Gene Makes Tomatoes Tolerate Salt

The birthplace of agriculture, the Mideast’s Fertile Crescent, became largely a desert long ago, and salt in the soil had a lot to do with it. Today, according to some estimates, salt-laden soil ruins the farming potential of more than one-third of all irrigated lands worldwide.

Genetically engineered tomato plants (top) thrive in a salty solution. Normal ones (bottom) don’t. Blumwald et al./Nature Biotechnology

“Every time we water the land, we’re depositing minute quantities of salt. It catches up with us,” notes Eduardo Blumwald of the University of California, Davis.

Blumwald and a colleague have now made a dramatic advance in combating this agricultural nightmare (SN: 11/10/84, p. 298; 11/17/84, p. 314). They genetically modified a traditional crop plant, the tomato, so that it can thrive in salty water. Besides providing farmers with a cash crop for salted lands, such plants may also pull salt out of soils, enabling other crops to thrive again.

“It’s a remarkable feat,” says UC-Davis’ Emanuel Epstein, who decades ago proposed endowing commercial crops with salt tolerance.

“It’s a really important breakthrough,” concurs plant biologist Edward Glenn of the University of Arizona in Tucson.

While some wild plants flourish in salty conditions, traditional crops become stunted or die when exposed to high concentrations of sodium chloride.

“There’s hardly anything for farmers to plant that’s salt-tolerant,” says Glenn. Researchers have for decades struggled to breed this trait into already domesticated plants. Their failure left many scientists convinced that salt-tolerance derives from multiple genes.

In 1999, however, Blumwald’s group reported that adding active copies of a single gene normally inactive in the weed Arabidopsis thaliana made the plant salt-tolerant. The gene encodes a protein that shuttles sodium into sacs, or vacuoles, inside plant cells, protecting them from salt damage. Salt-tolerant plants use this trick, but traditional crops seem to have turned off the gene, says Glenn.

Blumwald has now duplicated his Arabidopsis work in the tomato. In the August Nature Biotechnology, he and Hong-Xia Zhang of the University of Toronto report that their altered plant can grow hydroponically in solutions with sodium chloride concentrations of 200 millimolar (mM). Most crops start dying off at

50 mM salt; seawater contains 530 mM.

The altered tomato plant draws salt from the soil mostly into its leaves, not into its fruit. According to Blumwald’s unofficial and admittedly biased testing, the tomatoes “taste great.”

While praising Blumwald’s work, Clyde Wilson of the U.S. Salinity Laboratory in Riverside, Calif., offers some cautions. Field testing of the new plant must demonstrate qualities required for a commercial tomato, he says. The fruit must ripen uniformly, for example, and have tough enough skin for handling.

“It is difficult to predict how successful this particular approach will be with other crops,” adds Wilson, noting that the tomato has a simple genome compared with many other crops, such as wheat.

Blumwald remains confident. He already has introduced the salt-tolerance gene into canola, the seeds of which provide a valuable oil.

He hopes eventually to further improve plants’ salt tolerance to the point where they could be irrigated with seawater. Says Blumwald: “It’s not a dream anymore. It’s a real possibility.”

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