Dartmouth scientists studied genes and discovered a new chemical compound responsible for titus arum’s pungent odor. The unusual scent of the titan arum, often referred to as the corpse flower because it smells like rotting flesh, attracted crowds of curious visitors to greenhouses around the world in the 19th century. rare flowering. What also intrigues scientists is the corpse flower’s tendency to heat up before flowering through a process known as thermogenesis, an unusual plant trait that is not well understood.

Now Dartmouth-led research is looking beneath the hood of the corpse flower to uncover the underlying genetic pathways and biological mechanisms that control the plant’s production of heat and odorous chemicals during flowering. In a paper published November 4 in the journal PNAS Nexus, Professor of Biological Sciences G. Eric Schaller also identified a new component of corpse flower scent: an organic chemical called putrescine.

Schaller and colleagues used several flowers of Morphy, the 21-year-old Dartmouth corpse flower housed in the Life Sciences Greenhouse, to collect tissue samples for genetic and chemical analysis.

Titan arum is not a single flower, but a group of small flowers called spadixes, hidden inside a giant central stem that can grow up to 12 feet tall and is the plant’s most striking visual feature. The plant may not bloom for years (usually the bloom interval is 5-7 years), but when it does bloom it blooms overnight. “Blooms are rare and short-lived, so we only have a small window to study these events,” says Schaller.

At the base of the blade, a frill-like petal-like layer called the scapula opens around a central handle to form a cup with a dark red or maroon interior. Spadix begins to warm up, the ambient temperature rising to 20 degrees Fahrenheit, soon the plant’s distinctive scent appears; This smell comes from a cocktail of foul-smelling sulfur-based compounds that attract flies and carrion beetles that help the plant reproduce. .

Genetic analysis and results

When Morphy bloomed in 2016, researchers collected nine tissue samples over three nights from the moment spadix temperatures peaked; from the lip and base of the spadix, as well as from the long pointed end of the spadix, known as the appendix. They later added two more leaf specimens to their collection.

Alvina Zulfikar, a metabolism researcher working in Schaller’s laboratory at the time, figured out how to extract high-quality RNA from tissue; This allowed the team to sequence the RNA and determine the genes’ role in heating the plant and causing disease. smell.

“This helps us see which genes are expressed and which ones are particularly active when the appendix gets hot and emits an odor,” says Schaller, a molecular biologist who studies how plant hormones regulate their ability to grow and respond to changes in the body. . their environment. She also dabbles in writing short fiction, particularly horror fiction: “Corpse Flower fits both of those worlds very well,” she says.

Thermogenesis, or the ability to produce heat, is common among animals but rare among plants. In animal cells, a class of proteins called uncoupling proteins interrupts the process of accumulating chemical energy, releasing it as heat, Schaller says.

RNA analysis showed that genes related to the plant counterparts of these proteins, known as alternative oxidases, showed higher expression in tissues removed at the beginning of flowering, particularly the appendix. Genes involved in sulfur transport and metabolism were also active during this period.

The role of amino acids in corpse flower odor

To track the mechanisms that trigger these genes, the team isolated plant tissues during subsequent flowering and, working with colleagues at the University of Missouri, used mass spectrometry to identify and measure the levels of different amino acids (molecules that make up proteins) in the plant tissues. them.

They found high levels of a sulfur-containing amino acid called methionine, a precursor to sulfur-containing compounds known to volatilize easily when heated and produce a pungent odor, as predicted from RNA analysis. After a few hours, methionine levels decreased rapidly in the collected tissues.

Schaller said the surprise was that tissues taken from the aviary found high levels of another amino acid that serves as a precursor to the production of the compound putrescine, the odor found in decomposing dead animals.

This study, for the first time, unlocked the secrets of corpse flower scent at the molecular level, identified the processes by which titanium arum regulates temperature, and revealed the roles that different parts of the flowering cluster play in creating the carcass cologne that attracts pollinators. .

Schaller says Morphy still holds many mysteries; is currently focused on understanding the triggers that predict flowering and whether co-housed specimens can synchronize flowering and collectively increase scent levels to attract more pollinators.