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Module 1: Plant Cell Technology

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Anatomy of Plant Cells

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Welcome back.So, we are starting with an introduction to anatomy of plant cells where we will discusswhat are the different organelles of plant cells, what are the functions of those organelles,and then coming on to what are the different plant cell types which you can come acrossin a whole plant, and what are the different functions of those plant cell types or planttissue types.So, starting with the plant organelles this you must have already seen . So, what arethe different kind of organelles we find in different eukaryotic organisms, you can findthe major organelles are mitochondria, then plastids endoplasmic reticulum .Golgi apparatus.Golgi apparatus, then nucleus, ribosomes, then in plant cells or.peroxisomes Peroxisomes are also there.There are many micro bodies, then vesicles are there and in plants you find vacuoles.So, what are the different functions of these let us start and moreover in plants as wellas in bacteria and fungi, you will find cell wall.Now, the cell wall composition in bacteria and fungi is different from the plant cellwall.In what way, any example, how is it different?What contains?Fungi contain So, talk in terms of plant cells versus theothers, what plant cells have the others do not have.Cellulose.So, cellulose, then what else, hemicelluloses, lignin, pectin, so these are components ofplant cell walls.Now, plant cell wall itself is is divided into primary cell wall and secondary cellwall.Now, primary cell wall majority of the plant cell types which you will find in the plantwill have primary cell walls also all the plant cells, but not all plant cells willhave secondary cell wall structure . So, we will be talking in details giving you someidea about how primary cell wall is different from secondary cell wall.Now, what is cell wall, cell wall is a component it is a layer surrounding the cytoplasm orprotoplasm.Now, protoplasm is composed of cytoplasm and the nucleus.Nucleus hm.So, everything of the cell apart from the cell wall.So, the function of the cell wall is to protect the plant cell.Now, depending on the various stages of the plant development, the cell wall compositionmodifies.Now, let us talk about chloroplast.Now, chloroplast it is a distinct feature in plant cells you may find it in many microalgaesas well or algae.But in majority all the plant cells they have chloroplast.What is the function of chloroplast, these are nothing but modified which class of organelles,chloroplasts are the organelles which we were talking about it belongs to which class?Plastids.Plastids.Now, plastids there their pre original form when it further differentiates into differentkinds of plastids is pro plastids.Pro plastids when divides and gets a specialized function, then it becomes plastids.Now, there are many different types of plastids, you must have heard about chromoplast, amyloplast,leucoplast, elaioplast, proteinoplast.So, depending on the specialised function, they do in a plant development and growththe name is there.For example, chromoplast is the most common which you must have heard, chromoplast isapart from chloroplast.Chromo, so where the coloured pigments are stored.So, now, talking about chloroplast.Chloroplast among them are the most abundant plastids found in plants.Now, their purpose we know it is primarily carrying out photosynthesis.Now, in photosynthesis, there are light reactions and dark reactions.So, we will be talking when we come to photosynthesis some idea about light and dark reactions,but these chloroplast, they are responsible for capturing sunlight and helping the plantin manufacturing the food.When I say food, it is synthesis of carbohydrates.hm.Then endoplasmic reticulum.We all know what function does it play in the cell.Endoplasmic reticulum this is it is a connection between the nucleus and the cytoplasm.And it helps in what, it helps in manufacturing, processing, transportation of various proteins,fats, many molecules.Now, there is smooth endoplasmic reticulum, rough endoplasmic reticulum.Rough endoplasmic reticulum is differentiated from smooth in terms of ribosomes sides forprotein.synthesis.Synthesis.So, it acts like a bridge between the nuclear double layered nuclear envelope and the cytoplasm. So, it is a connection between the two.Now, peroxisomes.What are peroxisomes?You will hear about peroxisomes many a times in plant metabolism, peroxisomes can playa role where, have you heard of something where peroxisomes play a major role whichpart of plant metabolism?So, it takes part in photo respiration.Any idea what part of photo respiration?Peroxy.So, we will take it up later.Photo respiration, then there is because of photo respiration there is generation of lotof peroxy radicals.So, plant has to have a mechanism of the degrade off because then they are highly reactivespecies that can cause damage to cellular membranes and cellular components.So, continuously the plant cell is working on to counter this damage.Then