By Richard Black
BBC News website environment correspondent
US scientists have developed a new method for genetically modifying crops which they believe may remove some concerns over safety.
Public distrust of GM crops is partly over fears of antibiotic resistance
Most GM plants contain a gene for antibiotic resistance, but there are fears this could transfer to bacteria, making them immune to common drugs.
Researchers from Tennessee say their new method carries no such risk.
Environmental groups say the work does not make the approval of new GM crops any more likely.
Genetically modifying plants usually has a rather low success rate - and researchers need to be able to select plants which have successfully taken up the introduced gene from those that have not.
Traditionally, this has been done by giving, alongside the desired gene, a gene which makes the plants resistant to an antibiotic.
Growing the plants in soil containing the antibiotic provides an easy way to sort them; those which have not "absorbed" the introduced genetic material will be poisoned by the antibiotic. The antibiotic gene is called a "marker" because, in effect, it is marking out the successes from the failures.
This could do something to mitigate the regulation and public perception hurdles.
But the genes used have traditionally come from bacteria - and this has led to concerns that they could find their way back into bacteria, making them resistant to antibiotics used by doctors to treat human disease.
"If you go back to the years 2000 to 2002, around 60-70% of all GM plants reported in the scientific literature were made using markers which make them resistant to the antibiotic kanamycin," Professor Neal Stewart told the BBC News website.
Professor Stewart heads the team from the University of Tennessee at Knoxville, which reports its alternative approach in the journal Nature Biotechnology.
They use instead a gene which comes from a plant, Arabidopsis thaliana, perhaps the most widely investigated plant in science; and they have inserted it into tobacco.
The gene increases production of a protein called an ATP binding cassette (ABC), and - by a mechanism which is not fully understood - makes the plants kanamycin-resistant.
"I would like to see a science-based approach to the regulation of GM crops," said Professor Stewart, "and this could do something to mitigate the regulation and public perception hurdles.
"We have been trying to simulate what would happen if this gene was transferred to microbes; and we can show that if this ABC gene is inserted into E. coli, for example, it does not make them kanamycin-resistant."
The Agricultural Biotechnology Council, the lobby group for GM crop companies in Britain, described the work as "an interesting development".
"But," argued the council's deputy chairman Tony Combes, "it should be noted that existing marker systems that have helped scientists in their research have a proven safety record.
"The so-called 'horizontal transfer' of these genes presents a very small risk."
Dr Huw Jones, research group leader at Rothamsted Research, one of the leading UK institutions in the field of GM crops, agreed.
"This discovery represents a significant advance because it avoids the need for cross-kingdom gene transfer," he said, noting that many other scientists are working towards the total removal of selection markers.
The reaction from environmental groups was less enthusiastic.
"Products on the market now may well have antibiotic-resistant marker genes in them," Clare Oxborrow, GM campaigner with Friends of the Earth, told the BBC News website, "so this won't have any importance when it comes to the approval process.
"Also, the researchers point out that they aren't clear on the function of the inserted gene; so although it does carry this potential benefit, they don't know what else it might do to the plant, and there doesn't seem to have been any serious investigation of the type which would be required by food safety assessment authorities."
The Tennessee team is now working with food crops as well as tobacco, and to extend its studies on gene transfer.