"Despite its efficacy, there are two major challenges in the micropropagation process. Micropropagation entails higher costs compared to propagation by cuttings, due to the complexity of the medium and operational facility. In addition, a significant environmental contrast exists between in vitro and ex vitro conditions: the limited air exchange in vitro environment." According to researchers from North Carolina State University, Photoautotrophic Micropropagation (PAM) system has the potential of addressing economic and environmental challenges in the micropropagation process.
PAM is a plant tissue culture technique that involves the in vitro cultivation of plants without the addition of organic carbon sources such as sugars in the culture medium. Instead, plants rely solely on photosynthesis for their carbon needs, using light, carbon dioxide, water, and inorganic nutrients to grow and develop. This method mimics the natural process of photosynthesis more closely than traditional micropropagation methods that use sucrose or other sugars as a carbon source.
In a recent study, researchers aimed to establish photoautotrophic micropropagation of cannabis during the early shoot stage and to examine the impact of air change rate on shoot growth in PAM and traditional tissue culture (TC).
"Results affirm the positive effect"
According to the researchers, the PAM method is a promising alternative to traditional tissue culture techniques. The study showed distinct advantages for cannabis micropropagation when subjected to increased ventilation rates within the vessels such as simultaneous root development and high node to axillary bud ratio. "These findings affirm the positive impact of elevated air change rates on cannabis explant growth within the PAM framework."
Enhanced diffusion and growth
Enhanced diffusion of molecules by increased air change rates contributed to the observed benefits of Cannabis shoot growth and development. The study found that higher air change rates facilitated CO2 diffusion into the vessels, resulting in higher concentrations at the plant level. This, in turn, increased shoot dry mass through photosynthesis in both PAM and TC systems.
The researchers explain that in non-ventilated vessels, CO2 concentrations can drop to as low as 50 µmol/mol, negatively affecting photosynthesis and plant health by triggering reactive oxygen species (ROS) accumulation. Increased air change rates also reduce relative humidity, enhancing transpiration rates and alleviating the buildup of inhibitory gases like ethylene, further contributing to improved explant growth.
Advantages of PAM in rooting
The PAM system supports simultaneous root and shoot development, significantly shortening the tissue-to-plant acclimation period. Previous studies have demonstrated successful photoautotrophic rooting processes for Cannabis, and the current study builds on this by advancing the plant material stage, thus further shortening the micropropagation process. Robust root systems are vital for efficient water and nutrient uptake, especially under high air change rates where transpiration rates are increased.
Nutrient solution and environmental optimization
The nutrient solution in PAM, consisting of quarter-strength DKW basal salt, plays a pivotal role in the successful growth of explants under varying air change rates, the researchers add. This solution's low salt concentration contributes to a lower electrical conductivity (EC), which is beneficial for plant health.
Cannabis' light saturation point is around 1500 µmol/m²/s, and its high photosynthetic capacity necessitates careful consideration of light intensity and CO2 concentration. The study used a photosynthetic photon flux density (PPFD) of 100 µmol/m²/s, similar to traditional plant tissue culture, but this may not be optimal for cannabis explants in PAM. The results suggested that higher air change rates might require increased light intensity to meet the energy demands of photosynthesis fully.
Conclusion
"The present study underscores the advantages of photoautotrophic culture in cannabis micropropagation when combined with enhanced natural ventilation," the researchers conclude. "Additionally, it highlights the photoautotrophic capabilities of cannabis shoots at a younger developmental stage than previously studied. The integration of natural ventilation via filters offers a practical and feasible approach for adoption within existing practices."
To read the complete study, go to www.sciencedirect.com