In this chapter of AS/A-level Biology, we will learn about how plant hormones are used commercially .
Auxins
In AS/A-level Biology, Artificial auxins can prevent leaf and fruit ‘drop’, promote flowering and high concentrations of auxins can promote fruit drop.
- Taking Cuttings – dipping the end of a cutting in a rooting powder (containing auxins, a fungicide and talcum powder) before planting to encourage root growth.
- Seedless Fruit – treating unpollinated flowers with auxin can promote growth of seedless fruit (parthenocarpy), by promoting ovule growth, which triggers automatic production of auxin by tissues in developing fruit.
Herbicides – artificial auxins are used as herbicides to kill weeds. They promote shoot growth so much that the stem cannot support itself, buckles and dies.
Gibberellins |
- Brewing– gibberellins stimulate barley seeds to hydrolyse starch stores into maltose, by encouraging the aleurone layer of the seed to produce more amylase enzymes. This sugar is important in beer manufacture (as malt).
- Sugar Production – gibberellins stimulate growth between the nodes (where sugar is stored), making the stems elongate in sugar canes, so that more sugar is available from each plant.
- Plant Breeding:
- Gibberellins can induce seed formation in young trees and in biennial plants (flower only in their second year of life, e.g. sugar beet).
- Inhibiting gibberellin synthesis is useful to keep flower short and stocky (e.g. poinsettias) and to prevent lodging (where stems bend over because of the weigh of water collected on the ripened seed heads) in crop plants.
4. Fruit Production:
- Gibberellins delay senescence in citrus fruit – fruits can be left unpicked making them available in the shops longer.
- Gibberellins and cytokinins elongates apples and improves their shape.
- Gibberellins elongates stalks of bunches of grapes allowing grapes to grow bigger.
Cytokinins |
- In AS/A-level Biology, they can delay leaf senescence and are sometimes used to prevent yellowing of lettuce leaves.
- Used in tissue culture to help mass-produce plants. They promote bud and shoot growth from small pieces of tissue taken from a parent plant.
Ethene
In AS/A-level Biology, 2-chloroethylphosphoric acid can be sprayed in solution as ethane is a gas. It is easily absorbed and slowly releases ethane inside the plant. Commercial uses include:
- Promote fruit ripening in apples, tomatoes, citrus fruits.
- Promote fruit drop in cotton, cherry and walnut.
- Promote female sex expression in cucumbers, reducing the chance of self-pollination.
- Promoting lateral growth in some plants, yielding compact flowering stems.
Inhibiting ethane synthesis (by storing in a low temperature with little oxygen and high carbon dioxide concentration) can prevent fruit ripening, which is useful when transporting fruits.
This is the end of this topic!
