Why leaves fall from trees

Us researchers have published a paper in the Proceedings of the National Academy of Sciences (PNAS) in which they explain the sequence of events that cause plants to shed their leaves.

Writing in the UK’s Telegraph newspaper, science editor Roger Highfield explained that trees use an elaborate cellular mechanism to part company from their leaves, which act as “solar cells” in the summer but become superfluous in the darker winter months.

Reporting the researchers’ findings, he said that at the base of each leaf is a special layer called the abscission zone.

When the time comes in autumn to shed a leaf, cells in this layer begin to swell, slowing the transport of nutrients between the tree and leaf.

Once the abscission zone has been blocked, a tear line forms and moves downwards, until eventually the leaf is blown away or falls off. A protective layer seals the wound, preventing water evaporating and bugs getting in.

The discovery into how trees take on their winter aspect follows a study explaining the bright colours of autumn foliage.

Source: UK Telegraph newspaper

Date: 22/09/2008

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