Chemical Warfare by Plants

Professor Byron Lamont from Curtin University of Technology Australia, and his colleagues, has come up with some surprising findings regarding the defence mechanism of plants. The Australian native plant Hakea is using chemical warfare to prevent its bright red flowers being eaten by animals. This goes against established beliefs. The belief till now was that flowers evolved as a way for plants to attract birds and animals for cross-pollination.

The team studied 51 species of Hakea, and found that they could be easily divided into two groups, insect-pollinated species and bird-pollinated species. Insect-pollinated species have predominantly tiny, white flowers surrounded by spiky, dense foliage. This stops animals such as emus and cockatoos from eating the flower. Bird-pollinated species have soft open leaves and bright, easily accessible, usually red, flowers where birds can easily land. This makes the plant vulnerable to being eaten by emus and cockatoos.

Professor Byron Lamont and his colleagues macerated the flowers on-site and then used an enzyme and a strip of paper that was sensitive to cyanide to test for its presence. They found that plants with red flowers contain 10 milligrams of cyanide per gram. This was enough to make an animal sick. It is presumed that animals that eat the red Hakea flowers may learn to associate the colour with the bitter taste produced by the cyanide. The colour red acts as a warning to herbivores like emus, parrots and kangaroos sending the message that the flower contains distasteful cyanogenic compounds.

Details of the study appear in the latest edition of journal New Phytologist.