Not every scientist would choose to spend a peaceful summer Sunday morning perched on a jittery scaffold 40 feet up a red oak tree, peering through a microscope to jab a leaf with a tiny glass needle filled with oil. But Michael Knoblauch, a plant cell biologist at Washington State University, is in the stretch run of a 20-year quest to prove a longstanding hypothesis about how nutrients are transported in plants. He’s nearing the end of a sabbatical year, much of which was spent at Harvard Forest, a 3,500-acre research plot in Massachusetts. So he found himself up in the tree on a recent Sunday, accompanied by an assistant, his 19-year-old son, Jan, to collect more data for his research. While his son monitored the image from the microscope on a laptop, Knoblauch fiddled with a device that held the glass needle. This kind of work is tediously difficult even in the calm of a laboratory, because the tip of the glass needle is delicate and tiny — far smaller than a human hair — and has to impale a specific kind of cell. On the scaffold, vibrations make the job practically torturous. “You hold everything, not just your breath,” Knoblauch said. In the few hours before the wind became strong enough to scuttle the exercise, he hoped to make at least one successful measurement of the pressure inside the long tubes of living cells, called phloem, that deliver the sugars produced by photosynthesis in the leaves through the trunk to fruits and roots. When the needle punctures the cell wall, the pressure of the water inside instantly compresses the oil. Knoblauch then uses before and after images to calculate the amount of compression and thus determine the pressure. Knoblauch spent three years developing the needles, which he calls picogauges. And it’s just one of several techniques he has developed over the years to test the hypothesis that what drives the flow of nutrients in the phloem is pressure differential. That hypothesis was developed in 1930 by a German plant physiologist, Ernst Münch, and has been widely accepted because it makes intuitive sense: Nutrients should flow from areas with higher pressure to areas with lower pressure. The hypothesis “is super plausible,” Knoblauch said. “But it’s untested.” Proving the hypothesis would be far more than an academic exercise. Fully understanding how plants function could lead to improvements in crop yields or resistance to pests and disease. Knoblauch’s work is so trying that he and his son had gotten fewer than 20 valid pressure measurements in the oak tree. “In about half a year, we will have all the data to say whether Münch is right or wrong, finally and definitively,” he said. As to which it will be, Knoblauch said that if he’d been asked a few months ago, he might have said Münch was wrong. He’s still cautious, he said, “but it’s looking like he was right.” NYT
