Scientists may soon be able to produce genetically-modified (GM) crops without transferring genes between species.

The method might be an answer to the objections of groups opposed to GM crops who say that, for example, taking an anti-freeze gene from a fish and inserting it into a strawberry is unnatural and dangerous.

Protestors may not be impressed

If this research reaches fruition it could provide a new way to modify plant characteristics, such as improving the nutritional value of foods or enhancing plant productivity.

The technique is described in the Proceedings of the National Academy of Sciences.

It involves preparing a section of DNA and RNA, the molecules that hold the organism's genetic blueprint.

The DNA/RNA molecule is called a chimeraplast. It attaches itself to the specific part of the gene that needs changing.

Farmers may benefit

Dr Chris Baszczynski, one of the scientists involved, said that the technique "doesn't use anything physically from the source gene. The changes are all chemically synthesised."

Dr Charles Arntzen, another of the researchers, believes the new technology "would be used to benefit farmers and food producers".

"We may one day be able to quickly reduce caffeine in coffee beans, or shorten the long-chain fatty acids found in plants like soybeans - making the fat in them more heart-healthy like olive oil."

The method will not work for the introduction of completely foreign genes, Braszczynski said. "You have to use the information that exists in the organism and then you design a molecule to make a change."

Working with corn, the scientists created a strain resistant to a herbicide. They based it on a natural mutation found in some strains of corn.