If you smell a rotting corpse, it could be one of two things: an actual rotting corpse, or—if you’re lucky—just a giant smelly flower called titan arum. Now, scientists have identified the molecular reasons behind this iconic plant’s pungent aroma.
A team led by G. Eric Schaller from Dartmouth College has shed light on the molecular mechanisms that drive titan arum’s stench as well as its warming ability, which gets triggered directly before blooming. A new study, published on November 4 in PNAS Nexus, reveals for the first time that the titan arum contains a chemical called putrescine. Although putrescine is a known compound, this is the first time it’s been identified in the titan arum, where it plays a key role in creating the plant’s distinctive stench.
Appropriately dubbed the “corpse flower,” the titan arum is actually a cluster of tiny flowers within a huge central stalk called the spadix, which can grow up to 12 feet (3.7 meters), according to a Dartmouth College statement. The spike at the top of the spadix is called the appendix. The flowers typically bloom every five to seven years, when a petal-like layer called the spathe unwraps from the bottom of the spadix into a cup-like shape.
At that point, the spadix and appendix begin to heat up in a process called thermogenesis, which can make the spadix up to 20 degrees Fahrenheit warmer than the surrounding temperature. Thermogenesis is a known trait in animals (such as shivering in humans) but it’s less common and less understood in plants, according to the statement. Soon after, the plant releases its signature rotting flesh smell: a medley of sulfur-based compounds intended to attract insects that will help the plant reproduce.
“The blooms are rare and also short-lived, so we only get a small window to study these phenomena,” Schaller, a molecular biologist, said in the statement.
Schaller and his colleagues collected tissue samples from their local corpse flower—a 21-year-old specimen named Morphy that lives in Dartmouth’s Life Sciences Greenhouse—during several blooming periods for genetic and chemical analysis. On the genetic side, they extracted and sequenced titan arum RNA to understand which genes were involved in the plant’s thermogenesis and smell.
“This helps us see what genes are being expressed and to see which ones are specifically active when the appendix heats up and sends out odor,” Schaller explained.
The biologists found that samples collected early in the corpse flower’s bloom showed higher expression of genes associated with sulfur transport, sulfur metabolism, and heat production in plants, as compared to other samples.
The Dartmouth team also collaborated with researchers from the University of Missouri to take a look at the plants’ amino acids—the building blocks of proteins—via mass spectrometry (a technique used to identify chemical substances). The results confirmed what the RNA analysis had already suggested: Elevated levels of methionine, a sulfur-containing amino acid, were present in tissue samples from the start of the bloom. Methionine is a precursor to sulfur-based compounds that vaporize easily when heated, producing pungent odors, according to the statement.
However, the scientists also detected something unexpected in samples from the titan arum’s spathe: higher levels of an amino acid that serve as a precursor for producing putrescine, the compound responsible for the smell of putrefying flesh.
This study is the first to shed light on the corpse flower’s warm and smelly mechanisms—why some greenhouses around the world smell like a murder mystery every half a decade—at the molecular level. Next, Schaller plans to investigate the triggers behind the corpse flower’s blooming, and whether multiple flowers in the same space will synchronize this process. As if we needed more stink…
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