The Mental Life of Plants and Worms, Among Others

Mr.Samsa · **#41** by **Mr.Samsa** » Apr 10, 2014 10:39 pm

DavidMcC wrote:
Mr.Samsa wrote:...
But we can, as the authors in the linked papers do. It is no more unproblematic than talking of animal and plant cells, despite them being radically different things.

They are not THAT different, and are known to have evolved from a common ancestor. The same cannot be said of plant "neurons".

Yes it can: Recent surprising similarities between plant cells and neurons

"Glutamate is one of the best understood and the most widespread excitatory neurotransmitter which is perceived via glutamate receptors at brain synapses in animals and humans. These neuronal receptors have, in fact, deep evolutionary origin in prokaryotic bacteria33,34 and are present also in plants.35,36 Importantly, the plant glutamate receptors have all the features of neuronal ones,37 and glutamate induces plant action potentials.18,19 All this strongly suggest that glutamate serves in neurotransmitter-like cell-cell communication in plants too".

Teuton wrote:If there are plant neurons, how do they look like?

What does it matter what they look like? It we were to categorise scientific concepts based on appearance then we'd be in a sad state right now. The more important question is do these claimed plant neurons perform the same functions through essentially the same mechanisms? And the answer there is undeniably yes.

Teuton · **#42** by **Teuton** » Apr 11, 2014 1:53 am

Mr.Samsa wrote:
Teuton wrote:If there are plant neurons, how do they look like?

What does it matter what they look like?

It matters to me, because I'm curious; but actually it's a rhetorical question, since plants are known not to have neurons. If there were plant neurons, there should be pictures of them.

Mr.Samsa wrote:It we were to categorise scientific concepts based on appearance then we'd be in a sad state right now. The more important question is do these claimed plant neurons perform the same functions through essentially the same mechanisms? And the answer there is undeniably yes.

It's not only a matter of function, cell morphology is relevant as well.
That there are certain similarities is undeniable, but what is deniable is that the degree of similarity is so high that the concepts of a neuron (nerve cell) and of a nervous system can adequately be applied to plants (in a non-metaphorical way). I doubt they can.
There's a perfectly acceptable distinction between plant electrobiology/-physiology and animal electrobiology/-physiology, but only the latter is properly called neurobiology/-physiology. (You could at best use the ugly phrase "plant quasi-neurobiology".)

Teuton · **#43** by **Teuton** » Apr 11, 2014 2:13 am

"Electric Signaling: Ever since the discovery of electrical responses to stimulation in plants, obscure ideas about plants’ neurology were brought up (e.g., Tomkins and Bird 1973). This was always strongly provocative when one considers neurology as the study of nerve systems inferring foresight, intention, and consciousness to be restricted to the realm of cognitive behavior of (higher) animals. Astonishingly using such terminology plant neurobiology quite recently even comes up as a new move in plant biology (e.g., Trewavas 2003, 2005 ; Baluska et al. 2004, 2005; Brenner et al. 2006; Gurovich and Hermosilla 2009, with a rebuttal by Alpi et al. 2007). All kinds of interactions and communications involving plant cells are called “synapses” (Baluska et al. 2005). However, plants do not have neurons as specialized cells transmitting nerve impulses.

Reference is made to Charles and Francis Darwin. They discovered and in controversy with the dominating German plant physiologist Julius von Sachs, they rightly maintained that the kalyptra of the root tip is the site of perception of the gravitational stimulus eliciting gravitropical bending of roots (Darwin 1880, 1909). It is now known that electrical signaling is involved. The so-called geo-electric effect first described by Brauner and Bünning (1930) was confirmed by Stenz and Weisenseel (1991 , 1993). An electrical field is built up in the root under gravitational stimulation and the root is bending towards the lower physical side which is more positive. Very detailed studies by the group of Andreas Sievers (e.g., Behrens et al. 1985) then unraveled the interaction of cushions of endoplasmatic reticulum with the amyloplasts serving as statoliths in the cells of the kalyptra. This generates an asymmetric distribution of membrane potentials and a polarization forming electrical fields and eliciting electrical signals followed by gravitropical bending. While it is evident that perception and primary signaling reside in the kalyptra, it is much too far reaching to conclude that the root tip functions like a brain (Baluska et al. 2004) and to appeal to Charles Darwin for support of such a postulation. Charles Darwin tended to compare roots and also moving plant tendrils with earthworms having tiny brains in their tips. However, evidently the Darwins were not aware of the current progress in genuine neurobiology. Therefore it is not fair to quote them as authorities for plant neurobiology. Electrical phenomena are a basic and general property of all living proteo-lipid biomembranes. Clearly membrane-electrical properties evolved earlier than the organs of a nervous system (Volkov 2000). However, the crevasse between the functions of electrical signaling in plants and bona fide neuronal activities in (higher) animals is so deep that it is misleading to draw analogies (Alpi et al. 2007). Electrical signaling per se is not neurology. On the other hand, by no means whatsoever this permits defending the error of taking plants as merely modular organisms with denying them the quality of being unitary individuals (Haukioja 1991). Rejecting the term “plant neurobiology” does not at all distract from the fascination inherent in much work that is currently performed on electrical signaling in plants and its importance for integrated whole-plant functioning."

