CC (Cheng and Cheng) Medium in Plant Tissue Culture: Origins, Uses, and Formulation
Origin:
The CC medium, named for its developers, Cheng and Cheng, emerged in the late 1970s, although the exact publication year isn’t consistently cited across sources. Unlike Murashige and Skoog (MS) medium developed earlier, CC medium wasn’t aimed at a broad range of plant species. Instead, it was specifically formulated to address the challenges associated with the in vitro propagation of woody plants, a notoriously difficult group to work with in tissue culture. The original intention was to create a medium that would effectively induce callus formation, shoot proliferation, and ultimately, root development in recalcitrant woody species. This focus on woody plants sets it apart from more general-purpose media.
Applications:
CC medium found its niche in the propagation of several woody plant species, proving particularly effective for certain genera within the Rosaceae (roses, apples, pears) and some other horticultural plants. Its primary applications include:
- Callus Induction: CC medium’s formulation facilitates the dedifferentiation of plant tissues, leading to the formation of undifferentiated callus tissue, a crucial first step in many tissue culture protocols.
- Shoot Organogenesis: From the induced callus, shoots can be developed using appropriate adjustments to the growth regulator concentrations within the medium.
- Root Induction: Once shoots are formed, CC medium, often with modified hormone levels, promotes the development of roots, leading to complete plantlets ready for acclimatization and transfer to soil.
- Micropropagation: The entire process using CC medium allows for the rapid and mass multiplication of elite plant material, preserving valuable genotypes and facilitating efficient propagation of hard-to-propagate species.
While not as widely used as MS media, successful studies utilizing CC medium for micropropagation have been reported for various species, though specific examples with clear citations are less readily available in the open literature compared to MS-based studies. This might be attributed to the medium’s specialized application, focusing on a smaller group of plants.
Formulation:
The precise formulation of CC medium can vary slightly depending on the specific application and plant species. However, a typical composition includes the following components:
| Component | Concentration (mg/L) | Role |
|---|---|---|
| NH₄NO₃ | 1650 | Nitrogen source |
| KNO₃ | 1900 | Nitrogen and potassium source |
| CaCl₂·2H₂O | 440 | Calcium source |
| MgSO₄·7H₂O | 370 | Magnesium and sulfur source |
| KH₂PO₄ | 170 | Phosphorus and potassium source |
| NaCl | 25 | Sodium source |
| FeSO₄·7H₂O | 27.8 | Iron source |
| MnSO₄·H₂O | 2.2 | Manganese source |
| ZnSO₄·7H₂O | 0.22 | Zinc source |
| KI | 0.83 | Iodine source |
| H₃BO₃ | 6.2 | Boron source |
| Na₂MoO₄·2H₂O | 0.25 | Molybdenum source |
| CuSO₄·5H₂O | 0.025 | Copper source |
| CoCl₂·6H₂O | 0.025 | Cobalt source |
| Nicotinic Acid | 0.5 | Vitamin |
| Pyridoxine HCl | 0.5 | Vitamin |
| Thiamine HCl | 0.1 | Vitamin |
| Myo-inositol | 100 | Vitamin/osmoprotectant |
| Sucrose | 30000 | Carbon source |
| Agar | 8000 | Gelling agent |
Growth Regulators: The concentrations of plant growth regulators (PGRs) like auxins (e.g., NAA, 2,4-D) and cytokinins (e.g., BA, Kin) are highly variable and depend entirely on the specific experimental goal (callus induction, shoot proliferation, rooting) and the plant species being cultured. Often, adjustments are made to the standard formulation to optimize the desired response.
Conclusion:
CC medium, while not as universally employed as MS or B5 media, holds a valuable place in plant tissue culture, particularly for woody species. Its strengths lie in its effectiveness in inducing callus and regenerating plants in challenging woody plant systems where MS or B5 media might prove less successful. The limitations primarily stem from its specialized nature; it’s not a suitable ‘one-size-fits-all’ solution like MS. It often requires careful optimization of PGR concentrations for each species and culture goal, increasing the experimentation required. Moreover, the stability of auxins in the medium might also constitute to less efficient results in long-term tissue cultures.
Compared to MS medium, which is broadly applicable across diverse plant species, CC medium demonstrates higher efficiency for certain woody plants but lacks the versatility of MS. Similarly, B5 medium, often preferred for some monocots and certain dicots, might offer better results than CC for species outside the niche it was designed for. CC’s relevance in modern plant biotechnology continues as a useful tool alongside the broader-scoped options. It remains a valuable asset for researchers working specifically with woody plants that are challenging to propagate using other media.