You will find out:

> about producing transgenic plants

> costs and benefits of genetic modification of crop plants

> about flavonoids in purple tomatoes

> about genes for insect resistance in crop plants

Anti-cancer plants?

Flavonoids are found only in plants. They give flowers and fruits their red, blue and purple colours. It is thought that they may help to prevent heart disease and some types of cancer.

Figure 1: What gives vegetables their bright colours?

Creating transgenic plants

Plants that have been genetically modified (GM) to create plants with beneficial characteristics obtained from the genes of other organisms are called transgenic plants.

Crops can be modified advantageously to:

> resist herbicides, so that insects can be killed but not the crop

> grow in places where rainfall is low

> resist the microorganisms causing crop diseases

> produce substances that kill their own insect pests.

There are concerns, however, that pests and diseases will develop a resistance to the modified crops.

GM technology allows us to improve the quality of food as well as the amount of it. The introduction of flavonoids in purple tomatoes is an example.

Scientists have isolated genes encoding flavonoids from snapdragon plants and inserted them into tomatoes. The result is modified purple tomatoes with nearly three times the flavonoid content of unmodified red tomatoes.

A study published in a scientific journal found that mice who ate the modified tomatoes lived longer and there are hopes that this 'superfood' will provide health benefits to humans. However, costly crops such as these are expensive to buy and are, in the short term at least, likely to be available only to wealthy consumers in developed countries.

Costs and benefits of GM crops

To feed the 6.7 billion people living in the world today, new approaches to producing more food are needed. This is particularly important in developing countries where harsh climate and poor soil can make growing crops difficult and food is sometimes in short supply.

A review by the UK government into the costs and benefits of GM crop cultivation over the next 10 years concluded that while there could be some advantages, any economic benefit is likely to be limited by the negative view of the public and retailers.

Question

1. What is a transgenic plant?

2. Explain the advantages of eating purple tomatoes in developed and developing countries.

Genetic modification of crops

A method of creating a transgenic plant is by using a common soil bacterium called Agrobacterium tumefaciens as a vector:

> Agrobacterium's plasmid is called the Ti plasmid.

> Ti means 'tumour inducing'. It causes the cells of a plant infected with Agrobacterium to multiply more quickly than usual.

> A tumour-like mass of solid tissue (a crown gall) develops.

> The Ti plasmid is used as a vector for useful genes.

> The cells of the crown gall formed from genetically engineered Agrobacterium each contain the Ti plasmid with its useful gene.

> Small pieces of the crown gall can then be cultured and develop into small plants.

> The cells of each of these plants carry a genetically engineered Ti plasmid.

Figure 2: A crown gall growing on a chrysanthemum plant. What is a crown gall?

Figure 3: Genetically modifying crop plants with a herbicide resistance gene helps farmers to control weeds more efficiently.

Questions

3. Describe what happens when a plant becomes infected with Agrobacterium tumefaciens.

4. GM crops and GM food can stir up fierce debate in countries like the UK where there is enough food. Discuss whether the issues are the same for developing countries where food is in short supply.

Bacterial insecticides (Higher tier only)

Globally, 40% of the crops grown each year are damaged or eaten by insects. Insecticides are used to protect crops, however, they also kill other wildlife, are harmful to humans and costly to use.

The soil bacterium Bacillus thuringiensis produces a toxin called Bt insecticidal crystal protein (Bt ICP). The toxin kills a variety of insect pests. For example, it will attack the gut of a leaf-eating caterpillar. The caterpillar stops eating and dies. Bt ICP also kills the larvae of flies and beetles.

The gene from B. thuringiensis encoding Bt ICP is inserted into the Ti plasmid of Agrobacterium. Crop plants infected with the GM bacterium develop crown galls. Pieces of tissue cut from the galls are cultured and grown into plants that produce their own Bt ICP toxin. The plants are able to resist insect attack.

Advantages of Bt-modified crops

Bt ICP is selective: different versions of the toxin kill different insect species and only those species. This means that it is possible to target particular pest insects and not harm beneficial species. Also, Bt ICP is harmless to humans, other mammals, birds and fish.

Different studies suggest that growing Bt-modified crops can reduce the harmful impact of insecticides by up to 24%. The advantages arise because:

> the toxin is produced within the modified plants and only affects the insects feeding on them

> modified plants produce enough toxin to kill the insects feeding on them, replacing the need to use insecticides.

Disadvantages of Bt-modified crops

Other studies focus on the limitations of Bt-modified crops. Perhaps most important is the appearance of Bt-resistant strains of pest species. The development is an example of evolution in action. The population of any pest species will contain a few individuals resistant to the control measures taken against them. These individuals survive and produce offspring also with the resistance characteristic.

Questions

5. Draw a flow diagram to show how the gene encoding Bt ICP and the Ti plasmid of Agrobacterium tumefaciens are used in the culture of insect-resistant plants.

6. Discuss the significance of the appearance of Bt-resistant strains of pest species.

Soil bacteria
Ti plasmid vector
GM crop debate
Flavonoids
Bt GM crops