Scientists studying resistance to infection in tobacco plants have discovered that a natural form of genetic engineering has introduced foreign genes into their genetic make-up.

The discovery came about when Professor Conrad Lichtenstein of Queen Mary and Westfield College in London began to introduce genes which help resist virus infections into tobacco plants.

He was surprised to discover that hundreds of similar genes already existed in the genetic blueprint of the tobacco plants having "jumped" there from other plants.

It is believed that these genes are currently inactive but may have been useful to the plant in the past giving the tobacco plants resistance to certain viruses.

The scientists now wish to determine the genetic history of the tobacco plant to discover how and when the genetic implant occurred.

The transfer of genes from one species to another is known as horizontal transmission, as opposed to vertical transmission when genes are passed to future generations.

It is currently a mystery as to how the likes of tobacco plants came naturally to assimilate foreign viral genes into their genetic make-up. Evidence points to a genetic accident at some point in its early evolution.

Professor Lichtenstein said: "A study of when and how the plants acquired the foreign genes through natural processes could provide vital information to help assess the possible risks of artificial plant genetic engineering."