s children, we’re often taught complex subjects in very simplified ways. Life was easier in black and white, but as we move into adulthood, we find that the world is far more colorful than that.

Even as young adults, we learn that a basic experimental setup should have a control and a single independent variable to test. But the world is not the vacuum our textbooks taught us, and in our experiments, we must consider other variables that interfere with our research, which often go severely undetected.

One element of interference is contamination. Thankfully, in lab classrooms, we’re taught sterile methods right away, and we develop a “when in doubt, throw it out” philosophy with our pipette tips, gloves, tubes and, as much as it kills us, our samples.

In the field of plant research, specifically in agronomical crops like rice and corn, Norman Best and a research team from Purdue University and Chicago State University investigated another avenue for interference: unfavorable biochemical reactions in plant media.

In experiments requiring the study of larger plants, the neutral Murashige and Skoog medium is not as efficient or affordable. Instead, researchers use soilless growth substrates such as sphagnum peat moss and calcined clay. Other additives such as perlite or vermiculite are also included. Each of these products are chosen for different reasons and have unique characteristics that optimize growth in certain ways. Peat moss retains large amounts of water within the cells of live and dead plants, and it can retain water up to 60% of its volume. Though water retention is a benefit from this medium, it is not very nutrient rich and the soil tends to become more compacted. It also has a pH of 3.0-4.0, while optimal levels are usually around 5.5-7.0.Perlite is often used in potting soil, and has also become a widely used medium in hydroponics. This is because it is known for having greater permeability. Since the material is derived from volcanic rock, it holds its structure over time, allowing the long lasting aeration. It is also has a pH of 7.5. The downside to perlite is that it has lower water retention, and it requires nutrient rich water to nourish plants. Vermiculite is used similarly to perlite, in that it’s meant to condition the soil for proper aeration. While it does retain slightly more water than perlite, it does not hold its structure for very long. Therefore, it is not good for outdoor growth or hydroponics. The most popular growth medium for larger plants, however, is calcined clay because nutrients are more slowly release. Clays like Turface®, which are used in baseball fields, can absorb its weight in water, keeping water levels at an optimal amount.

While people tend to choose a specific medium for its ability to facilitate growth, Best examined interactions between soilless growth media and various plant hormones such as brassinosteroid and its inhibitor propiconazole.

Brassinosteroids, also called BRs, are plant hormones involved in a number of activities. Most notably, they promote stem elongation, cell division, pollen elongation and stress protection. Mutants lacking proper levels of BRs demonstrate lower seed germination, flowering delays and dwarfism. Therefore, inhibitors such as propiconazole allow scientists to better understand molecular pathways involving this hormone.

Along with the brassinosteroid inhibitors, Best also gained more insight into reactivity with the plant growth media using GoldBio’s GA3, and its inhibitor uniconazole. Gibberellic acid stimulates cell elongation and excites the cells of germinating seeds. Its inhibitor, uniconazole or Ucz, is an ingredient in plant growth retardants, and is often very active in small concentrations.

Through his experiments, he observed significant interactions between the plant growth regulators and the growth substrates, which greatly reduced the inhibitors’ efficacy. This was particularly observed in calcined clay, which was attributed to hydrophobic interactions between the plant growth regulators and growth media.

hile calcined clay is often preferred, its heavy interaction between plant growth regulators may decrease experimental optimization. However, vermiculite showed much lower chemical reactions with the plant growth regulators. And, the results showed that there was very little interaction between GA3 and soilless growth substrates, which might be reassuring to researchers who use the hormone.

The analysis of this study provides researchers a new criterion to be considered when choosing the appropriate growth media. For basic gardening, using growth media based on its ability to hold water or nutrients is appropriate. However, when studying molecular pathways, it becomes even more important to understand new elements of interference which may have an undesired influence on the result.

Though we may at times be oblivious to the shades of green of hidden variables within our experiment, the results from Best and his team have highlighted one more variable, allowing subsequent research to become slightly better controlled as a result.

Best, N., Hartwig, T., Budka, J., Bishop, B., Brown, E., Potluri, D., Cooper, B., Premachandra, G., Johnston, C., Shulz, B. (2014). Soilless plant growth media influence the efficacy of phytohormones and phytohormone inhibitors. Plos One. Doi: 10.1371/journal.pone.0107689

Karen Martin
GoldBio Marketing Coordinator

"To understand the universe is to understand math." My 8th grade
math teacher's quote meant nothing to me at the time. Then came
college, and the revelation that the adults in my past were right all
along. But since math feels less tangible, I fell for biology and have
found pure happiness behind my desk at GoldBio, learning, writing
and loving everything science.

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