(Lüttge, Ulrich. "Whole-Plant Physiology: Synergistic Emergence Rather Than Modularity." In Progress in Botany 74, edited by Ulrich Lüttge, Wolfram Beyschlag, Dennis Francis, and John Cushman, 165-190. Berlin: Springer, 2013. p. 170)

Mr.Samsa · **#44** by **Mr.Samsa** » Apr 11, 2014 2:35 am

Teuton wrote:
Mr.Samsa wrote:
What does it matter what they look like?

It matters to me, because I'm curious; but actually it's a rhetorical question, since plants are known not to have neurons. If there were plant neurons, there should be pictures of them.

Exactly, my question was getting at the fact that no matter what I provided, you'd dismiss it as you already think you have an answer. If I presented a plant structure that looked similar to neurons, like the growth of branches:

then it would be dismissed as a superficial similarity. If I presented a proposed structure that functions in ways similar to neurons, like pollen tubes:

then it would be dismissed as not being similar enough.

Teuton wrote:
Mr.Samsa wrote:It we were to categorise scientific concepts based on appearance then we'd be in a sad state right now. The more important question is do these claimed plant neurons perform the same functions through essentially the same mechanisms? And the answer there is undeniably yes.

It's not only a matter of function, cell morphology is relevant as well.

Yes and no. Function is of primary importance because when talking about trying to integrate two wildly different things (i.e. plants and animals) because there are necessarily going to be significant structural differences as they have diverged at a very early stage in evolutionary history.

This is why biologists for a long time scoffed at the idea of "plant physiology" or "animal cells" because they look radically different. The important feature, however, is that they share the same function which allows us to categorise them together.

Teuton wrote:That there are certain similarities is undeniable, but what is deniable is that the degree of similarity is so high that the concepts of a neuron (nerve cell) and of a nervous system can adequately be applied to plants (in a non-metaphorical way). I doubt they can.
There's a perfectly acceptable distinction between plant electrobiology/-physiology and animal electrobiology/-physiology, but only the latter is properly called neurobiology/-physiology. (You could at best use the ugly phrase "plant quasi-neurobiology".)

To be honest, I was initially on the fence about this topic and I thought that it was just an interesting avenue of research that appeared to have enough evidence to warrant looking into, but the more I've read from the papers you've presented as 'arguments against' and the more I've read of the evidence supporting it, it seems that there is no valid reason at all to think that there is a problem with the term 'plant neurobiology' except "but we define neurons as belonging to animals!".

DavidMcC · **#45** by **DavidMcC** » Apr 11, 2014 12:28 pm

Mr.Samsa wrote:... These neuronal receptors have, in fact, deep evolutionary origin in prokaryotic bacteria33,34 and are present also in plants.35,36 Importantly, the plant glutamate receptors have all the features of neuronal ones,37 and glutamate induces plant action potentials.18,19 All this strongly suggest that glutamate serves in neurotransmitter-like cell-cell communication in plants too". [/i]

...

I hardly think that the common inheritance of a receptor type means that plants have neurons. All it shows is that the tree of life has a single origin, and that the divergence of plants from animals occurred after the evolution of glutamate receptors. Paramecium, for example, has glutamate receptors, too:
http://snowbio.wikispaces.com/Paramecium+%28protist%29

Although the paramecium lacks gustatory, auditory, and visual senses, it can quickly respond to physical sensations, such as those caused by the stimulus of bumping into something. In addition, the paramecium can respond to various chemical concentrations in its environment, such as ones associated with glutamate, a type of salt that functions as an important attractant chemical cue. Glutamate often signals the presence of bacteria, which the paramecium feasts on

Mr.Samsa · **#46** by **Mr.Samsa** » Apr 11, 2014 12:36 pm

DavidMcC wrote:
I hardly think that the common inheritance of a receptor type means that plants have neurons.

Nobody claimed that it did.

