SCIENCE: FEEDING THE WORLD

Can the genetic engineering of food plants improve on nature? John Newell reports

Genetic engineering is producing an ever-growing number of new opportunities to feed the world better, which would have been unthinkable 20 years ago. But, as two recent advances make clear, these opportunities have the potential to do harm as well as good to the economies of developing countries.

Scientists have discovered how to use genetic engineering to make tropical crops resistant to low temperatures, so they could be grown in temperate countries. In the short term, this may disadvantage growers in the tropics by allowing new competition from richer countries. But experts believe that, in the long term, it is among the developments that are essential in order to feed the world's expanding population.

Other scientists have discovered how to add genes to cassava, the starchy root used to make tapioca, which is the staple food of 500 million people in Africa and Asia. The breakthrough means it will be possible to make new varieties of cassava resistant to the insect pests and viral diseases that prey on the crop today.

This is good news for tropical farmers. But it also opens the way to engineering cassava to produce starch to be used as the raw material for new biodegradable plastics. These could be the basis of profitable industries in the tropics. But competition from such crops could reduce the acreage of cassava grown as an essential food for some of the world's poorest people.

These opportunities and problems are coming about because genes can now be moved into crop plants, not just from any other plant, but from any other living thing. Geneticists regard all life-forms as froth on the surface of the river of DNA, the stuff genes are made of, flowing down the generations. DNA, having constructed all forms of life as its survival machines, is more or less equally at home in all of them.

The ability to move DNA from one living thing to almost any other living thing, sometimes called genetic engineering, is beginning to revolutionise plant breeding. In the past, no matter how badly breeders wanted to make their crops resistant to pests, viruses, or drought, the only place where they could look for a gene that might provide the wanted property was in the wild relatives of the crop plant. Only their pollen would fertilise the ova of the cultivated crop. If the wild relatives didn't have the wanted gene, too bad.

Now, genes can be taken from any living thing and put into plants. To give an idea of its scope, genes for a natural antifreeze have been taken from flatfish, which use it to avoid freezing in Arctic waters, and put into strawberries to protect them against frost.

The techniques needed to do this are still far from perfect where the world's most important crops, the cereals, are concerned. The best available means of getting genes into cereals is literally to shoot them into the plants using a miniature gun, firing minute golden bullets coated with genes. The success rate isn't very high. But once genes have been successfully added to a plant, it can be bred from to produce any number of offspring.

Many crops other than cereals can be engineered much more easily using a natural genetic engineer, a bacterium called Agrobacterium tumefaciens. Genetically engineered cassava and tropical crops for temperate countries are two of the most recent products of its skills. The first crop to have been made resistant to freezing temperatures is tobacco. The leader of the low-temperatures gene team is Dr Osamu Ishikazi-Nishizawa of the Carnegie Institution in Stanford, California. He and his colleagues took the genes they needed from a bacterium, Anabaena nidulans, which is able to survive at freezing temperatures.

The gene Dr Ishikazi-Nishizawa transferred into tobacco from A. nidulans has the effect of softening the tobacco plant's fats by making them less saturated with hydrogen. Saturated fats harden near freezing point, which is why, for example, the saturated animal fats in butter are hard to spread when the butter comes straight from the fridge.

Dr Ishikazi-Nishizawa's gene makes an enzyme that reverses saturation - makes the fats unsaturated. No higher plants possess an enzyme that can unsaturate fats, so freeze-resistance could never have been introduced into any crop by conventional plant breeding. But now that tobacco has been used to show the way, it should be possible to introduce the gene into literally any plant, using either A. tumefaciens or the gene gun.

The next step will be to introduce the gene into food plants. As well as making them cold-resistant, it will also make the plants healthier to eat, by reducing their content of saturated fats (linked to a higher risk of heart disease). It will also allow, what are now tropical crops, to be grown in temperate countries.

But who will benefit? There has to be a danger that making it easier to grow tropical crops in the temperate world, and engineering the temperate version to be more attractive to health-conscious Western consumers, will disadvantage traditional growers in the poorer tropics. Dr Ishikazi-Nishizawa believes that may happen in the short term. But, along with other experts, including the Food and Agriculture Organisation of the UN, he believes that it will only be possible to feed the world's ever-growing population by improving crops with the use of genetic engineering.

Similar dilemmas may come about through the crucial breakthrough made by British, American and Swiss scientists who, between them, have shown it is possible to use similar techniques to add extra genes to cassava. Cassava is a staple food in tropical Africa. But cultivation is severely hampered by the insect pests and viral and fungal diseases that ravage the crop. Attempts by breeders to build in resistance to pests and diseases, by finding varieties of cassava with natural resistance, have met with little success.

Being able to add genes to cassava from other sources opens up an astonishing range of new possibilities. Dr Johanna Puonti-Kaerlas of the Swiss Federal Institute of Technology says: "The first thing we would like to tackle is disease resistance. Then, we'd like to try to give cassava resistance to its insect pests, like the mealy bug, using a gene for a natural pesticide. We'd also like to increase the protein content of the root, which is very low for a staple foodstuff."

The gene for virus resistance has already been found, and should go into cassava in the next few months. The gene for a natural pesticide will come from Bacillus thuringiensis, a bacterium which produces just such a pesticide.

Eventually, viruses and pests will probably evolve their way past these new obstacles. There are no, or precious few, permanent victories in such wars. But if scientists don't keep coming up with new weapons, they aren't standing still. They are losing ground.

Dr Nigel Taylor of Bath University sees genes being added to cassava for still more purposes. "When you pull the roots out of the ground to harvest them", he says, "they deteriorate very rapidly. This means they have to be processed in just one or two days, otherwise the roots will rot. We'd like to lengthen the time they last out of the soil, to make it easier for farmers to market their crops and get a cash return.

"And there are problems with toxicity. Some varieties of cassava contain compounds that release cyanide into the body and these have to be processed to remove it all before they can be eaten. It should be possible to engineer cassava to get rid of the cyanide (though some people think it ought to be left because it's really cassava's natural means of pest control.)"

Nigel Taylor played a vital role in this research, by persuading complete cassava plants to grow from single cells taken from ordinary plant tissue, after it had genes added to it. Dr Taylor worked with a French scientist, Dr Christian Schopke and American colleagues at the Scripps Research Institute in La Jolla, California, who used the "gene gun" technique to add the genes to cassava. The Swiss team's parallel work used A. tumefaciens to get the genes in. Both approaches worked.

None of this research has been supported by private companies. This has made it easy for the scientists involved to set up an international "cassava network", to ensure that when improved varieties of cassava have been created, they are made freely available to the nations most in need.

But further in the future lurks the unsettling and controversial prospect of altering cassava's genes for starch to create a suitable raw material for producing biodegradable plastics.

In its favour, such materials will be produced from renewable plants, rather than non-renewable fossil fuels, as well as being biodegradable. In addition, these non-food crops could form the basis of new, highly profitable industries for the tropical developing world. And these are the sorts of environmental arguments which are becoming more compelling as time goes on.

Alternatively, in the hands of multinational chemical companies, cassava grown to manufacture plastics could end up replacing cassava grown for essential, staple food, benefiting only people in the richer, developed nations.

The genetic genie is well and truly out of the bottle now, and the benefits he can provide are too overwhelming for anyone responsible to want to put him back - not that that would be possible in any case. But these examples show that medicine is not the only area where our new ability to reshape life needs to be controlled by more than just market forces. !