Tissue Culture Questions in English

(A) Micropropagation is the practice of rapidly multiplying stock plant material to produce a large number of progeny plants using modern plant tissue culture methods.
Since the plants are produced through tissue culture (asexual reproduction), they are genetically identical to the parent plant.
These genetically identical plants are referred to as $True-to-type$ plants.

(D) An explant is the excised piece of tissue or organ used for plant tissue culture.
Before organogenesis occurs,the explant cannot synthesize its own food through photosynthesis as it lacks fully developed photosynthetic machinery and is typically grown in a closed vessel on a synthetic medium.
Therefore,it relies on external nutrients,primarily sucrose,provided in the culture medium,making it heterotrophic.

(A) Plants are more rapidly manipulated by genetic engineering than animals because a single somatic cell possesses the property of totipotency,which allows it to regenerate a whole plant body. This characteristic makes it easier to perform genetic transformations on a single cell and then develop it into a complete transgenic plant.

(C) cybrid (cytoplasmic hybrid) is a cell or plant produced by the fusion of a protoplast containing the nucleus of one parent with a cytoplast (enucleated protoplast) of another parent. Therefore,it contains the cytoplasm from both parents but the nuclear genome of only one parent.

(D) Protoplasts are plant cells that have had their cell walls removed.
Because they lack the rigid cell wall,they are highly susceptible to bursting due to osmotic pressure changes.
Sorbitol or mannitol are non-metabolizable sugar alcohols added to the culture medium to maintain the osmotic balance,acting as osmotic stabilizers to prevent the protoplasts from lysing.

(C) Murashige and Skoog's $(MS)$ medium is a widely used plant tissue culture medium. It provides essential nutrients, vitamins, and hormones required for the growth and development of plant cells, tissues, and organs. Therefore, it is primarily used for raising plants through micropropagation.

(D) Callus culture and suspension culture are two types of plant tissue cultures.
In plant tissue culture,auxins are essential for cell division and root initiation.
$2,4-D$ ($2$,$4$-Dichlorophenoxy acetic acid) is a synthetic auxin that is most commonly used in both callus and suspension cultures to promote rapid cell proliferation and growth.

(C) In callus culture,the process begins with an $Explant$ (a piece of plant tissue).
When placed on a suitable nutrient medium,the cells of the explant undergo $Cell division$.
This continuous division leads to the formation of $Callus$,which is an irregular,unorganized,and undifferentiated mass of actively dividing cells.
To maintain or manipulate growth,the culture medium is supplemented with growth regulators like auxin $(2,4-D)$ and cytokinin (e.g.,$BAP$).
These regulators ensure that the cells within the callus acquire and maintain $meristematic$ properties,allowing for further growth or differentiation.

(D) In the $1950$s,Skoog and Miller observed that the callus of tobacco stems proliferated only when,in addition to auxin,the nutrients medium was supplemented with one of the following: extracts of vascular tissues,yeast extract,coconut milk,or $DNA$. This led to the discovery of the growth-promoting factor known as kinetin.

(C) The capacity to generate a whole plant from any cell or explant is known as $Totipotency$. This is a fundamental principle of plant tissue culture,where a single cell has the genetic potential to differentiate into all types of cells and eventually form a complete organism.

(D) The 'Pomato' is a classic example of somatic hybridization.
In this process,protoplasts from two different plant species (in this case,tomato and potato) are fused together to create a hybrid cell.
This hybrid cell is then cultured to regenerate a new plant that contains the genetic material and characteristics of both parent species.
This technique is particularly useful for combining desirable traits from different species that cannot be crossed through conventional sexual reproduction.