Teuton · **#47** by **Teuton** » Apr 11, 2014 12:47 pm

Mr.Samsa wrote:Exactly, my question was getting at the fact that no matter what I provided, you'd dismiss it as you already think you have an answer. If I presented a plant structure that looked similar to neurons, like the growth of branches:…then it would be dismissed as a superficial similarity. If I presented a proposed structure that functions in ways similar to neurons, like pollen tubes:…

"Electrical phenomena are a basic and general property of all living proteo-lipid biomembranes. Clearly membrane-electrical properties evolved earlier than the organs of a nervous system (Volkov 2000). However, the crevasse between the functions of electrical signaling in plants and bona fide neuronal activities in (higher) animals is so deep that it is misleading to draw analogies (Alpi et al. 2007). Electrical signaling per se is not neurology. [my. emph.]"

(Lüttge, Ulrich. "Whole-Plant Physiology: Synergistic Emergence Rather Than Modularity." In Progress in Botany 74, edited by Ulrich Lüttge, Wolfram Beyschlag, Dennis Francis, and John Cushman, 165-190. Berlin: Springer, 2013. p. 170)

The self-declared plant neurobiologists conceptually jump too rashly from electrical/electrochemical signalling to neural processing.

Mr.Samsa wrote:To be honest, I was initially on the fence about this topic and I thought that it was just an interesting avenue of research that appeared to have enough evidence to warrant looking into, but the more I've read from the papers you've presented as 'arguments against' and the more I've read of the evidence supporting it, it seems that there is no valid reason at all to think that there is a problem with the term 'plant neurobiology' except "but we define neurons as belonging to animals!".

Neurons are a special type of cell which we find only in animals. This is not a necessary definitional truth (such as "Bachelors are unmarried") but a contingent empirical truth. Plants could have contained neurons or a nervous system but in fact they do not.

Here's an excerpt from an interview with Daniel Chamovitz, author of "What a Plant Knows":

"Do you see any analogy between what plants do and what the human brain does? Can there be a neuroscience of plants, minus the neurons?
 First off, and at the risk of offending some of my closest friends, I think the term 'plant neurobiology' is as ridiculous as say, human floral biology. Plants do not have neuron just as humans don’t have flowers!
But you don’t need neurons in order to have cell to cell communication and information storage and processing. Even in animals, not all information is processed or stored only in the brain. The brain is dominant in higher-order processing in more complex animals, but not in simple ones. Different parts of the plant communicate with each other, exchanging information on cellular, physiological and environmental states. For example root growth is dependent on a hormonal signal that’s generated in the tips of shoots and transported to the growing roots, while shoot development is partially dependent on a signal that’s generated in the roots. Leaves send signals to the tip of the shoot telling them to start making flowers. In this way, if you really want to do some major hand waving, the entire plant is analogous to the brain."

Mr.Samsa · **#48** by **Mr.Samsa** » Apr 11, 2014 12:50 pm

I'm just not that convinced by an argument from definition, when the whole discussion is about whether it's valid to considering broadening the definition we have..

DavidMcC · **#49** by **DavidMcC** » Apr 11, 2014 12:56 pm

Mr.Samsa wrote:
DavidMcC wrote:
I hardly think that the common inheritance of a receptor type means that plants have neurons.

Nobody claimed that it did.

In that case, you should be careful to qualify statements about the "amazing similarities between plant cells and neurons".

Mr.Samsa · **#50** by **Mr.Samsa** » Apr 11, 2014 12:57 pm

DavidMcC wrote:
Mr.Samsa wrote:
DavidMcC wrote:
I hardly think that the common inheritance of a receptor type means that plants have neurons.

Nobody claimed that it did.

In that case, you should be careful to qualify statements about the "amazing similarities between plant cells and neurons".

Why would I need to be careful about that? I do believe that. I simply refuted your claim that supposedly someone suggested that common inheritance of a receptor type meant that plants have neurons. That's absurd and makes no sense so I don't see why someone would think that.

DavidMcC · **#51** by **DavidMcC** » Apr 11, 2014 1:05 pm

Mr.Samsa wrote:
DavidMcC wrote:
Mr.Samsa wrote:
DavidMcC wrote:
I hardly think that the common inheritance of a receptor type means that plants have neurons.

Nobody claimed that it did.

In that case, you should be careful to qualify statements about the "amazing similarities between plant cells and neurons".

Why would I need to be careful about that? I do believe that. I simply refuted your claim that supposedly someone suggested that common inheritance of a receptor type meant that plants have neurons. That's absurd and makes no sense so I don't see why someone would think that.

I didn't claim that "someone suggested that common inheritance...", because I was the first to use that phrase in this thread, AFAIK. I was merely suggesting that specific molecular simlarities between the kingdoms of life say little about the similarities of function of the relevant parts/structures within them.

