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Washington State University
CAS Connect September 2014

Big step forward for plant science

The book could soon be closed on one of plant biology’s longstanding mysteries.

Professor Michael Knoblauch, a plant cell biologist in the School of Biological Sciences, is trying to discover how plants circulate the sugars made in their leaves—a question that has flummoxed scientists for decades.

 Michael Knoblauch, professor of biology and director of the Franceschi Microscopy and Imaging Center at WSU

Michael Knoblauch, professor of biology and director of the Franceschi Microscopy and Imaging Center at WSU

Knoblauch and his 19-year-old son, Jan, a freshman at WSU who has worked in his father’s lab for the last three years, are analyzing data from tree specimens that could finally provide the answer. If successful, their work will be an important step forward in understanding how plants function and could lead to improved crop yields and development of plants that are more resistant to pests and disease.

“Not knowing what drives food circulation in plants is akin to not knowing the heart is pumping your blood,” Knoblauch said. “This research will fill a critical gap in our knowledge and provide a solid basis for future studies in this and other related fields.”

The prevailing theory to explain how nutrients are transported through plants was proposed by German plant physiologist Ernst Münch in 1930. Münch said the flow of sugar from one end of a plant to the other is likely driven by a pressure differential, similar to how water is pumped through a garden hose. While Munch’s theory is intuitive and easy to describe, it has proven difficult to confirm.

Over the decades, many people have attempted to test the hypothesis. During the 1960s and ’70s, between 80 and 100 investigators worked on the problem but failed to provide definitive proof.

“One of the biggest problems was most investigations showed massive agglomerations in the tube system which would prevent the flow of water and nutrients, like dirt in a garden hose,” Knoblauch said. “The technology to follow up and measure the pressure inside the tubes was not available.”

At least until now.

Knoblauch experimented repeatedly in the past three years until he finally designed a tiny, oil-filled needle that can be delicately inserted inside a phloem cell to measure the pressure of the fluid inside. Once inside a cell, oil in the needle is slightly compressed by the pressure of the sugar and water flowing through the plant, enabling the researchers to take a pressure reading.

The Knoblauchs tested the needle, called a picogauge, at the Harvard Research Forest in central Massachusetts where, for seven months, they collected pressure readings from phloem cells in towering red oaks and morning glory vines.

Perched on scaffolding, at times as high as 40 feet in the air, Knoblauch used a remote control device to drive the picogauge, which is far smaller than a human hair, into a phloem cell while Jan monitored the image on a computer screen.

Tree-top breezes caused the scaffolding to sway dangerously, making the task of impaling a microscopic plant cell with an even smaller needle more difficult than it already sounds. Weather was not the only problem. Needles often broke or bent when inserted into a cell, obscuring data the researchers were trying to collect.

“Needless to say, it took a lot of trying and frustration to get everything working right,” Jan said. “It took us about six months to get the system optimized.”

Over the course of their stay in Massachusetts, Knoblauch and Jan collected around 20 pressure measurements from the oak tree. In the future, the picogauge could be used to measure intracellular pressure in other types of plants.

“Many processes, like root or shoot bending, distribution of seeds, etc., are dependent on intracellular pressure,” Knoblauch said. “The picogauge will be a useful tool to study these processes.”

While Knoblauch would not venture a guess as to whether the pressure readings and various other data he has collected over the years will provide conclusive support for Münch’s hypothesis, he is confident his team will have an answer within the next six months.

“This is something I’ve been working on for 20 years,” he said. “I’m looking forward to getting to the bottom of it.”

Watch a New York Times science video on Knoblauch’s research.

A journey through the microscopic world of plants

Professor Michael Knoblauch, a plant cell biologist and director of the Franceschi Microscopy and Imaging Center at WSU, uses powerful imaging technology to study the microscopic world of plants.

In 2010, he used scanning electron microscopy and a new preparation technique to produce the first images of the mesh-like sieve plates through which nutrients must pass to go from one end of a plant to the other. His work behind the microscope has proven critical in attempting to resolve a longstanding hypothesis about how nutrients are transported in plants. These photographs trace the journey of carbon as it is converted to sugar and travels through specialized cells to reach the plant’s roots and storage organs.

Visit the photo gallery