In the face of climate change, being able to increase crop yields by
enabling plants to take up nutrients and water more efficiently becomes
increasingly important, as fertiliser and water supplies incur significant
energy and environmental costs.

New research from the University of Bristol, published today in Nature Cell
Biology, has shown how to increase the length of root hairs on plants,
potentially improving crop yields, as plants with longer root hairs take up
minerals and water more efficiently.

Angharad (Harry) Jones, a PhD student in Biological Sciences at the
University of Bristol, and lead author on the paper, said: ?Each root hair
is a single, elongate cell and the length of each hair depends on having an
adequate supply of the plant hormone auxin. Auxin is used, for example, in
hormone rooting powders to encourage cuttings to root. The difficulty has
been in understanding how auxin is delivered to the root hairs in order to
promote their growth.?

Since auxin cannot be observed directly, Jones used a computer model built
by physicist Eric Kramer at Bard College, USA, to calculate where auxin was
likely to be in plants. The model was based on current knowledge of auxin
transport through and around the relevant cells.

What the model showed was very surprising: auxin is not delivered to root
hair cells directly, but via the cells next door which act as canals through
which the auxin is transported. During transport, some of the auxin leaks
out, supplying hair cells with the auxin signal to grow. This new
understanding will be crucial in helping farmers to produce food sustainably
and to reduce fertiliser waste, which can cause severe damage to ecosystems.

Dr Claire Grierson, senior author on the paper added: ?This important new
work is an example of ?integrative biology?, an innovative,
interdisciplinary approach that uses experimental results alongside
mathematical models and computer simulations to test ideas that are
difficult or impossible to investigate with experiments alone. This approach
has produced groundbreaking and surprising insights into a biological
mechanism that might otherwise have eluded us.?

The results also suggest that increasing the number of root hairs is likely
to interfere with auxin supply and cause problems with other important
traits like a plant?s response to gravity and root branching. The new
understanding of how to increase the length of roots hairs, rather than
their numbers, will now avoid these kinds of problems.

It was Charles Darwin and his son Francis who, in 1880, first discovered
that plants direct their growth towards the light. These observations would
later lead to the discovery of auxin.
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