August 3, 2004
Turning Genetically Engineered Trees Into Toxic Avengers
ast summer, on the site of 35 former hat factories where toxic mercury was once used to cure pelts, city officials in Danbury, Conn., deployed a futuristic weapon: 160 Eastern cottonwoods.
Dr. Richard Meagher, a professor of genetics at the University of Georgia, genetically engineered the trees to extract mercury from the soil, store it without being harmed, convert it to a less toxic form of mercury and release it into the air.
It was one of two dozen proposals Dr. Meagher has submitted to various agencies over two decades for engineering trees to soak up chemicals from contaminated soil. For years, no one would pay him to try. "I got called a charlatan," he said. "People didn't believe a plant could do this."
He will begin to assess the experiment's success this fall. But his is not the only such experiment with trees.
In laboratories around the country, researchers are using detailed knowledge of tree genes and recombinant DNA technology to alter the genetic workings of forest trees, hoping to tweak their reproductive cycles, growth rate and chemical makeup, to change their ability to store carbon, resist disease and absorb toxins.
The research is controversial. Environmentalists and others say that because of the large distances tree pollen can travel, altered genes will migrate to natural populations, leading to damage to ecosystems and other unforeseen consequences.
Dr. Jim Diamond, a retired pediatrician who is chairman of the Sierra Club's national genetic engineering committee, sees trees as a bastion of the natural world.
"It's quite possible the stands of trees that are left will be domesticated new varieties of trees and the natural varieties will cease to exist," he said. "Where do you draw the line?"
Dr. Meagher's toxic-avenger trees are intended to remove heavy metals from contaminated soils in places where other forms of cleanup are prohibitively expensive. Because mercury is an element, it cannot be broken down into harmless substances; the Danbury trees release the diluted mercury into the atmosphere, where it dissipates and falls back to earth after a few years.
This has opened Dr. Meagher to the charge that he is engaged in a shell game, simply moving toxins from one place to another. He does not disagree, but says the risk of human exposure will be lower if the chemicals are not concentrated in certain areas. In time, he says, such trees may be deployed in places like Bangladesh and India, where mercury- and arsenic-laden drinking water has created a growing health crisis.
"I really believe we're on the way to doing something great, and 20 years from now this is how these things will be taken care of," he said.
Tree geneticists are acutely aware that public acceptance will depend at least partly on whether altered trees can be made sterile or their reproductive capacity tightly controlled.
Dr. Steven Strauss, a professor of forest science at Oregon State University, directs the Tree Biosafety and Genomics Research Cooperative, a group working on strategies for gene containment, including control of flowering cycles and sterility. He is also exploring ways to link desirable traits to traits that make a tree unlikely to spread.
"If you take a gene for herbicide resistance that you don't want to spread, and you link it to a gene that makes a tree shorter and fatter, that's a tree that's not going to be very invasive," he said.
Not everyone is convinced that these containment strategies will work.
"Any number of molecular geneticists will tell you, 'Oh, these things are not a problem, we've got various ways of making sure the genes won't function outside of their intended plants,' " said Dr. Yan Linhart, a biologist at the University of Colorado who studies the ecology and evolution of forest trees. "But just as confident as they are, you will find any number of ecologists and evolutionary biologists like myself who believe in the Missouri motto, 'Show me.' "
Dr. Strauss and his colleagues view genetic engineering as a way to ease the pressure for logging in wild forests. If they can engineer trees in a plantation setting that grow faster and possess other desirable commercial traits, they say, then the industry will have less incentive to go after old-growth trees.
"It is possible," said Dr. Ron Sederoff, a professor of forestry at North Carolina State University, "that we could engineer trees that are so much better for specific purposes that you wouldn't want to cut down a natural tree."
Among the goals is the creation of trees that produce less lignin - a substance similar to plastic that makes wood fibers stiff - so they can be turned into paper and lumber using fewer chemicals. Lignin production is important to trees in the wild, contributing to the strength of their trunks, but less so on a plantation, where trees will be harvested every few years. Researchers have discovered a link between low lignin and faster growth, which could make the engineered trees desirable for plantation foresters.
Still, this has not satisfied critics.
"Perhaps part of growing faster is that it won't put all this effort into useless pine cones," said Dr. Diamond of the Sierra Club, "so there's no sustenance for the chipmunks. What if the tree in your backyard turns out to be a low-lignin tree but just happens to fall on your house or your car in a moderate wind? There are all kinds of risks besides just my aesthetic problem with remaking nature."
Dr. Strauss is also trying to use genetic engineering to address climate change. He wants to create trees that would store more carbon in their root systems - "sequestering" it from the atmosphere, thereby cutting atmospheric concentrations of carbon dioxide, the heat-trapping greenhouse gas. In a project sponsored by the Department of Energy, Dr. Strauss and colleagues at the Oak Ridge National Laboratory are modifying tree architecture and cell wall chemistry to increase the amount of carbon stored below ground.
Much of the research relies on basic tree genetics - made easier by the sequencing of the poplar tree genome, a major effort in forest biotechnology whose results are to be made public this month. Scientists can now study classes of genes that affect absorption of sugars and carbohydrates, which in turn can change the chemical processes that affect the rates at which trees rot and release stored carbon.
"In the U.S., there are about 40 million acres of excess, surplus or idle agricultural land," said Jerry Tuskan, a researcher at Oak Ridge, who led the effort to sequence the poplar genome. "If we could economically capture those and deploy fast-growing trees bred and created for carbon sequestration over a 10-year period, we could reach 25 percent of the Kyoto prescription for the U.S." The Kyoto treaty, never signed by the United States, calls for reductions in the growth of greenhouse gas emissions.
The aboveground portion of the trees would be harvested every 10 years and used for ethanol, which Dr. Tuskan believes would offset the use of petroleum and, by extension, carbon dioxide emissions.
In another forest biotechnology project that has been making strides, researchers are using genetic engineering to produce a disease-resistant strain of American chestnut, a tree that once dominated Eastern forests but was decimated by the mid-20th century by a fungus introduced from Asia. The American chestnut project has proved among the least controversial, in part because the tree's demise was caused by human intervention.
Elsewhere, researchers are using forest biotechnology to quicken the pace of traditional breeding experiments. At the University of Georgia's Warnell School of Forest Resources, Dr. Jeffrey Dean monitors individual genes to learn how they react to changes like the addition of fertilizer or the presence of a fungus.
Dr. Dean said he had spent the past several years "philosophizing" about the genetic engineering of trees, weighing the pros and cons. "We probably don't want to be thinking about genetic engineering as a magic bullet or cure-all," he said. "There will be times where we may want the magic bullets, but they have to be applied in specific ecological contexts."
Said Dr. Linhart of the University of Colorado: "One always needs to put into the equation biological caution and common sense. It's a case-by-case basis. One has to not make sweeping judgments that say this particular type of activity is all good or all bad."