Lecture Seven

Commercial use of plant hormones

Selective Weed killers

• Plant hormones can be extracted or artificial copies can be made. They can be used as weed killers, to grow cuttings or to ripen fruit.

• Most weeds growing in fields of crops or in a lawn are broad leaved. However, grasses and cereals have narrow leaves.• Selective weed killers have been developed from plant growth

hormones which only affect the broad leaved plants.• They disrupt their normal growth patterns which soon kills them,

leaving the grass and crops untouched.

Growing Cuttings

• A cutting is part of a plant that has been cut off it. • Normally if you stick cuttings in the soil they will not grow, but if you

add rooting powder (which contains a plant hormone) they will produce roots rapidly and start growing in new plants.• This enables growers to produce lots of clones of a really good plant

very quickly.

Ripening Fruit

• Plant hormones can be used to delay the ripening of fruits, either when they are still on the plant or during transport to the shops.• This allows the fruit to be picked while its still unripe, therefore firmer

and less easily damaged.• Ripening hormone is then added and the fruit will ripen on the way to

the supermarket so that it is perfect when it reaches the shelves.

Controlling Dormancy

• Lots of sees wont germinate (start growing) until they have been through certain conditions e.g. cold weather, dryness etc. This is called Dormancy.• A hormone called Gibberellin breaks this dormancy and allows the

seed to germinate.• Commercial growers can treat seeds with Gibberellin to make them

germinate at times of the year when they would not usually.

Quiz time !!

Name three things plant hormones can be used for commercially.Selective weed killers target which leaved plants?What is a cutting?How does plant hormones enable the growth of cuttings?How can plant hormones control the ripening of fruit?What is meant by the term “dormancy”?What is meant by the term “germinate”?What is the name of the hormone that can be used to allow seeds to germinate?