Brussels, June 2002
It may be easier to design plants that make their own nitrogen fertiliser than previously thought, according to new research published in the journal Nature on 26 June.
The roots of legume plants (members of the pea and bean family) form an unusual symbiosis with bacteria of the genus Rhizobium. This symbiosis enables the bacteria to take nitrogen gas from the atmosphere and convert it into nitrate and ammonia, which are absorbed and used by the plant in the same way as artificial fertiliser would be. In return, the bacteria are able to absorb and use sugars produced by the plant.
Scientists at the Sainsbury Laboratory in Norwich, UK, discovered that this nitrogen-fixing symbiosis between legumes and rhizobia, up to now considered a unique relationship, uses some of the same genes that control the common mycorrhizal relationship of plant roots and fungi. This symbiotic relationship, common to many plants, involves the exchange of nutrients absorbed by arbuscular mycorrhizal fungi for plant sugars that are absorbed and used by the fungus.
Project leader Dr Martin Parniske said: 'Scientists had always imagined that the nitrogen-fixing symbiosis between legumes and rhizobia bacteria was a unique relationship, so the discovery that it actually uses some of the same genes that control the very common mycorrhizal association of plants roots with fungi is really exciting.'
He added: 'We now know that part of the genetic blueprint needed to establish a symbiotic relationship with nitrogen-fixing bacteria is present in all major plant types, including important crop species such as wheat and rice.'
Dr Parniske said the new knowledge might enable breeders to develop plants that can manufacture their own nitrogen fertiliser by establishing symbiotic relationships with nitrogen-fixing bacteria. This would help to cut down on the user of man-made nitrogen fertilisers, blamed for environmental problems.
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