Fruit ripening can be blocked by antisense RNA directed at thegene for ethylene production in tomatoes, according toscientists at the University of California, Berkeley.

Ethylene is the agent that turns fruit soft and ripe. Key toethylene formation within fruit is the synthesis of an enzymeto form the gas. Researchers at the university's Plant GeneExpression Center placed antisense RNA, derived from thesequence of the gene that codes for the rate limiting enzyme,into tomato plants to block the enzyme.

Transgenic plants produced fruit that turned orange, but neverred or soft, nor did they develop an aroma. Ethylene productionwas inhibited by 99.5 percent in these plants' fruit.

But exposing the antisense tomatoes to propylene, a gas thatmimics ethylene, could induce ripening so that the fruitbecomes "indistinguishable" from those from normal plantsthat ripened naturally, the researchers reported inScience.

Several biotech companies are attempting slow ripening toprolong the shelf life of fruits and vegetables. Calgene Inc. hasfiled for Food and Drug Administration permission to marketits antisense tomato that resists ripening by slowing thebreakdown of pectin. Monsanto Co. is field-testing tomatoeswith a bacterial gene that inhibits production of ethylene. --Roberta Friedman, Ph.D.

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