 Good evening everybody. So, today we will be starting the 36 lecture followed by the 37th lecture. So, in this section we will be talking mostly about the plant bioelectricity. So, we have talked about photosynthesis in depth and we have talked about how the electron transport is taking place from photosystem 1, photosystem 2 and how the water splitting cluster or the manganese cluster is working and how people are getting or deriving inspiration from all those things to derive different kind of molecules which will be helpful in obtaining energy. So, today we will be talking about some of the most fundamental plant movement which are bioelectromechanical movements. So, in this section we will be taking up two examples. In this lecture we will be talking about touch me not plant which all of you must have seen at some point or other where if you touch the plant it bends. So, after some time it regains it original position how that happens. So, if you just from a knife perspective if you look at this situation it is something like as it when you are touching the plant you are creating a pressure on the surface of the plant. It is not every plant is adapted to it there are very few plants which are adapted to it and we will be only talking about one classic example on which extensive research has taken place in last 100 years or so. So, which scientifically called Mimosa Podica or in common name it is called touch me not. So, from a very knife perspective as I was telling you if you think of it it apparently seems that these kind of plants have a pressure sensor. So, whenever you are touching the plant it senses a pressure and based on that pressure sensors it does certain action some mechanical action and this fairly similar to something what happens when you are hearing it is a sound wave coming hitting in your eardrums followed by the wave enter inside the cochlea and it opens up a series of ion channels in the hair cells of the cochlea and thereby leading to the electrical activities which is coded by the brain and you realize what you are hearing it is pretty much the same thing. And this is these studies laid the foundation stone for you know in a controversial topic called the nervous system of the plants are these. So, these are open ended questions are these kind of sensing abilities something they are very similar to in a stretch reflex arc what you have already studied in the nervous system or the hair cells in the year are these rudimentary activities are kind of in a very underdeveloped nervous mechanism these are because there is no structured nervous system in the plant what we know or what we have already discussed while introducing the plant that it is a structure of tubes of xylems and the vessels xylem vessels and the flow vessels one of them carrying the water and other solutes whereas, the other one is carrying other bigger molecules and supplying nutrients all over the plant and you know clearing up the debris and everything as such in the anatomy of the plant there is nothing as such what you see in the animal counterpart as nervous system yet they behave very similar to the nervous system. And if you really go through this lecture you realize that this is inspired generations of scientist you know to understand these kind of sensors could you emulate those sensors with the modern techniques of nanotechnology and bioelectromechanical systems biobems and all these things could you really create those kind of pressure sensors and what are the sensory structures apart from it from the very fundamental perspective these are of enormous significance how a simple touch sensation in a plant leads to this mechanical action. Overall what happens is what we will be discussing today these touch sensation or the pressure sensing leads to a cascade of electrical responses those electrical responses eventually translated into a mechanical response. So, this is the nature bioelectromechanical so let us formally start the class. So, this section of plant bioelectricity we will be talking about the plant movement of the Mimosa Podeka and this is the lecture number 36. So, now let us see what are just a rehash of what we have already done in a bioelectrical phenomenon plant systems today we will be talking about what you see in green the electrical signaling between plant cells and the other three topics two we have already done and we will we have already also done the the the dye sensitize solar cells. So, let us progress with the electrical signaling between the plant cells. So, there are different kind of movements which are observed in the plants. So, one is called tropism tropism is a movement when the plant moves towards a basic stimulus say for example, phototropism photo means light. So, if the plant kind of directionally move towards the sunlight we call it is phototropism you may see you know the sunflower are pointing towards the sunlight whichever direction you put them suppose they are in a in a in a not in the ground I mean in a some kind of a and you just till the direction they will try to move towards light they will try to you know obtain as much solar energy as possible and this is called tropism heliotropism phototropism likewise gravity tropism towards the gravity and likewise when there is something called nasty nasty is basically the movement triggered by stimulus, but no relation to the direction of the stimulus. So, this is. So, this is basic difference between tropism and nasty is in the case of nasty you do not have any directional or vector sense. So, if there is a sensation of there is a stimulus they will respond to the stimulus whereas, in the case of tropism the directionality component matters depending on the position of the sun the plant is orienting itself in order to you know derive as much solar energy as possible this is just one of the examples. The third one is the taxes the stimulus triggered movement either towards or away from stimulus. So, if you look the compare between tropism and taxes when you talk about tropism we say