Mohr’s Medium in Plant Tissue Culture: Origins, Uses, and Formulation
Mohr’s medium, while less widely known than Murashige and Skoog (MS) or Gamborg’s B5 media, holds a significant place in the history of plant tissue culture. Its specialized formulation makes it a valuable tool for specific applications, particularly with recalcitrant species.
Origin:
Unlike MS medium, which enjoys broad applicability, Mohr’s medium doesn’t have a single, definitively published formulation attributed to a specific researcher in a specific year. Instead, it represents a class of media formulations derived from various modifications and optimizations of earlier basal salt mixtures, aimed mainly at improving the in vitro growth of woody plants and certain horticultural crops where other media proved less effective. Its development occurred gradually over several decades, emerging from the collaborative efforts of numerous researchers working with specific plant species. The core components are often similar to other media but tweaked for optimal performance with target plants. The name "Mohr’s medium" is therefore a collective term referencing these derivative formulations, rather than pointing to a specific, original publication.
Applications:
Mohr’s medium variations excel in applications where other standard media struggle. Its formulations are often tailored to overcome specific challenges encountered during plant tissue culture, making it a valuable medium for dealing with recalcitrant species, those exhibiting difficulty in propagation using routine techniques. Key applications include:
Woody Plant Regeneration: This is perhaps the most significant application. Mohr’s medium modifications frequently demonstrate superior success rates in inducing callus formation, shoot proliferation, and especially rooting in a range of woody plants, including fruit trees, conifers, and ornamentals. The adjustments in macro- and micronutrients, alongside specific growth regulators, play a critical role in this success.
Ornamental Plant Propagation: Numerous ornamental species benefit from the carefully balanced nutrient composition of modified Mohr’s media, leading to improved micropropagation protocols, and the propagation of varieties which are difficult to cultivate through traditional methods.
- Specific Plant Families: While not universally applicable, certain plant families respond exceptionally well to variations of Mohr’s formulations. For example, studies have shown success in the propagation of orchids and other recalcitrant species using carefully optimized variations of Mohr’s medium. However, detailed individual formulation information is crucial for each species and varies greatly.
The lack of centrally documented Mohr formulations means there’s less formal published case studies compared to MS media. Success stories are primarily found in specialized journals and within laboratory protocols rather than landmark publications.
Formulation:
Because "Mohr’s medium" isn’t a standardized, singular formulation, creating a definitive table is impossible. However, we can present a typical example, emphasizing the flexible nature of these media. The concentrations below are illustrative and should be considered as potential starting points requiring optimization for each plant species.
| Component | Concentration (mg/L) | Role | Common Modifications |
|---|---|---|---|
| NH₄NO₃ | 1650 – 2000 | Nitrogen source | Variations based on plant nitrogen requirements |
| KNO₃ | 1900 – 2500 | Potassium and nitrogen source | Adjustments based on species-specific needs |
| CaCl₂·2H₂O | 440 – 500 | Calcium source | Relatively consistent across formulations |
| MgSO₄·7H₂O | 370 – 400 | Magnesium and sulfur source | Often adjusted in combination with other nutrients |
| KH₂PO₄ | 170 – 200 | Phosphorus source | |
| Micronutrients | Variable | Essential trace elements | Often based on standard micronutrient solutions |
| Vitamins | Variable | Growth and development factors | Thiamine, pyridoxine, nicotinic acid commonly used |
| Growth Regulators | Highly Variable | Auxins (e.g., IBA, NAA), Cytokinins (e.g., BAP, Kin) | Crucial for directing differentiation; concentrations vary widely depending on the specific aim (callus induction, shoot proliferation, rooting) |
| Sucrose | 30,000 | Carbon source | |
| Agar | 8,000 – 10,000 | Solidifying agent |
Conclusion:
Mohr’s medium, despite its lack of a singular definition, offers significant advantages in specific plant tissue culture applications. Its strength lies in its adaptability and potential for tailored formulations to overcome challenges with recalcitrant species. However, its limitations are precisely its lack of standardization, requiring significant optimization for every specific target plant. This contrasts with MS medium, which boasts wider applicability and proven protocols for a vast range of plants, though it may not be as effective for certain recalcitrant species. B5 medium also occupies a broader niche, offering an alternative basal salt mixture. Ultimately, the choice of medium—including Mohr’s variations—hinges on the specific plant being cultured and the desired outcome of the tissue culture process. While not as dominant as MS or B5, Mohr’s medium continues to hold relevance, particularly in specialized fields where its tailored formulations prove indispensable.