The most advantageous characteristic of the tissue culture is the ability to utilize “any piece of tissue from any part of the plant” to grow another plant. Other advantages include the production of a large number of plants in a shorter timespan compared to conventional techniques, production of disease-free plants, etc.
The piece of plant tissue that's placed on the growth media is called the explant. Though it’s known that any plant tissue can be used to grow the entire plant, there are some conditions applied! There's only type of plant tissue that's not suitable to grow all species of plants in tissue culture. Some factors determine which explant will be suitable for your culture; by carefully choosing healthy explants for your culture, you can increase the culture productivity multifold.
This article explains what kind of explants are used in tissue culture and factors should be considering while choosing explants.
Types of Explants used in Tissue Culture
All parts of plants can be used as explants for tissue culture purposes: leaves, stems, a portion of shoots, flowers, anthers, ovary, single undifferentiated cells, or mature tissues. However, the cells should be capable of de-differentiating and resume cell division and have cytoplasm.
Some parts, like the root tip, are rarely used as explants for tissue culture processes. Root tips are difficult to isolate and contain microbes in their tissues, forming a strong association with them. Also, soil particles are attached to roots which are difficult to remove without damaging some tissues.
Factors to be Considered while Choosing Explants
1. Age of the Organ used to Source the Explant
The age of the explant is an important factor when choosing the right explant. It’s advised by researchers to use young parts as a source of tissue for culturing because younger tissues correlate to better physiological responses in laboratory research. Since young tissues are newly generated, they are better suited for the rough process of surface sterilization. Surface sterilization is a process that can potentially damage tissue and helps to establish clean cultures.
2. When the Explant was Collected
The season in which the explant is collected impacts its contamination and growth response in culture. Different seasons have different effects on the explants. For example, the explants (like buds or shoots) collected during the spring (while in their flush state) are more responsive compared to explants collected during the winter season (while in their dormant state).
The dormant explants are generally unresponsive in culture, meaning they must undergo several chemical treatments to make them responsive to tissue culturing processes. Moreover, the chances of contamination also increases toward the winter time.
3. Size and Place of the Explant
Smaller explants are difficult to culture and are less responsive than the larger size explants. Larger pieces of tissues contain enough nutrient reserves and plant growth regulators to stimulate their growth in cultures. Smaller explants require additional components to sustain the culture.
The other factor that decides the health of cultures is source of extraction from the plant. For example, a report published by Tran Thah Van (1977) shows that depending on whether the explants are taken from the base, middle, or top of the stem, the growth regulators in explants also vary. The growth hormone level of explants shows different in vitro responses.
4. Quality of the Source Plant
The health of the plant is an essential factor to be considered before obtaining the explant. Researchers advise taking explants from the healthy plants compared to plant under nutritional or water stress or showing any disease symptoms.
5.Purpose of Tissue Culture
Before choosing the explant for your culture, you should consider what value you want to receive from the culture. Depending on the desired response, the choice of explants varies. For example, for clonal propagation, the suitable explant will be a lateral or terminal bud shoot or shoot; for callus induction, pieces of the cotyledon, hypocotyl, stem, leaf, or embryo are usually used. For haploid production, anther or pollen is cultured.
6. Plant Genotype
All species of the plants don’t equally respond in tissue culture. Large differences exist between different genotypes, species, or cultivars, making some easily grown and some non-responsive or recalcitrant.
- Smith, R. H. (2013). Explant Preparation. Plant Tissue Culture, 45–51. doi:10.1016/b978-0-12-415920-4.00004-9
- Kubota, C. (2001). Concepts and Background of Photoautotrophic Micropropagation. Molecular Breeding of Woody Plants, Proceedings of the International Wood Biotechnology Symposium (IWBS), 325–334. doi:10.1016/s0921-0423(01)80089-7
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