FIU scientists find animal pigment in plants

The jaundice pigment bilirubin, only thought to exist in animals, has been discovered in the seed arils of bird-of-paradise trees.

By Sissi Aguila

A team of FIU scientists have found the bilirubin pigment – the yellowish hue associated with bruises and jaundice sufferers – in the white bird-of-paradise tree. This is the first example of animal pigment in a plant.

The findings were reported earlier this year in the prestigious Journal of the American Chemical Society. The primary author is Cary Pirone, a doctoral student in biology at FIU. Contributors include David Lee, professor of biology; Martin Quirke, professor of chemistry; and Horacio Priestap, a visiting researcher in the Department of Biological Sciences.

“This study, along with future work, will help with our understanding of the evolutionary history of bilirubin in the plant kingdom,” explains Pirone, who was the first to discover that bilirubin is the major pigment of the orange aril of Strelitzia nicolai, commonly known as the white bird-of-paradise tree.

“It will likely necessitate the revision of the plant tetrapyrrole pathway since there is currently no known mechanism of bilirubin production in the plant kingdom.”

In the animal kingdom, bilirubin is leftover in the breakdown of blood. How plants produce this pigment is still a mystery.

“The fact that bilirubin exists in both plants and animals may demonstrate the depth of evolution,” Pirone said. “If bilirubin is synthesized via the same biochemical pathway which is responsible for producing bilirubin in animals, this would indicate that the pathway was likely conserved throughout evolutionary history in both the plant and animal kingdom.”

The white bird-of-paradise tree first struck researchers as interesting because its color stays vibrant at least a decade. Native to South Africa but widely cultivated in South Florida and the tropics, the plant produces woody capsular fruits with black, pea-sized seeds that grow a bright orange aril or tuft of waxy ribbons.

The bird-of-paradise tree’s furry seed

After closer examination, Pirone found that the orange pigment’s compound did not match the chemical properties of any known plant pigments. For more than a year, she ran several tests to identify the pigment. A nuclear magnetic resonance test confirmed it was bilirubin.

“This research was conceived entirely at FIU and conducted completely by FIU scientists,” said Lee who has been interested in plant pigments for 15 years.

It was a collaborative effort that required both biologists and chemists. “Science is moving toward this type of interdisciplinary work,” said Pirone, of working with FIU chemist Martin Quirke.

Pirone is now expanding her research – funded by the U.S. Environmental Protection Agency, the McBryde Science Program at the National Tropical Botanical Garden, and RISE Biomedical Research Initiative – to provide a more thorough understanding of the evolutionary origin of this pigment in plants. She has already found bilirubin in sister species with orange and blue flowers.