plasmodesmata, plasmodesmata plant cells as I was mentioning that they have a tendencyto act grow as aggregates, they you will always found find them in clumps.So, one of the reasons is that plant cells are found to be attached to each other inmany plants generally.Why, because of this phenomena.There are holes in the cell wall which you can clearly see through light microscope,these holes are called pits.They are at the result of thinning of the cell wall during the plant cell division.When the cell wall, so the middle lamella is one of the part of the cell wall, all wherethe endoplasmic reticulum because every component is divided into two, now the endoplasmic reticulumwhile diving all the does not get divided completely and gets compressed.Now, these thinner regions then therefore become the continuity between the two daughterplant cells or the plant cells in connection.So, now this continuity is not only just a simple gap, but it causes a live bridge betweenthe two plant cells.So, there is a cross talk in terms of the endoplasmic reticulum and your what else plasmamembrane, this is how the plant cells are found to be connected to each other.So, this is called as plasmodesmata or plasmalemma, the continuity the live bridge between theadjacent plant cells.Now, plasma membrane plasma membrane is what that you should be able to tell me plasmamembrane is?Thatthe people saying it is a PLP structure.What is that, PLP means what?protein . So, phospholipids .hm.And proteins . hm.There can be some fatty acids.So, phospholipid molecules and it is a bilayer phenomena . So, what is the use of plasmamembrane, it acts like a.semi permeable membrane.It acts like a semi permeable membrane.When I say semi permeable which means that there is regulation of movement of moleculesinside and outside the cell, this regulation can be active which means.So, where these protein transport proteins at the cellular membrane and the fluidityof the cellular membranes helps in the to and fro movement.Why is that needed?During metabolism during plant growth or during survival, you may need to secrete out certainmolecules, you may need to take up certain molecules.So, there plasma membranes helps and it also forms a barrier.Then ribosomes, ribosomes they are the sight of protein synthesis, 60 percent is RNA and40 percent is protein.Nucleus we all know it is a double layered organelle, it is the brain centre of the cell.It regulates all the different functions, cell division, cell metabolism, growth, thenprotein synthesis, all that is regulated by the, and what else nucleus is the sight forgenetic material storage.Then mitochondria, energy centre of the cell.Now, in plant cells when light energy is not applicable, mitochondria is the organellewhich caters to energy generation . In the presence of light, majority comes from chloroplastyour photo synthesis ATP generation, and which is then utilized for or reducing power into it ok, which is then utilized for synthesis of carbohydrates in dark reactions.Then vacuole, vacuole I said is a distinctive feature in plant cells . Now, vacuoles youwill find I said mentioned earlier also that vacuoles in younger plant cells you will findthey will be smaller in size and many numbers.But as the plant cell matures grows in size, the matured plant cells generally have vacuolesingle vacuole all clubbed together, and they can occupy as far as 80 percent of the cellvolume.So, turgor pressure it causes the cell to maintain the cell turgor or the vacuole whenextends it will prevent plasmolysis.The other added advantage would be if there is good turgor pressure then all the cellorganelles will be extended and pushed towards the cell membrane .So, all the cell organelle specially which organelles are the targets chloroplast whensunlight is there . So, that all the chloroplast is exposed on the surface, and they can captureas much as possible the sunlight.Then she said storing molecules, generally what kind of molecules, it acts as degradingtoxic molecules, degrading waste products or which even acts as a site for storage ofintermediate molecules for higher secondary metabolites or even those toxic secondarymetabolites which can be toxic to the plant cell itself .So, that in case of a herbivore attack or a pathogenic attack because the vacuoles areextended big in size, they rapture and the secondary metabolite which is toxic is released,otherwise it is held.So, now, anyways the cell is normalised, why do you think it is happening at least to preventthe neighbouring cells or further damage . Then Golgi apparatus there is also generalin all eukaryotic cells it is used for processing your shipping . So, processing when I saywhat kind of processing, for transport also they might be need to be conjugated with certainmolecules . So, that also happens in Golgi apparatus and transport proteins or transportthese conjugates will help it to cross the cytoplasm and be transported outside the cellmembrane.Then so now, talking about the protoplast.What was protoplast?Protoplast was nothing but nucleus plus the cytoplasm that is protoplast.Now, distinctive feature, what all distinctive features I told, one was the cell wall