Five years ago, Dr. Eduardo Blumwald of the University of California announced that he and his team had succeeded in genetically modifying tomato plants so that they could grow in soil with a high salt content. Not only that, but these plants actually removed the salt from the soil, storing it in their leaves. This was big news.

Salt in soil is one of the issues of environmentalism. Demand for food means demand for crops means demand for arable land, and that means that a lot of land that is unsuitable for farming has to be made suitable, and that means irrigation. But most water has salt in it - maybe only trace amounts, but it builds up. After a few years of intensive farming, you're left with a plot of land that has so much salt in it that it's effectively desert. And once the land has turned barren, it stays that way.

So research into salt-tolerant crops is a big deal, and crops that promise not only to tolerate salt but to remove it have the potential to re-fertilize man-made deserts. The planet is helped, and poor farmers get to make a living selling juicy tomatoes. What could be better for the environment?

But there's a catch: this breakthrough has been made possible by genetic modification. Few things have been opposed by the environmental movement as thoroughly and vigorously. What happens when it provides the solution to one of their biggest problems?

Clare Oxborrow of Friends of the Earth is skeptical. "Despite promises made by scientists and claims by the biotech industry that salt tolerance has been produced through genetic engineering, it is important to stay focused on the reality," she says. "Salt tolerance is very complex, and GM technology has not been able to come up with the answers."

Professor Tim Flowers of the University of Sussex says he's hedging his bets. He's an expert on salt tolerance in plants, and he's not completely convinced by Dr. Blumwald's tomatoes. But he does think the problem will be cracked eventually: "Since there are plenty of salt-tolerant plants about, I can't see why it wouldn't be achieved."

Flowers thinks the real problem is that salt-removing plants could only rarely be useful. "We can do the sums. It's possible to remove about seven-and-a-half tons of salt per hectare using plants, but irrigating those plants typically requires water containing about seven-and-a-half tons of salt per hectare every year." So, for plants to make any headway against soil salination, the water used on that soil first needs to change. That's not often going to happen -- water's heavy, so farmers use what's nearest. He also points out that plants' roots reach only into the surface layer of soil, leaving ground water unaffected. In many cases, surface water is replenished -- and resalinated -- by ground water.

However, Flowers is optimistic that when GM does finally yield a benefit to the environment -- whatever that benefit might be -- public opposition to the technology will die down. And even some environmentalists are more open to the idea than you would expect from their more strident protests. "Friends of the Earth doesn't have an absolutist position," says Oxborrow. "We would not completely rule out that there might be a GM product some time in the future that provides a benefit for consumers or the environment, doesn't undermine food security, is outside of the current corporate industry driven system, and outweighs the risks posed." They just don't think it's likely to happen any time soon.

Greenpeace, on the other hand, is absolutist. Asked about the possibility of a GM plant that could benefit the environment, Lisa Weatherley, a spokesperson for Greenpeace UK, says, "Greenpeace opposes all releases of genetically modified organisms into the open environment because of their risks to the environment, eco-systems and health."

Blumwald believes in the potential of GM to improve people's lives. His job, he says, is to contribute to science by finding out how plants work and what genes do, regardless of their commercial potential. "We are not focused on the development of applications for these processes because it is not our mandate. Private companies do so," he says. "Biotech companies have their own agenda and do not necessarily try to find applications to our findings." That doesn't sound much like the "corporate industry driven system" that Friends of the Earth describes.

At least one biotech company is confident enough to have bought the university's patents and invested in field trials.

"The fact that a few biotech companies are making a profit with a few inventions based on transgenic plants has nothing to do with the potential of transgenic research to solve some of our problems and to ameliorate others," says Blumwald. He has a point: while the big biotech firms are busy exploiting the potential of genetic modification to give us more and cheaper food, many scientists clearly share his excitement about the technology's potential to make the world a better place in a thousand other, less profitable ways. Current projects include making elms resistant to Dutch elm disease so that they may be reintroduced to Britain -- a project that Friends of the Earth opposes -- and making cress turn red in the presence of explosives so that it can be used to detect land mines. Projects like these, if successful, could do a lot to persuade the public that maybe GM's not so bad after all.

The author is a computer programmer, Web designer, musician, & gardener. He lives in Northern Ireland and at Squander Two Blog.