permaculture

["Lawrence F. London, Jr." <lfl@intrex.net>]

http://www.nature.com/news/2006/060626/full/060626-7.html
Published online: 28 June 2006; | doi:10.1038/news060626-7
Crops could make their own fertilizer

Plants that build homes for bacteria could do without chemical nitrogen.
Michael Hopkin


Plant geneticists have induced plants to form 'fertilizer factories' without
the aid of bacteria that are normally crucial to the process. If the
technology can be transferred to plants such as wheat or rice, industrial
fertilization of these crops could be reduced or even abolished.

When bacteria known as rhizobia enter the roots of a leguminous plant, such
as a pea or bean, the plant develops lumps, or nodules, on its roots to
house the microbes. The bacteria take nitrogen from the air and turn it into
ammonia that feeds the plant.

Two research groups have now made legumes that produce nodules in the
absence of rhizobia, potentially paving the way for crops that would not
need to be treated with nitrogen fertilizer, but instead would rely on
nitrogen-processing bacteria that are omnipresent in the soil to colonize
their nodules.

Feed me

Fertilizing crops is inefficient and environmentally damaging, says Giles
Oldroyd of the John Innes Centre in Norwich, UK, who led one of the research
teams. Besides polluting waterways, chemical fertilizer production accounts
for an estimated half of the fossil fuels burnt by agriculture.

Nitrogen-fixing bacteria are a better way for plants to gain their nitrogen,
Oldroyd adds. Many farmers and gardeners alternate legumes such as broad
beans or clover with their other crops. Traditional Latin American farmers
plant beans alongside their maize.

"Cereals have a huge nitrogen demand. But legumes not only provide nitrogen
for themselves, but also for other plants," says Oldroyd. He and his
colleagues are attempting to genetically engineer related plants such as
tobacco and tomato to produce root nodules.

 Cereals have a huge nitrogen demand. But legumes not only provide nitrogen
for themselves, but also for other plants.

Self help

Nodule production is normally initiated when nitrogen-processing bacteria
enter a plant's root cells. The plant senses the bacteria and its root cells
grow to form a nodule.

But the two research groups, Oldroyd's team and a group led by Jens
Stougaard of the University of Aarhus, Denmark, found that by mutating a
gene that produces a cellular messenger called CCaMK, root cells can be
converted into nodule-forming cells, even without the bacteria. They report
their discovery in this week's Nature1,2.

The idea that a self-fertilizing facility could be set up in other crop
plants has not yet been tested, although Oldroyd says that his work on
tobacco and tomato should reveal whether this occurs.

There is no theoretical reason why it shouldn't work, says Oldroyd. "We can
make empty nodules, but the plant has to allow the bacteria to invade," he
says. "But if legumes can do it, others should be able to as well."

The technology is in its infancy: "A number of key steps need to be
achieved," Stougaard warns. But he hopes that it could be used to make
self-fertilizing versions of the world's main food staples: maize, wheat,
barley and rice.

****************************************************************

Nature 441, 1149-1152 (29 June 2006) | doi:10.1038/nature04812;
Nodulation independent of rhizobia induced by a calcium-activated kinase
lacking autoinhibition
Cynthia Gleason1, Shubho Chaudhuri2, Tianbao Yang2, Alfonso Muñoz1, B. W.
Poovaiah2 and Giles E. D. Oldroyd1

Nature 441, 1153-1156 (29 June 2006) | doi:10.1038/nature04862;
Deregulation of a Ca2+/calmodulin-dependent kinase leads to spontaneous
nodule development
Leïla Tirichine1, Haruko Imaizumi-Anraku2, Satoko Yoshida3, Yasuhiro
Murakami2, Lene H. Madsen1, Hiroki Miwa4, Tomomi Nakagawa5, Niels Sandal1,
Anita S. Albrektsen1, Masayoshi Kawaguchi5, Allan Downie4, Shusei Sato6,
Satoshi Tabata6, Hiroshi Kouchi2, Martin Parniske3, Shinji Kawasaki2 and
Jens Stougaard1