7 Jan 2026

The Advantage of Temporary Immersion Systems Over Solid Media

Anjali Singh, MS

As a content and community manager, I leverage my expertise in plant biotechnology, passion for tissue culture, and writing skills to create compelling articles, simplifying intricate scientific concepts, and address your inquiries. As a dedicated science communicator, I strive to spark curiosity and foster a love for science in my audience.

Table of Contents

Introduction

Is it finally time to transition away from agar?

If you manage a commercial tissue culture lab or a high-output research facility, you have likely asked yourself this question while staring at a mountain of culture vessels waiting to be subcultured.

For over fifty years, the plant tissue culture industry has relied on a stable, predictable foundation: semi-solid media.

From the humble home hobbyist to the massive industrial propagator, gelling agents like agar and gellan gum have been the standard-bearers for holding plants upright and feeding them nutrients.

But as the global demand for disease-free plant material skyrockets—driven by industries ranging from ornamental floriculture to massive timber plantations—we are forced to confront the inherent limitations of the old ways.

Solid media is reliable, yes, but it is also labor-intensive, difficult to automate, and physiologically restrictive.

Here comes the Temporary Immersion System (TIS).

This technology represents a radical paradigm shift, promising to combine the rapid growth rates of liquid culture with the safety and aeration of solid media.

But is it too good to be true?

In this deep dive, we will explore how these systems differ in plant growth and cost, helping you decide if TIS is the right choice for your lab.

The Evolution of Culture Systems

To understand where we are going, we have to look at why we started with solid media in the first place. Historically, the heavy reliance on solid matrices was driven by a single, overriding necessity: the prevention of asphyxia.

If you simply submerge a plant explant in liquid nutrients without complex aeration, it drowns. Oxygen deprivation leads to rapid physiological collapse.

Solid agents provided an elegant, passive solution to this problem. They acted as a scaffold, holding the explant upright so that the aerial tissue could breathe while the basal tissue absorbed nutrients.

However, this simplicity came with a hidden cost: the "static diffusion barrier." The gel matrix restricts the movement of nutrients, creating a localized depletion zone around the roots.

TIS technology emerged specifically to resolve this dichotomy. By intermittently immersing the explants in liquid and then draining it away, TIS ensures that the entire tissue surface is bathed in nutrients—eliminating those depletion zones—while the subsequent drainage phase renews the atmosphere, preventing the dreaded asphyxia that plagued early liquid culture attempts.

Physicochemical Dynamics of the Culture Environment

The difference between a plant growing in an agar jar and one in a TIS bioreactor is not just about the presence of a gelling agent; it is a fundamental alteration of the physics governing the plant's life. This environment dictates everything from water availability to how ions move into the cells.

The Solid Matrix: Diffusion and Water Potential

In traditional micropropagation, we often view the agar (typically 6–8 g/L) or Gelrite as an inert support, but it is actually a physiologically active competitor. The gelling agent contributes to the matric potential of the medium, effectively lowering the total water potential. This means the water is thermodynamically "held" by the gel, making it harder for the plant to extract compared to a liquid solution.

The implications here are profound and often contradictory:

• Hyperhydricity risks: Surprisingly, low concentrations of agar can lead to hyperhydricity because the water is held loosely.

• Water Stress: High concentrations can induce water stress, restricting growth but creating robust, lignified tissue.

• The Diffusion Trap: Perhaps most importantly, the gel creates a boundary layer resistance. As the plant eats the sugar and nitrate immediately touching it, a "depletion zone" forms. The plant then has to wait for new nutrients to passively diffuse through the tortuous path of the gel lattice, which is significantly slower than mass flow. This acts as a biological brake on your production speed.

Fluid Dynamics in Temporary Immersion

TIS operates on the principle of mass flow. When the immersion cycle activates, nutrient medium is actively pumped or tilted into the chamber. This turbulent flow shatters the boundary layer at the explant surface.

This mechanism creates three distinct advantages:

• Total Epidermal Contact: In solid media, the plant gets the nutrients only from the point that touches the gel (the basal cut). In TIS, the entire explant—leaves, stems, and meristems—is temporarily submerged, allowing for foliar uptake and significantly increasing the absorptive surface area.

• Elimination of Gradients: The mixing action ensures homogeneity. There are no "hot spots" of toxic exudates or "dead zones" of nutrient depletion.

• Transient Hydrodynamics: Even after the liquid drains, a thin film of nutrients remains on the tissue due to capillary action. This allows nutrient exchange to continue during the dry phase without blocking the stomata.

Gas Exchange and Atmospheric Renewal

If you are looking for the most significant benefit of TIS, it is likely the management of the gaseous phase. In standard Magenta boxes, gas exchange is passive and often poor, leading to ethylene buildup and CO2 starvation.

TIS systems, by contrast, typically employ pneumatic cycling. Every time the medium is moved by air pressure, the stale headspace gas is displaced and renewed with fresh air.

This active ventilation performs a triple duty:

• Ethylene Removal: It flushes out ethylene, the aging hormone that causes yellowing and leaf drop.

• Oxygen Replenishment: It drives oxygen to the root tissues, which is vital for high-energy organogenesis.

• CO2 Supply: It maintains ambient carbon dioxide levels, which are the prerequisite for photosynthesis.

Physiological Impact: Nutrient Dynamics and Metabolism

Because the growth environment differs fundamentally, plantlets in TIS show distinct metabolic behavior compared to agar-grown cultures.

Nutrient Uptake

In TIS, nutrients are more readily available, leading to much faster uptake than in solid media. Studies show macronutrients and micronutrients (such as iron) can be rapidly depleted in liquid systems while remaining available in agar-based controls. Since standard MS media was designed for slow nutrient release, TIS requires adjusted formulations or feeding strategies to avoid nutrient imbalance.