(A) The process of somatic hybridization involves the following steps:
$1$. Isolation of cells $(IV)$: First,cells are isolated from the plant tissue.
$2$. Digestion of cell wall $(II)$: The cell wall is removed using enzymes like cellulase and pectinase to obtain protoplasts.
$3$. Isolation of protoplasts $(I)$: The naked protoplasts are isolated.
$4$. Fusion of protoplasts of two different varieties $(V)$: The protoplasts from two different species are fused using agents like $PEG$ (polyethylene glycol).
$5$. Formation of hybrid protoplasts $(VI)$: The fused protoplasts form hybrid protoplasts.
$6$. Regeneration of somatic hybrid plants $(III)$: The hybrid protoplasts are cultured to regenerate into new somatic hybrid plants.
Thus,the correct sequence is $IV \rightarrow II \rightarrow I \rightarrow V \rightarrow VI \rightarrow III$.

(D) Micropropagation is a technique used in plant tissue culture to produce large numbers of genetically identical plants (clones) from a small piece of plant tissue (explant) in a very short duration.
$1$. Somaclones are the genetically identical plants produced through tissue culture.
$2$. Explant is the part of the plant used for tissue culture.
$3$. Totipotency is the inherent capacity of a plant cell to regenerate into a complete plant.
Therefore,the process of rapid multiplication is known as Micropropagation.

(B) The capacity to generate a whole plant from any plant part taken and cultured in a test tube under sterile conditions is known as $Totipotency$. The specific plant part that is taken from the parent plant and used for tissue culture is called an $Explant$. Therefore,the term for the plant part itself is $Explant$.

(D) The meristem (apical and axillary) of a plant is free from virus infection even if the plant is infected.
This is because the rate of cell division in the meristem is faster than the rate of viral replication.
Scientists have successfully extracted this meristem and grown it in vitro to obtain virus-free plants.
This technique has been successfully applied to commercially important plants like banana,sugarcane,and potato.
Therefore,all the given statements are correct.

(D) The concept of cellular totipotency,which states that a single cell has the potential to regenerate a whole plant,was established in the early $1950$s.
Specifically,in $1950$,$F$.$C$. Steward and his colleagues demonstrated that a complete carrot plant could be regenerated from phloem cells of a carrot root explant.
This discovery laid the foundation for modern plant tissue culture techniques.

(B) In plant tissue culture, the nutrient medium (such as $MS$ medium) is supplemented with essential components to support growth and differentiation.
$1$. $Sucrose$ serves as a carbon and energy source.
$2$. $Inorganic$ $salts$ provide essential macro and micronutrients.
$3$. $Vitamins$ and $amino$ $acids$ are added as growth supplements.
$4$. $Auxin$ and $cytokinin$ are plant growth regulators (hormones) essential for inducing cell division and callus formation.
$Abscisic$ $acid$ $(ABA)$ is a growth inhibitor that generally suppresses growth and is not required for the induction of callus formation in standard tissue culture protocols.

(D) Totipotency is defined as the inherent capacity of a plant cell to divide,differentiate,and regenerate into a complete,mature plant under suitable laboratory conditions. This biological principle forms the basis of plant tissue culture.

(B) Somatic hybridization is a technique in plant tissue culture where the cell walls of two different plant varieties are removed to obtain protoplasts. These protoplasts are then fused together using chemical agents like $PEG$ (polyethylene glycol) or electrofusion to create a somatic hybrid cell,which can then be regenerated into a new plant.

(B) Protoplast fusion: The fusion of protoplasts from two different plant species results in somatic hybrids,such as 'Pomato' (a hybrid of potato and tomato). Thus,$(a)-(ii)$.
$(b)$ Plant tissue culture: This technique relies on the property of totipotency,where cells are genetically identical to the parent plant,known as somaclones. Thus,$(b)-(iii)$.
$(c)$ Meristem culture: Meristems are virus-free even in infected plants,so they are used to produce virus-free plants. Thus,$(c)-(iv)$.
$(d)$ Micropropagation: This is the method of producing thousands of plants through tissue culture,utilizing the principle of totipotency. Thus,$(d)-(i)$.
Therefore,the correct matching is $(a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)$. However,based on the provided options,the closest logical match is $(b)$.

