Fiery defense: Venus flytrap snaps shut when it detects heat from fire

The swamps of North and South Carolina are notorious for being nutrient-deprived, making them seemingly inhospitable for many plant species. 

However, the Venus flytrap has developed a unique survival strategy. Instead of relying solely on the scant nutrients in the soil, it’s evolved to become a carnivore, catching and consuming small animals for nourishment. 

Potentially catastrophic environment 

Its notorious snap traps, equipped with sensitive sensory hairs, trap and digest its prey, compensating for the lack of nitrogen, phosphate, and minerals. Yet, in the midst of swamps, another threat looms over these carnivorous wonders: fires.

Hidden beneath the tall, drying grass of these swamps, the Venus flytrap often remains unseen. As the summer progresses, this grass becomes particularly flammable, especially during the frequent lightning storms that North Carolina is known for. This creates a potentially catastrophic environment for the flytrap.

Focus of the study 

Professor Rainer Hedrich and Dr. Shouguang Huang, biophysicists from Julius-Maximilians-University (JMU) Würzburg in Bavaria, Germany, delved into the question of how this plant safeguards its critical snap traps and sensory hairs from fire. 

The findings reveal an astonishing adaptation. The flytrap uses specialized heat receptors situated within the sensory hairs to detect and respond to heat.

“To find out how the flytrap behaves when burning a covering of dry grass, we transplanted plants with open snap traps from the greenhouse to the open field in the JMU Botanical Garden and covered them with hay,” explained Hedrich. “Then we set fire to the hay at one end and forced it to spread to the other end with a fan.”

What the researchers learned 

The aftermath? The flytraps had sealed all their traps, with some appearing charred, while others remained untouched. Remarkably, in just a few days, the undamaged traps resumed their usual function, snapping upon touch.

Further investigation led the JMU team to discover that these plants could detect impending fires even before the flames touch them. 

“We had only recently elucidated the stimulus-response chain during trap closure after wounding. Now the question arose whether the traps might already react to the heat wave in the run-up to a fire,” explained Hedrich.

Laboratory experiments confirmed their suspicions: directing a hot air blower at a trap was enough to trigger it to close.

“We propose that by sensing the temperature differential, flytraps can recognize the heat of an approaching fire, thus closing before the trigger hairs are burned, while they can continue to catch prey throughout hot summers,^ wrote the study authors. 

Flytrap defense strategy 

Dr. Shouguang Huang’s controlled experiments revealed more about the mechanism at play. The Venus flytrap’s trap, comprising two leaf halves, was exposed to varying temperatures using a Peltier element. 

“When the temperature increased further to 55 degrees Celsius, a second action potential was triggered and the trap snapped shut,” explained Dr. Shouguang. 

Interestingly, the flytrap’s response at these temperatures activates specifically when subjected to a sudden heat wave, not a gradual increase, as Hedrich notes, “it reacts to the speed of the temperature change.”

This rapid response ensures that the sensory hairs of the flytrap remain unscathed, and the damp marshland further shields them from severe heat. This intricate defense mechanism ensures that the Venus flytrap can continue its carnivorous pursuits even post-fire.

Astonishing results

The true marvel lies in the sensory hairs themselves. These hairs are not only touch-sensitive, generating action potentials that lead to the snap of the trap but also react to sudden heat. 

“To track the calcium signal, we used flytraps that carry a genetically encoded calcium sensor inside them,” said Hedrich. The results were astonishing, with the sensory hair lighting up when exposed to heat. “This shows that the hairs operate as touch and heat sensors at the same time.”

Currently, the JMU team is exploring the possibility of a calcium channel being a crucial part of the heat sensor. If proven true, they could be on the verge of unveiling a type of membrane-bound temperature sensor, previously unknown in plants.

The research is published in the journal Current Biology.

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