5.3 Application of Phytohormones in Agriculture
Phytohormones are chemical substances that play direct roles in regulating the growth and development of plant structures such as roots, stems, flowers, and fruits. In agriculture, both naturally extracted and laboratory-synthesised phytohormones are widely applied to increase crop yield, control growth habits, propagate plants, manage post-harvest storage, and coordinate fruit ripening.
Learning Objectives
- State and describe the agricultural applications of five major phytohormones: auxin, gibberellin, cytokinin, abscisic acid, and ethylene.
- Design and carry out an experiment to investigate the effects of ethylene on the ripening of fruits.
- Explain the role of phytohormones in commercial agricultural practices such as parthenocarpy, tissue culture, and post-harvest preservation.
Summary of Agricultural Applications of Phytohormones and Experiment 5.2 Setup
A comparative reference of the five phytohormones alongside an illustrated diagram showing the comparative setup of Bag A and Bag B.
Auxin
Rooting of cuttings, seedless fruits, weed control, potato dormancy, low-lying lush growth.
Gibberellin
Stem elongation, reversing dwarfism, larger grapes, breaking seed dormancy.
Cytokinin
Cell division in tissue culture, organogenesis, delaying cut flower senescence.
Abscisic Acid
Growth inhibition, seed dormancy, water retention through stomatal closure.
Ethylene
Rapid and uniform fruit ripening, simultaneous field flowering.
Short Explanation
What are phytohormones?
Phytohormones are powerful chemical regulators used across commercial agriculture to maximise yield, control developmental timing, and preserve produce quality.
Growth Promoters
Auxin, gibberellin, and cytokinin generally stimulate growth and organ formation. Auxin enables vegetative stem cuttings to strike roots and forms seedless fruits; gibberellin breaks seed dormancy and elongates stems to create larger fruit clusters such as grapes; cytokinin promotes cell division in micropropagation and keeps cut flowers looking fresh by slowing senescence.
Growth Inhibitors & Stress Regulators
Abscisic acid suppresses germination and growth, preventing premature sprouting and limiting water loss when temperatures rise.
Gas-Phase Ripening Agent
Ethylene is unique because it is a gaseous hormone. A ripe fruit naturally emits ethylene gas, which triggers nearby unripe fruits to ripen simultaneously and evenly.
Experiment 5.2
The tomato in Bag B ripens faster, changing colour from green to red/orange and turning softer compared to the tomato in Bag A. The ripe banana releases ethylene gas, which acts as a ripening hormone that accelerates the maturation and softening of the neighbouring tomato.
Try to Answer First
Answer in your mind, then press “Check Answer”.
State one specific agricultural application for gibberellin and one for cytokinin.
Based on Experiment 5.2, why is a ripe banana placed inside paper bag B together with an unripe tomato?
Explain how hormone X (abscisic acid) helps a plant retain water content when the surrounding temperature increases.
Common Mistakes
- Confusing the specific roles of auxin and cytokinin in tissue culture: auxin primarily encourages root formation when balanced with cytokinin, whereas cytokinin stimulates cell division and shoot/stem differentiation.
- Stating that plastic bags should be used for fruit ripening experiments: plastic bags trap moisture, promoting fungal growth and premature rotting rather than clean ripening; ventilated paper bags are correct.
- Assuming ethylene is applied only as a liquid spray: ethylene naturally acts as a gas that can accumulate in enclosed spaces to coordinate ripening.
Concept Misunderstandings
Growth inhibitors like abscisic acid are entirely harmful to agricultural production.
Abscisic acid is beneficial because it prevents premature seed germination during unfavourable conditions and induces dormancy in seeds and buds until ideal planting conditions return.
Parthenocarpy produces fruits that contain genetically modified seeds.
Parthenocarpy induced by auxin produces completely seedless fruits without fertilisation taking place.
Summary
- Phytohormones are natural or synthetic chemical regulators applied in modern farming and post-harvest handling.
- Auxin: Rooting of cuttings, seedless fruits (parthenocarpy), weed control, potato storage dormancy, low-lying lush plant growth.
- Gibberellin: Stem elongation, reversing dwarfism, increasing grape size, breaking seed dormancy in cold or dim environments.
- Cytokinin: Cell division and organogenesis in tissue culture, delaying cut flower senescence.
- Abscisic Acid: Growth inhibition, seed dormancy, water retention through stomatal closure.
- Ethylene: Rapid and uniform commercial fruit ripening, simultaneous field flowering.
Short Activity
Objective: identify the agricultural applications of phytohormones and the role of ethylene in fruit ripening.
A. Objective Quiz
Which phytohormone is applied by farmers to produce seedless fruits via parthenocarpy?
What is the primary reason for avoiding plastic bags in Experiment 5.2 when investigating fruit ripening?
B. Fill in the Blanks
In tissue culture techniques, is used together with auxin to stimulate cell division and form plant organs such as roots and stems.
Auxin is sprayed on potatoes during storage or distribution to induce so that sprouting is prevented.
C. Matching / Drag and Drop
Match each phytohormone to its correct agricultural application. On a phone, tap a choice first, then tap the matching box. Tap the Answer Choices area to return a selected item.
C. Match the Phytohormone to Its Agricultural Application
Write the correct phytohormone next to each application.
| Agricultural Application | Phytohormone |
|---|---|
| 1. Induces root growth on woody stem cuttings and prevents potato sprouting during storage | |
| 2. Used to produce larger grapes and treats mutated dwarf plants to reach normal heights | |
| 3. Delays leaf senescence in newly cut flowers and promotes cell division in tissue culture | |
| 4. Promotes commercial fruit ripening quickly and evenly and induces simultaneous flowering |
Answer choices: Auxin • Gibberellin • Cytokinin • Ethylene
