Commercial Use of Plant Hormones (OCR A Level Biology)

• As the growth and development of plants is controlled by hormones, the use of these hormones is of great interest to those growing plants on a commercial scale
• Hormones can be used to benefit commercial plant growing in a variety of ways, including:
  • As selective weed killers
  • As rooting powders
  • To control ripening

Selective weed killers

• Although auxins are normally growth-promoting, in high enough concentrations they can cause such rapid growth that plant tissues (e.g. the roots) become distorted and damaged, allowing pathogens to enter the plant
• Synthetic auxins can be used for this purpose and are applied to plants in concentrations 100 times greater than the natural hormones that are found in plants
• This treatment is effective against weeds that occur in fields of cereal crops or grass lawns, as grasses are significantly less sensitive to these selective weed killers than broadleaved weeds and so remain behind as the weeds die

Rooting powders

• At low doses, auxins can be used to stimulate cuttings to grow new roots
• These auxins, present at the correct dosage, are sold commercially in the form of rooting powders
• The lower end of the cutting is dipped in the powder before being planted in compost and with the correct environmental conditions, roots begin to grow shortly afterwards
• This technique is often used by florist businesses (commercial flower-sellers)

The control of ripening

• Ethene can be used to stimulate fruit to ripen
• This is often used for fruits that are delicate and soft when they are ripe (e.g. bananas and tomatoes) and that can be easily damaged during transport as a result
• Instead, these fruits can be harvested when unripe (and therefore harder), transported and then ripened artificially using ethene during transport or when they have arrived at their destination

Other uses

• Auxins and gibberellins can be used to make unpollinated flowers develop fruit (in nature, this can only normally occur once a flower has been pollinated and fertilised)
• This is often used in the production of seedless fruits (e.g. seedless grapes)
• These are known as parthenocarpic fruits (fruits formed without fertilisation)
• Auxins can also be used to stop trees from dropping their fruit before it has been harvested (dropped fruit is no longer of use as they become bruised and soon rot on the ground)