RESEARCHERS in the United States and Britain are waging an all-out battle against the mushy tomato.
You know the kind. They look just right until you pick them up. Then they split and ooze. Mouth-watering turns to plain watery.
Traditional breeders have pushed tomatoes a long way. Today's varieties have less water, more solids, and tougher skins. But mushiness is buried deep into the genetic code of a tomato. Many scientists think biotechnology can change that.
Calgene Fresh Inc., in Evanston, Ill., has gotten the most publicity. By next year, it hopes to begin selling Flavr Savr, a bio-engineered tomato. The company claims that its new tomato will take twice as long to ripen after picking as today's varieties. That could be a tremendous boon to supermarkets.
Commercially grown tomatoes are typically picked green. Even those with just the slightest pink are discarded, because they'll get mushy before reaching the store.
While some green ones have developed their full flavor, tomato pickers sometimes harvest immature ones without much flavor.
But at the supermarket, they all look ripe. That's because supermarket tomatoes are usually treated in an ethylene chamber. Ethylene is the gas that tomatoes emit to turn themselves red. Immature tomatoes don't create much ethylene, so the chamber does it for them.
Timing is crucial. Once picked, most tomatoes last only one or two weeks before they're too mushy to sell. Distributors can lengthen that time by refrigerating them, but that spoils their taste.
By getting tomatoes to ripen more slowly, commercial growers could pick their fruit later, when they're sure it has developed its full flavor.
Calgene Fresh, a subsidiary of the biotechnology firm Calgene Inc. in Davis, Calif., hopes to begin selling its product next year. Approval by the US Food and Drug Administration is pending.
The key to Calgene's Flavr Savr is polyglactaronase. The PG gene, as it's called, creates an enzyme by the same name. Normally, the PG enzyme develops quickly in a tomato and begins to break down its solids. That's what turns the fruit mushy.
But Calgene researchers have managed to turn that process off. They do it by cloning the PG gene, turning it around so that it's "backward," and reinserting it into the tomato seed. This backward orientation is known as the "antisense" direction.
When it's time for the tomato to start softening, the PG gene sends out its traditional genetic message. But the altered PG gene in the tomato sends out its antisense message. Result: The messages cancel each other out. Most of the PG enzyme doesn't get produced. The Flavr Savr's mushiness is delayed.
Calgene's tomato will likely be the first major bioengineered agricultural plant to hit the market. More such products will trickle out of biotechnology labs in the next several years. Besides Calgene, researchers in Britain, at Monsanto Company, the University of California, Ohio State University, and elsewhere are also working on tomatoes.
Monsanto researchers are trying to get tomatoes to produce less ethylene, the ripening gas. They have already identified a gene that slows down the production of ethylene. By inserting it into the tomato, they claim they can slow the ripening process from two weeks to four or five. Such products could move into store shelves in the next few years, Monsanto scientists say.
Why tomatoes? Because they're part of a family of plants that is easier to manipulate than, say, corn. "The corn people are finding it so much more difficult," says Michael Knee, professor of horticulture at Ohio State.
Work is also going on with other members of the nightshade family, which includes petunias, tobacco, potatoes, and apples. Dr. Knee used to work with apples but found it frustrating because the growing cycle took years. With tomatoes, the cycle is only months. Researchers can more quickly determine whether their experiments have worked.
Tomatoes also represent a huge market - about $5 billion a year at the retail level and $3.5 billion at wholesale, estimates Tom Churchwell, chief executive officer of Calgene Fresh. "It's a big enough market to be very inviting," he says.
According to Monsanto, a tomato is the nation's third most popular vegetable (even though it's really a fruit). Only the potato generates more revenue.
SO far, researchers can only deal with the simple traits of a plant, the ones controlled by a single gene. Knee is working on the malic enzyme. The enzyme regulates a tomato's production of malic acid and, he says, citrus acid as well. As a tomato ripens, the malic enzyme breaks down the acid.
That's good for fresh fruit. (A green apple tastes tart because its acid hasn't been broken down.) But it's bad for processed food. The acid levels of processed tomatoes are crucial to preserving the taste of everything from canned stewed tomatoes to salsa. If the acid levels fall too low, the tomatoes spoil and, in extreme cases, cause botulism, Knee says.
Commercial processors often add citric acid to keep tomatoes from spoiling. Knee hopes to convince them to use bioengineered tomatoes that lose their acids more slowly. As Calgene has already done with Flavr Savr, he hopes to clone the malic gene, turn it in an antisense direction, then reinsert it. The genetic messages should cancel each other out. The malic enzyme would work far more slowly.
So far, plant biotechnology has attracted far less controversy than animal biotechnology. It's hard to argue against more flavorful tomatoes. But the spotlight will probably become brighter as scientists engineer other traits.
Monsanto, for example, is trying to make a whole range of crops resistant to its best-selling herbicide, called Roundup. Its scientists argue that the new plants will allow farmers to avoid using more hazardous chemicals and, in the end, reduce pesticide use.
That research worries Rebecca Goldburg, senior scientist at the Environmental Defense Fund, a New York-based environmental group. "Some herbicide-tolerant crops are probably acceptable," she says. But the Environmental Protection Agency should see whether such a crop really cuts pesticide use. On some, EPA should say no." -PATHNAME- /usr/local/etc/httpd/plweb/DBGROUPS/paper/database/tape/92/sep/day30/30121.