Use of plant hormones

There are many types of plant hormones. They are used in agriculture and horticulture to have a specific effect.

Auxins were the first class of plant hormones to be discovered. Their main function is to help plants grow and auxin stimulates plant cells to elongate. The apical meristem of a plant is one of the main places where auxin is produced. The apical meristem is also the location that all other parts of a plant grow from - the stem, leaves, and flowers.

Auxins are one specific group of hormones that are used:

  • as weed killers
  • as rooting powders

Weed killers

Image of a dandelion

Selective weed killers kill some plants, but not others. This can be useful for getting rid of dandelions in a lawn without killing the grass. The selective weed killer contains a growth hormone that causes the weeds to grow too quickly and die. Because the weeds have broader leaves, the weed killer is absorbed in larger quantities by the weeds than it is by the grass. Selective weed killers can reduce biodiversity within treated areas due to specific plants being killed.

Rooting powder contains plant hormones to promote growth.

A small potted plant bring dipped in rooting powder

Plant cuttings can be dipped in hormone rooting powder before planting.

Synthetic plant hormones are used to control plant growth. For example, rooting powder contains growth hormones that make stem cuttings develop roots quickly.

Other plant hormones

Gibberellins are a group of plant hormones responsible for growth and development. They are important for initiating seed germination. Low concentrations can be used to increase the speed of germination, and they stimulate cell elongation so plants grow taller.

They are naturally produced by barley and other seeds.

Sprouting bean plants
Sprouting bean plants

Gibberellins can be used to:

  • end seed dormancy
  • promote flowering
  • increase fruit size
A poinsettia
Gibberellins promote flowering as shown in this poinsettia

Seed dormancy must be broken for seeds to germinate, and this can be done by using gibberellins.

Seedless grapes
Seedless grapes are sprayed with gibberellins to increase their size

Gibberellins can promote flowering, which can result in more financially profitable flowers to sell due to the increased speed of flower growth. More attractive flowers and larger specimens are also produced.

Flowering also has an impact on the rate of fruit growth. Gibberellins are used in the production of seedless fruit such as seedless grapes, which are normally sprayed with gibberellin to increase the size of each grape.

Controlling fruit ripening

Unripe bananas
Ethene speeds up the ripening of bananas

Some hormones slow the ripening of fruits and others speed it up. These hormones and their inhibitors are useful for delaying ripening during transport or when fruit is displayed in shops. Ethene is a plant hormone which causes fruit to ripen.

Ethene is used routinely within the food industry to provide controlled ripening during storage and transport or when fruit is displayed in shops, in sealed packages. Bananas are picked when they are green and unripened. Ethene is a hydrocarbon gas and it speeds up ripening in bananas and other fruit. The effect of ethene released from bananas is clearly visible if you keep them in a bowl with other fruit, as it causes other fruits to ripen very quickly.

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