iscomposed of cellulose, hemicelluloses, pectin and lignin.What is cellulose composed of cellulose is made up of it is a polymer.Polymer.Polysaccharide made up of deglucose simple chains.What kind of linkages you must have read all this.I am just revising it.Beta 1, 6 ok, go back and read ok . So, beta linkages one thing is correct . So, beta linkagesdeglucose units that is cellulose.But if you see under some images of these cellulose, you will find that it is only canbe observed under electron microscopy, and you will find it as fine thread like structureshighly complex matrix, very multi layered.And in each of those fibrils, I will show you a picture, each of those fibril themselvesare composed of thousands of chains of de glucose.So, that is the reason why cellulose is crystalline in nature and it is hard .Talking about hemicelluloses, it is a hetero polymer.Now, hetero polysaccharide hetero polymer in the sense and it is amorphous in nature,beaker.Why, because it has it is made up of many different kinds of sugar units, xylose, thengalactose, find out there are others also.So, in and it is amorphous in structure that is hemicelluloses.Now, pectin that jam and jelly, you people must be eating, fruit jam, fruit jelly, thatjelly part and that jell like structure is because of because of because I am asking,so it is pectin . So, this pectin gives that jell like structure.And this pectin is again a hetero polymer which glues the plant cells and this plantcell wall different components together.Your middle lamella which is above the primary cell wall is very rich in pectins and thatis what helps if it dissolves in water, if you will spring water it will jell, so thatis what causes these plant cells to glue to each other.So, then talking about plasmodesmata is another distinctive features in plant cells, cell-cellcommunication pathways, chloroplast are distinctive which means plastids.Plastids are not only for photosynthesis or storage, but sometimes in secondary metabolismyou will find that they are sight of synthesis of certain intermediates of bio syntheticpathway.If you will see certain bio synthetic pathways like alpha tocopherol or vitamin e biosyntheticpathway, you will find some part of the secondary metabolic pathway also carries out is carriedout in plastids.So, not only storage, but also or sight of synthesis .So, cell wall middle lamella that is above the primary cell wall the which which is richin pectins.So, those yellow threads these are shown in the picture as pectins.And cellulose if you see the primary cell wall, primary cell wall is generally all theplant cells will have primary cell walls, they will have.Secondary cell walls are the once which not all plant cells will have.Now, this primary cell wall what is the function of the primary cell wall is to provide protectionand support to the plant cells, but it is still flexible in nature.Why flexible, because these plant cells the cells are still growing, once they are youngthey still need to grow the cells are flexible to increase in size, to stretch to becomeelongated.So, the primary cell wall has the ability to is more flexible in nature .So, I have already spoken about the major carbohydrates in the primary cell wall.Cellulose under same looks like this complex fibrils like your if you have seen linen fibrilsof flux, your fabrics there.Now, secondary cell wall is under the primary cell wall.It generally appears its major function is to prevent the attack from herbivore and togive rigid support to the well grown plant organ.So, secondary walls appear which are richer in lignin.Now, lignin which lignin you already must be knowing it is very hard to degrade.Now, precisely the reason is because hard to degrade which means that its purpose innature must has been to protect and support the full grown plant.So, this secondary wall structure appears in cells which are already matured, and nowhigher specialised function is not the growth, but to protect the cell, then the secondarywall structure appears . So, its nature function is to protect the plant cell .Now, cell wall openings I said these are pits, which are holes in the primary cell wall andthrough which the plasmalemma or the plasmodesmata passes through which is composed of your plasmamembrane and your endoplasmic reticulum.So, these are live bridges . So, this is how plasmodesmata is formed, whichis formed when the portions of your endoplasmic reticulum, they trapped across the middlelamella.You remember the middle lamella above the primary cell wall as the cell is dividing. So, what happens the cell wall does not get made near these regions or it is so thinthat the endoplasmic reticulum the plant cell wall is then made in continuity with the adjacentcells.And those compressed regions of endoplasmic reticulum then become the continuity or whocall them as holes among the adjacent plant cells.Now, vacuoles, vacuoles are very interesting organelles in plant cells . So, we were talkingabout it helps in cell turgor, pressure maintain that turgor pressure.Then you said it helps in storage; it also helps in maintaining the cytoplasmic pH.So, how does it help do you think in doing all