(A) The correct matching is $A$.
$1$. Callus is an unorganised mass of actively dividing cells produced in tissue culture.
$2$. Protoplast fusion is a technique used in somatic hybridization,not micropropagation.
$3$. $A$ protoplast is a plant,bacterial,or fungal cell that has had its cell wall completely or partially removed using either mechanical or enzymatic means,but it retains the cell membrane.
$4$. Cytokinins are plant hormones that primarily promote shoot regeneration,while auxins promote root regeneration.

(A) The apical and axillary meristems of plants are generally free from viruses,even in infected plants.
This is because the virus cannot replicate in the rapidly dividing meristematic cells due to high metabolic activity and the presence of specific antiviral compounds.
Therefore,by culturing the meristem in a sterile medium (Meristem culture),scientists can regenerate healthy,virus-free plants from infected parent plants.
This technique is widely used in agriculture for the clonal propagation of disease-free crops like banana,sugarcane,and potato.

(D) Meristem culture is a technique used in plant tissue culture to produce virus-free plants. Since the meristematic tissue (apical or axillary) is generally free from viral infection even in an infected plant,it is used as an explant. Scientists have successfully regenerated virus-free plants from the meristems of various economically important crops,including $banana$,$sugarcane$,and $potato$. Therefore,all the given options are correct.

(D) Virus-free plants are obtained through $Meristem$ culture.
This is because the $meristem$ (apical and axillary) is free from viral infection even in an infected plant.
The $meristem$ divides faster than the virus can replicate and spread into the newly formed cells.
By isolating and culturing these $meristematic$ tissues in vitro,healthy,virus-free plants can be regenerated.

(C) Micropropagation is a tissue culture technique used for the rapid multiplication of plants.
It allows for the production of a large number of plantlets in a small space and within a short period of time.
Since it is performed under controlled laboratory conditions,it is independent of seasonal variations.
Crucially,micropropagation is highly beneficial for the conservation and multiplication of rare and endangered plant species.
Therefore,the statement that it is 'not useful' for such species is incorrect and represents a disadvantage/false claim,making option $C$ the correct answer.

(C) Both callus culture and suspension culture involve the growth of plant cells or tissues on a nutrient medium.
As the nutrients in the medium are consumed and toxic metabolic waste products accumulate,the cells eventually stop growing and may die.
Therefore,to maintain the viability and continuous growth of the culture,it is essential to transfer a portion of the cells or tissue to a fresh nutrient medium at regular intervals,a process known as subculturing.
Thus,subculturing is necessary for both techniques.
Hence,Statement $I$ is correct and Statement $II$ is incorrect.

(A) Totipotency is the ability of a single cell to divide and produce all the differentiated cells in an organism. Examples include spores and zygotes. In plant tissue culture,this property is utilized to regenerate whole plants from explants.

(B) Micro-propagation is a technique of plant tissue culture used to produce large numbers of plants in a short duration.
Since these plants are produced through asexual means (vegetative propagation),they are genetically identical to the parent plant and to each other.
Such genetically identical individuals are collectively referred to as $clones$.

(D) In plant tissue culture,the callus is an undifferentiated mass of cells.
To regenerate a complete plant from this callus,specific growth hormones like auxins and cytokinins are added to the culture medium.
The ratio of these hormones determines the development of roots and shoots,a process known as organogenesis.
Therefore,growth hormones are provided to induce organogenesis.

(C) In plant tissue culture, the pH of the nutrient medium is a critical factor for the growth and development of explants.
It is generally adjusted to a slightly acidic range, typically between $5.0$ and $5.8$.
This range is optimal because it ensures the solubility of essential nutrients and minerals, prevents the precipitation of salts, and supports the activity of plant growth regulators added to the medium.

(C) Micropropagation is a tissue culture technique used to produce a large number of genetically identical plants (clones) from a small explant in a short period of time.
This method is widely used in agriculture and horticulture for the rapid multiplication of economically important plants.

