[Intro]
Being warm-blooded is really convenient.
For one thing, you can go outside when it’s snowing or hot without having to worry too
much about your body processes shutting down.
But not all organisms regulate their body temperature, because it’s a big drain on
energy resources.
It’s mostly just birds, mammals… and some plants.
A few hundred species of plants produce their own heat in a process called thermogenesis,
and some of them use that heat to regulate their body temperature.
It’s based on the same idea as warm-bloodedness in animals: energy can be released as heat.
Plenty of your normal, everyday metabolic processes, like digestion, release heat as
a byproduct.
But if that’s not enough, you can also shiver, causing the chemical processes involved in
muscle contractions to release more heat.
When an animal can’t shiver -- like a newborn human baby, or a hibernating bear -- it can
burn brown fat instead, a special kind of fat that’s full of glucose and produces
lots of heat when it’s broken down.
But plants can’t shiver, and they don’t have brown fat.
So plants produce heat using another mechanism, a type of cellular respiration known as thermogenic
respiration that takes place in their mitochondria.
Mitochondria are usually described as the powerhouses of the cell, and for good reason:
their job is to store energy in the form of the molecule ATP.
But in thermogenic respiration, the mitochondria skip the ATP and just release the energy as
heat.
At the most basic level, thermogenesis just keeps these plants warmer than their surroundings.
But a handful of species, like the eastern skunk cabbage and the sacred lotus, take it
one step further, with feedback mechanisms that they use to keep their body temperatures
within a certain range -- or thermoregulate.
In thermoregulatory plants, decreasing internal temperatures trigger more cyanide-resistant
respiration, keeping them warm.
And if their temperatures get too high, they just produce less heat and start to cool off.
Now thermogenesis might seem like a huge waste of energy -- and it is.
But for these plants, the advantages make the energy loss worth it.
In some cases, it helps them avoid frost or keep snow away.
The skunk cabbage, for example, can melt through snow, giving it early access to pollinating
insects while other plants are still buried.
But many thermogenic plants are tropical, so they wouldn’t have much reason to develop
resistance to frost.
And plenty of plants bloom just fine when it’s cold out.
Other plants are trying to attract pollinators, either by providing the perfect temperature
for mating insects, or just by making themselves smellier.
Like a dumpster on a hot day, a warmer plant will smell a lot worse.
For instance, when a dead horse arum is blooming, it releases more than a hundred volatile compounds
in its attempt to lure hungry bugs to the smell of rotting flesh.
It only blooms for a couple of days every few years, so it needs to attract as many
pollinators as possible.
But it also needs to trap them there for a while.
In the dead horse arum, the female florets mature on the first day, but the male florets
mature on the second day.
So the pollinators are most effective if they stick around long enough for both phases.
When a fly crawls down into the base of the flower, a series of spines keep them from
getting out again.
Hopefully, the fly’s picked up pollen from an earlier-blooming flower, so the female
florets get pollinated.
The next day, the male florets release their pollen, which attaches to the fly.
Then, the spines wither, so the fly can go free, and it falls for the same trick again,
landing on what it thought was a lump of dead flesh but turns out to be another flower in
disguise.
Good news for the bugs though: there might be benefits for them too.
One study looked at the species of beetles that pollinate thermoregulating philodendrons.
Normally, these beetles have to produce lots of heat themselves so that they can stay active
at night.
But the researchers found that when the insects were trapped in the flowers overnight, they
only needed to use about half as much energy.
For an insect, landing a thermogenic plant is like curling up next to a nice, warm radiator.
Just… one that happens to smell like a dead horse.
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