4 Mar 2021

Examining The Axillary Bud Proliferation Technique!

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 a technique to grow whole plants from the tissue in a short duration of time. This method has been very popular for gene conservation, cloning plants, endangered species protection, and several research studies. The technique involves the use of several different explants to convert them into a whole plant. It includes meristem cells, shoot-tips, and axillary buds.

These different explants are used to serve different applications. For example, meristem cells are best to prevent virus infection from the plants and clonal propagation. Similarly, shoot-tip culture is used for clonal propagation. These explants are involved in the processes of different plantlet production including direct organogenesis, indirect organogenesis, and axillar bud method.

This article is focused on the brief introduction of axillary bud methods and their procedure and application. Let’s begin!

Axillary Bud Method

The axillary buds or lateral buds are formed in the angle between leaf and stem which lead to the formation of several branches. The axillary bud method involves the development of the axillary bud. The shoot tips are isolated from the tip of the axil of leaves that develop axillary bud under the effect of a high concentration of cytokinins. The role of cytokinin is to suppress apical dominance and promote the development of axillary buds. The axillary bud method is often combined with the single node method.

Key points include:

1. The ratio of auxin and cytokinin used in the axillary bud method is 10:1.
2. The developmental stage of explant in culture is directly proportional to the concentration of cytokinin to be used in the culture media. For example, mature culture requires a higher concentration of cytokinin compared to the juvenile culture.
3. The cytokinin requirement and concentration used in axillary bud proliferation are also dependent on the species or cultivar of the plant you want to culture.
4. Often it is advisable to induce the formation of shoot tip before increasing the cytokinin concentration to induce axillary bud formation.
5. If the growth and development of the axillary bud are unsatisfactory, you must remove the apical meristem from the cultured explant.
6. Often, liquid media promotes the axillary shoot formation.
7. It has been observed that, in a wide range of species, several substituted pyridyl phenyl urea compounds and thidiazuron stimulate axillary branching.

Factors That Impact Axillary Bud Proliferation

Several factors affect the axillary bud proliferation under in vitro conditions, out of which of them are discussed below. Please note that the effect of factors varies depending on the species of the plant you are working on.

• Plant growth regulators Axillary bud growth is highly dependent on the presence of benzyl adenine (BA-synthetic cytokinin that promotes the growth and development of the in vitro cultures by stimulating cell division). More callus and shoots are produced by the explants cultured in the media containing BA compared to the media without BA. Moreover, rooting in the explants is induced by keeping them in basal media without any growth regulators. The presence of 1-Naphthaleneacetic acid (NAA) in the media induces negative effects on the root formation.
  
  
• Explant size It has been observed that the explants larger in size showed more positive responses compared to the smaller ones. It’s because the larger explants contain more nutrient reserve and endogenous plant growth regulators that support the in vitro development of axillary buds.
  
  
• Explant density The number of explants cultured in a jar determines the multiplication rate and output of the cultures. For example, a jar containing 10 explants will show a lower rate of multiplication and explant survival compared to a jar containing 5-6 explants.

Applications of Axillary bud proliferation technique

1. Mass propagation of plant species
   
   The axillary bud proliferation method provides genetic stability to the plants and is the most preferred technique for the mass production of plants. This technique is adopted for the clonal propagation of several plants including almond, apple, Acacia mangium Willd, Cedrus, Eucalyptus, tea, Curcuma longa L., hazelnut, olive, barley, and rice. The axillary bud proliferation technique doesn’t involve the dedifferentiation of differentiated cells but the growth and development of a whole plant through pre-existing meristem. For this reason, this technology is very popular to produce genetically stable true-to-type progenies.
   
   
2. Somaclonal Variation
   
   Somaclonal variation is defined as a variation in the in vitro cultured plants. It can be due to changes in chromosomal numbers of plants, mutations in the genetic components of the plants (sequence change, gene activation, or silencing). These changes affect the productivity and health of plants on large scale. However, among all the other micropropagation techniques, axillary bud proliferation offers the least risk in this case. This observation has been recorded in many plants including Bambusa balcooa Roxb., Myrtus communis L., and Solanum tuberosum L.
   
   
3. Plant Biodiversity Conservation
   
   The axillary bud method is considered one of the best techniques to conserve the restore the plants with their original characteristics and features. It is advantageous and fruitful in the case of saving the endangered plant species. So, the axillary bud method plays a major role in plant biodiversity conservation.

The axillary bud method is an extensively used technique. Following this series, we will talk about the procedure of establishing culture through the axillary bud method in our future blogs! So, keep checking the Plant Cell technology updates visiting your mails!

Happy Culturing!

References

1. F. Ngezahayo, B. Liu, "Axillary Bud Proliferation Approach for Plant Biodiversity Conservation and Restoration", International Journal of Biodiversity, vol. 2014, Article ID 727025, 9 pages, 2014. https://doi.org/10.1155/2014/727025.
2. 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.
3. Pickens, K. A., Cheng, Z. M., & Trigiano, R. N. (2005). Axillary bud proliferation and organogenesis of Euphorbia pulchurrima winter rose. In Vitro Cellular & Developmental Biology - Plant, 41(6), 770–774. doi:10.1079/ivp2005706..
4. https://watermark.silverchair.com/25-4-477.pdf?