ometimes, scientific inquiry is marked by serendipity. Consider the work of Dr. Dominique “Niki” Robertson, professor of botany in the College of Agriculture and Life Sciences. What began as an attempt to determine, as Robertson puts it, “whether calcium is involvedin the gravitropic response” of plants may ultimately provide a way not only to improve the nutritional value of crops but also to make crops more drought- and salt-tolerant.
Gravitropism refers to how plants respond to gravity. Tip a plant on its side, and it will change its direction of growth. The roots will grow toward a gravitational pull, while the shoots grow away from the gravitational pull.
The National Aeronautical and Space Administration (NASA) is very interested in learning more about this response. It could be useful information if plants are taken into space, where there isn’t much gravity to speak of. So it’s not surprising that NASA funded Robertson’s work.
Why calcium? Robertson explains that many developmental events and environmental responses in plants are controlled by a process called protein phosphorylation, which is regulated by substances called protein kinases, which can be modulated by calcium.
So, she adds, “It makes sense to ask if calcium is involved in helping a plant realize the gravity vector has changed.”
Calcium is primarily found in two parts of a plant cell, the vacuole and the endoplasmic reticulum. It was Robertson’s good fortune that she chose to look at what happens to a plant when the amount of calcium in the endoplasmic reticulum increases.
Working with Dr. Wendy Boss, William Neal Reynolds Professor of Botany, Robertson genetically engineered plants to contain more calcium than normal in the endoplasmic reticulum. Dr. Sarah Wyatt, a postdoctoral researcher at the time, and graduate students Pei-Lan Tsou and Sang Yoon Lee were also involved in the project. Robertson, Boss, Wyatt and Tsou have since patented the process they used to make these transgenic plants.
As it turns out, increasing the amount of calcium in the endoplasmic reticulum doesn’t have much effect on a plant’s gravitropic response. High-calcium plants respond slightly more quickly than normal plants when their orientation is changed, but the difference is hardly noticeable.
What was noticeable and a lot more interesting was that the high-calcium plants appeared to be considerably more stress-tolerant than normal plants. Robertson said the high-calcium plants are salt-tolerant and appear to be drought-tolerant.
Robertson and Boss worked with Arabidopsis thaliana, a plant with little commercial value that is often used as a floral lab rat. Robertson says it should be possible to do the same thing with plants grown as crops, that is transform crops genetically to contain more calcium, thus increasing their stress-tolerance. She tried this unsuccessfully with corn, which is notoriously difficult to transform genetically, and is now seeking funding to produce transgenic high-calcium tomatoes.
Robertson points out that increasing the calcium in crops would also enhance them nutritionally.
“To me, this is exciting,” she says. “If you put more calcium in plants, the plants will be a better source of calcium. There will be a nutritional benefit as well as stress tolerance.”
And where tomatoes are concerned, there might be yet another benefit. Among the maladies from which tomatoes suffer is blossom end rot, which is caused by a calcium deficiency. So high-calcium tomatoes might be more stress- and disease-tolerant and better for you. Now, that’s serendipity.