Roots are widely considered important by plant scientists, despite the difficulty that comes with studying them – they are buried underground after all! Root studies commonly focus on the water or nutrient uptake and root interaction with the plant.
The MU Drought Team’s research specifically focuses on how corn roots respond to water deficits in both lab and field settings. To finely control soil conditions of the root types – primary and seminal (seedling) roots and nodal (adult) roots – the team uses a technique called the split-root system.
The Split-Root System
The split-root system allows the MU Drought Team to examine how lack of water affects individual parts of the root system by separating the primary/seminal and nodal roots.
As a corn plant sprouts, the primary roots, then the seminal, are the first to emerge. These roots establish the young plant and are initially the most important source of water and nutrients. Once the shoot emerges above ground, the nodal roots begin to grow. Nodal roots supply a majority of water to the plant through the rest of the development process and must grow through hard, hot and dry soil. They grow out of the shoot and provide structural support to the plant as well. For this research project, the team primarily focuses on the nodal roots of corn. Using the split-root system allows them to subject the nodal roots to drought conditions, while keeping the rest of the plant healthy.
The first step of the split-root system is to soak the seeds in dilute bleach, then fungicide to prevent fungus growth on the plant, in a process called “imbibing.” Next, they are tightly rolled in the paper, almost resembling cigars. In lieu of the traditional pot of dirt, the MU Drought Team uses germination paper for the seeds.
“The paper helps us forego all of the digging around in the soil, looking for the roots,” said Nicole Niehues, a research specialist on the team.
Then, the paper is stacked vertically in the “humid room” which remains at around 99 percent humidity at all times. From there, the roots will begin to descend the rolled germination paper itself – no soil required.
Once the seeds are germinated and the seminal roots have emerged, the baby plant is placed in a funnel with the top cut off and a watering tube attached. The funnel is then flipped, and soil and water is added. The seminal roots need to stick out of the seed so they, and the primary roots, can be pressed into the soil to grow in the inner chamber. The funnel is filled the rest of the way with soil and put into a PVC tube filled with more soil. The plant is then left to grow for two days.
At the end of two days, the plant’s leaves will start to unfurl from the shoot. A team member will fill the larger PVC tube with soil and attach it around the original tube so there are two chambers – one for the seedling (primary and seminal) roots and another for the nodal roots. Each section has separate soil and separate watering systems. This two chamber setup is the essence of the split-root system.
The soil in the inner chamber houses the seminal roots and can be well-watered, while the outer chamber houses the nodal roots and is exposed to drought conditions and is given little water, making it dry, but not bone dry. The team uses the system to get node two of the plant to an average length of 20 centimeters. After a week or two, the roots will reach the necessary length. They will then be removed from the split-root system and the tips where growth accrues will be harvested. This is done in the hopes of better understanding how to ensure the corn maintains growth to survive in harsher soil conditions. Team members will look at the chemical makeup of the roots and isolate which genes are the most important.
Mutations help characterize plant behaviors
To better understand the mechanisms of this growth maintenance, several members of the team working with the split-root system are also studying mutated corn plants, which may help characterize these plant behaviors. Much of the mutations research at South Farm Research Center is based off of the work done with the split-root system. New varieties of corn are grown based on what genes are found important through experiments with the split-root system.
To better explain how mutations work and the difference between homozygous and heterozygous mutations, Laura Greeley likened the research to cleft chin genes.
“Homozygous plants are like when you have a smooth chin,” Greeley said. “Therefore if you have one, both of your parents had to have that gene and your genes are homozygous recessive. Heterozygous plants are like when you have a cleft chin. If you have a cleft chin, but one of your parents has a smooth chin, then you are heterozygous.“
The goal is to get 1) an inbred line of plants with the mutation to adapt when water is limited. Basically, this would be the same gene over and over until they have all dominant or recessive genes, depending on what the mutation is. It would also be helpful to get 2) worse mutations, because that would show a clear reliance on a specific gene. Regardless, research with mutant varieties of corn can take years since it takes time to plant and harvest the new varieties.
The split-root system enables the team to examine how water deficit affects the growth of individual parts of the root system, while maintaining overall healthy growth of the plant. The goal is to better understand how the nodal roots adapt when water in limited, and to use that understanding to improve the production and survival of corn in water-stressed environments.