MARY, Mary, quite contrary, how does your garden grow?

The question in this famous old nursery rhyme was today answered - by biology scientists at the University of York.

In a massive global breakthrough, scientists working at the Heslington campus have followed in the footsteps of Charles Darwin and discovered exactly how the garden grows.

The answer could be a boost to green-fingered plant lovers and farmers everywhere.

Pruning has always been an essential weapon in the gardener's armoury. But reasons why it should have such a beneficial effect on bushes, plants and trees have always been cloaked in mystery.

Now York academics have uncovered the secret of the role plant hormone auxin plays in growth.

The discovery, by biologists Professor Ottoline Leyser and Dr Stefan Kepinski, could eventually help develop more productive tomato plants, more beautiful roses and even more efficient and user-friendly renewable energy crops.

Auxin's existence was predicted by Charles Darwin in the 1880s and was finally established by researchers more than 70 years ago.

It plays a critical role in nearly every aspect of the growth and development of a plant. But the way it exerts such fundamental effects on flowers has puzzled scientists - until now.

Prof Leyser and Dr Kepinski identified the elusive auxin receptor, which binds the hormone in the cells.

Prof Leyser - who has been researching auxin for 15 years - said: "The auxin receptor is the first element in the signalling process.

"It is the way cells know how much auxin there is, and so how to respond, by for example, changing their shoot branching.

"Pruning works because the leading shoot produces auxin which is pumped down the plant and inhibits the growth of side shoots.

"Once the main shoot is removed, the auxin disappears and the side shoots grow out. The only way the side shoots know that the auxin is gone, is because it is no longer binding

to the auxin receptor."

The York research is likely to have a range of agricultural and horticultural implications in the search for sustainable energy sources.

Research results are published in the latest issue of Nature.

Updated: 08:53 Thursday, May 26, 2005