We could grow more food by 'teaching' more plants to capture nitrogen from the air. A UCD team is helping to work out how to do it, writes Dick Ahlstrom.
Scientists in the US and Europe are trying to understand why some plants can take growth-promoting nitrogen from the air but others can't. Discovering the reasons could increase food production dramatically without the need for costly fertilisers.
Farmers in the developing world struggle to keep crop yields up, because they can't afford expensive products such as nitrogen fertiliser. Yet some crops, such as legumes, don't need added nitrogen, because they take theirs from the atmosphere.
They do it by joining with rhizobia, nitrogen-fixing bacteria that are common in the soil, in a symbiotic relationship that benefits host plant and bacteria.
The plant forms specialised cell structures once infected by the bacteria where complex chemical reactions help both partners equally.
The bacteria receive carbohydrates in the form of sugars as part of this bargain; the plant receives fixed nitrogen needed for growth, explains Dr Bruce Osborne of the ecophysiology research group at University College Dublin's botany department.
"There is a two-way transfer and a two-way benefit because of that," he says. "The bacteria gain because of the carbon and the plant gains because of the nitrogen."
This symbiotic relationship forms for legumes but not, unfortunately, for other valuable crops. He and fellow researchers are trying to find out why.
The US National Science Foundation recently awarded a "planning grant" to Virginia Commonwealth University and the University of California at Davis to study plant- bacteria symbiosis.
They have been joined by six EU labs, including Dr Osborne's group, for this work, which focuses not on rhizobia but on another nitrogen-fixing bacterial group, the cyanobacteria.
Cyanobacteria, basically forms of blue-green algae, have a particularly useful symbiotic trait: they are happy to fix nitrogen for a wide range of plants. Unfortunately, they tend to ignore plants that form flowers, a group that includes virtually all of the important crop plants.
There is one exception, however: the gunnera. "One of the puzzles of this is that cyanobacteria can be observed in a range of plants and yet there is only one flowering plant that does this," says Osborne.
Gunnera represents a 60-species range of fleshy, leaf-forming plants that happily join with cyanobacteria, which help them fix nitrogen. "This is an ancient symbiosis," says Osborne; the plant is at least 100 million years old. The question for the researchers is why gunnera and not other flower-forming plants and crops.
"We in UCD have consistently argued that further work on this symbiosis is essential if we are to provide a rational approach to creating new cyanobacterial partnerships," says Osborne.
The object is to encourage the bacteria to provide their nitrogen-fixing benefits for crops such as rice, as a way to boost yields.
"Unfortunately, for a number of reasons, most attention in the past has been focused on the cyanobacterium rather than on the host plant."
This project changes all that, however, with a powerful focus on the biochemistry and physiology of the plant as it interacts with the bacteria.
To narrow down the search for answers, the research teams will set up model plant cell systems, using four species that form symbiotic relationships with cyanobacteria: a moss, a liverwort, a cycad and a gunnera.
In vitro cell cultures will be created, then genetically altered "to get different cell lines and then use these to look at the interaction with the cyanobacteria", says Osborne.
He and his team are looking for what genes are switched on and what proteins are produced to allow the complex chemistry involved in the symbiosis.
This knowledge may provide clues about how to encourage crop species to join with cyanobacteria to capture fertiliser from the air. The hope is that cyanobacteria's readiness to fix nitrogen in many plant species may make it easier to achieve this function in crops.
The planning grant could lead to a much larger grant of $3 million to $5 million, he says, but UCD's involvement will be complicated. "The difference with this is we can't receive funds directly from the National Science Foundation. The only way we could be supported is if we sent personnel to the US."
This, in fact, is what UCD has done. Germaine Levieille, a postgraduate student, will go to Virginia, paid for by the National Science Foundation, and another UCD researcher will head for Davis as part of the project. Their work will feed back into UCD, where related research can take place without NSF funding.
"We also benefit independently through techniques learned in the US labs," adds Osborne. "There is no reason why we can't pursue things here that are found in the US labs."