Meristem tissue culture

Did you know that you can have virus free plants using meristem tissue culture even though there is infection in the stock plant?

An important fact is that many plants carry internal viral, bacterial, and other infections. Pests and pathogens lead to considerable losses for the agricultural sector. These plants with infections then show slow growth, curling of leaves, streaks or patches in leaves and flowers, yield reduction and even plant death. Among different pathogens, viruses are the most lethal for plants as there is no chemical treatment to get rid of viral infection. However, most viral infections do not pass on from the parent plant to the next generation of plants. Unlike, bacterial and fungal infections, they are generally not present in seeds.

But how do viral infections spread in plants?

Different kinds of pests such as whitefly, green lacewing fly, aphids, etc. serve as carriers for viruses. These pests transfer viruses to the plants while feeding on them. When you use the same infected plant as the mother plant and extract explants such as leaves, nodes, etc. there is a high probability that you will have the same infection in new plants as well. Also, plants such as potatoes, garlic, pineapple, orchids, etc. which are vegetatively propagated, are more prone to carry and transfer viral contamination.

How plants deteriorate due to viral infections?

Along with curling of leaves, streaks, and patches on leaves, these infections also cause changes in flower colors for ornamentals plants and reduce flower size. Viral infections can lead to smaller fruit sizes or no fruit at all, depending on the plant growth stage when the infection started. This has a significant negative impact on consumer acceptability.

So what do we do to solve this problem using plant tissue culture?

Meristem tissue culture!

It is one of the most popular methods of virus elimination in the plant science world. Not only this, but it also has the potential to eradicate fungal and bacterial infections from mother plants. Several ornamental plants such as orchids and fruits like bananas are cultured using meristem tissue culture for large-scale production. This method is also used extensively for the long-term storage of germplasm of different plant species.

Apart from meristem culture, there are some more methods of tissue culture to obtain healthy in vitro plants. You can read more about them in our article on "7 methods of plant tissue culture".

Let us discuss briefly meristem tissue culture:

What is meristem?

Meristems are the centers of plant growth present in apical and lateral buds and even roots. Meristematic tissue possesses an undifferentiated group of cells that are capable of dividing. These cells can produce new cells that can differentiate into different kinds of plant organs as they mature. We can also call this ability 'totipotency' ! These cells are present at several locations in the plants. 

For instance, in roots and shoots, we can observe these tissues at the tip. They are called root apical meristem and shoot apical meristem, respectively. In these regions of the plant, meristem leads to shoot and root development.

Meristem tissues are also present at plant parts where new branches are coming out. These tissues are called intercalary meristem and they indirectly help in increasing plant height. Lastly, meristem tissues are also present in the lateral side of stems and roots. These tissues are present to increase the thickness of plants. Below is an illustration indicating different types of meristems and their location in a plant.

What does meristem culture mean?

Meristem culture means the culture of the meristematic cells by isolating, sterilizing, and placing meristematic tissues on the culture media for further development of complete plantlets. Based on the size of explant used in the culture, we can also call this method as shoot tip culture, meristem tip culture, tip culture, or culture of shoot apices.

The plant development stages involved in meristem culture are same as the normal procedure followed in plant tissue culture. It includes:

• Culture initiation
• Shoot multiplication stage
• Rooting stage
• Hardening or acclimatization of developed plantlets

However, for you, the main difference between meristem culture and other plant tissue culture methods lies in determining the size of explants (5-10mm) and choosing the right type of meristem. You need to extract meristem tissues from actively growing buds, preferably terminal buds. Interestingly, in some plants such as chrysanthemums, apical meristem explants give better tissue culture results than intercalary meristem. However, for strawberries, intercalary meristem gives better results. Also, it is important to use a fixed size of explant for developing an efficient micropropagation protocol.

Constraints for meristem isolation

One of the major problems we can face with meristem culture is 'oxidation'. This happens due to the release of phenolic compounds from the tissues to the culture media. Such compounds in the medium are a disturbance or contamination for plant tissue culture. They turn the meristem tissues brown which means a reduction in cell division and explant regeneration capacity. Thus, the oxidation of meristems during the in vitro establishment process affects the development of virus-free plantlets.

So what can we do to avoid or reduce oxidation?

We can reduce the chances of oxidation by carefully managing the explants/meristem tissues. Another way is to modify environmental conditions for growth, for instance regulating light duration on the basis of plant species. One of the most common methods to deal with this problem is to add antioxidants in the culture medium.

At the end, it is necessary for you to check whether the plant material is actually free from viruses. You need to get your material checked for specific viruses through various tests by an accredited laboratory. Only those plants which receive negative test result for the concerned virus should get a label of virus free and then further used for multiplication and planting.

We hope you got a glimpse of what is meristem tissue culture and why it is one of the popular methods in the plant tissue culture industry. For more informational posts on different methods of plant tissue culture, keep checking this space!

By Nancy Bhatia | 23-June-2021

References

• Robert H. Smith (2013). Plant Tissue Culture- Techniques and Experiments. Elsevier Inc.
• Kyte, Kleyn, et al (2013) Plants from test tubes: An introduction to micropropagation. Timber press, Inc.
• Bhojwani, S.S., & Dantu, P.K. (2013). Plant Tissue Culture: An Introductory Text. Springer India
• Sharma, V., & Alam, A. (2015). Plant Tissue Culture. I.K. International Publishing House Pvt. Ltd.
• Meristem culture and subsequent micropropagation of Chilean strawberry (Fragaria chiloensis (L.) Duch.). Retrieved from https://biolres.biomedcentral.com/articles/10.1186/s40659-017-0125-8