Mr.Samsa · **#52** by **Mr.Samsa** » Apr 11, 2014 1:16 pm

DavidMcC wrote: I was merely suggesting that specific molecular simlarities between the kingdoms of life say little about the similarities of function of the relevant parts/structures within them.

And everybody agrees with that claim, so again I don't understand who you're supposed to be responding to.

DavidMcC · **#53** by **DavidMcC** » Apr 11, 2014 1:34 pm

Mr.Samsa wrote:
Teuton wrote:
I emphatically disagree with you, because there is no reason to think that plants contain cells which are sufficiently similar to nerve cells. If they did, those special plant cells would have already been discovered. A few superficial similarities and analogies do not justify the neuro talk in botany.

But these cells have been discovered and it's far more than a "superficial similarity" or "analogy". The problem is simply the implicit assumption that only animals have neurons and so if we define neuron as being limited only to animals, then of course plants don't have neurons because they're not animals. That's not a particularly useful definition though and we'd need actual reasons for restricting the use of the term.

...

Mr.Samsa · **#54** by **Mr.Samsa** » Apr 11, 2014 1:43 pm

DavidMcC wrote:
Mr.Samsa wrote:
Teuton wrote:
I emphatically disagree with you, because there is no reason to think that plants contain cells which are sufficiently similar to nerve cells. If they did, those special plant cells would have already been discovered. A few superficial similarities and analogies do not justify the neuro talk in botany.

But these cells have been discovered and it's far more than a "superficial similarity" or "analogy". The problem is simply the implicit assumption that only animals have neurons and so if we define neuron as being limited only to animals, then of course plants don't have neurons because they're not animals. That's not a particularly useful definition though and we'd need actual reasons for restricting the use of the term.

...

Sorry, I can't find the part where I state that the common inheritance of a receptor type means that plants have neurons, or that specific molecular similarities between kingdoms of life says something about the similarities of function of the relevant parts within them.

It must be my eyes but the quoted section simply doesn't say that.

Teuton · **#55** by **Teuton** » Apr 11, 2014 1:48 pm

That only animals have neurons is not an a priori assumption following from the definition of "neuron" but an a posteriori assumption based on the empirical fact "that there is no evidence for structures such as neurons, synapses or a brain in plants." (Plant Neurobiology. No Brain, No Gain?)

DavidMcC · **#56** by **DavidMcC** » Apr 11, 2014 1:51 pm

Mr.Samsa wrote:...

Sorry, I can't find the part where I state that the common inheritance of a receptor type means that plants have neurons, or that specific molecular similarities between kingdoms of life says something about the similarities of function of the relevant parts within them.

It must be my eyes but the quoted section simply doesn't say that.

Sounds like wriggling to me.

Mr.Samsa · **#57** by **Mr.Samsa** » Apr 11, 2014 2:07 pm

DavidMcC wrote:
Mr.Samsa wrote:...

Sorry, I can't find the part where I state that the common inheritance of a receptor type means that plants have neurons, or that specific molecular similarities between kingdoms of life says something about the similarities of function of the relevant parts within them.

It must be my eyes but the quoted section simply doesn't say that.

Sounds like wriggling to me.

If I was wriggling then it would be easy to stop me dead - quote the section where I say, or even imply, what you are suggesting I've said. Literally just copy and paste it.

DavidMcC · **#58** by **DavidMcC** » Apr 11, 2014 4:09 pm

Mr.Samsa wrote:
DavidMcC wrote:
Mr.Samsa wrote:...

Sorry, I can't find the part where I state that the common inheritance of a receptor type means that plants have neurons, or that specific molecular similarities between kingdoms of life says something about the similarities of function of the relevant parts within them.

It must be my eyes but the quoted section simply doesn't say that.

Sounds like wriggling to me.

If I was wriggling then it would be easy to stop me dead - quote the section where I say, or even imply, what you are suggesting I've said. Literally just copy and paste it.

There is no point in repeating the previous post again. We obviously interpret the sentences differently.
[/pointless argument]

Mr.Samsa · **#59** by **Mr.Samsa** » Apr 11, 2014 11:11 pm

So you can't find me saying that then?

DavidMcC · **#60** by **DavidMcC** » Apr 12, 2014 3:49 pm

Mr.Samsa wrote:So you can't find me saying that then?

I thought you had said it, but in other words - the ones I quoted you as saying.

[aside]I think it odd that your current avatar is an invertebrate because, if anything, you have an excess of backbone! :scratch:

[/aside]

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