5.4.3 Uses of Plant Hormones

Auxin

1. As weed killers

• Many weeds are broad-leaved
• Weedkillers, containing auxin, have been synthesised so they only affect broad-leaved plants
• The increased amount of auxin causes the cells to grow too rapidly
• This results in the weed dying

2. As rooting powders

• Plants with desirable features are cloned to make more plants with the same feature
• One way to clone a plant is to take a cutting from the original plant
• Rooting powder containing auxin is applied to it and it is placed in the ground
• Roots grow and the new plant begins to grow very quickly

3. To promote growth in tissue culture

• Another way to clone a plant is to use tissue culture
• Cells from the plant are taken are placed in a growth medium containing lots of nutrients
• Hormones such as auxins are added
• The cells begin to form roots and shoots

As ethene controls ripening, it is used in the food industry.

• Fruit is picked when it is not ripe
• It is firm which means that during transport it gets less bruised and damaged
• When it is needed to be sold, it is exposed to ethene and warmer temperatures
• Ethene is involved in controlling cell division and stimulates enzymes that result in fruit ripening.
• This reduces wastage as more fruit is suitable to be sold and it does not ripen too early

Gibberellins are used for:

1. Ending seed dormancy

• In the brewing industry, the germination rate of barley seeds is increased to make malt.

2. Promoting flowering

• Instead of requiring certain conditions such as longer days and low temperatures to flower, applying this hormone allows it to flower in any conditions and with bigger flowers.

3. Increasing fruit size

• The seeds in fruit produce gibberellins to increase fruit size.
• This means that seedless fruit is generally smaller.
• Seedless fruit can be sprayed with gibberellins to increase their size.