So you want a delicious, vine-ripened tomato in mid-winter that survived a week of shipping and handling and remains firm on your kitchen counter for another week or more?

Your wish is the command of Agricultural Research Service scientists in the Produce Quality and Safety Laboratory, Beltsville, Md.

Research Leader Kenneth C. Gross and molecular biologist David L. Smith are closer to providing industry with the tools to develop such a tomato: a clearer picture of some of the genes involved in turning a firm tomato into mush.

They have produced vine-ripened tomatoes that are 40 percent firmer than unmodified siblings and stay firmer for at least two weeks. The plants were engineered with a reversed gene for an enzyme that removes a sugar from cell walls. The reversed gene actually blocks removal of the sugar galactose.

Those firm tomatoes support their theory that the loss of galactose plays a key role in the loss of structural integrity of cell walls. And structurally sound cell walls are essential to tomato firmness. The researchers focused on galactose because it's the sugar that changes most throughout fruit development.

They actually identified and sequenced seven different genes that code for the galactose-removing enzyme-beta galactosidase. They have inserted five of those genes into the tomato genome but have so far tested tomatoes with only one of the reversed, or antisense, genes-number 4. A U.S. and international patent application on all seven genes has been filed for ARS, the U.S. Department of Agriculture's chief scientific research agency.

The concept is similar to that used to produce the short-lived Flavr Savr tomato six years ago, but it targets a different component of the cell wall. The Flavr Savr tomato never caught on because it was costly to produce.

With growing competition in today's fresh tomato market-worth nearly $1 billion in 1999-the time may be ripening for a tasty tomato that ages gracefully.