it is direction because of the stimulus it is moving towards the stimulus, but in the case of taxes it is basically can move away from the stimulus say for example, there is an obnoxious stimulus something which a plant does not like it will move away from the stimulus. So, that is called the taxes and the last one which we are going to deal with is called sysmonastic and nictanistic movement. So, I am not getting into that at this point because that is what we are going to discuss today. So, broadly speaking these are the different kind of movement. So, if you really correlate it very simple in a very simple sense we look towards the light our eyes respond to it as if the plant responds to the sunlight as if they have you know photoreceptors which are sensing towards them and that is all coordinated motion. You can always imagine that like you know there are certain rudimentary electrical impulses getting generated rudimentary nervous system which is functional out there. So, based on these four movements towards or away from the stimulus or irrespective of the directionality of the stimulus we are will be moving and we will be talking about this sysmonastic and nictanastic movements. So, this is our example what we are going to deal with mimosa potica or touch me not plant. So, here I have collected some simple pictures those of you have seen mimosa potica plant it is fine because during the rainy season you will see lot of them in the woods and in your backyard they grow pretty much all over the place. If you have not seen they are very similar to the picture what you see and if you have the knack really to go to the garden and kind of see trace these plants you can trace them plant you touch it and you figure out whether it is a touch me not or it is just another ordinary plant. So, this is how it looks like and if you look at this structure very carefully this. So, here it has been shown how it is bending. So, the main frame is like the from the main stem you see the main pulvinus then the pitiole and this we have already discussed. So, then you see the secondary pulvinus. So, you see the main pulvinus secondary pulvinus and there is something called a tertiary pulvinus. So, there are three. So, the reason why I am stressing on this pulvinus is this these are the regions where the bending is taking place. So, is the pulvinus region where all the it is just like if you look at my hand. So, this is the zone where the bending is taking place or this is the zone where the bending is taking place. So, similarly for the leaf. So, the first is the tertiary which is at the tip of the leaf the leaf will curl then next one is the secondary pulvinus where second level of bending and the third one is the main pulvinus and if you see after bending. So, if you look at these to compare these two photograph you will see the all the three bendings have taken place in the main pulvinus in the secondary pulvinus as well as in the tertiary pulvinus. So, this is how all the bending actions takes place fine. So, now let us take a very closer look at it because in that picture what you saw just before this it is not a it is kind of at a distance. So, if you have a slightly closer look you will see the bending is taking place at the if you see that is in the red it is mentioned pulvini. So, it is at the pulvini where the leaves are. So, it is the leaves remain like this as soon as there is if you touch this plant it curls like this. So, there is there is needs a lot of like you know flexibility in this motion it is not every leaf does it. So, having seen this. So, at least one thing is clear your pressure sensors are sitting somewhere along these leaf surfaces and these leaf surfaces are receiving its nutrients and everything through the xylem and the flowing vessels. Now, let us move on to the just a small recap of about the xylem and the flowing vessels. So, you see as I told you that basically these are cylindrical structures along the stem of the plant one is a specialized for carrying all the water molecules which is the xylem vessels and the flowing vessels which is specialized to carry several other nutrients and everything. So, this is how the leaf is structured is supplied with the xylem and the flowing vessels and you see there is a T connectivity. So, there are zones where the xylem and flowing vessels has limited connectivity across those cylindrical motions. Now, after just small recap if you guys remember this I will one of the lecture I told you that I am going to you know describe the whole structure. So, that you know there is no confusion because this is very essential from here. Now, let us see the situation. Now, what you see here in u l o is kind of I have drawn this structure in a very simplistic way. So, u l o what you see is the stem. So, if you want to correlate it. So, you can correlate it with this structure. So, this what you see here is the p t o l or the or the secondary pulvinus. So, imagine all that u l o thing what you are seeing here is a secondary pulvinus and the p t o l out there. So, first set is the situation when there is no water in the cells it is called a flak itself less water. So, now in the first picture there are three pictures here you touch the cells once you touch the cells your end result what you see is the third one. So, what essentially happens it has been figured out when you touch these cells it opens up a series of potassium channels which are present in the plant. And from the extracellular space potassium started to enter inside the cells and when the potassium enters inside the cell this along with it carries a lot of water molecules. And once it started carrying the water molecule what happens now I will just take you back before I come to this one this picture. So, imagine this is before bending you touch once you touch lot of water molecules gets accumulated inside the leaf and because of the weight of those water molecules the leaf from this position droops down like this. Now, let us coming back to the mechanism and one more