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Scientists Tinker With Tomatoes

The fleshy fruit arrive at the supermarket red, ripe - but sometimes mushy. Researchers aim to halt the maturing process through biotechnology. One company hopes to have its bioengineered tomato on produce shelves by next year.

By Staff writer of The Christian Science Monitor / September 30, 1992


RESEARCHERS in the United States and Britain are waging an all-out battle against the mushy tomato.

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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.