TREES REDESIGNED

Cellulose can replace corn as raw material to make ethanol. But cell cellulose is covered by lignin that needs breaking down

It might be true that 8220;only God can make a tree,8221; as the poet Joyce Kilmer wrote. But genetic engineers can fundamentally redesign them. Aiming to turn trees into new energy sources, scientists are using a controversial genetic engineering process to change the composition of the wood. A major goal is to reduce the amount of lignin, a chemical compound that interferes with efforts to turn the tree8217;s cellulose into biofuels like ethanol.
Vincent L. Chiang, co-director of the forest biotechnology group at North Carolina State University, has developed transgenic trees with as little as half the lignin of their natural counterparts. 8220;I think the transgenic tree with low lignin will contribute significantly to energy needs,8221; he said.
Environmentalists say such work can be risky, because lignin provides trees with structural stiffness and resistance to pests. Even some scientists working on altering wood composition acknowledge that reducing lignin too much could lead to wobbly, vulnerable trees. 8220;Nature would have selected for lower-lignin trees if they could survive,8221; said Shawn Mansfield, associate professor of wood science at the University of British Columbia.
People working in the field also acknowledge that they will face resistance from others who see trees as majestic symbols of pristine nature that should not be genetically altered like corn and soybeans. 8220;The general public is not going to look at trees at this point as a row crop,8221; said Susan McCord, executive director of the Institute of Forest Biotechnology in North Carolina. 8220;The same is true of foresters. The people who go into that work, they love trees. They view them very differently than a row of corn.8221;
Ethanol is mainly made from the starch in corn kernels. To increase the supply to make a dent in the nation8217;s energy picture, scientists are looking at using cellulose, a component of the cell wall in plants. Proponents of using trees for this say they are good sources of cellulose and are also good at absorbing carbon dioxide, helping to fight global warming. Also, trees can be cut as needed rather than having to be harvested at a given time each year like a crop.

But the cellulose is covered by lignin, another component of the cell wall, making it difficult for enzymes to reach the cellulose and break it down into simple sugars that can be converted to ethanol. Pulp and paper companies break down lignin using acids and steam. Ethanol producers would have to do the same.
Trees that have less lignin might reduce or eliminate these steps. That could save at least 10 cents a gallon in ethanol costs, said Michael Ladisch, director of the Laboratory of Renewable Resources Engineering at Purdue.
Scientists understand the steps in creating lignin and can make lower-lignin trees by blocking one of them. One way is to put in a reverse copy of a gene that codes for an enzyme in lignin formation. The reverse copy silences that gene and reduces production of that enzyme. Chiang said a 50 percent reduction in lignin appeared to be the maximum achievable. 8220;The tree doesn8217;t allow you to go further.8221;
Chiang said his trees appeared normal, at least in the greenhouse. He has found that trees that produce less lignin might produce more cellulose, making them even more useful in producing ethanol, pulp or paper without reducing tree strength.
-ANDREW POLLACK New York Times