6.16B - Commercial uses of plant hormones

6.16B - Higher-only: commercial uses of auxins

Higher-only Biology (6.16B). Plant hormones are chemical messengers that coordinate growth and development. Growers can apply hormones or synthetic growth regulators to produce a useful response. A commercial explanation connects what is treated with the resulting change in the plant.

Selective weedkillers

Some weedkillers contain synthetic auxins. At the concentration used as a herbicide, they cause abnormal, uncontrolled growth in susceptible broad-leaved weeds. This disrupts the tissues that transport water and other substances, and the weeds die.

Grasses and many cereal crops are much less affected by these selective auxin weedkillers. A grower can therefore kill broad-leaved weeds among grass or cereal plants while leaving the crop relatively unharmed. Selective does not mean that the chemical is harmless to every non-target plant; it means that the target weeds are more susceptible than the crop in that use.

Rooting powders

A cutting is a piece of a parent plant used to grow a new plant. Its cut end can be dipped into a rooting powder containing auxin before it is placed in a growing medium. The auxin stimulates the formation of roots from the stem, so the cutting establishes more quickly or reliably. The powder triggers a growth response; it is not simply supplying the cutting with mineral ions.