By Roger Highfield
One of the great mysteries of gardening has been solved - scientists
now think they know why roots manage to grow into soil and not above it.
The work could help develop new crops to deal with poor soils in
developing countries, according to the British team that made the discovery.

The reason that, when seeds germinate, their roots burrow instead of
pushing the seeedlings out of the flower pot is down to special hairs that
tether the root in the soil and help the roots grow their way past
obstacles, a team at the John Innes Centre in Norwich reports in the journal
Science.

"The key is in the fuzzy coat of hairs on the roots of plants" says
Prof Liam Dolan. "We have identified a growth control mechanism that enables
these hairs to find their way and to elongate when their path is clear".

Root hairs explore the soil in much the same way as a person would
feel their way in the dark. If they come across an obstacle, they grope
their way around until they can continue growing in an opening. In the
meantime, the plant is held in place as the hairs grip the soil.

The hairs are guided by a clever chemical trick that makes them seek
out soil. A protein at the tip of root hairs called RHD2 helps stimulate the
uptake of calcium from the soil, boosting growth, the production of more
protein and further uptake of calcium.

But when an obstacle blocks the hair's path, or indeed it encounters
the surface of the soil, the cycle is broken and growth starts in another
location and direction.

"This remarkable system gives plants the flexibility to explore a
complex environment and to colonise even the most unpromising soils", says
Prof Dolan. "It also explains how seedlings are able to grow so quickly once
they have established".

In nutrient-poor soils such as in parts of Australia and sub-Saharan
Africa, native plants have adapted by producing enormous numbers of root
hairs. A better understanding of this adaptation will allow the development
of hairy rooted crops able to grow in inhospitable environments.

"Breeding for plants with longer hairs will allow the development of
crops with better nutrient uptake capabilities," says Prof Dolan. "The
knowledge gained from this research will aid in the breeding of such crops
through either conventional breeding techniques or genetic modification.

"Research in the John Innes Centre is taking a conventional breeding
approach to increase hair length in wheat but it will be some time before
new cultivars are developed."


[www.telegraph.co.uk]