The genes for two different protein "sub-units" are needed to make haemoglobin, and have to be assembled into the correct formation. When the researchers added the genes to the plants, they found that haemoglobin was produced - and that when extracted and purified, it functioned just as in the human body, binding both to oxygen and to carbon monoxide.
Reporting on their work today in the science journal Nature, the team hope that such transgenic plants could in future provide a cheap and safe source of various human proteins.
At present, the haemoglobin used for a range of artificial blood substitutes is mainly derived from human donors, animal blood or genetically engineered animals. But those sources all carry the risk of contamination and infection.