4.13 Plant Hormones - Comercial Uses

Question 1

Give three examples of how auxins can be used commercially

Answer 1

• They can be used to help cuttings grow. Normally, if you stick cuttings in the soil they won’t grow, but if you add rooting powder, which contains auxins, they will produce roots rapidly and start growing as new plants. This enables growers to produce lots of clones of a really good plant very quickly.
• They can be used to stimulate growth in plant cells. For example, if you had a collection of plant cells in a tissue culture, you could grow lots of plant clones by using a growth medium that contains auxin (in addition to the other nutrients that plants need).
• They can be used to kill weeds. If you add enough auxins, they can completely disrupt a plant’s growth patterns, which causes it to die. Most weeds are broad-leaved plants, whereas most commercial plants are narrow-leaved plants. This means we can develop selective weedkillers that we can spray everywhere but only kill the broad-leaved weeds.

Question 2

What is dormancy?

Answer 2

When seeds won’t germinate until they’ve been through certain conditions (e.g. a period of cold or of dryness).

Question 3

Give three examples of how gibberellins can be used comercially

Answer 3

• They can be used to break dormancy and allows seeds to germinate. By exposing the seeds to gibberellins, farmers can induce germination at times of the year when it wouldn’t normally happen. This means that they can grow multiple crops per year and also ensures all of the plants start growing at the same time.
• Gibberellins trigger a plant response called ‘bolting’ in response to a cold spell or lack of water. This is when a plant produces lots of flowers in an attempt to reproduce before it dies. This means commercial growers can use gibberellins to make plants flower earlier than they would usually do so, or under conditions in which they wouldn’t usually flower.
• Gibberellins can make fruits grow larger. This is particularly useful for seedless varieties of fruit, which naturally don’t grow as large as it’s seeded relatives. Gibberellins make sure that their fruits grow well.

Question 4

What is ethene produced by?

Answer 4

Aging leaves

Question 5

Give two examples of how ethene can be used comercially

Answer 5

• Ethene can be used to stimulate the shedding of leaves. It stimulates cells that connect the leaf to the rest of the plant to expand - this breaks the cell walls and causes the leaf to fall off the plant. Commercial growers sometimes use ethene to remove the leaves from a crop (e.g. cotton) before it’s harvested. This makes collecting the seeds or fruits easier.
• Ethene also stimulates enzymes that cause fruit to ripen. This means ethene can be used to control the ripening of fruits either while they are still on the plant, or during transport to the shops. The fruit is picked while it’s still unripe (and therefore firmer and less easily damaged) and ethene gas is added. The fruit then will ripen on the way to the supermarket and be perfect just as it reaches the shelves.

Question 6

Auxins stimulate cells to grow and divide, so how can they be used as weedkillers?

Answer 6

If large amounts of auxins are added to other plants, it can disrupt their growth process by overstimulating them. This can kill the plant.

Question 7

What is the benefit of selective weedkillers?

Answer 7

They kill some plants but not all.

Question 8

Which plant hormone can stimulate a plant to germinate?

Answer 8

Gibberellin

Question 9

Which plant hormone is responsible for inducing fruit to ripen?

Answer 9

Ethene

Question 10

Explain how ethene is used in the transport of food

Answer 10

Ethene stimulates fruit to ripen. Fruit is picked unripe so that it’s still hard which means it isn’t damaged during transport or storage. Ethene gas can then be used to stimulate the enzymes involved in ripening the fruit so that it’s soft for consumers.