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Bruising in tomatoes.

You've been thanking about it all the way home--that huge, mouth-watering tomato on the windowsill, so perfect for that cool summer salad. You pick up the tomato and inwardly groan as you feel the soft spot that means a bruise and, possibly, a spoiled fruit.

We take the bruising and consequent spoiling of fruits and vegetables as a simple, annoying fact of life. But in fact, "there is nothing simple about it. Bruising sets in motion a complex set of genes. It is a process that we don't yet fully understand," says molecular biologist Barbara L. Parsons, who works at the Beltsville Agricultural Research Center in Maryland.

"If we can find all the genes involved in the bruising process, we may be able to change the genetic makeup of plants so they can resist the spoilage caused by bruising," says Parsons.

When a fruit or vegetable is bruised or wounded, certain genes are turned on while others are turned off.

"in our studies, we've isolated three new genes that are involved with the wounding process," says Parsons.

"Ethylene--a natural plant hormone that causes aging and is produced during bruising--normally turns on each of these genes. However, one of the genes we isolated was turned off during bruising, presenting us with another puzzle to solve," says Parsons.

"This gene also produces a protein rich in glycine that may impart plasticity to the cell wall. Our goal is to decode the sequence of events regulating all of the genes that are involved in bruising."

Millions of dollars are lost annually as a result of braising during harvesting, shipping, and storage. For one crop alone--tomatoes--30 to 40 percent are bruised and consequently spoil, says plant physiologist Autar K. Mattoo, who is in charge of ARS' Plant Molecular Biology Laboratory in Beltsville, Maryland.

Tomatoes are shipped green and do not produce ethylene, the natural ripening agent, for a few days. This ensures that they won't ripen until they reach the supermarket.

If these same tomatoes are bruised, ripening is accelerated by the ethylene that is turned on by bruising. The initial production of ethylene causes more to be produced. "It is a selfperpetuating process--the hormone stimulates the gene to produce more and more ethylene-causing premature ripening," says Mattoo.

"To add insult to injury," says Mattoo. "there are many wound pathogens--bacteria and fungi--that attack the fruit only when injury occurs. That is why bruising that beautiful tomato results in a rotten spot or a completely spoiled fruit."--By Vinee Mazzola, ARS.

Barbara L Parsons and Autar K. Mattoo are at the USDA-ARS Plant Molecular Biology Laboratory, Bldg. 006, 10300 Baltimore Ave., Beltsville, MD 20705-2350. Phone (301) 5045148 and (301) 504-5103.
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Title Annotation:research by Barbara L. Parsons
Author:Mazzola, Vince
Publication:Agricultural Research
Date:Jun 1, 1992
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