Types of plant tissue culture

Types of plant tissue culture Introduction:

Types of plant tissue culture are based on the parts of the plant(explant) that are used in tissue culture technique. The different types of tissue culture are used for variety of applications and it also depends on type of the plant.

Plant tissue culture is culturing/growing plants on a chemically defined synthetic nutrient media under controlled conditions. It is a collection of techniques to grow plant cells. There are several types of plant tissue culture that are widely used to produce multiple copies of plants.

Types of plant tissue culture:

Based on the type of explant and type of medium (liquid or solid) used, plant tissue culture is further classified into,

1. Callus culture
2. Suspension culture
3. Meristem culture
4. Protoplast culture
5. Anther/pollen culture
6. Root tip culture
7. Bud/flower culture
8. Ovule/Embryo culture

Types of plant tissue culture

1.Callus culture:

Callus is mass of irregular and undifferentiated actively dividing cells. When explant is cultured in nutrient medium and kept under confined condition callus is formed.

Along with auxin and cytokinin, nutrient media inducts cell division in explant. This leads to formation of callus.

In plants, callus contains unorganized mass of parenchyma cells.

When callus is formed, it is sub cultured regularly with new medium in every 28 days to avoid production of toxic metabolites.

Callus culture are of two types based how the cells are associated among them,

• Compact callus – Densely clustered cells
• Friable callus – Loosely arranged cells

Callus is the fine source of karyotype and genetic variability which can be used to regenerate a whole plant. Also, it is used to obtain secondary metabolites.

2.Cell/Suspension culture:

One of the next steps in callus culture is suspension culture. Most of the tissue culture techniques uses solid media with agar. But in suspension culture liquid medium without agar is used.

It can be obtained either from callus or explant. Cell of suspension culture is initiated by transferring a piece of callus to a liquid medium,

where the medium will be in continues agitation to avoid the formation of clumps. The continues agitation is achieved using rotating/shaking incubators.

There are two types of suspension culture,

• Batch culture
• Continuous culture

Batch Culture: 

In batch cultures cells are grown in fixed volume of agitated liquid medium. It is a closed system, which helps in initiating single cell cultures. 

Cells is batch culture undergo lag phase, log phase, exponential and death phase based on initiation, growth, multiplication and ceasing of cell division.

Batch culture is sub divided into,

• Slowly rotating culture
• Spinning culture
• Shake culture
• Stirred cultures

 

Continuous Culture: 

It can be either closed or open system, where the liquid medium is constantly replaced with fresh medium to avoid detoxification and depletion of nutrients.

Continuous culture is further classified into chemostat system and turbidostat system.

Suspension cultures have main application in observing the growth and development process of plant. It is used to study the embryoid or organ formation.

Single cells can be obtained from mass of cells using cell or suspension cultures.

3.Meristem culture :

If actively dividing meristematic tissue of shoot tip, vegetative bud, root tips are taken as explants and cultured in nutrient medium then it is called as meristem culture.

Meristem culture is more successful in case of herbaceous plants. The main application of meristem culture is to eliminate virus in certain plants to obtain disease free plants.

It is often employed for mass propagation and germplasm storage because meristematic tissues are less differentiated which is why it has the capability to produce identical progeny.

4.Protoplast culture:

In many types of plant tissues culture, protoplast culture is seen as vital type. 

Protoplasts are the cells without cell wall. They are cultured either in semi solid or liquid media. Protoplasts can be isolated from roots, fruits, leaves, callus tissue, tubers etc.,

Protoplasts can be isolated by two methods

Mechanical method: Epidermis of the cell is subjected to plasmolysis and the cell wall is cut to release the protoplast. This process is tedious and not often used

Enzymatic method: In enzymatic method, cells are subjected to enzymatic solution that mainly contains pectinase and cellulase. This method is sub divided into direct and sequential method.

Protoplast culture is mainly used in producing genetically modified plant species, hybrids (fusion of two different plant nucleus) and cybrids (fusion nucleated and enucleated cell).

Another striking application of protoplast culture is somatic hybridization. Protoplast fusion of two different plant species or varieties is called somatic hybridization and the hybrid plant obtained is known as somatic hybrid.

5.Anther/pollen culture:

Anther/pollens are collected at the stage of uninucleate microspores and cultured in suitable media (MS or white media). They are cultured mainly in liquid media.

They develop into callus which is further sub cultured to obtain plants.

It is mainly used in production of haploid plants

6.Root tip culture:

Lateral root tips of radical tip of germinated seeds are taken as explants for root tips culture. 

Liquid mediums are mainly used for root tip culture.

Root tip culture is done to understand carbohydrate metabolism, dependence of roots on shoots and effect of various compounds on roots.

7.Bud/flower culture:

Flowers can be cultured in different stages of their growth. While bud and a young flower required complex media with high growth regulators whereas the matured flower need simple media as they are fully grown.

The main application is to study the development of flowers. Pollinated flowers are cultured to study the fruit development.

8.Ovule/embryo culture:

Embryo culture involves in isolating and culturing the mature or immature embryos to produce viable plants.

In some plants when seed dormancy occurs, embryo is isolated and cultured in nutrient media to develop viable seedlings.

Main application is to production of interspecific or inter-generic hybrids.

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