these functions based of coming selectivelyhaving some molecules stored in, then so it has some degrading enzymes also stored inwhich will be useful in degrading the waste-products, degrading the toxic molecules or peeping thetoxic molecules.How do you think all this is getting managed in vacuole which is the inside the cytoplasm?Some enzymes.Enzymes are doing what, what is helping the vacuole in carrying out all this function?Very nice.So, it has a membrane called as tonoplast.So, tonoplast is very rich in lot many number of diverse proteins.Now, these proteins are transport proteins, then very different very kind of transporterscan be simple protein through active transport can be iron transporters, can be channel proteins.So, there are many different kinds of proteins in this tonoplast which is a single layeraround the vacuole which helps in the selective movement of the molecules from the cytoplasmto inner.So, it contains water and all these salts in side.And the tonoplast is the one where the a true active transport even and the electrochemicalgradient is maintained, I said it helps in maintaining the pH of the cytoplasm . Andyou will find that the vacuole pH is acidic in nature.Why do you think it is acidic in nature, and many of these enzymes things which are presentinside, they they are active at acidic field.Now, plastids, they are very different kinds of plastids I was mentioning.Chromoplast, chromoplast are the kinds of plastids which can store your coloured molecules.Then chloroplast for photo synthesis, echoplast for echoplast is for storage of many differentkinds of molecules where they are further divided into amailoplast for.Amailoplast you must have heard for starch, then alio plast for oils, granules, then proteinoplastfor proteins.Now, there are three different kinds of plant cells, one is parenchyma, then sclerenchymaand collenchymas.Now, talking about parenchyma cells, parenchyma cells are the majority of cells present inthe plant . They form the mass of the cells the plant.Now, parenchyma cells are those protei potensers which we keep referring to.They form the mass of the plant and they are for their entire life they remain protei potent. Protei potent means they have the ability to organize themselves into a specializedfunction, and again re divide and come back to protei potent stage, and again redirectthere metabolism to carry out another specialised function .So, these are parenchyma cells.Generally, where you will find them you will find them in all growing parts in your yourphoto synthetic cells your spongy cells then your mesophyll cells which are there in yourphoto synthetic process in leaves, you will find these kind of cells . So, the cell wallthey only have primary cell wall because as they are present in the young cells whichare cells which are growing going the plant cell wall the size will keep increasing, thereis change happening in the cell size, shape.So, the cell wall needs to be flexible . So, in all these parenchyma type of cellsyou will find there is only primary cell wall, so that they are more flexible.You will find them square shaped generally, but still theyshape can change a little bit.Collenchyma cells here the cell wall thickens . So, collenchyma cells are layered cellswhich the role of these cells they become a little more specialized.The role of these cells now is to support.So, you will find them in regions where the growth is still happening which means theroot which is still elongating, growing or the stem which is still elongating in thegrowing parts of the plant where so they are more elongated cells.So, again they are although lesser flexible than parenchyma, but still the cell wall isflexible.Now, sclerenchyma cells.Sclerenchyma cells if you remember walnut, you must have seen walnut, then peach suchhard geode is there.And in your flax or in your linen which are very difficult to tear apart.So, these are sclerenchyma cells.Sclerenchyma cells appear when the plant has the cell has completely matured, there isno more growth happening . And at maturity, now the secondary wall develops and the secondarywall there is large amount of lignin in it.So, because of thickness of the plant cell wall, and there is gradually you will findthat a cytoplasm will be lost and they will become vacuumed empty cells, empty chambers.So, most of these cells if you will observe, they will be empty cambers with only cellwall.So, generally their purpose is to provide structure, and to provide protection againstthe external environment, so that is the sclerenchyma cells.So, you will find them only in matured parts of the plants where there is no more growthrequired . So, there are two types, fibres and sclereids.Fibres I was mentioning these are all long length even up to 50 centimetres long cells. So, like in your fibres your fabrics I said linen and flax.So, then sclereids, sclereids you will find they they have much thicker cell wall, evenmore than fibres . And even small group of cells, they will youcan see them together or even single cells with large size.I is there will be used to protect that peach pit and your what else walnut, those are allyour sclereids.