We will
never stop carrying a torch for plants — they are way more amazing than most people
give them credit for. They can hear oncoming attackers, & many send
noxious chemicals into their leaves to fight back. Some even have a
primitive sense of sight. So believe me when I say this: They don't like it
when you pet them. According to research, they have a very strong reaction to
touch.
Plants' hatred of cuddles is nothing
new to scientists. In the early 1960's, for instance, scientist Frank Salisbury
was studying how cocklebur plants grew by measuring their leaves with a
ruler every day. Weirdly, he noticed that the plants he was measuring didn't
grow as much as their neighbors & they eventually shriveled up & died.
He concluded that it was simply the act of touching the plants that killed
them.
A decade later, a plant physiologist named Mark Jaffe published
the first work on this phenomenon & coined the first word for it:
thigmomorphogenesis (in Greek, thigmo means "touch," morpho
means "shape," & genesis means "origin."). Of the dozen
or so plant species he used in his study, six had slowed growth after being
touched daily. After a few more days of no touching, however, they resumed
their regular growth rate.
In 1990,
plant biochemist Dr. Janet Braam discovered that this stunted growth
happened because of a genetic change. Touching a plant led to a specific
handful of its genes being activated, which she named the "touch"
(TCH) genes.
In
December, researchers at La Trobe University in Australia took a closer
look at this phenomenon to uncover exactly what was going on inside of the
plant to activate these genes. For their study, the researchers used a plant
called thale cress (Arabidopsis thaliana), a plant that's known to pump
its leaves with toxic mustard oil when insects attack. The
scientists stroked the leaves of the plants with a soft paintbrush every 12
hours, then measured their biological response at varying periods of time after
each stroke.
They
found that within 30 minutes of being touched, 10 percent of the plant's genome
had been altered. At the site where the plants had been stroked, their
mitochondria had ramped up their activation of genes known to suppress the
touch response. Even more interesting, the same thing had happened at other
places on the plant that hadn't been touched, though to a lesser degree.
Specifically, the mitochondria altered the genome by tweaking the plant's
immune system & hormone levels.
"This
involves a huge expenditure of energy which is taken away from plant growth. If
the touching is repeated, then plant growth is reduced by up to 30
percent," said professor Jim Whelan, the lead researcher on the study
& research director of the La Trobe Institute for Agriculture & Food.
Why would
this be? It makes sense for a plant to send out toxic chemicals when it feels
the brush of a caterpillar since that could help convince the predator that
it's not a tasty snack. But to inhibit growth after too much touching? That
seems like cutting off the nose to spite the face.
But
there's some logic there. For example, if plants grow too close together,
they'll get less light & fewer nutrients. Growing smaller could be a way to
ensure that there's enough to go around, co-author Dr. Yan Wang explained.
This new
research might help farmers know exactly how far to space their plants to
ensure they grow as big as possible. Knowing the genetic mechanisms at play in
a plant's touch defenses might even help scientists engineer plants that aren't
as touch sensitive. For that, though, they have to be careful, since it could
be easy to knock out some other important senses in the process, like
sensitivity to cold & heat & disease defense.
But as for houseplants, the message is clear: water them, give
them sunlight, even play them music if you'd like to. But don't pet them. They
don't like it when you pet them.
(curiosity.com/Ashley Hamer)
(curiosity.com/Ashley Hamer)
