Why nitrogen fixing may fail using GM
The conversion of nitrogen to ammonia is energy intensive (see box above).
Peas use seventeen grams of carbon from sugars to fix one gram of nitrogen.v The carbon is
supplied by the plant, so in cereals this would divert energy from growth and grain formation.
The rate of nitrogen fixation is regulated by the bacteria, which ensure that only the required
amount of nitrogen is fixed to avoid overloading the plant’s metabolism, and the plant, which
controls the number of nodules produced. These metabolic processes are controlled by
several genes from the plant and the bacterium.
To enable cereals like maize or wheat to be genetically modified to fix nitrogen all these
processes have to work as they do in legumes. Such complex outcomes have so far eluded
researchers, raising serious doubts about the feasibility of achieving nitrogen fixation in nonleguminous
crops. Even if GM nitrogen fixation is successful in cereals it is likely to result in
yield reductions because of the demands it would place of the plant’s energy resources.