Root of the Problem

Growth chambers

Root of the Problem

How can scientists be sure that their dirt is just as dry as a colleague’s dirt when testing drought effects on roots? Some of our scientists have been looking into that.

Think of root experiments like the ones conducted by kids in elementary schools. Each student is given a seed, a paper towel, and a plastic bag, and told to keep the seed well-watered until it sprouts. Simple, right? 

But in scientific experiments, there are so many more variables to worry about. Are all the paper towels the same kind? Are they the rough brown kind or a kitchen brand? If it’s the latter, is it Brawny or Sparkle? What kind of water are they using: tap water, or mineral water, or purified water? How much and how often are the plants being watered? These are the kinds of minutiae that go into experiments like those done on our Roots in Drought grant. The problem? There’s not an in-depth understanding of how different mediums (the paper towels) and water potential (how well the seeds are watered) affect a plant, which is a problem if the experiment depends heavily on the tiniest detail of the plant root (as ours does). To better understand how different mediums and water thresholds affect plant growth, Dr. Robert Sharp, Dr. David Braun and doctoral student Tyler Dowd conducted a review experiment published in Plant, Cell & Environment.

Fig. 12 from paper. “MWD” stands for “Mild Water Drought” and “WW” stands for “Well-Watered.”

“It’s important to understand the medium you’re growing in,” said Dowd, “Weight or percentage of water doesn’t actually tell you how available it will be to the plant.” 

Studying how different materials affect roots in a water-stress experiment will help scientists understand what exactly within the plant is helping it adapt to drought. Drought is the biggest contributing factor to crop limitations, and this will only get worse as the effects of global warming is exacerbated. 

“We wanted to find a medium that would hold water threshold evenly, and this let us choose which one we would focus on for the rest of the studies,” Dowd explained. 

Two genetic lines of maize were used, the samples B73 (a basic genetic line that lots of labs use) and FR697 (our test subject). The experiment consisted of growing maize separately in QUIKRETE Premium Play Sand, ceramic particles, vermiculite, and potting soil. Growing the plants in these different kinds of soil (mediums) allows the scientists to study how well they can grow in each (does the plant do better with Brawny or Sparkle?). The water threshold levels were carefully measured out, and the researchers found that water absorption changed based on the potting material. Transpiration rates, which is the process of water evaporating from the plants leaves, were different too. 

How axial (side-roots) and lateral (up-and-down) roots grew varied from medium to medium. “Under mild levels of water stress we were getting longer lateral roots, and maintaining that root length [which helps the plant survive in adverse conditions] is very important,” Dowd said. That root length will be studied in future experiments.

Understanding how each medium and water stress level affects different aspects of plants, such as root length, will help scientists better understand the underlying mechanisms that drive growth. While there’s still a lot left to be understood, these experimental findings help us better understand how plants behave under water stress. 

The team also just published a second paper to Plant, Cell & Environment, with a perspective focused more on root anatomy. Other related studies being done by the team are looking into similar issues with medium and its effect on plants. 

The FR697 sample was more resistant to water threshold changes but still showed effects. It’s possible that the water treatment affected this particular sample’s growth programming, but not in the B73. That means that if there is a consistent, mild drought, this plant’s behavior is going to be way different than that of a B73 plant. Through RNA sequencing of the genetic structure, we can study this difference and create more drought-resistant corn.

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