Morel and Wetmore Medium in Plant Tissue Culture: Uses and Formulation
Plant tissue culture techniques have revolutionized plant research and agriculture, enabling rapid clonal propagation, study of plant development, and preservation of endangered species. Among the many media formulations used in plant tissue culture, Morel and Wetmore Medium has played a significant role, especially in the study of orchids and other monocotyledonous plants.
In this blog post, we will explore the origin, uses, and formulation of Morel and Wetmore Medium in plant tissue culture.
What Is Morel and Wetmore Medium?
Morel and Wetmore Medium (commonly known as MW medium) was originally developed by Georges Morel and Ralph H. Wetmore in the 1950s as a specialized nutrient medium for studying the growth and development of orchids in in vitro conditions. Orchids, especially Dendrobium and Cymbidium species, often exhibit slow growth and complex germination requirements due to their symbiotic relationship with specific fungi in nature. Morel and Wetmore Medium provided the controlled and balanced environment required for the successful culture of these plants.
This medium promotes the rapid germination of orchid seeds (often referred to as "dust seeds" due to their small size) and the subsequent growth of their embryos into healthy plantlets. Over the years, the use of MW medium has expanded beyond orchids to serve in the tissue culture of other monocots and even some dicotyledonous species.
Uses of Morel and Wetmore Medium
1. Orchid Seed Aseptic Germination:
Orchids typically rely on a symbiotic relationship with mycorrhizal fungi for successful germination. Tissue culture methods like MW medium help bypass this dependency by providing the seeds with essential nutrients for germination, allowing micropropagators to grow orchids in sterile, controlled environments.
2. Protocorm and Callus Induction:
Protocorms (embryonic orchid structures) are crucial in the first stage of orchid growth. Morel and Wetmore Medium provides the correct nutrient composition to support the formation and maturation of protocorms, as well as callus formation—a mass of unorganized plant cells that can differentiate into shoots or roots depending on the hormonal balance.
3. Plant Regeneration and Micropropagation:
Once orchids or other plants are successfully germinated, MW medium continues to support plantlet regeneration and development. The medium enables controlled micropropagation, where large numbers of plants can be derived from a single explant, offering an ideal protocol for commercial propagation of rare and exotic plant species such as orchids.
4. Study of Orchid and Monocot Development:
Researchers use MW medium as a foundation for studying the growth and development processes of orchids and other monocot plants in vitro, including early-stage embryo development, morphogenesis, and use of different plant hormones to encourage vegetative or reproductive growth.
Components of Morel and Wetmore Medium
The composition of Morel and Wetmore Medium is designed to provide all the essential elements required for plant growth, including macro and micronutrients, vitamins, and a carbon source. Below is the more modern version of the Morel and Wetmore Medium formulation per liter of medium:
Formulation per Liter
Macronutrients:
- Calcium Nitrate (Ca(NO₃)₂·4H₂O): 200 mg/L
- Potassium Phosphate, Monobasic (KH₂PO₄): 200 mg/L
- Magnesium Sulfate, Heptahydrate (MgSO₄·7H₂O): 100 mg/L
- Ammonium Sulfate ((NH₄)₂SO₄): 100 mg/L
Micronutrients:
- Iron (Fe) Chelate/EDTA: 5 mg/L
- Manganese Sulfate (MnSO₄·H₂O): 0.75 mg/L
- Boric Acid (H₃BO₃): 0.5 mg/L
- Zinc Sulfate (ZnSO₄·7H₂O): 0.005 mg/L
- Copper Sulfate (CuSO₄·5H₂O): 0.005 mg/L
Vitamins:
- Thiamine HCl (Vitamin B1): 0.5 mg/L
- Myo-Inositol: 100 mg/L
- Nicotinic Acid: 0.5 mg/L
- Pyridoxine HCl (Vitamin B6): 0.5 mg/L
Carbon Source:
- Sucrose: 20 g/L
Gelling Agent (optional for solid media):
- Agar: 7-8 g/L
- pH: Adjust media to a pH range of 5.6 to 5.8 before autoclaving.
Conclusion
In conclusion, Morel and Wetmore Medium is a fundamental recipe in the world of orchid tissue culture and research. It provides an effective nutrient platform for the production of orchid seedlings, callus induction, and in vitro plant regeneration. By paying attention to the precise formulation, this medium continues to play a vital role in plant laboratory research and the commercial propagation of monocotyledonous species.
Whether you are a researcher studying orchids or looking to optimize micropropagation in your laboratory, Morel and Wetmore Medium offers a well-balanced formulation tailored for successful tissue culture.
References:
- Morel, G., & Wetmore, R. H. (1951). Growth Hormones in the Orchids: Their Role in Cultivating Orchids In Vitro.
- Arditti, J. (1979). Aspects of the Physiology of Orchid Seed Germination and Seedling Growth.