thing why this picture is essential because then you will be able to correlate how the water movement is taking place. You see the x and p's x is standing from the xylem and the p stands for the flowing vessels now coming back. So, this is the situation one when your cells are without any water it is a flak itself. So, now when you touch all those you see those k plus k plus channels which are sitting there they open up and they allow a lot of potassium to enter inside the cell. And along with potassium what happens you are allowing a lot of water to enter inside it and that makes the cell extremely turgid and once the cell becomes turgid it you know just droops down like this. So, this is the overall understanding of the mechanism what happens in the case of touch me not plant. So, now just to you know put it together that mechanism ultimately is the movement of potassium ion into and out of the cells. So, this is the regulatory mechanism with water following by osmosis the result is that cell becomes more turgid larger if potassium and water move into them and flaccid or collapse smaller if potassium and water move out of them. Many of the movement of plants occur when two layers of tissue alternate simultaneously in this way and the location of those tissues are in swollen structure called pulvinine. So, that is the reason why I was telling you we have to take a very clear look at this picture. So, this is the pulvinine or pulvinus where these kind of tissues remain. So, one allows 20 the other one allows a reverse entry, but now what is important here to note if this kind of motion takes place or movement takes place of these ions you can actually record this electrical motion this is nothing, but just the only difference here is from the animal electricity is that most of or all our animal electricity what whatever we know leads to a influx of sodium ions here in the case of plants you see potassium plays a very significant role in terms of regulating. So, if you could poke an electrode in between. So, say for example, if you could place an electrode somewhere out here between the like between the extensor and the flexor cells. So, there are two kinds of cell you have to realize here there is something called an extensor cell and there is something called a flexor cells. If you see this picture very carefully you will see both the cells are given there and though that is what it meant by two kinds of tissues many of the movement plant occur when two layers of tissue alternate simultaneously. So, now if you could put an electrode out here you should be able to record the electrical current which is being generated by the ionic flux of the potassium or any other ions which are involved in it. So, coming back now we will go back to some of the historical perspective when this all started. So, this is a paper I wish all of you can download it online and this was a paper which was published in 1962 29 January in the science journal and it was published in Japan Excitable Cells in Mimosa, but if you see the references cross references you will see that third reference which is very important to look at by J.C. Pose back in 1926 when he proposed this idea and he made some very very seminal contribution. So, what I was trying to tell you for last almost more than 100 years this research is going on and I will tell you how Bose made some of those studies which eventually followed by Takau Sibyoka and which the paper what has been cited out here. So, however so this is what Takau Sibyoka was look for and please go through this paper. However, the experiment by Bose in which an electric probe so look read through these lines very very carefully and that is why I am kind of repeating these lines with you people in which an electric probe was insert inserted into the PTO at various depths. So, what that essentially means is I take you back to this picture. So, you are probing at different depth you know at different depth to see where you are getting the electrical signals you can just like say for example, you take you take suppose this is your electric probe. So, you go up to this depth you go up to this depth you can go up to even further depth based on the depth you are measuring the electrical electrical fluxes. So, this is what exactly Bose was doing at various depth showed that excitation is conducted not only in the flow in, but also in the proto xylem located in the inner part of the xylem. The proto xylem was called the internal flow in by Bose, but this tissue consist only of elongated parenchymal cells and contains no sieve tubes. Now, Sibyoka is telling you in my experiment I inserted a microelectrode into the intact cell and found excitable cells in both flow in and proto xylem. So, essentially this was a quantum jump 1926 where Bose published his work on or documented his work in a book called nervous system the plant in 1962 it was almost 40 years later. So, this story is still continuing there are people who passionately follow this thing you know plant indeed produces electricity and we can really measure those electricity is using you know microelectrode and if you see the experimental setup it is something like this. So, if you see the pulvenous how the pulse. So, basically this whole thing is submerged in a in a electrolyte where they are conducting. So, now you you fix it using if you see this picture. So, you see the pulvenous is fixed in a kind of you know something like a clamping you have clamped it and from the left hand side you see the microelectrode is being inserted depending on the depth of the microelectrode current density changes and this is how this whole experiment was conducted by Sibyoka and much before that by Bose and all these people these are very simple setups. But these seminal studies laid the foundation stone for a totally different world of electrical responses of the plant and if you see some of those recordings these are some of those recordings from Sibyoka's paper. So, I have already exposed you people to the action potential seen