Dr Colin Lazarus and his team at Bristol University engineered a new strain of Arabidopsis, a relative of the cabbage, by adding two genes from algae and a third from a fungus.
They report in Nature Biotechnology online (16 May doi:10.1038/nbt972) that this led to substantial quantities of two very long chain polyunsaturated fatty acids, arachidonic acid (ARA) and eicosapentaenoic acid (EPA), in the plant.
It is thought to be the first time that these fats have been produced in plants through genetic engineering, paving the way for development of vegetables with added health benefits in the future.
EPA is an omega-3 fatty acid, the class of fats shown to have a major benefit to human health. They have been found to reduce the risk of heart disease, relieve the symptoms of inflammatory conditions such as rheumatoid arthritis, fight depression and may also protect against Alzheimer's.
ARA, an omega-6 fat found in meat, eggs and milk, is also important for mental health and is a precursor to a group of hormone-like substances called eicosanoids, which impact immunity, blood clotting and other vital functions in the body.
However both omega-3 and omega-6 fatty acids have to be obtained from our diet and most of their sources are animal- or fish-derived. Transgenic plants could offer a better source of the fats for vegetarians.
The modified plants are also described as "a breakthrough in the search for alternative sustainable sources of fish oils". With fish stocks declining, and concerns over high levels of toxins, such as polychlorinated biphenyls (PCBs) and dioxins, biotech crops could provide a safer and more sustainable source of omega fatty acids.
And according to the scientists, the genes could be added to many other plants.
"Any plants with green tissue, they all have the potential to produce these long-chain fatty acids," co-researcher Dr Baoxiu Qi told BBC News Online.
"If we try to increase the omega-3 fatty acids in a plant, a good source would be linseed; and for the omega-6, I think rapeseed would be quite good, or soya," he added.