Gene Splicers Putting New Food On The Table

April 09, 1990|By Peter Gorner and Ronald Kotulak, Chicago Tribune.

To feed the world, the choice is plain: Either more farmland must be found or the productivity of existing farms must increase. Tillable acreage is fast disappearing in the United States, as at least a million acres of farmland each year vanish beneath houses, roads, factories and shopping centers. Then there is the soil erosion that blows or washes away some 24 billion tons of the world`s topsoil annually, roughly the amount on Australia`s wheatland.

``Worldwide, the potential for expanding the cultivated area profitably is limited,`` warns Lester R. Brown, president of the Worldwatch Institute.

``Food for the 921 million people to be added during the `90s will have to come from raising land productivity.``

Nowhere is the excitement over the new agriculture felt more keenly than in the thriving plant and crop biotech complex centered in St. Louis. In 1980 Monsanto, perhaps seeing the handwriting on the wall about coming restrictions on farm chemicals, decided to stake its future on products that need less of them.

``There was a sense of mission here when we walked in,`` says Robert Horsch, 36, a gr1984, Monsanto opened the doors to its futuristic $200 million Life Sciences Research Center on the western edge of the city, stocked the place with 1,100 scientists and unleashed them to do health care research and experiment with animals, plants and microbes. By 1986 Monsanto was spending $523 million in research, making it the world`s leading investor in biotechnology.

But to get under way, plant scientists first had to develop their own form of genetic engineering and find a vehicle to deliver new genes to the genetic material, or DNA, of plants.

For the answer, scientists turned to natural organisms-bacteria and viruses-that normally function by transferring some of their genes into plant cells. Bacteria genes are mostly packed into a single large chromosome, like a suitcase. But a few are contained in a smaller, circular structure that might be considered a handbag in comparison to the suitcase-like chromosome.

The handbag is called a plasmid, and it is the key to the genetic engineering of crops. Just as a handbag is more easily transferred than a suitcase from one airplane to another, plasmids more easily move from one bacteria to another, or from a bacteria to a plant cell. By splicing new genes into the plasmid handbags, scientists figured they would have a convenient vehicle to deliver genetic material into plant cells and produce desired traits.

After years of trial and error, researchers discovered a plasmid that delivered, but it had a drawback: It caused a kind of plasmid to make it harmless.

Next, scientists inserted genes for desired traits, such as virus resistance, into the now-tame plasmid. Then, when pieces of plant tissue were added to laboratory dishes containing the engineered plasmids, the latter mindlessly transferred the desired genes into the plants.

Using this system, Monsanto gene splicers designed a highly functional tobacco plant that borrowed a petunia gene. It makes the tobacco plant resistant to the weed-killer glyphosate, which Monsanto manufactures under the brand name Roundup.

Because glyphosate kills anything green that it touches, it can`t be applied to most crops during the growing season. Reasoned the Monsanto scientists: If the crops themselves could be engineered to be immune to the herbicide, farmers could apply it and the weeds would die while the crops thrived. Field tests have been under way for two years on glyphosate-tolerant tomatoes and on canola, a major source of vegetable oil. In the summer of 1988 Horsch and his colleagues introduced the trait into soybeans.

Using another strategy, geneticists are trying to engineer plants with insecticidal proteins. The key player here is Bt, a protein made by a naturally occurring bacteria that lives in soil.

Bt is harmless to people but deadly when it gets into the gut of an insect. Scientists isolated the bacterial gene that makes the Bt protein and inserted that gene into crop plants. The result was dramatic.

Imagine a picture-perfect tobacco plant growing in the sun. Along a broad leaf crawls a big tobacco hornworm caterpillar intent on devouring the plant for lunch. The insect starts to munch the leaf, then AARGH! Enzymes in its stomach react with Bt, causing paralysis and death. Because the genes affect only the plant leaves, not the fruit or vegetable, they should be harmless;

field tests have so far indicated that they are.

Biopesticides received worldwide headlines in 1987 with the first field test of genetically altered bacteria. Designed to inhibit ice formation, the bacteria alarmed biotechnology critics who said there was a chance the altered organisms could spread uncontrolled through the environment.