17 Dec 2020

Five Methods of Micropropagation

Anjali Singh, MS

As a content and community manager, I leverage my expertise in plant biotechnology, passion for tissue culture, and writing skills to create compelling articles, simplifying intricate scientific concepts, and address your inquiries. As a dedicated science communicator, I strive to spark curiosity and foster a love for science in my audience.

Table of Contents

Micropropagation is an artificial method for rapid multiplication of plants in a short duration using the tissue or cell culture techniques in a controlled environment. The method is extensively used to produce genetically identical plants, pathogen-free plants, mass production of plants, gene conservation, etc.

The plant can be propagated by both asexual (by vegetative propagation) and sexual (through seed) means. Sexual reproduction involves the fusion of gametes that lead to the production of seeds with a high level of heterogeneity. In micropropagation, plants are cloned. They are propagated either by asexual means of reproduction or vegetative propagation. Both ways involve the production of genetically identical plants by multiplying a single individual under in vitro conditions.

Why there is a need to grow plants under artificial conditions when you can grow them naturally? The natural propagation of plants can be done when the purpose is to grow plants in your kitchen garden or to decorate your home. You can easily do it by cutting, grafting, or budding. However, if there are large-scale industrial or commercial needs involved, they can only be fulfilled by the micropropagation of plants. In this case, the conventional techniques are not proven to be successful as they are expensive, difficult, and don't fit for the clonal propagation of every plant.

In this article, five different methods of micropropagation are discussed.

Methods of micropropagation

1. Meristem culture

In meristem culture, meristematic tissues are used as explant for culturing purposes. Meristematic tissues are the type of tissues that can continuously divide and produce new cells. The meristem culture technique was developed by Morel and Martin in 1952 to culture Dahlia. In this case, meristem tissue with a few leaf primordia is placed on a suitable media for the growth and development of plants. The size of the explant is essential to be considered depending on the goal of culturing before initiating the experiment. Meristem culture technique is best for virus elimination, gene conservation, genetic transformation, and plant breeding purposes. It has been successfully used to propagate several crops like sugarcane, strawberry, etc.

2. Callus culture

A callus is an undifferentiated mass of tissue. In vitro, the callus formation is induced by placing a piece of tissue in a growth culture media under favorable conditions. Then, the callus is transferred to another fresh media containing a high concentration of auxin or auxin and cytokinin (plant growth regulators) for organ development.

Some limitations of callus culture include high biochemical variability and slow growth rate. These limitations hinder the utilization of the callus culture techniques at a higher level by the culturists.

3.Suspension culture

The suspension culture method involves the formation of suspension by the multiplication of single cells or aggregates when agitated in an aerated and sterile liquid medium. The two types of suspension culture include batch culture and continuous culture.

In batch culture, cells are grown in a fixed amount of culture medium under suitable environmental conditions. In continuous culture, fresh medium is added and the leftover nutrients are continuously removed from the culture media in which cells are suspended. The most common problem in this method is the formation of clumps and failure of cells to separate after division.

4. Embryo culture

Embryo culture is the isolation of immature or mature embryos and culture them in a suitable growth media under favorable conditions. The zygotic or seed embryo is used as explant and the presence of nourishing tissue, endosperm, ensures the proper development of the plant. When the endosperms degenerate, as in the case of a cross between two distant species, the development of the embryo is hindered and the plants develop improperly. Therefore, endosperm has an essential role in embryo culture.

To produce healthy plants in cases where endosperms degenerate, the process is followed by culturing the immature hybrid embryo. This process is called embryo rescue. It is done to save embryos that could be aborted. The embryo rescue technique has massive application in crop improvement.

5. Protoplast culture

Protoplast is a spherical naked living cell without a cell wall. It is obtained by stripping the cell wall of plants by using chemical, mechanical, or enzymatic processes. Protoplast culture is the isolation of plant cells followed by degradation of cell walls and culturing them in a liquid media under suitable physiological conditions. The cultured protoplasts form cell walls followed by calli that are transferred to solid media for the development of the whole plant.

The explants used for protoplast culture are leaves, root tips, and embryos. Out of these three explants, leaves are the common source of protoplast. It’s a bit difficult to strip the cell wall of root tips and embryo and that’s why they aren’t commonly preferred as an explant source for the protoplast culture.

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Reference

1. Bhatia, S., & Sharma, K. (2015). Micropropagation. Modern Applications of Plant Biotechnology in Pharmaceutical Sciences, 361–368. doi:10.1016/b978-0-12-802221-4.00011-x
2. Tomar, Uttar & Dantu, Prem. (2010). Protoplast Culture and Somatic Hybridization.
3. Miller, R. A., Kao, K. N., & Gamborg, O. L. (1973). Plant Protoplast Culture11NRCC No. 13002. Tissue Culture, 500–505. doi:10.1016/b978-0-12-427150-0.50117-0
4. https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/embryo-culture.
5. https://byjus.com/biology/micro-propagation/.
6. https://en.wikipedia.org/wiki/Micropropagation