Photosynthesis and Gas Exchange

TIS supports a shift toward photoautotrophic growth. Regular air exchange maintains CO₂ levels, and controlled humidity improves stomatal function. As a result, TIS-grown plantlets often develop stronger photosynthetic capacity, improving survival during acclimatization.

Hormone Sensitivity

Liquid media increases the effectiveness of plant growth regulators due to direct tissue contact. This can boost multiplication rates at lower doses, but hormone levels suitable for agar may cause toxicity in TIS if not carefully reduced.

Hyperhydricity: The Central Physiological Challenge

We cannot discuss TIS without addressing the elephant in the room: Hyperhydricity (HH), formerly known as vitrification. This is the primary bottleneck preventing the universal adoption of liquid systems.

Pathophysiology and Symptoms

Hyperhydric tissues look glassy and water-soaked. Anatomically, they suffer from hypolignification (weak cell walls), apoplastic flooding (air spaces filled with water), and stomatal malfunction. Although these plants may appear vigorous and voluminous in vitro, they often collapse immediately upon transfer to soil because they cannot regulate water loss.

Causal Factors and Mitigation

Hyperhydricity is a primary risk in TIS because the plants are frequently submerged in liquid and surrounded by high humidity.

To prevent this, successful protocols use specific strategies:

• Optimized Cycles: Short immersion times (1–5 minutes) followed by long dry periods (4–12 hours) allow the tissue to dry out between feedings.

• Ventilation: Using lids with permeable filters allows excess moisture to escape, reducing humidity inside the vessel.

• Desiccation: Some advanced systems actively remove moisture from the air to prevent saturation.

Comparative Morphology and Development

When we look at the results, the data unequivocally suggest that for most species, TIS drives faster growth. But is bigger always better?

Shoot Proliferation and Biomass

Across a broad spectrum of crops, TIS consistently outperforms solid media. In bananas (Musa spp.), TIS has achieved multiplication rates of 4.20 compared to solid media controls. In Date Palms, a staggering 5.5-fold increase has been recorded. The combination of unrestricted nutrient access and the mechanical stimulation of the liquid flow (thigmomorphogenesis) drives this accelerated vegetative growth.

Rooting Efficiency

Rooting is where TIS surprises many critics. Historically, liquid was thought to drown roots. However, the intermittent nature of TIS provides arguably better oxygenation than a solid gel. While TIS roots often lack root hairs (because water is abundant), they are often more vigorous and rapidly produce new laterals upon acclimatization.

Acclimatization and Ex Vitro Survival

The ultimate test is the greenhouse. Despite the risks of hyperhydricity, properly managed TIS cultures often yield plantlets with higher survival rates. For species like Chrysanthemum and Birch, TIS plantlets have shown 100% survival during acclimatization. This is largely due to the photoautotrophic capacity developed in the ventilated bioreactors.

Bioreactor Technologies and Engineering

"TIS" is actually an umbrella term for several distinct engineering designs.

• Pneumatic Systems (e.g., RITA®, BIT®): These use air pressure to push medium from a lower reservoir to an upper chamber. They offer excellent aeration but can be complex to scale due to the tubing required for every single vessel.

• Mechanical Tipping Systems (e.g., BioCoupler™): These rely on gravity by tilting the platform. They are extremely simple and reduce contamination risks from air lines. You can get them for your lab visiting this link.

• Box/Tray Systems (e.g., SETIS™): These large, horizontal boxes are efficient for elongation and rooting phases. They can hold 50–100 plantlets per vessel, significantly improving the labor-to-yield ratio.

Operational and Economic Analysis

 Adopting TIS is a trade-off: you pay more upfront for equipment, but you save money in the long run.

• Cost & Labor Savings: While TIS vessels are expensive to buy, running them is cheap. TIS eliminates the need for expensive Agar and drastically cuts down on labor (the biggest cost in tissue culture). Because you can handle plants in bulk without washing off gel, production costs can drop by nearly 50%.

• The Main Risk: The downside is contamination. In solid jars, bacteria usually stay in one spot. In liquid TIS, bacteria swim and spread instantly to every plant in the vessel, ruining the entire batch. This means your cleaning protocols must be perfect.

Future Outlook and Strategic Synthesis

The trajectory of the industry points toward a hybrid future. Solid media will not disappear; it remains indispensable for culture initiation, germplasm storage, and rescuing sensitive species. However, for the "factory" phase of commercial mass propagation, TIS is rapidly becoming the standard.

Future developments will likely focus on automation integration, as the uniform biomass from TIS is more amenable to robotic handling than the irregular clumps grown on agar.

We are also seeing the rise of "Smart Bioreactors" integrated with sensors to monitor pH and dissolved oxygen in real-time, allowing for dynamic adjustments—a concept known as Precision Tissue Culture.

Ready to Upgrade Your Tissue Culture Lab?

Whether you are sticking with reliable, solid media or making the leap to high-tech bioreactors, the success of your lab depends on the quality of your supplies and the expertise behind your protocols.

Plant Cell Technology is your partner in this journey. If you are looking to experience the speed of Temporary Immersion without the high cost or complex tubing, the BioCoupler™ is the perfect solution—simple, effective, and electricity-free.

To protect those liquid cultures, our flagship PPM™ (Plant Preservative Mixture) is absolutely essential for managing contamination risks where pathogens can spread instantly.

Don't let contamination or poor growth rates hold you back. From simple TIS solutions to high-quality gelling agents, we have everything you need to optimize your production.

Visit us at www.plantcelltechnology.com and revolutionize your growth.