N.Wells
Posts: 1836
Joined: Oct. 2005
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| Quote (GaryGaulin @ Jan. 09 2016,15:50) | | Quote (N.Wells @ Jan. 09 2016,12:32) | | 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. |
You just described an "action potential" and agreed with me. Duh? |
I second NoName's assessment. I said "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." Note that "which possibly could be either an ion channel or pump mediated by another cation or ligand" indeed describes an action potential, as I intended it to: that is indeed a potential explanation that deserves consideration. However, after consideration, that explanation doesn't look so good, and calling the cycle 'like a neuron' is particularly unjustified in its details.
Your first statement was "The waveform shown in the video has all the features of an action potential spike of a neuron." This means that you in effect jumped from 'I see a rise and fall in potential' to 'I see an action potential' to 'I see something like neuronal activity'.
As Wesley said, neurons typically operate with an initial 70 mV difference in voltage, and some types of neurons can go through a cycle in a few thousandths of a second, which is not like the cycle described in Petunia. Wikipedia's description of a typical, fast, Na-K controlled, cycle for a neuron is | Quote | | The membrane potential starts out at -70 mV at time zero. A stimulus is applied at time = 1 ms, which raises the membrane potential above -55 mV (the threshold potential). After the stimulus is applied, the membrane potential rapidly rises to a peak potential of +40 mV at time = 2 ms. Just as quickly, the potential then drops and overshoots to -90 mV at time = 3 ms, and finally the resting potential of -70 mV is reestablished at time = 5 ms. |
The cycle in the movie starts at 0 mV, rises to 40 mV, and falls back to 0 mV (and briefly just barely under that) over about 70 seconds. The paper reports that the average for 50 cycles lasted about 100 seconds, peaking at about 25 ± 3 mV (SD = 24), with a baseline of 0 mV. That's not much like a neuron, beyond showing a rise and a fall: again following Wesley, 100 seconds vs 5 milliseconds and 25 mV vs 110 mV and a resting potential of 0 vs -70 mV is not 'similar in all its features'. In fact, it is more 'different in all its features'.
Action potentials are crucial in the operations of neurons, but not everything that uses an action potential is a neuron. Nearly all animal, plant, and fungi cells maintain a voltage differential between the inside and the outside of the cell, so there's nothing diagnostic of neurons there. The first action potentials to be described were in plant cells (insectivorous plants, in 1873), so I'm perfectly happy to talk about action potentials in plants. I read that action potentials in plants may last three seconds or more, but 100 seconds is still significantly longer than that. From https://www.novapublishers.com/catalog....d=16983 | Quote | | In plants the depolarization phase of AP consists of Cl-- and Ca++ fluxes. The following phase—a repolarization—relies in turn on K+ fluxes and active H+ flows that both drive membrane potential back to more negative values. |
Ca / Cl cycles are slower and have more negative resting potentials. In Chara (green algae) the average resting potential is -180 mV across the cell membrane and -10 mV across the vacuole's membrane, and during an action potential the differential across the cell membrane becomes 0 while the one across the vacuolar membrane becomes -50 mV ( http://labs.plantbio.cornell.edu/wayne......te1.pdf ). Evidently there is considerable variation here, but none of this sounds close to the cycle described for Petunia.
Note that you have not demonstrated changes in concentrations of any ligands, so your assertion of an action potential is (as with nearly all of your assertions) unsupported.
Can anything else cause a rise and a fall in electrical field strength? Does anything other than a neuron show a rise and fall in electrical strength? Yes, in answer to both questions. As I said earlier, one option, which has the advantage of already being documented at the appropriate time and space scale in plants by Stankovic et al. as well as numerous other papers, is electrical fields caused by hydraulic forcing of ion pumps, i.e. not necessarily anything like a neuron.
I'll let Wesley talk about alternative interpretations, but i'm noting that a) the cycle is not much like the cycle seen during neuron activity, b) other explanations are more reasonable, and c) as the paper concludes, the data suggests initial induction during close approach by the bee, unlike neuron firing.
You really need to raise your arguments above the level of 'OMG, it's a curve - I have a curve too, so I must be correct."
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