Posted originally: 19 February 2016
Being
adapted to floods isn’t ideal if you’re growing in a dry place
Peter Crisp
Plants can teach us a thing or two
about dealing with the ups and downs of life. They may have evolved the ability
to forget stressful situations, as a way of dealing with highly unpredictable
environments.
Such experience helps prime plants to
produce the necessary proteins and chemicals at short notice should stressful
conditions recur.
Plants can preserve such memories
across generations, at times via epigenetic mechanisms, which influence whether
or not genes are expressed.
Better to forget?
But
when Peter Crisp at the Australian National University
in Canberra and his colleagues scoured the literature for examples of such
memory of stressful events, they found that memory is more the exception rather
than rule. “Generally plants are good at forgetting,” says Crisp.
The team argues that plants are
making a trade-off. While being epigenetically primed against previously
experienced stress can be beneficial, it also comes with costs.
“You
could have an organism that’s spending way too much energy transcribing genes
that really aren’t necessary at a specific time,” says team member Steven
Eichten.
What’s
more, such memory can be bad for future generations. For example,
drought-stressed Polygonum hydropiper, a knotweed,
passes on its stress response to seedlings, which become smaller, with
slower-growing roots – even if they are grown in a drought-free environment.
Competing processes
Crisp and his team say that whether a
plant forms a memory depends on what happens after a stressful experience.
During this “recovery phase”, the plant can either consolidate its stress
response and remain genetically primed, or reset itself to its prior state.
For a new memory to be formed, a
plant has to make a protein that will affect its own DNA, affecting future
behaviour.
This memory formation has to contend
with a process called RNA decay. In cells, double-stranded DNA is transcribed
into single-stranded RNA, before being translated into proteins.
RNA decay regulates the amount of RNA
molecules that can be turned into proteins, and it can disrupt the RNA
molecules related to the stress response, thus preventing memory formation, say
Crisp and his colleagues.
Plants,
it seems, would rather forget than hold grudges. “I like this idea very much,”
says Frantisek Baluska, who studies plant intelligence and
behaviour at the University of Bonn, Germany.
But he points out that plants also
have “short-term memory”, which doesn’t depend on DNA and RNA. “This type of
memory is not studied properly in plants,” he says.
