MICROPROPAGATION INTRODUCTION

 

Micropropagation or tissue culture

It is culturing a plant tissue in vitro i.e. under controlled lab conditions. A very small amount of tissue or cells are used for micropropagation. Micropropagation is micro means small, propagation means culturing, it is using the tissue to grow a plant. For micropropagation we need explants.

 

Explant

The explant is any part of the plant(leaf/root/stem), tissue, or organ that has meristematic/living cells that are used for tissue culture.

Explant can be leaf where mesophyll tissue of leaves, or it can be living tissues of root, stem or callus. It can be a flower, bud, ovary, ovule, anther, or even pollen grains. A plant has a large number of living tissues that can be used for tissue culture. Xylem and phloem cells and other dead cells cannot be used for tissue culture. However, all the other types of cells can be used for plant tissue culture because the living cells of plants are totipotent.

Totipotent 

Totipotent cells are the cells that can divide and differentiate into all types of body cells. A host of the living cells in plants are totipotent cells and can be used for micropropagation. Schlerides, stone cells, and xylem cells are not totipotent, as they are dead cells so they cannot be used for plant tissue culture.

Sterilization of explant

 When we use explants from a  plant source , it is to be sterilized. As the explant's surface is contaminated by microorganisms. For sterilization, different hypochlorous acid, HgCl2 is widely used. The explant is washed with these acids and then surfaced sterilized using autoclaved double distilled water. If you are using explant cultured under sterilized conditions, severe sterilization is not needed.

There are different stages of micropropagation. The cells divide and they form a callus, Callus may develop into different organs, i.e. shoot or root. The process of the formation of organs is called organogenesis. When a complete plant is produced, it is called a plantlet. The in vitro cultured plant is hardened so that, it can grow in an outside environment, where conditions are not controlled, this process is called acclimatization.

Callus

The callus is an undifferentiated mass of cells. It is produced by totipotent cells after repetitively dividing, it is light green in color. It does not have any regular shape. The cells of the callus can form shoots or roots. As these are nonpolar cells i.e. they are not committed to produce root or shoot. The cells of the callus can be allowed to become polarized by inducing embryogenesis.

 Shooting and rooting

 Callus can form shoot under special conditions. For example, by using the growth hormones, especially auxin and cytokinin.  If the auxin and cytokinin ratio is one that tissue will develop into a callus. If auxin is more than cytokinin, then the tissue will develop into the root. If auxin is less than cytokinin, then the tissue will develop into the shoot. 

The formation of the different organs by plant tissue is called organogenesis.

Embryogenesis

 If the callus is induced to embryogenesis where the cell will become polar, similar to the cells of the embryo, where some cells are committed to forming the shoot and some cells are committed to form the root. That is the cells of the callus have become committed to form an embryo. This process is called embryogenesis. All the stages of embryo formation occur in vitro. The embryos can be used to form artificial seeds.

 Haploid plant

 Haploid cells can be cultured in the laboratory using Anther Cell(n), or egg cells(n) of the ovum. A haloid plant that  is produced has haploid (n) chromosomes, these plants are used to produce pure lines.

 Triploid plants can be produced using the fertilized polar cells of the ovum

 Single-cell culture

 Where a single cell isolated from tissue is used for culture.  Specific methods are used to produce a complete plant from a single cell

 

Protoplast culture

It is the process where protoplasts are isolated using enzymatic or physical methods and these protoplasts are cultured under aspetic conditions. This  is called protoplast culture.

 

GMO

Genetically modified plant or organism are organisms that have a complete set of genes from a different organism or they may have some gene modification.  These organisms have foreign genes.GMO may carry genes of the same species or different species.

Gene transfer can be done intraspecifically or interspecifically.

 Vector is a vehicle used to carry the foreign genes to host cells, these are called vectors.

 Plasmid is the circular DNA, that has its own origin of replication. The plasmids are usually extrachromosomal DNA.