Meristem Culture for Virus-free Plant Propagation

Meristem culture, also known as meristem propagation, is a technique in plant tissue culture that involves the growth of plants from meristematic tissues. Meristems are regions of plant tissue where cells actively divide, and they are responsible for the growth and development of the plant. There are two main types of meristems: apical meristems, which are located at the tips of stems and roots, and lateral meristems, which are responsible for the growth in girth of stems and roots.

Also, check out- Components Of Plant Tissue Culture Media – My Biology Dictionary

History of Meristem Culture

The concept of meristem culture for plant propagation dates back to the early 20th century when scientists began exploring methods for propagating plants in vitro (in a controlled environment outside their natural habitat). For the first time in 1952, Morel and Martin recovered virus-free Dahlia shoots. This was the first application of the meristem culture method, resulting in pathogen-free plants. In addition to that, the ability to propagate plants from meristems offers several advantages. To distinguish it from the in vivo technique of propagation by shoot-tip cultures, the term ‘meristem-tip culture’ is preferred for the culture of shoot tips in vitro as a plant tissue culture technique. Meristem culture is extensively used for the propagation of banana plants, particularly for the production of disease-free planting material. For the propagation of potatoes, meristem culture helps in producing disease-free seed potatoes, contributing to the control of potato diseases.

Why are Shoot Apical Meristem Virus-free?

Most meristem cultures are shoot-tip cultures, because of their ability to actively grow and divide. The cells that are responsible for this growth are called ‘meristematic cells’. Their high metabolic activity does not allow the virus to replicate. The shoot tip also consists of the leaf primordia and primary leaves (see figure). These new cells and leaf primordia are in their early stages of growth and hence in no contact with the main vascular system in the stem. The virus particles, which can only travel from cell to cell, are not present in the meristem. The older tissues though, have well-differentiated vascular elements, and therefore have high infection concentration. This is the reason why the virus concentration decreases acropetally, towards apical meristems and axillary buds. The meristems are also protected by a virus-inactivating system, which has high activity in the meristems.

Position of Shoot Apical Meristem

The Process of Meristem Culture

Schematic Representation of Shoot Tip Culture.  Image source: Bhale, U. N. (2016). Major constrains and verdict of crop productivity V. 1 & 2. New India publishing Agency, NewDelhi.

The apical meristem is the region lying distal to the youngest leaf primordium (about 250 nanometres long). This region along with one to three leaf primordia make up the ‘shoot apex’.

• The conditions are standardized only to allow specific and organized growth into a shoot. The process is carried out in aseptic conditions and with careful dissection. It begins with proper sterilization of the plant material to eradicate contaminants like bacteria, fungi, or viruses.
• Then the process of isolating the apical meristem part of the stem under a microscope is carried out. The plant material is held with a pair of forceps and the leaflets covering the apical dome are removed. Next, a clean cut is made to isolate the shoot tip.
• The tips are transferred to a suitable culture medium in the next step. The medium typically contains a combination of salts, sugars, vitamins, and plant growth regulators to support the growth and development of the cultured tissues. This is usually done in a sterile laminar flow hood to minimize the risk of contamination. The shoot tips are placed in culture vessels, such as Petri dishes or test tubes, containing the nutrient medium.
• Accordingly, depending on the goals of the culture, the regenerated shoots may be induced to form roots. For this, rooting hormones or specific culture conditions may be used to stimulate root development.
• Next, the plants are allowed to do something called ‘acclimatization‘. This is a gradual process that helps the plants adjust to the external environment.
• Lastly, the plantlets can be transferred to soil for further growth and development.

Advantages

Meristem culture provides several advantages in agriculture and horticulture. It enables the production of virus-free plants by isolating rapidly dividing undifferentiated cells at the growing tips, reducing the risk of contamination and preserving genetic uniformity. The resulting plants are clones of the parent, retaining desirable traits and eliminating somatic mutations. Hence, it ensures genetic uniformity. Meristem culture allows for the rapid multiplication of plants year-round, facilitating mass production and conservation of rare species. This method serves as a powerful tool for plant breeding, allowing customization and improvement of varieties.

Disadvantages

Despite its numerous advantages, meristem culture is not without its disadvantages. One significant drawback is the potential for the transmission of latent viruses. Additionally, the process can be technically challenging and labor-intensive, requiring specialized skills and equipment. The genetic uniformity that is an advantage can also be a drawback in situations where diversity is needed for adaptation to changing environmental conditions or resistance to evolving pests and diseases. There is a risk of somaclonal variations, and spontaneous genetic changes arising during the tissue culture process, which can affect the stability of desired traits. Furthermore, the cost associated with establishing and maintaining sterile conditions for tissue culture can be high, limiting the accessibility of this technique for small-scale or resource-constrained settings. These disadvantages highlight the importance of careful consideration and quality control in the application of meristem culture.

Use of Meristem Culture in Various Fields

Disease-free plants-

It is proven that by using the shoot tips or meristematic tissues, which are typically free from pathogens, it is possible to generate plants that are free from viral, bacterial, as well as fungal infections.

Conservation of species-

Another benefit is preserving the genetic material in vitro, by which researchers can maintain the biodiversity of these species and prevent their extinction.

Propagating Horticulture crops-

Many horticultural crops, including fruits, vegetables, and especially ornamental plants, benefit from meristem culture for the production of disease-free and genetically uniform planting material.

Transgenic plants-

Meristem culture provides a method for the development of transgenic plants by introducing foreign genes into the meristematic tissues. This is a common approach in genetic engineering and biotechnology.

Improving crop yield-

Meristem culture also contributes to improved crop yield. Particularly, it ensures that the propagated plants are free from diseases that can reduce productivity and affect the quality of the harvested produce.

Scientific Research-

The utilization of meristem culture extends across plant laboratories for the examination of plant development, cell division, as well as differentiation processes. Due to their capacity to undergo division and give rise to various cell types, meristems have been found to unravel numerous cellular mechanisms.

To sum up, meristem culture stands as a powerful and widely utilized technique in plant propagation, offering several key advantages. With careful application and quality control, meristem culture continues to be a cornerstone in the production of high-quality, uniform plant material for diverse agricultural and environmental needs.

Thanks for reading!

Team MBD