Years of irrigation can make soil too salty to grow crops. But a genetically engineered tomato with an extra salt-pumping gene thrives and bears fruit even in water salty enough to kill your garden-variety plant. If the gene can be transferred to other crops, it could help reclaim some of the 60 million hectares of salt-damaged farmland worldwide.
Conventional breeding hasn't created new salt-tolerant plants, and many researchers doubted that genetic engineering could either; they suspected many genes were necessary for salt tolerance. But plant biologist Eduardo Blumwald of the University of California, Davis, guessed that a sodium-pump protein in leaf cells might protect plants by socking sodium away in membrane-bound compartments called vacuoles, where it can't damage sensitive enzymes. In 1999, his team reported in Science that overproducing the protein enables a small flowering plant called Arabidopsis to grow in soil irrigated with salty water.
To see if a similar strategy works in a crop plant, Blumwald and Hong-Xia Zhang of the University of Toronto introduced the gene for Arabidopsis' sodium-pump protein into tomato plants. Normal tomato plants keeled over when grown hydroponically in water nearly half as salty as seawater, but tomatoes with the sodium pump grew fine and produced tomatoes, the researchers report in the August issue of Nature Biotechnology. The introduced protein appears to deserve the credit: Vacuoles from the leaves of transgenic plants pumped sodium 7 times faster than in normal plants, and they accumulated just 5% as much salt. The tomatoes would have tasted just fine, however: They had as much sugar and no more salt than typical tomatoes.
"This is a major breakthrough," says plant ecologist Allison Snow of Ohio State University in Columbus. She and other experts caution, however, that field trials are needed to see if the plant grows well in salty soils, and to make sure that the gene doesn't jump to other plants to create salt-tolerant weeds. The same hurdles exist for other crops, says plant pathologist Dennis Gonsalves of Cornell University. But if they are overcome, he says, "then you can get to salt tolerance in one jump."