GM crops: Bt gene is harmful to plants too

Syed Akbar
Hyderabad, June 2: A team of Indian scientists has found that genetic modification will have a detrimental effect on the growth and development of plants. This is the first time that scientists have found that Bt gene will trigger major problems in plants like stunted growth and sterility. Thus far, studies have centred around the
toxicity the Bt gene would cause in animals and human beings.
There has been considerable interest and activity in genetically engineering insect-resistant crop plants using "Cry genes" encoding insect toxins from the soil bacterium Bacillus thuringiensis, or Bt for short. The proteins encoded by these genes are called Bt-toxins and are thought to specifically affect only certain insects and not
other organisms, including plants themselves.
However, the team from the laboratory of Dr Pradeep Burma (Department of Genetics, University of Delhi South campus) has found that expression of the Bt-toxin "Cry1Ac" in cotton and tobacco is detrimental to growth and development of the plants. The study was published in the June issue of Journal of Biosciences.
"Many of the transgenic plants obtained showed developmental defects comprising abnormal growth (stunting) and/or sterility. These symptoms suggest that expression of Cry1Ac could be causing growth defects in plants," the team observed.
Consistent with this explanation, the researchers found that a majority of transgenic plants had very low or undetectable levels of Cry1Ac and that all plants having appreciable levels of Cry1Ac showed developmental abnormalities indicating a correlation between the levels of Cry1Ac expression and the developmental defects in the plants.
It was found that plants release defence-related molecules to fight the toxicity induced in them through Bt technology. Though studies have not been conducted whether these defence-related molecules will cause harm to human beings when they are consumed, scientists here feel that the toxins released may also be detrimental to human and animal health.
The authors went on to show that if the Cry1Ac is now modified so as to be located in one part of the cell –  the chloroplast which is the site of photosynthesis in plant cells, they are now able to recover plants that show higher levels of expression of Cry1Ac and the plants do not show developmental abnormalities.
Thus compartmentalisation of Cry1Ac within the plant cell so that it is confined to chloroplasts seems to alleviate the detrimental effects and the authors suggest that targeting Cry1Ac to chloroplasts can lead
to plants expressing higher levels of Cry1Ac and better insect resistance.
At the same time the finding that expression of a Bt-toxin is detrimental to plants is unanticipated since the toxin is thought to be very specific to certain insects. The reason for the detrimental effects of Cry1Ac on plant growth and development is not known and its understanding would require further investigation, they pointed out.