Pretty on the inside

We have some plants in Sydney's Royal Botanic Gardens that aren’t much to look at, but they tell a great story.

One good example is Leucaena leucocephala from Mexico. The National Botanic Garden of Cuba sent us some seed of this species in 1990.

It’s now a robust, but not particularly attractive, shrub, growing behind the Tropical Centre. It’s closely related to our wattles and has similar flowers and pods.

Outside not so interesting, but inside a different story. The leaves and seeds contain an amino acid called ‘mimosine’ (this species and our wattles are in the subfamily Mimosoideae of the pea family).

Mimosine is a simple chemical, but it has does one interesting thing. A Friend of the Gardens, and previously a Professor of Organic Chemistry at University of Sydney, Alex Robertson, describes it as having ‘depilatory properties’.

In the 1960s and 1970s it was being tested for chemical shearing of sheep. It can stop the growth of hair or wool, and in some cases cause the fleece to shed. In the end it proved unsuccessful, but work continues looking for a synthetic chemical that does the same kind of thing.

Shearing is a tough job and there are few young people entering the industry, so mimosine or something like it may be the saviour of the wool industry in a decade or two.

Mimosine may have other uses too. More recently it has been found to inhibit the replication of DNA in mammal cells and may have some potential in research into DNA synthesis and some medical applications. It has also been proposed as a herbicide or anti-fungal treatment.

Leucaena is a highly nutritious stock food, and planted widely in tropical regions including Australia. However due to some of these attributes mentioned above, cattle can be drenched in ‘mimosine-degrading bacteria’ if grazing heavily on this legume.

Also anything producing tough wattle-like seeds has to be watched for its weedy potential. So we do have to make sure a plant like this never escapes from the Gardens. But while it’s here you can think about sheep, shearing and maybe even shaving.

Image: The outside of the plant in question, in Sydney's Royal Botanic Gardens. *This posting is from the Radio Archives (April 2008).