This week RadioLab did an episode titled “Plant Parade”, which was a set of stories about the real, if bleeping crazy, science of plant cognition and communication .
The reports covered plant roots that sense the sound of water, plants that apparently exhibit Pavlovian learning, and the super-mega-awesome Wood Wide Web.
The latter I had heard of, and the others are akin to other studies, not to mention The International Laboratory of Plant Neurobiology and the Society of Plant Signalling and Behavior.
The radio report tied these findings together with the general idea that plants (and fungi) exhibit these behaviors, including memory and learning, but lack both brains and nervous systems.
This isn’t quite the paradox as it might seem, at least to me.
It is clear that these organisms do not have anything that resembles a human or any animal nervous system. But it is equally clear that they have systems that are analogous, even though we have little notion of how they might work.
For example, the tips of tree roots have tiny hairs, which very well could vibrate in response to sounds. This could, in principle, be translated into chemical signals, which could control the growth of the root. This hasn’t been documented, but it would amount to an auditory sense, just like human hearing.
But of all the wonders discussed, the reported ability of plants or forests (which are networks of many organisms of multiple species) can, in fact, learn and remember is the most intriguing. We have some understanding of how animals learn, which is definitely dependent on the nervous system and, in humans, our brain. We also understand engineered memory systems we have built for our computers, which depend on physical traces encoded in various media.
But we have no clear understanding of how plants, or forest networks, might “remember” something, or related, communicate something to another plant or organism.
This question of how they might do it really rang a bell for me, of course, because I had just read about transfer of memory via RNA between two snails.
The snail study seems to indicate that the long missing “engram” may, at least in part, involve epigenetic coding of DNA via RNA.
(It is particularly satisfying to think that the answer to one of the most grievous gaps in neurobiology, “the engram”, might be another of the most grievous gaps in molecular biology, “junk (sic) DNA”.)
If snails can transfer memories via RNA, and, indeed, these memories are encoded in the DNA of certain cells, then anything with DNA could do the same. (For that matter, any type of cell might store memories in DNA, not limited to neurons.)
Plants have DNA and RNA, as do fungi, and microbes of all types. I can’t think of any reason, in principle, why a plant couldn’t store memories in some cells in the same way that snails apparently store it in specific types of neurons. At least, in principle.
I would note that the forest web of multiple species of trees plus fungi and who know what else might also pass around RNA, or have some mechanism that effectively transduces RNA across a channel to create semantically equivalent RNA at the receiver.
If we understood this mechanism we could talk to the trees! We could program the forest!
Obviously, this is all speculation. But I think it’s reasonable enough that, were I a younger man, I’d want to investigate. And were I a billionaire, I’d want to fund teams to investigate.
- Robert Krulwich, Plant Parade, in RadioLab, R. Krulwich, Editor. 2018. https://www.wnycstudios.org/story/plant-parade