Imprinted genes are expressed primarily or exclusively from either the maternal or paternal allele, a phenomenon that occurs in flowering plants and mammals. Flowering plant imprinted gene expression has been described primarily in endosperm, a terminal nutritive tissue consumed by the embryo during seed development or after germination. Imprinted expression in Arabidopsis thaliana endosperm is orchestrated by differences in cytosine DNA methylation between the paternal and maternal genomes as well as by Polycomb group proteins. Currently, only 11 imprinted A. thaliana genes are known. Here, we use extensive sequencing of cDNA libraries to identify 9 paternally expressed and 34 maternally expressed imprinted genes in A. thaliana endosperm that are regulated by the DNA-demethylating glycosylase DEMETER, the DNA methyltransferase MET1, and/or the core Polycomb group protein FIE. These genes encode transcription factors, proteins involved in hormone signaling, components of the ubiquitin protein degradation pathway, regulators of histone and DNA methylation, and small RNA pathway proteins. We also identify maternally expressed genes that may be regulated by unknown mechanisms or deposited from maternal tissues. We did not detect any imprinted genes in the embryo. Our results show that imprinted gene expression is an extensive mechanistically complex phenomenon that likely affects multiple aspects of seed development.

The NanoSIMS ion probe is a new-generation SIMS instrument, characterised by superior spatial resolution, high sensitivity and multi-collection capability. Isotope studies of certain elements can be conducted with 50-100 nm resolution, making the NanoSIMS an indispensable tool in many research fields. We review technical aspects of the NanoSIMS ion probe and present examples of applications in cosmochemistry and biological geochemistry. This includes isotope studies of presolar (stardust) grains from primitive meteorites and of extraterrestrial organics, the search for extinct radioactive nuclides in meteoritic materials, the study of lunar samples, as well as applications in environmental microbiology, cell biology, plant and soil science, and biomineralisation.Secondary ion mass spectrometry (SIMS) is an analytical technique, which is used in a variety of fields spanning from the material sciences over biology to geo-and cosmochemistry. One incarnation of a SIMS instrument is the 'ion microprobe' or 'ion probe', which permits in situ studies at the micrometre or sub-micrometre scale. The ion probe uses a finely focused primary ion beam to erode the target and produce secondary ions that can be mass analysed. Ion probe SIMS offers lg g -1 or better detection limits for most elements, essentially periodic table coverage, imaging and depth profiling capabilities, and isotopic analyses of major and minor elements with (sub-) micrometre lateral resolution on a wide range of materials, for which the main requirements are that they can be prepared with relatively flat surfaces and introduced into an ultra-high-vacuum environment. Furthermore, a combination of imaging and depth profiling allows three-dimensional chemical and isotope maps to be created. The fundamentals of ion probe SIMS were developed some 50 years ago, but it was not until the 1980s that the technique became an important tool to a wider range of researchers in different fields. This development started with the advent of the IMS 3f (Lepareur 1980) and Sensitive High Resolution Ion Microprobe (SHRIMP; Clement et al. 1977) instruments, developed by Cameca and the Australian National University, respectively.In section 'NanoSIMS fundamentals' of this review, we provide a simplified description of how an ion probe functions, then focus on the specifics of the Cameca NanoSIMS 50/50L ion probe. NanoSIMS is the name of an instrument, but the term is now also used as synonym for ion probe analyses with submicrometre lateral resolution, which is what the development of the NanoSIMS instrument has made possible. Developed in the 1990s and originally intended for applications in biology, the first commercial NanoSIMS instruments were delivered at the beginning of this millennium to two laboratories conducting research in cosmochemistry at Washington University in St. Louis and the Max Planck Institute for Chemistry, respectively. Both these laboratories worked closely with Cameca to implement several improvements in the instrument design. It was quickly recogni...

SUMMARY Depth zonation on coral reefs is largely driven by the amount of downwelling, photosynthetically active radiation (PAR) that is absorbed by the symbiotic algae (zooxanthellae) of corals. The minimum light requirements of zooxanthellae are related to both the total intensity of downwelling PAR and the spectral quality of the light. Here we used Stylophora pistillata colonies collected from shallow (3 m) and deep (40 m) water; colonies were placed in a respirometer under both ambient PAR irradiance and a filter that only transmits blue light. We found that the colonies exhibited a clear difference in their photosynthetic rates when illuminated under PAR and filtered blue light, with higher photosynthetic performance when deep colonies were exposed to blue light compared with full-spectrum PAR for the same light intensity and duration. By contrast, colonies from shallow water showed the opposite trend, with higher photosynthetic performances under full-spectrum PAR than under filtered blue light. These findings are supported by the absorption spectra of corals, with deeper colonies absorbing higher energy wavelengths than the shallow colonies, with different spectral signatures. Our results indicate that S. pistillata colonies are chromatically adapted to their surrounding light environment, with photoacclimation probably occurring via an increase in photosynthetic pigments rather than algal density. The spectral properties of the downwelling light are clearly a crucial component of photoacclimation that should be considered in future transplantation and photoacclimation studies.

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