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Module 1: Plant Cell Technology

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History of Plant Cell and Tissue Culture

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So,for history of plant cell cultivation, it began as I saidthe minute that cell theorycame into the picture in parallel because of the world war going on, on they wereparalleldiscovery is happening in US and Europe.So,after the cell theory concept in parallel then they also discovered the cellular totipotencyin plant cells, so that came in in 1838, 39 around.And then so initialdiscoveries were what the idea was to see if the explants can remainviable, in the medium can be kept viable for a longer time apart after taking it out fromthe plant.So, the attempts were to keep the fragments which were cut from the parent plant to keepthem growing and viable, so that were one of the.So, the idea was what kind of media would be needed to sustain that growth.So, therefore, then IAA discovery came. was able to find IAA, which is indole acetic acidwhich is an auxin . So, then similarly people were again focusing on coconut milk.So, initial discoveries we will find the media people use to use complex medium.So, there coconut milk was being used.So, when coconut milk was being used, they also once auxin was discovered, they alsofound thatthere is a component in coconut milk which is unlike auxin, but is able tosupport the callus growth.Then in parallel they also found that how to induce, from single cells you can originatethe callus.So, techniques of inducing callus, nerves tissue technique.So, what is that, they took a callus of some other plant, and they had put a filter paperon top of that callus, and let it be get wet by that callus.So, whatever came out of the callus is was getting absorbed by the filter paper.And then on top of that filter paper single cell was of carrot or I do not remember tobaccomay be or some plant they added on that filter paper, and they kept on observing it understerile conditions.And they found that that single cell started dividing, dividing, multiplying and thencalluswas found to originate.So, these simple techniques of plant cell and tissue culture with form now basics ofplant biotechnology.Those were the initial discoveries which were very fast and very quick discovery is werehappening in that and parallel.So, then it came on to further refined media requirements depending on what kind of cultureyou need.So, from single cells, then totipotency, from carrot cell, so initially the carrot it theidea was to just maintain the explant and keep it viable, then the callus inductioncame out.Then somatic embryos also came into the light by a simple experiment where where the carrotdisc wereput in the suspension.And then because of the agitation some of the single cells they got dispersed and camein the medium.Because of the nutrient composition present in the liquid medium, these single cells,some of these single cells rapidly divided and formed embroidered like structures withboth primordiums shoot and the root primordiums later giving rise to the entire plant in thesolid medium that is how regeneration discoveries came into light.Then came agro bacterium mediated transformations where people found that these naturalvectorsystems can cause crown gall disease.Now, in this crown gall disease is when people tested the crown galls, they found that theyhave higher auxinity.Hyper auxinity means that they did not require any hormones in the medium to continue theirgrowth, and when detected now all this detection also goes in parallel with the discoveriesand advent of of higher analytical techniques microscopic technique.So, everything was lot of things were going in parallel and were being applied.So, then in this what they found in crown gall that there was hyper auxinity which meansthat there were genes present which themselves in inherently producing auxins in large amount,so that was one discovery.Then somebody also found opines present in these crown galls.Opines were nothing butthe act as carbon and nitrogen sources with for the bacteria.So, when present in the bacteria it does not get expressed.So, but once it infects in the plant cell, they get express and these opine start gettingformed, so which is then utilized by the bacteria as food source.So, initially these opines because their expression was transient; then it was also find thattheir expression is not permanent, it is only transient .And so initially they use to be used even as markers fortesting successful transformations.So, these opines used to be used, but then latermore pool proof conformations were usingPCR, and your TDNA integration has happened or not.Then meristem culture also came into the picture.Now, why did people were looking they were depends on the objective to begin with andthen the experiments design to reach to that objective.So, now, the objective was to see if virus free plants can be obtained.Now, for virus free plants then people came with an idea of meristem culture.Now, we will be talking about in detailwhere in these meristematic tissuesif you use themfor plant regeneration, then you find that they become free of viruses.It is an interesting question to think upon right now how that why would a meristematicregion would be free of virus and while the other matured parts of the plant and are areeasily invaded by the virus.So, think about it, when we come to the meristem culture, then we will talk about it . So,then meristematic or meristem culture came into the picture for plant regeneration inorder to produce virus free plants.Yeah, then as I said initially and media because people did not have an idea which criticalnutrient or what nutrient is the most significant nutrient.So, people use to use complex media, in that people have also tried is extractor.Even now is extractor is used.So, now, then later with more refinement coming in in people replaced is extract with foundthatvitamin B, B vitamins are also very significant in induction of in vitro cultures plant celland tissue cultures.So, then the each extract was then replaced by three of these vitamins, pyridoxine, thiamineand what else nicotinic acid, so then it was . So, gradually all these then got betterand better and more refined well defined media compositions.Then White's medium came into the picture which was specific to who root induction.Then MS media till now it is used for callus induction . So, it is not only single ms peopleeven use half MS, MS by 4 compositions which may impact the induction of in vitro cultures.So, now you know what is totipotency, totipotency is the potential of the any plant cell torevert back and reprogram itself l from a specialized function to to its original, andthen re specialize itself towards a different function.So, what is needed for atotipotent cell to regenerate into a plant is that the cell shouldbe able to have an embryogenic capacity so as to form primordiums for shoot and rootgeneration, and then there has to be a nutrient environment created around that cell to makethe development of that cell as the cell is rapidly dividing in similar to what a zygoteundergoes . So, then you will end up in having the entire regeneration entire into a wholeplant.Now, this is what I was talking about.So, this is how the entire plant came into the picture from using and explants, a discof carrot which was suspended in the liquid some of the free cells because of the shakingin became free in suspension.And these cells and the media which was used was favorable for embryoid formation .And then those totipotent cells else divided with embryogenic competence, they start dividingas they divided the reprogrammed and started behaving like embryoids, and then leadingto shoot and root primordium.And they are after transfer to the solid medium, it gave rise to roots and the entire plant.