Health & Science: Chemical helps plants fight gravity, researchers find

By DAN KANE, The News & Observer of Raleigh, N.C.
February 19, 2001 The Nando Times

Thanks to our eyes, nervous system and some fluid in our inner ears, we have a pretty good idea which way is up. Plants lack all three, yet when they are knocked down by wind or hail, they find a way to reach back to the sky.
How they do it has long been a mystery. But after five years of study, researchers at North Carolina State University and the University of Michigan say they've found a signaling chemical - also in human brains - called inositol trisphosphate that helps plants right themselves.

Their discovery could have significant implications for plant preservation and food production. NASA financed the research with hopes it would yield clues to raising plants, without benefit of gravity, in space.

"If humans are going to go on sustained space missions, we'll need to use plants to turn carbon dioxide into oxygen, to cleanse water and to provide food," said Wendy Boss, an NCSU botany professor who led the project. "Before we create such long-term life-support systems, we need to know how gravity affects the growth of plants."

On Earth, the research could lead to new strains of wheat, oats and corn that can right themselves more quickly without expending as much energy. The longer a plant stays on the ground, the more susceptible it is to disease. Plants that are not upright also have less sugar available for producing grains, and this makes them less tasty and less nutritious.

On the other hand, the research might lead to flowers that don't bend upward when laid flat. Florists could then guarantee that when they ship their bouquets, the flowers won't appear to droop when they arrive at your home and you stick them in a vase.

Boss is one of about 20 people who worked on the project, which drew in some of NCSU's top researchers. She presented the team's findings Sunday at the annual meeting of the American Association for the Advancement of Science in San Francisco.

The research began in 1996 with a five-year NASA grant totaling $5 million. As part of their grant proposal, NCSU researchers committed to putting on workshops about plant gravitational response to science teachers across the state.

Boss said those workshops served as a guide to help the researchers search for answers. "If you teach and are really good at it and focused at it, you will come up with ideas for research," Boss said.

When they started, they were working with one significant clue: that plants trying to right themselves were producing lots of calcium. Israeli researchers had even developed a solution that removes the calcium, and the plants stayed flat on the ground. They also didn't live very long, however.

What triggered the calcium increase remained a mystery. Using maize, NCSU's team learned early in the project that there was an increase in sugar within the elongating cells on the underside of the fallen plant's pulvinus, a narrow section within the plant's stem.

They started slicing rings of the pulvinus and dipping them into liquid nitrogen to look at chemical composition. They discovered that within 15 seconds of the maize being placed flat, the amount of inositol trisphosphate (InsP3) surges fivefold.

Many other life forms, including humans, use InsP3 to transmit chemical signals between cells.

The pulvinis, a narrow section within a plant's stem, doesn't immediately begin its irreversible elbow-like bend upward. That's because a plant that is swaying in the wind will return upright without needing a change in the pulvinis.

So, to distinguish between swaying and falling, the plant waits until the inositol trisphosphate begins to build in the lower half of the pulvinus. That takes at least two hours in maize and about 30 minutes in oats.

The concentrated amount of InsP3 in the lower half tells those cells to begin elongating. Within 10 hours, the plants will begin bending upward.

As for what triggers the production of InsP3, the researchers think that as the plants fall over, dense particles of starch within the pulvinus shift in accordance with gravity's pull. The plant senses that shift and begins production of the InsP3.
They found when they added a chemical to the plant that inhibited the production of InsP3, the plants were far less likely to bend upward.

Glenda Gillaspy, a biochemistry professor at Virginia Tech, said the finding is important. She has been studying the role of InsP3 in plant life.
"It is groundbreaking to find any signaling molecule that is correlated with the gravity response," she said. "I think this is going to be a model system for studying how all plants grow in response to gravity."