TOKYO (AFP) - As well as brightening your room, pot plants may one day help to prevent headaches in "sick" houses by absorbing toxic gas, according to Japanese scientists. Researchers have genetically engineered plants that can absorb formaldehyde, a pungent chemical compound used as adhesive in building materials and furnishing, one of the researchers said Tuesday. Formaldehyde is seen as a major factor in what is known as sick-house syndrome " headaches, dizziness and other health problems triggered by chemical substances in the home. "We expect the plants to absorb it steadily" along with carbon dioxide for photosynthesis, said Katsura Izui, a professor of molecular plant physiology at Kinki University in western Japan. The plants have two kinds of genes imported from micro-organisms known as methylotrophs, which use formaldehyde for their growth. One host plant was tobacco and the other was thale cress, a small plant formally called Arabidopsis, which has a short life span of two months and is widely used as a model plant in biology. Izui said the amount of formaldehyde absorbed by the plants was small compared with the carbon dioxide they use. But the study showed that modified Arabidopsis survived four weeks in boxes dense with formaldehyde with the level of toxic gas falling to some one-tenth of the original level. All wild Arabidopsis died in the same circumstances. Similar results were also obtained with experiments using modified tobacco plants, he said. Izui said the density drop may have also stemmed from absorption by the agar used as a substitute for soil in the experiment boxes because formaldehyde is highly soluble in water. "We are now trying to make new devices for more precise observation," he said, adding they were trying to apply the technology in common foliage plants. The study was conducted jointly with Professor Yasuyoshi Sakai, an expert on micro-organisms at Kyoto University.