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Last Updated:  Wednesday, 5 March, 2003, 11:29 GMT
Gene clue to secrets of the fall
A genetic "calendar" produces autumn's beauty
Dozens of genes may help tell trees when it is time to shed their leaves for winter, say scientists from Sweden.

They believe that altering the genetic makeup of trees could help make species used to warmer climes able to flourish in colder regions.

The researchers, based at Umea University and the Royal Institute of Technology in Stockholm, tested leaves from native aspen trees to see which genes were active at various times of year.

They found more than 2,400 expressed in the leaves at various times of the year - but only 35 expressed in huge quantities in leaves as they changed colour ready to drop in Autumn.

The transformation of deciduous trees in autumn is a key factor in their ability to survive harsh winters.

Recycling plant

The plant must retrieve and recycle as many nutrients of the leaf as possible prior to the arrival of cold weather.

In the future, it should be possible to apply genetic technology to the creation of trees that have another inner calendar than the 'natural' one
Professor Stefan Jansson, Umea University
Once severe frosts are killing leaf cells, this process is halted and the leaf can only fall off.

Effectively, the tree needs an inner mechanism that predicts the arrival of the first frosts of winter - and starts the recycling process going in advance of this.

Scientists believe that trees that shed their leaves have an inbuilt mechanism, perhaps triggered by the reduction in daylight hours as autumn approaches.

The Umea team thinks that that some of the 35 genes that it has found could be instrumental in the breakdown of the green chlorophyll in the leaves and the formation of the yellow and red chemicals which give autumnal colour to the leaves.

On and off

Professor Stefan Jansson, in the university's Department of Physiological Botany, said: "The aim of this research is to understand how it all works, and to do this we are now studying when all of these genes are turned on and off during the autumn.

"If we grasp what determines when autumn leaves turn yellow, we can identify those trees which have an optimal 'calendar' for various climactic zones, that is, those that do not turn colour too late and therefore lose nutrients and suffer frost damage, or turn too early and therefore stop growing too early in the fall.

"In the future, it should be possible to apply genetic technology to the creation of trees that have another inner calendar than the 'natural' one.

"But whether we can modify the genes of peach trees so they can survive in the Umea area is another matter entirely."

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