Subcellular investigation of photosynthesis-driven carbon assimilation in the symbiotic reef coral Pocillopora damicornis.

Reef-building corals form essential, mutualistic endosymbiotic associations with photosynthetic Symbiodinium dinoflagellates, providing their animal host partner with photosynthetically derived nutrients that allow the coral to thrive in oligotrophic waters. However, little is known about the dynamics of these nutritional interactions at the (sub)cellular level. Here, we visualize with submicrometer spatial resolution the carbon and nitrogen fluxes in the intact coral-dinoflagellate association from the reef coral Pocillopora damicornis by combining nanoscale secondary ion mass spectrometry (NanoSIMS) and transmission electron microscopy with pulse-chase isotopic labeling using [(13)C]bicarbonate and [(15)N]nitrate. This allows us to observe that (i) through light-driven photosynthesis, dinoflagellates rapidly assimilate inorganic bicarbonate and nitrate, temporarily storing carbon within lipid droplets and starch granules for remobilization in nighttime, along with carbon and nitrogen incorporation into other subcellular compartments for dinoflagellate growth and maintenance, (ii) carbon-containing photosynthates are translocated to all four coral tissue layers, where they accumulate after only 15 min in coral lipid droplets from the oral gastroderm and within 6 h in glycogen granules from the oral epiderm, and (iii) the translocation of nitrogen-containing photosynthates is delayed by 3 h. IMPORTANCE: Our results provide detailed in situ subcellular visualization of the fate of photosynthesis-derived carbon and nitrogen in the coral-dinoflagellate endosymbiosis. We directly demonstrate that lipid droplets and glycogen granules in the coral tissue are sinks for translocated carbon photosynthates by dinoflagellates and confirm their key role in the trophic interactions within the coral-dinoflagellate association

Highly dynamic cellular-level response of symbiotic coral to a sudden increase in environmental nitrogen

Metabolic interactions with endosymbiotic photosynthetic dinoflagellate Symbiodinium spp. are fundamental to reefbuilding corals (Scleractinia) thriving in nutrient-poor tropical seas. Yet, detailed understanding at the single-cell level of nutrient assimilation, translocation, and utilization within this fundamental symbiosis is lacking. Using pulse-chase 15N labeling and quantitative ion microprobe isotopic imaging (NanoSIMS; nanoscale secondary-ion mass spectrometry), we visualized these dynamic processes in tissues of the symbiotic coral Pocillopora damicornis at the subcellular level. Assimilation of ammonium, nitrate, and aspartic acid resulted in rapid incorporation of nitrogen into uric acid crystals (after ~45 min), forming temporary N storage sites within the dinoflagellate endosymbionts. Subsequent intracellular remobilization of this metabolite was accompanied by translocation of nitrogenous compounds to the coral host, starting at ~6 h. Within the coral tissue, nitrogen is utilized in specific cellular compartments in all four epithelia, including mucus chambers, Golgi bodies, and vesicles in calicoblastic cells. Our study shows how nitrogen-limited symbiotic corals take advantage of sudden changes in nitrogen availability; this opens new perspectives for functional studies of nutrient storage and remobilization in microbial symbioses in changing reef environments. IMPORTANCE The methodology applied, combining transmission electron microscopy with nanoscale secondary-ion mass spectrometry (NanoSIMS) imaging of coral tissue labeled with stable isotope tracers, allows quantification and submicrometric localization of metabolic fluxes in an intact symbiosis. This study opens the way for investigations of physiological adaptations of symbiotic systems to nutrient availability and for increasing knowledge of global nitrogen and carbon biogeochemical cycling. © 2013 Kopp et al

The toroidal mirror for single-pulse experiments on ID09B

Abstract ID09 is a dual-purpose beamline dedicated to time-resolved and high-pressure experiments. The time-resolved experiments use a high-speed chopper to isolate single pulses of x-rays. The chopper is installed near the sample (focal spot) and the shortest usable opening time depends on the sharpness of the vertical focusing. In the 16-bunch mode, the opening window of the chopper has to be reduced to 0.300 µs to select single pulses of x-rays. This can only be achieved by lowering the height in the chopper tunnel to 0.143 mm. To ensure a reasonable transmission though the tunnel, we have built a very precise toroidal mirror that focuses the beam 22.4 m downstream in M= 0.677 geometry. The 1.0-m long silicon mirror is curved by gravity into a near perfect toroid with a meridional radius of 9.9 km. The curvature is fine-tuned by a push stepper motor that works from below. The figure error from the gravity sag and the correcting force is less than 0.3 µrad and the polishing error is 0.7 µrad (rms) over the central 450-mm part of the mirror. The measured size of the polychromatic focus is 0.100 x 0.070 mmh x mmv in agreement with the prediction from the long-trace-profiler at the ESRF. The small focus, which integrates the entire central cone of the U17 undulator, is the result of superb optical quality, fine-control of curvature, a strain-free mount, a vibration free cooling system and careful alignment

X-ray transfocators: focusing devices based on compound refractive lenses

A tunable X-ray focusing and/or monochromating device, called a transfocator, is described. Examples of its implementation on ID11 at the ESRF are given

Future metrology needs for synchrotron radiation mirrors

An international workshop on metrology for X-ray and neutron optics, the first of its kind, was held March 16-17, 2000, at the Advanced Photon Source at Argonne National Laboratory. Engineers and scientists from around the world met to evaluate current metrology instrumentation and methods used to characterize the surface figure and finish of long, grazing-incidence optics used in synchrotron radiation beamlines, and to consider future needs for synchrotron, FEL, and neutron sources

Future metrology needs for synchrotron radiation mirrors

An international workshop on metrology for X-ray and neutron optics, the first of its kind, was held March 16-17, 2000, at the Advanced Photon Source at Argonne National Laboratory. Engineers and scientists from around the world met to evaluate current metrology instrumentation and methods used to characterize the surface figure and finish of long, grazing-incidence optics used in synchrotron radiation beamlines, and to consider future needs for synchrotron, FEL, and neutron sources

Optical configurations for X-ray imaging by projection

Several optical configurations aiming to create images of sub-millimetre objects with magnification from 1 to 100 have been experimentally tested at the ESRF BM5 beamline. A Kirkpatrick-Baez (KB) System is used for focusing the beam into a 30 microns spot and then direct projection images are recorded. Some results using a spherical crystal downstream from the KB System are presented. The possibility to focus the synchrotron beam into a 40 microns spot using an spherical crystal in quasi-normal incidence is demonstrated and its use for projection microscopy is discussed.