It has long been recognized that trees absorb carbon dioxide (CO2) and are of great value in cleaning up the atmosphere. Planting trees is one way some countries plan to meet their obligation under global climate change agreements to reduce net emissions of CO2 into the atmosphere.

Now scientists at Japan's Toyota Motor Corp. are conducting genetic engineering studies in an effort to develop trees that consume even more pollution than standard varieties.

• It takes 20 regular trees to absorb the gases of one car in a year.

• Toyota's researchers report they have improved that performance by 30 percent.

• The scientists report that doubling the number of chromosomes in experimental trees widened the tiny air inlets on stems and leaves -- allowing them to absorb more nitrous oxide.

• So far the process only works on six types of seeds out of every 100.

The researchers found that the altered trees better withstand salty ocean winds. Eucalyptus trees absorb 30 percent more of certain pollutants, while the altered London plane trees absorb 20 percent more.

Company researchers are also trying to grow trees in acid-drenched soil -- a technique that could be used to restock ravaged rain forests in Southeast Asia.

Meanwhile, Toyota wants to plant more standard trees along the highways of Japan in order to absorb more carbon dioxide. But it is having to fight government regulations for permission to do so.