N.Wells
Posts: 1836
Joined: Oct. 2005
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| Quote (GaryGaulin @ Jan. 09 2016,09:03) | | The question is how can "passive transfer of charge from bee to flower" be justified when the voltage kept rising steadily long after the bee was gone, then went well below zero volts. |
The research is really interesting, but NoName is right in viewing Gary as attaching lamprey-like to anything that he thinks fits his preconceived ideas, usually incorrectly. In this case, Gary immediately jumped to drawing analogies with neurons, but as Wesley noted, the time and magnitude scales are inappropriate and the mere fact of a rise and fall in potential is not unique to neurons. Also, Gary's inference runs counter to earlier findings, as reported in the article that he cites.
First, all cells produce and/or conduct electricity in a variety of ways in their general course of operations, so it wouldn't be a surprise if an electrical field in a cell showed patterns vaguely similar to patterns seen in firings of neurons (i.e., a rise and a subsequent fall in field strength).
The big news here, correctly identified in the synopsis in Nature and in the original article in Science, is that the bees can pick up on these signals in ways that are advantageous to them.
(It would also be very interesting if plants had evolved a way to amplify electrical signals to bees in ways that benefited both of them, along with all the other visual / chemical / hormonal / odor signals that flowers send to pollinators that say "it's profitable for you to visit me now". However, it is difficult to see how the plant could replenish its supply of pollen as quickly as the electrical potential recovers its base state, and because [AFAIK] petunias are dioecious there would be no advantage to the plant in signalling against a visit at any time. Therefore, in my opinion but not the opinion of the authors of the study, the electrical signal seems unlikely to be an adaptation on the part of the plant.)
The article provides a reasonable explanation for a secondary rise in potential after the bee leaves. The article ( http://www.sciencemag.org/content....66.full ) actually says that | Quote | | This change in potential is often initiated before contact with the bee (movie S1), suggesting that this is not simply a hydraulic wound-response variation potential as in (16) but involves direct electrostatic induction between the charged bee and the grounded flower as hypothesized in (7, 8). |
Note the phrase "not simply."
Reference 16 (Stankovic et al., 1997, http://www.plantphysiol.org/content....df+html ) says | Quote | | Taken together, the results presented here support the hypothesis that VP results from a hydraulic pressure surge transmitted rapidly in the xylem and sensed by living cells, triggering change in the activity of mechanosensitive channels or pumps and yielding an altered ion flux across the plasma membrane, which is monitored as a change in apoplastic potential. Therefore, VP is not a long-distance, self-propagating electrical signal, and it does not appear to be a consequence of wound hormones released from the xylem into adjacent living cells. Instead, it appears to be a local consequence of a transmitted hydraulic signal, which elicits local electrical changes along its pathway. |
The fact that the plant's electrical potential starts rising as the bee approaches (an increase of about 20 mV while the bee is close but before it has actually landed, at 1:01 minutes into the movie) indeed strongly suggests initial induction, as some earlier research had suggested.
Contact between the bee and the flower continues equalization of charges between them. The moment the bee leaves (8 seconds later) the increase in charge halts momentarily, but then it starts to rise again, reaching a peak at 1:18. This indeed suggests a second pathway kicking in to change the plant's electrical potential, which possibly could be either an ion channel or pump mediated by another cation or ligand or a channel or pump that is mechanically stimulated. However, given the 1997 research that shows electrical fields resulting from mechanical stimulation and passive hydraulic response in sunflowers, that would most likely be the cause of the delayed-onset peak in petunias, contra Gary's imaginings.
The evidence therefore suggests that the change in potential is an unintended, unconscious, unintelligent, and non-adaptive consequence of the normal operation of the plant with no particular similarity to neuronal activity, but which is noticed by bees, to their benefit.
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