Research Highlights

NCMIR's Telescience is featured in Science Grid This Week

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Electron tomography reveals dramatic differences in chloroplast ultrastructure in phytoplankton cells grown under high and low light conditions. Colonies of Phaeocystis (background image) were grown under low light and high light conditions and subsequently fixed and examined using 400keV electron microscopy (top row) for reconstructing 3D sections (center row) from a tomographic tilt series. The biggest difference between the two light regimens is portrayed in tracings of 3D sections (bottom row), highlighting the number of thylakoid membranes (green) within the chloroplast and the density of packing of these thylakoids: low light condition show packed concentrations of thylakoids while high light condition portray low stacking. Procedure details (Background micrograph of Phaeocystis colony courtesy of PD Countway and DA Caron, University of Southern California; inset micrographs and reconstructions courtesy of T Moisan and NCMIR)

Tiffany Moisan of NASA’s Goddard Space Flight Center at Wallops Island Virgina teamed up with NCMIR researchers to investigate the morphological changes associated with a marine alga, Phaeocystis antarctica, grown in light-limiting and high light environments. Their study, reported in the journal Marine Biology, presents the first 3D structures determined by electron tomography of an ecologically important phytoplankton species. By using electron tomography—capable of characterizing sections ten times thicker than those used in transmission electron microscopy—the researchers suggest a new perspective on the complex interactions between the alga’s thylakoid membranes, the pyrenoid, and the chloroplast membrane. The ability to resolve chloroplast structures in three dimensions allowed the team to characterize the dynamic response of P. antarctica at the subcellular level to changes in light intensity.

Characterizing how the subcellular structure of a phytoplankton contributes to its ecological fitness under environmentally variable light levels has profound implications for photophysiology and is an important step in bridging the gap between processes operating at the cellular and ecosystem levels.

Data acquired in this chloroplast study are publicly available through the Cell Centered Database, an online resource for 3D light and electron microscopic data. This observed 3D thylakoid structures have profound implications for cellular photophysiology and making the data publicly availalbe will benefit future computational analyses and perhaps optical models of light absorption by phytoplankton in the marine environment.