewing industry?
    • A. Promotes flowering
    • B. Enhances seed germination
    • C. Increases berry size
    • D. Induces α-amylase production
    • Answer: D
  • Which plant hormone is sprayed on tree crops to regulate fruit drop at the end of the season?
    • A. Cytokinins
    • B. Gibberellin
    • C. Auxins
    • D. Abscisic acid
    • Answer: D
  • What is the effect of cytokinins on fresh leaf crops like cabbage and lettuce?
    • A. Induces flowering
    • B. Delays senescence
    • C. Promotes root growth
    • D. Inhibits bud initiation
    • Answer: B
  • Which plant hormone promotes lateral bud growth and breaks bud dormancy?
    • A. Auxins
    • B. Cytokinins
    • C. Gibberellin
    • D. Ethene
    • Answer: B
  • What is the primary effect of ethene on pineapple plants?
    • A. Promotes flowering
    • B. Inhibits root growth
    • C. Enhances fruit ripening
    • D. Delays senescence
    • Answer: C
  • Which plant hormone promotes the closing of stomata under conditions of water stress?
    • A. Cytokinins
    • B. Gibberellin
    • C. Ethene
    • D. Abscisic acid
    • Answer: D
Further Reading:  Populations and Population Growth

 

FAQs related to Hormones in Plants (Phytohormones) Tutorial

  1. What are plant hormones, and what role do they play in plant development?
    • Plant hormones are signal particles produced within plants that regulate various aspects of plant development and growth. They control processes such as embryogenesis, organ size regulation, pathogen defense, stress tolerance, and reproductive development.
  2. What is the role of auxins in plant development?
    • Auxins, such as indole acetic acid (IAA), promote cell augmentation in the stem, cellular division in the cambium, root growth at low concentrations, and inhibit abscission. They also play a role in bud initiation, apical dominance, fruit growth, and can induce parthenocarpy.
  3. What are synthetic auxins, and what are their commercial applications?
    • Synthetic auxins, like NAA (Naphthalene acetic acid) and Indole propionic acid, stimulate fruiting, act as selective weed killers, and prevent early fruit drop. They are more economical to produce than natural auxins and find applications in agriculture.
  4. How are Gibberellins commercially produced, and what functions do they serve in plant growth?
    • Gibberellins are commercially produced from fungal cultures. They promote cell enhancement, ‘bolting’ in rosette plants, bud initiation, leaf and fruit growth, and may induce parthenocarpy. They also break bud and seed dormancy.
  5. What are some commercial applications of Gibberellins?
    • Gibberellins are used to promote fruit setting, increase berry size, and delay ripening in fruits. GA3, a specific type, is used in the brewing industry to enhance a-amylase production in barley for malting.
  6. How do Cytokinins affect plant growth, and what are their commercial applications?
    • Cytokinins promote stem growth, inhibit primary root development, stimulate lateral root growth, and delay leaf senescence. They find commercial applications in postponing the aging of fresh leaf crops, maintaining flower freshness, and breaking seed dormancy.
  7. What is the role of Abscisic acid in plants, and how is it used commercially?
    • Abscisic acid inhibits stem and root growth during stress, promotes bud and seed dormancy, and induces flowering in short-day plants. Commercially, it can be sprayed on tree crops to regulate fruit drop at the end of the season.
  8. How does Ethene influence plant growth, and what are its commercial applications?
    • Ethene inhibits stem and root growth during stress, breaks bud dormancy, promotes flowering in pineapple, and induces fruit ripening. It is applied to the rubber plant as ethephon to promote latex flow.
  9. What is the significance of delaying leaf senescence in plants, and which hormone is involved in this process?
    • Delaying leaf senescence is significant for maintaining the freshness of fresh leaf crops. Cytokinins play a role in postponing senescence, contributing to the prolonged shelf life of these crops.
  10. How do plant hormones contribute to agricultural practices and crop management?
    • Plant hormones are extensively used in agriculture for various purposes, such as enhancing fruit setting, regulating growth, preventing weed growth, delaying senescence, and improving storage life. Understanding their roles is crucial for effective crop management.
Further Reading:  Basic Techniques of Genetic Engineering in Plants

 

Summary: Hormones in Plants (Phytohormones) Tutorial

The tutorial on hormones in plants delves into the intricate world of phytohormones, highlighting their crucial roles in plant development and growth. Phytohormones, produced in minimal concentrations within plants, intricately manage various aspects, ranging from embryogenesis to reproductive development. The tutorial explores five major types of plant hormones:

  1. Auxins (Indole acetic acid or IAA):
    • Promote cell augmentation in stems and cellular division in the cambium.
    • Regulate root growth at different concentrations, inhibiting growth at higher levels.
    • Initiates bud formation in shoots and promotes apical dominance and fruit growth.
    • Can induce parthenocarpy and delay leaf senescence.
    • Inhibit abscission.
  2. Synthetic Auxins (NAA, 2,4 D):
    • Used for stimulating fruiting and preventing early fruit drop.
    • Acts as a selective weed killer in cereal crops and grass.
    • Widely applied in commercial settings for cost-effectiveness.
  3. Gibberellins (GA, GA3):
    • Commercially produced from fungal cultures.
    • Promote cell enhancement and division, ‘bolting’ in rosette plants, and bud initiation.
    • Break bud and seed dormancy, and may induce parthenocarpy.
    • Used in various industrial applications, including fruit setting and malting in the brewing industry.
  4. Cytokinins:
    • Stimulate stem growth and lateral bud development.
    • Hinder primary root development and promote lateral root growth.
    • Delay leaf senescence and promote stomatal opening.
    • Used in agriculture to postpone senescence in fresh leaf crops and break seed dormancy.
  5. Abscisic Acid:
    • Inhibits stem and root growth during physiological stress.
    • Induces bud and seed dormancy and promotes flowering in short-day plants.
    • Promotes abscission and stomatal closure under water stress.
    • Applied commercially to regulate fruit drop and extend storage life.
  6. Ethene (Ethylene):
    • Inhibits stem and root growth during stress and breaks bud dormancy.
    • Promotes flowering in pineapple and fruit ripening.
    • Applied industrially to promote latex flow in rubber plants.

The comprehensive tutorial not only introduces these plant hormones and their functions but also provides insights into their commercial applications, showcasing their significance in modern agriculture and horticulture practices.