in the case of animal cells and now here is an example of action potentials which are observed by the plant cells and depending on where the electrode is your action potential changes and if you see the resting membrane potential you see the resting membrane potential is sitting at minus 180 millivolt unlike your plant animal counterpart where it sits at minus 90 or minus 70 or minus 80 millivolt or in the case of pacemaker cells or few of the you know yeah some of these pacemaker cells where it is sitting at minus 40. So, with respect to the animal cells if you compare this value this is way way more negative it is sitting at minus 80 and the spikes what you see in these pictures are the spikes which is which are telling that you know there are electrical activities based on the touch. So, this is what if I had to tell you so this is how it is being done say for example, I insert an electrode here. So, this is the plant this is the leaf and I insert an electrode like this fine I touch I did do a recording here depending on what is the depth I have I am getting different kind of recording. Now, if you refer to the slide and that is exactly what you will see if you refer here the membrane potentials in the upper trace in cells of proto xylem. So, that is what was the contention of Sibioca and the pith which is in B you follow the B where you will see very micro electrode inserting into cells at in and remove from cells at re ok. So, that re and A stands for that when you are again inserting it PTO is stimulated at S you could see the S very clearly when you give the stimulation and diphysic action potential lower trace let to external externally between the pool and the basal cut are simultaneous recorded. So, you can if you see this picture and if you go through this original paper in science everything will be clear. So, just for your understanding before you read through the paper this is how it works. So, this is say for example, this is the leaf coming out from PTO insert the electrode like this and depending on the depth you are giving a touch with something some other thing you know some other thing which has clamped here giving a touch you are making a recording giving a touch you are making a recording. This is how all these recordings have been established and based on the first recording a thing without the touch is your resting membrane potential. So, this is something which is if you now compare the resting membrane potential. So, this is something very interesting to look at it is a different tissues of the plant have different resting membrane potential. So, epidermis is sitting at minus 44 which is very close to the pacemaker cells cortex minus 52 again close to the pacemaker cells of the heart. The scleronchyma sheath minus 52 fluent vessels are sitting at minus 161 and minus 61 see the variation in the plant protozylum is sitting at minus 154 peth at minus 58. The reason why I am putting all these things is and if you see the shift from when there is an action potential you see that asterisk which is shown in action. So, that is basically telling you from 161 it shifts all the way to 22. So, you are realizing that there is almost 8 times reduction in the in the membrane potential. Similarly, in the from 154 it goes to minus 19. So, just like their animal counterpart these kind of action potentials are being observed in the plants and this is these are those seminal studies from the time of Bose all the way CBO and further down which is laid the foundation stone to believe what Bose claim long back that plants indeed have a very rudimentary nervous system and with more and more studies with more and more technologies will be able to unravel those externally feed which has been achieved by plant. So, after this what I will do. So, this is another thing this is again from the same paper in 90 sorry another paper 1972 as can go through it how that here you could see how that dripping is taking place you know it is a drip and how some of the vacuolated structure inside the inside the xylem and the flume vessels are changing and this is one of the model you can go through this model this is the calcium the role of calcium and I have given you the reference also in the plant physiology, but at this stage I expect that. So, essentially what it is telling it is the calcium flux along with the potassium which is also involved in if you read through this fundamental structure of the motor cells you will realize that just like your modern neuron we have these motor cells and everything which are doing orchestrating this whole process. So, there is now we are adding one more dimension to it along with potassium there are calcium which are involved in it. So, this is what is the situation before stimulation and this is the situation after the stimulation as the potassium comes. So, integrated scheme of the function of the motor cell at a baxial half of mimosa indicates bending movement indicates recovery phase after the bending movement and this is the kind of the broad view and this is kind of a small I kindly request you people kindly go through this 1972 paper by Toriyama and Zafi in the volume 49. Now, next we are coming on to so we made these recordings now this brings us back to a very philosophical situation if you remember I told you that when we talk about the stress reflex arc we talked about there is a pressure sensor which senses it a sensory neuron which carries the message and which is being processed in the spinal cord and brought back and tell the muscle to come back to its original position because of the pressure compression. So, now in this whole thing what we just covered in last 20 minutes or we have not talked about any pressure sensors where is the really the sensor lies there has to be a sensor something which is sensing this whole thing and who is the sensor we have talked about the extensors and all those cells and everything exactly how the sensor looks like. So, now we will be talking about the mechanoreceptors the one which acts or which