Why does the corpse flower smell like rotting flesh?

The corpse flower is infamous for its rare blooms and its signature odor, which mimics the stench of rotting flesh, drawing crowds to greenhouses worldwide. The plant’s blooms are infrequent and short-lived, making it difficult for scientists to study. 

Alongside its unusual scent, the corpse flower, or titan arum, possesses a rare ability among plants: it heats itself up just before blooming, a process called thermogenesis. 

Now, a study led by Dartmouth College delves into the molecular workings behind the corpse flower’s odor and heat production.

Source of the corpse flower’s odor

The study, published in PNAS Nexus, was led by G. Eric Schaller, a Dartmouth professor specializing in plant biology, who, with his team, used blooms from Morphy, a 21-year-old corpse flower at Dartmouth’s Life Sciences Greenhouse, to analyze the plant’s unique biological processes. 

This study not only revealed how the plant warms itself but also uncovered a new component of its distinctive odor: putrescine, a compound often found in decaying animal tissue.

“The blooms are rare and also short-lived, so we only get a small window to study these phenomena,” Schaller said, explaining the challenges of studying such an elusive plant.

Structure and blooming cycle 

The titan arum bloom structure isn’t a single flower but a cluster of small flowers hidden within a massive spadix – the central spike-like structure that can grow up to 12 feet tall. 

The spathe, a frilly petal-like layer at the base of the spadix, unfurls to reveal a deep red interior. As blooming begins, the spadix heats up significantly, sometimes reaching up to 20 degrees Fahrenheit above the surrounding temperature, while releasing its pungent scent. 

This unique “carrion cologne” attracts pollinators like flies and beetles, which are drawn to the sulfur-based compounds emitted by the spadix.

Genetic pathways of the corpse flower 

To investigate how the titan arum generates both heat and odor, the research team collected tissue samples from Morphy during a 2016 bloom, focusing on various areas of the spathe and spadix over three nights. 

By extracting high-quality RNA from the tissues, exchange scholar Alveena Zulfiqar enabled the team to analyze RNA sequences and determine which genes were active during the plant’s heating phase.

“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 RNA analysis revealed that genes linked to sulfur transport, metabolism, and a plant protein known as alternative oxidase – essential to heat production – were especially active in the appendix area during flowering.

The role of amino acids

The team turned to mass spectrometry to measure different amino acids within the plant’s tissues, working with collaborators from the University of Missouri. 

The analysis confirmed high levels of methionine, a sulfur-based amino acid, in tissues collected as flowering began. 

Methionine, known for vaporizing when heated, contributes to the corpse flower’s sulfurous smell. Levels of methionine dropped quickly in tissues collected just hours later, supporting its role in the plant’s initial odor production.

Unexpectedly, the researchers also detected elevated levels of another amino acid in the spathe tissues: a precursor for putrescine, a compound common in decaying animals. 

What came as a surprise, Schaller noted, was finding putrescine – which adds an authentic element to the corpse flower’s cadaver-like scent.

Thermogenesis in plants

Thermogenesis, or heat production, is common in animals but rare among plants. In animals, this process involves uncoupling proteins that release energy as heat instead of storing it. 

In the titan arum, the plant counterparts of these proteins – alternative oxidases – play a similar role in heating. By examining the unique ways these proteins function in the corpse flower, the researchers shed light on the mechanisms plants can use to generate heat.

Unanswered questions about the corpse flower 

While the team’s findings reveal much about the corpse flower’s odor and heat production, Schaller and his colleagues are still investigating other mysteries. 

One area of interest is understanding the triggers that prompt flowering and exploring whether multiple corpse flowers could synchronize their blooms. 

Schaller suggests that synchronized blooming could amplify the plant’s scent, potentially increasing the attraction of pollinators.

With this study, scientists have taken a significant step in understanding the molecular processes behind the corpse flower’s unique traits. 

Future research may further reveal how these mechanisms contribute to the plant’s survival and its interactions with the environment, providing valuable insights into the unusual adaptations of this giant, mysterious bloom.

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