5.4.2 Use of plant hormones

People Use Plant Hormones in Farming and Gardening

1. Plant hormones can be extracted from plants or made artificially and used in agriculture and horticulture.
2. They are used to control plant growth, for example to raise crop yields or to produce plants for sale.
3. The three you need are auxins, ethene and gibberellins.

Using Auxins

1. As weed killers
   1. Auxins are used as selective weed killers; broad-leaved weeds absorb more and are sent into uncontrolled growth and die, while narrow-leaved cereals and grasses are largely unharmed.
2. As rooting powders
   1. Dipping the cut end of a stem cutting in auxin rooting powder makes roots grow, so a gardener can quickly produce many identical plants.
3. In tissue culture
   1. Auxins promote growth and cell division in tissue culture, helping to grow many identical plants (clones).

Using Ethene

1. Ethene is used in the food industry to control the ripening of fruit during storage and transport.
2. Fruit is picked and transported while it is unripe and firm, so it is less easily damaged.
3. Ripening can be delayed in storage by removing ethene, then ethene is added to ripen the fruit just before it is sold.

Using Gibberellins

1. End seed dormancy
   1. Gibberellins make seeds germinate when growers want them to, for example the barley used in brewing and malting.
2. Promote flowering
   1. They can make plants flower when they otherwise would not, or flower all year round.
3. Increase fruit size
   1. They make fruit grow larger, for example spraying seedless grapes, which would otherwise be small because they have no seeds to make gibberellins.