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Seeing the Calcium in Plant Root Cells Could Benefit Growth on Earth and in Space

Will Krogman

By Will Krogman, Research Associate 1 - FTT

Posted Sep. 30, 2020

Nutritionists often tell us that our bodies need calcium for healthy bones. However, there is more to calcium than bones. The more than 20 trillion microscopic cells and organs in our bodies use calcium for many things. For example, we use calcium to move muscle, to think, to breathe and to keep our heart beating. When we think or feel pain, calcium moves in and out of our nerve cells very quickly. These rapid changes in calcium inside nerve cells is one way the cells talk to each other and send messages to other parts of the body.

A similar process happens in the cells of plants, allowing them to react to their environment.

Plants Need Calcium to Feel

A good example is a root growing into the soil. When root cells touch soil particles or small rocks, those cells change the level of calcium inside them. Then, the cells surrounding these surface root cells also increase their calcium levels, which rapidly spreads to other cells in the root, similar to a wave. One consequence of this calcium-based communication is that it tells the root to change its growth direction so that it can grow deeper or grow toward a source of water or nutrients.

Another example is an insect feeding on the leaves of a plant. The cells being fed on can communicate with nearby cells by changing the levels of calcium inside them, which serves as an initial warning sign that the plant is in danger.

Researchers in the Noble Research Institute’s Plant Cell Biology Laboratory study how roots use calcium to react to stressful environments. They expect to use this knowledge to develop plants that are more resilient when grown in low-input regenerative grazing lands.

Seeing Root Cells Talk

Springtime in Oklahoma and the southern Great Plains indicate thunderstorms and the beginning of tornado season. During weather forecasts, Doppler radar images flashing on the TV screen show areas on the map that have intense storms. These images give us warning in time to make plans to avoid inclement weather. In a fashion similar to Doppler radar-generated images, we can view areas in the root that have more calcium than others.

How are these Doppler radar-like images generated in roots to tell us about calcium? First, a molecule is placed in the cell that releases more light when calcium in the cell increases. Second, the root with the molecule is viewed with a special microscope that can measure the amount of light released by that molecule. Higher light indicates more calcium in a cell, which is depicted as warm colors (red, yellow, orange). On the other hand, low light indicates low levels of calcium, which are shown as cool colors (blue, green, purple) (Figure 1).

A Glimpse Into Root Cells for Earth and Space

In their new publication, Will Krogman, Alan Sparks and Elison Blancaflor, Ph.D., researchers in the plant cell biology lab, developed plants that allow calcium changes to be seen as they happen within specific cells of a root.

Just like the human body, roots have different kinds of cells. These different cells behave in unique ways and studying them individually, instead of looking at a mixture of different cells, can provide more detailed information about how a root grows into the soil. The team made the plants so that the calcium-sensing molecule only goes into a particular root cell. In some cases, it goes to cells on the edges of the root while in other cases it goes to cells located inside the root (Figure 1).

Plant roots cell imaging
Figure 1. Doppler radar-like images in plant roots show cells that have high calcium levels. Warm colors (red, orange, yellow) indicate a large amount of calcium inside the plant cells while cool colors (blue, green, purple) show a small amount of calcium.

Seeking to understand how gravity affects root growth is an example of the usefulness of looking at only one kind of cell instead of a mixture of cells within the entire root. Gravity is detected by roots in cells called columella cells, which are located deep inside the root tip.

In some plants developed by the team, the calcium-sensing molecule was placed specifically in these gravity-detecting cells so the team could see how these cells behaved without interference from other cells around them. The plants reported in this study, which was partially funded by NASA, also have implications for understanding how plants react to the stressful environments of space. For example, with these tools, NASA can ask questions about how root cells communicate when growing in outer space.

Studying these glowing roots could not only shine light on understanding root-soil interaction on Earth, but also determine the requirements for healthy plant growth in space.

To learn more, you can access the full peer-reviewed research paper freely available from the International Journal of Molecular Sciences.