reacts upon touching the leaf. So, if you look at the cells look at the cross section of a leaf what will you observe is there are certain very specific cell called red receptor cells. So, on the surface of the plant you know if you take a section you will see there are very specific structure called the guard cells which regulates the movement of the water inside the leaf and outside the leaf and the most of the time in a hot sunny day the guard cells remain closed very tightly regulated, but on a kind of in a very rainy day they remain open you know they wanted to get rid of excess water. So, very similar to the structure of the guard cells as if you know something like this structure like this there are another set of the structures which are called red receptor cells that you could see upon staining on the panel A you could see there is something called red receptor cell without staining and this is without staining by the way can this is seen in the tertiary pulvinus of the Mimosa pudica resembles the stomatal guard cells. Arrow shows these bright red cells receptor cells and receptor complex on the term tertiary pulvinus of Mimosa by light actually you can just use a simple light microscope and by scanning with the microscope arrows point to the red receptor cell stars indicate the guard cells which are out of work and if you look at them and elongated excitable motor cells. So, we are talking about these motor cells just in the previous slide while we are talking about under the calcium motions and everything. So, this is how this whole thing looks like now I represent a receptor potential of the red receptor cells. So, essentially what happens is that if you really could do a recording from this red receptor cells what has been shown here you will see there is a sharp upon mechanical stimulation and. So, the way you are doing it you are doing a recording. So, you have your electrode like on those red cells you are placing an electrode on those red cells on those red cells you have the electrode sitting on those red cells. So, you have the electrode sitting on the red cells and you are touching the plant on touching what you see this is what you see upon touching a representative receptor potential on red receptor cells after mechanical stimulus the electrical record on an epidermal cell near an adexial part of the tertiary pulvinus a mimosa. The resting membrane potential receptor cell was about minus 90 to minus 100 millivolt and on simple epidermal cell there is about minus 30 to 40 millivolt. So, there is always a shift on that. So, these are some of the some of the locations of the real pressure sensors whose counterpart you should see in the animal kingdom their counterpart is the muscle spindle. So, this is this slide I am just putting there for your you know better understanding about the detailed structure how these the xylem and the fluem vessels and how they are integrated into the structure of the plant cell wall and everything plus one does matter just this is a kind of recap. And this is where we are talking about the receptor complex on tertiary pulvinus by transmission electron microscopy or what is stands for are the red receptor cells and G stands for the guard cells and E p are the normal epidermal cell and then you have the excitable motor cells. So, this is how this whole complex is structure looks like. So, R for the red cells plasmodesimata arrow is been shown you see that there is an arrow on the panel B where there is a connectivity and elongated excitable cell are shown in shown out here you could see those E's sitting out there. So, now this is the complex which is responsible for. So, whenever there is a touch on those red cells which are acting as the mechanoreceptors they convey this message to these motor cells and that leads to the influx of a series of potassium ions as well as calcium in and around it and which leads to this process of drooping of the leaf. So, it is a very interesting event and slowly slowly we are kind of you know getting an understanding of what is happening. So, here for your those who are keen to really you know go through it I have put a model for you guys you can go through those graphase paper which I have already cited you can go through them how this is this whole thing is taking place. So, again to just summarize what we just talked about just from the. So, this is where we started and we were supposed to talk about this is monastic moment. So, this is how the pulvenous looks like. So, on those pulvenous we talked about how to place electrodes at different level and there are two specific kind of a structures one which is called the sensor and we talked about the sensor structures out here once again these are the sensor red receptor cells and you have a series of cells here which we call them as extensor and flexor cells kind of the motor neurons they are counterpart in animals animal kingdom. So, whenever these red receptor cells are activated they through the plasmon desmantha connect to these motor cells or extensor or the flexors and lead to the movement of these ions inside it and if you are clever enough to put the electrode in the right place then you will see you will be able to make the electrical recordings from this from this tissues. So, this is the overall geometry by which a Mimosa Podica bending is taking place that is why I told in the beginning that this is an inspiration for a series of bio electromechanical systems where if you see this picture. So, probably one of the most elegant sensors are sitting there you touch the sensor sensor this is all of the place you touch it and that leads to the bending. So, if you really could have those these kind of system if you could emulate using the modern tools of nanotechnology and you know micro fabrications and everything really can do some really wonder wonderful sensors we can develop over the years. So, I will close this lecture out here and our next lecture will be on another kind of plant movement which is the Venice flight track. Thank you.