The unusual scent of titan arum (Amorphophallus titanum), more commonly known as the corpse flower for its strikingly putrid smell, has fascinated scientists for a very long time.
They've also been intrigued by the plant’s peculiar ability to warm itself up just before flowering (itself another curiosity, for it blooms only very rarely), using a process called thermogenesis – an unusual trait among plants, which remains poorly understood.
In a recent study led by New Hampshire's Dartmouth College, researchers have delved into the flower’s inner workings to uncover the genetic pathways and biological processes that drive both heat production and odour release during its bloom.
Published in PNAS Nexus, the paper, led by Professor G. Eric Schaller (a molecular biologist and horror fiction writer), reveals a new and significant ingredient of titan arum’s pungent scent – an organic compound known as putrescine.
A warm, putrid scent
Schaller and his team seized the opportunity of several blooms by 'Morphy', a 21-year-old titan arum housed at Dartmouth’s Life Sciences Greenhouse in New Hampshire, USA, to collect tissue samples for genetic and chemical analysis.
Interestingly, the titan arum isn’t a single flower, say the researchers, it’s a cluster of many small flowers hidden within a colossal central structure called the spadix, which can reach up to three metres (12 feet) in height – that's as tall as a large Asian elephant.
This spadix is a key visual feature of the plant and, when it finally blooms after a typical wait of five to seven years, it does so overnight. “The blooms are rare and short-lived, so we only have a small window to study these phenomena,” Schaller explains.
At the base of the spadix, a ruffled petal-like layer called the spathe unfurls, forming a cup around the stalk with a deep-red or maroon interior. Shortly after, the spadix begins to heat up, rising up to 20 degrees Fahrenheit above the surrounding air temperature. This warmth is followed by the plant’s signature foul scent – a blend of sulphur-based compounds that attract flies and carrion beetles to aid in pollination.
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Into the flower
When Morphy bloomed in 2016, the research team gathered nine tissue samples over three nights, including sections from the lip and base of the spathe and the spadix's towering spike, known as the appendix. Two additional leaf samples were later added to the collection.
Alveena Zulfiqar, an exchange research scholar in Schaller’s lab, developed a technique to extract high-quality RNA (a molecule found in most living organisms) from the tissue samples. This enabled the team to analyse RNA sequences and reveal the roles specific genes play in producing both heat and the characteristic odour.
“This helps us identify which genes are active, especially those involved in heating the appendix and emitting scent,” explains Schaller, whose work as a molecular biologist explores how plant hormones regulate growth and environmental response. Schaller, also a writer of horror fiction, says, “the corpse flower fits well in both these worlds.”
Thermogenesis – the ability to produce heat – is common in animals but rare among plants. Schaller explains that in animal cells, proteins known as uncoupling proteins disrupt the storage of chemical energy, releasing it instead as heat.
The team’s RNA analysis showed that genes linked to plant analogues of these proteins, called alternative oxidases, exhibited higher expression during flowering, especially in the appendix. Genes involved in sulphur transport and metabolism were also particularly active at this stage.
To further investigate the biochemical processes at work, researchers isolated tissues from Morphy during a later bloom, collaborating with the University of Missouri to measure amino acid levels. The analysis revealed high concentrations of methionine, a sulphur-containing amino acid that can easily vaporise upon heating, contributing to the plant’s strong odour. Methionine levels dropped noticeably in tissues sampled a few hours later.
A surprise finding was the elevated levels of another amino acid in the spathe, serving as a precursor to putrescine – a compound found in decaying animals.
What's next?
This study marks the first time researchers have decoded the titan arum’s scent at a molecular level, identifying the processes through which it regulates temperature and how its different parts contribute to the odour that attracts pollinators.
Morphy holds yet more secrets, Schaller says, as his team now aims to uncover the signals that predict blooming and whether plants housed together might synchronise their blooms to increase the odour and draw more pollinators.
Main image: a close-up shot of the spathe on a titan arum at Arnold Arboretum, Boston, USA/Jessica Rinaldi, Getty
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