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Ethylene gene control: research ripens.

Ethylene gene control: Research ripens

Plants, like people, produce a variety of hormones as they enter adolescence and grow to maturity. In plants, however, these hormonal changes generally don't result in ruined complexions or an overwhelming desire to borrow the family car. Instead, they trigger a series of chemical reactions that cause, among other things, changes in the color and texture of fruiting bodies -- a process we call ripening.

Scientists have now cloned the gene for the enzyme regulating production of the major plant ripening hormone, ethylene. The work advances prospects for engineering plants that ripen only at grocers' convenience. It also may result in an energy-efficient way to mass-produce the colorless gas, which today is syntesized from petroleum for use in making plastics and other products.

Ethylene ([C.sub.2.H.sub.4]), one of the simplest organic molecules showing biological activity, plays a major role in fruit ripening, seed germination and flowr maturation. Plants tightly regulate its production with several enzymes that sequentially convert a precursor molecule into the biologically potent gas. The chemical cascade leading to ethylene' synthesis ends with the production of 1-aminocyclopropane-1-carboxylic acid, or ACC, by a plant enzyme called ACC synthase. The plant makes ethylene from ACC.

For years, scientists have sought to clone the gene coding for ACC synthase. Their efforts proved furitless, partly because the substance occurs in such minuscule quantities in plants. In a ripe tomato, for example, ACC synthase makes up only 0.0001 percent of the fruit's total protein. But using a novel combination of immunological and molecular biological techniques, Agricultural Research Service researchers Takahide Sato and Athanasios Theologis cloned the elusive gene from an unpurified preparation of ACC synthase. They performed the work at the USDA's Plant Gene Expression Center in Albany, Calif., and report their findings in the September PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES (Vol.86, No.17).

With the ACC synthase gene now available for genetic tinkering, several lines of investigation become attractive, say these and other researchers. Using molecular biological techniques such as antisense engineering (SN: 6/10/89, p.360), scientists may gain the ability to block ethylene production in fruit- or vegetable-bearing plants or at least reduce its synthesis to slow the ripening process. Once the unripened food reached the market, grocers could expose it to ethylene in chambers, thus triggering ripening immediately before consumer purchase.

The procedure could save much of the billions of dollars lost worldwide each year from overripening of fruits and vegetables during transportation, the USDA researchers say. In the United States alone, they note, almost half the fresh fruits and vegetables harvested each year are lost to spoilage.

Moreover, inserting the gene for ACC synthase into bacteria or yeast -- something the researchers have already accomplished -- could allow mass production of ethylene gas. U.S. industry produces more than 50 billion pounds of ethylene from petroleum each year to make polyethylene plastic, antifreeze and high-tech fibers. The team hopes to splice the gene into photosynthetic bacteria or algae that could serve as solar-driven, ethylene-producing biofactories.

"There's thousand different ways of playing with this," says Patricia Zambryski, a plant biologist at the University of California, Berkeley. She cautions, however, that ethylene plays many different roles in plants and that reducing its natural production may have untoward effects on some species.

Nonetheless, she says, the new technique for cloning genes should help other scientists working with genes whose products occur in very low concentrations.
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Publication:Science News
Date:Sep 16, 1989
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