St Louis Special: Danforth Center


Rebecca Pool

Sunday, August 6, 2017 - 22:00
Confocal microscopy at Danforth: Cyanobacterium with photosynthetic pigments shown in red (chlorophyll a) and cyan (phyobilisomes), [Danforth].
Founded in 1998, the Donald Danforth Plant Science Center is a not-for-profit scientific facility located in St Louis, Missouri, United States, with a mission to "improve the human condition through plant science". 
Today, twenty research teams conduct basic research that is intended to improve agricultural productivity and preserve natural resources by reducing the need for pesticides and fertilizers, increasing the nutritional content of crops and improving resistance to drought, pests and disease.
When Dr Howard Berg established the Danforth Center's Integrated Microscopy facility in 2001, his aim, as facility Director, was to provide researchers with the best instruments to image plant cells and better understand cell biology.
With a background in plant cell structure, Dr Howard Berg helps to design and implement imaging experiments at the Danforth Center. [Danforth]
And sixteen years later, he has a host of microscopes at his fingertips, including a Leica SP8-X confocal, a Zeiss PALM laser microdissection microscope, a Hitachi tabletop SEM and LEO 912 AB TEM.
Research has been varied, with current projects including RNA processing in maize anthers and how plant defensin peptides fight infection in cells.
But as Berg points out, a lot of his facility's research hinges on confocal microscopy, with many researchers using its Leica instrument. 
Confocal microscopy: Sections of rice leaf tissue used to analyze chloroplast (red) number and size in a genetic study of factors affecting bundle sheath cell chloroplasts. [Danforth]
"We acquired this instrument in 2013, following a Major Research Instrumentation grant from the National Science Foundation," he highlights. "The committee evaluating the options at the time, were unanimous that this offered us the best options."
For example, given the need for live cell imaging, the instrument's sensitive hybrid detectors - HyD - were a huge draw.
Meanwhile, the instrument's white laser light produces 200 lines, offering versatility for fluorescence imaging, especially, as Berg points out, when coupled with the sliding mirrors for selecting bandwidth detection.
Confocal microscopy: Autofluorescence in a transverse section of tomato leaf. [Danforth]
"We also have a fast resonance scanner so we can do time-lapse imaging and preserve cell viability," he says.
"And the HyD detectors also have time gating so you can adjust the detection window of decay of a fluorophore," he adds. "This means we can eliminate auto-fluorescent compounds; plants are loaded with these compounds."
More stunning confocal microscopy at Danforth: Seed in a seed pod of Arabidopsis.
Confocal microscopy aside, many researchers also use the facility's Zeiss PALM system to capture tissue components.
Here, the microscope's focused laser cuts out and isolates selected specimens without contact. And, as such, many researchers have exploited this to survey plants for expression of fluorescent protein constructs.
"In the past we have used this for investigating parasitic feeding sites from root-knot nematodes," says Berg. "These [sites] are very large regions, and the idea is to capture the giant cells that the nematode induces."
Crucially, the facility also integrates light microscopy with TEM; specifically the LEO 120 kV TEM - which, according to Berg, has provided so much useful information over the years.
TEM: Pollen and the tapetum in an anther of Arabidopsis. [Danforth]
"Now, researchers are realizing that they need even more detail," he says. "With super-resolution microscopy you can't see the context of the fluorophore, yet with TEM you see everything."
"TEM is back on the upsurge again for biology research, which is great," he adds.
In its next issue, Microscopy and Analysis will be publishing a full-length Laboratory Focus on the Danforth Center with more information on Center's Integrated Microscopy Facility as well as its industrial-scale X-ray Computed Tomography (X-ray CT) system.
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