(A) All the options provided are examples of $ex-situ$ conservation. However, tissue culture, $in-vitro$ fertilization of eggs, and cryopreservation (preservation at low temperature $-196^{\circ}C$) are classified as modern biotechnological techniques. Seed banks are traditional methods used to conserve genetic diversity of wild varieties of food grains and vegetables.

(C) In plant tissue culture,the process of organogenesis (differentiation of shoots and roots) is primarily regulated by the balance between two major classes of plant hormones: auxins and cytokinins.
$1$. $A$ high ratio of auxin to cytokinin typically promotes root development (rhizogenesis).
$2$. $A$ high ratio of cytokinin to auxin typically promotes shoot development (caulogenesis).
$3$. Therefore,the morphogenic differentiation is controlled by the interaction and specific ratio of these two hormones.

(A) Apical meristem is used to produce disease-free plants in tissue culture.
This is because the apical meristem is generally free from viral infections,even in a virus-infected plant.
By culturing the apical meristem,healthy and virus-free plants can be regenerated.

(A) Plants produced through tissue culture are genetically identical to the original plant because they are derived from somatic cells through asexual reproduction (mitosis).
These genetically identical individuals are collectively referred to as $Somaclones$.
Therefore,the correct option is $A$.

(A) Somatic hybridisation is a technique in plant tissue culture where protoplasts from two different plant species are fused to form a hybrid protoplast.
To achieve this,the cell walls and the middle lamella must be removed or digested using enzymes like cellulase and pectinase.
Once the cell walls are removed,the resulting protoplasts are fused to create a somatic hybrid,which can then be regenerated into a new plant.
Therefore,the correct process involves the digestion of cell walls and middle lamella before fusion.

(D) micropropagation.
To meet societal demands for large numbers of plantlets quickly,the technique used in floriculture and horticulture is called micropropagation.
This method allows for the rapid production of multiple plantlets from a small tissue sample in a controlled environment.
$A$ Hybridoma technology is used for producing monoclonal antibodies.
$B$ Somaclonal variation refers to genetic variation in plants regenerated from tissue culture.
$C$ Somatic hybridisation involves the fusion of somatic cells to create hybrids.

(A) $A-14$.
Pollen grains are haploid reproductive cells produced by meiosis,containing $n$ chromosomes.
Given that the diploid number of the plant is $2n = 28$,the haploid number is $n = 28 / 2 = 14$.
In tissue culture,when pollen grains are cultured to form callus,the cells of the callus retain the same genetic constitution as the pollen grains.
Therefore,the cells of the callus will be haploid and contain $14$ chromosomes.

(B) The correct answer is $B$ (shoot apex culture).
In plant tissue culture,the shoot apical meristem is generally free from viral infections even if the rest of the plant is infected.
This is because the virus multiplication rate is slower than the rate of cell division in the meristematic region.
By excising and culturing the shoot apex,scientists can regenerate healthy,virus-free clones of the parent plant.
This technique is widely used in agriculture to produce disease-free planting material for various crops.

(B) Somatic hybridization is a technique in plant tissue culture that involves the fusion of protoplasts from two different plant species.
$1$. The cell walls of the plant cells are removed using enzymes to obtain protoplasts.
$2$. These protoplasts are then fused together using chemical or electrical methods to form a hybrid cell.
$3$. This hybrid cell is then cultured to develop into a new somatic hybrid plant.

(D) The process of somatic hybridization involves the following steps:
$1$. Isolation of single cells from two different plant varieties $(D)$.
$2$. Digestion of cell walls using enzymes like cellulase and pectinase $(A)$.
$3$. Isolation of naked protoplasts $(B)$.
$4$. Fusion of protoplasts to obtain hybrid protoplasts $(C)$.
$5$. Growing of hybrid protoplasts to regenerate a new plant $(E)$.
Therefore,the correct sequence is $D, A, B, C, E$.