Commercial Uses of Plant Hormones

Plant hormones have many practical applications in agriculture and horticulture. Understanding how auxins, gibberellins and ethene are used commercially is an important part of the Edexcel GCSE Biology (1BI0) specification. This lesson covers the main commercial applications and the science behind them.

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Overview of Plant Hormones Used Commercially

Hormone	Natural role	Commercial uses
Auxins	Cell elongation, tropisms	Rooting powder, selective weedkillers
Gibberellins	Seed germination, stem elongation	Seed germination, fruit production, promoting flowering
Ethene	Fruit ripening	Controlling ripening during transport and storage

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Auxins: Commercial Uses

1. Rooting Powder

When gardeners want to grow new plants from cuttings (pieces of stem cut from a parent plant), they use rooting powder (or rooting gel/liquid), which contains synthetic auxins.

How it works:

1. A healthy stem cutting is taken from the parent plant
2. The cut end is dipped into rooting powder containing auxin
3. The cutting is placed in compost or a growing medium
4. The auxin stimulates the cells at the cut end to differentiate and produce roots
5. Once rooted, the cutting grows into a new plant that is genetically identical to the parent (a clone)

Why is this useful?

• Allows growers to produce many identical plants (clones) from a single desirable parent plant
• Faster than growing from seed
• Ensures the new plant has the same characteristics as the parent (important for commercial crops and ornamental plants)

Exam Tip: Remember that rooting powder contains auxin, which promotes root growth. Without it, many cuttings would not develop roots quickly enough to survive.

2. Selective Weedkillers (Herbicides)

Auxin-based weedkillers are used to kill broadleaf weeds (such as dandelions and daisies) in lawns and cereal crops without harming narrow-leaved plants (such as grasses and cereals).

How they work:

1. The weedkiller contains a high concentration of synthetic auxin
2. When sprayed on a field or lawn, the auxin is absorbed by all plants
3. Broadleaf (dicot) weeds absorb much more of the auxin due to their larger leaf surface area
4. The excess auxin causes uncontrolled, rapid growth in the weeds — cells elongate and divide abnormally
5. The weed cannot sustain this growth and dies
6. Grasses and cereals (monocots) have narrow, upright leaves that absorb much less auxin, and they are also less sensitive to auxin — so they are unharmed

Why is this useful?

• Removes weeds that compete with crops for light, water and minerals
• Increases crop yield
• Does not damage the crop plants

Plant type	Leaf shape	Auxin absorption	Effect of weedkiller
Broadleaf weeds	Wide, flat	High	Uncontrolled growth → death
Grasses/cereals	Narrow, upright	Low	Unaffected

Exam Tip: The key mechanism is that high auxin concentration causes uncontrolled growth that kills the weed. Do not say it simply "poisons" the weed — describe the biological mechanism.

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Gibberellins: Commercial Uses

Gibberellins are a group of plant hormones that promote various aspects of growth and development. They have several important commercial applications.

1. Promoting Seed Germination

Seeds contain starch reserves that provide energy for the growing embryo during germination. Gibberellins play a crucial role in this process:

1. When a seed absorbs water, the embryo produces gibberellin
2. Gibberellin signals the aleurone layer (in cereal seeds) to produce amylase enzymes
3. Amylase breaks down the starch stores into maltose (a sugar)
4. The sugars provide energy for the growing embryo through respiration
5. The seedling emerges from the seed

Commercial application:

• In the brewing industry, barley seeds are treated with gibberellins to speed up germination and increase the production of amylase and maltose (which is then fermented to produce alcohol)
• Gibberellins can be used to break dormancy in seeds, allowing germination at times when the seed would naturally remain dormant

2. Stimulating Flowering

• Some plants require specific conditions (e.g., certain day length or cold period) to flower
• Applying gibberellins can induce flowering without these conditions being met
• This allows commercial growers to produce flowers and fruits out of season, extending the growing period and increasing profits

3. Increasing Fruit Size

• Gibberellins can be sprayed on developing fruits to increase their size
• In the grape industry, gibberellin application produces larger, more elongated grapes with longer stalks, improving appearance and value

4. Producing Seedless Fruit

• Gibberellins can stimulate fruit development without fertilisation (a process called parthenocarpy)
• This produces seedless fruits — e.g., seedless grapes, seedless citrus fruits
• Seedless fruits are preferred by consumers and are easier to eat

Gibberellin application	How it works	Commercial benefit
Seed germination	Triggers enzyme production to break down starch	Speed up malting (brewing), break dormancy
Flowering	Induces flowering without specific environmental cues	Out-of-season flower and fruit production
Fruit size	Promotes cell elongation in fruit	Larger, more attractive fruits
Seedless fruit	Stimulates fruit growth without fertilisation	Consumer preference, easier to eat

Exam Tip: Gibberellins have MULTIPLE uses. Be prepared to describe at least two or three. The brewing/germination application is the most commonly examined.

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Ethene: Commercial Uses

Ethene (also written as ethylene — C₂H₄) is a gaseous plant hormone that promotes fruit ripening.

Natural Role

• As fruits mature, they produce ethene
• Ethene triggers the ripening process: colour changes (e.g., green to red in tomatoes), softening of flesh, development of flavour and aroma, conversion of starch to sugars
• Ethene from one fruit can trigger ripening in nearby fruits — this is why "one bad apple spoils the barrel"

Commercial Application: Controlling Ripening

The commercial fruit industry relies heavily on controlling ethene levels:

Step 1: Harvesting

• Fruits such as bananas, tomatoes and avocados are picked when they are still unripe (green and hard)
• Unripe fruit is more durable and resistant to damage during transport

Step 2: Transport

• Fruits are transported in controlled atmosphere conditions:
  • Low temperature (slows metabolism)
  • Low oxygen (slows respiration)
  • Low ethene levels (prevents premature ripening)
• Some fruits are stored in atmospheres with ethene-absorbing chemicals

Step 3: Ripening on Demand

• When the fruit arrives at its destination (e.g., a supermarket distribution centre), it is placed in ripening rooms
• The rooms are flooded with ethene gas at controlled concentrations and temperatures
• The ethene triggers rapid, uniform ripening
• This allows supermarkets to sell perfectly ripe fruit at the desired time

Why is this useful?

• Fruits can be shipped over long distances without spoiling
• Ripening can be timed to match consumer demand
• All fruits in a batch ripen at the same time, producing a uniform product