Genetic Dissection of Apomixis in Dandelions Identifies a Dominant Parthenogenesis Locus and Highlights the Complexity of Autonomous Endosperm Formation

Apomixis in the common dandelion (Taraxacum officinale) consists of three developmental components: diplospory (apomeiosis), parthenogenesis, and autonomous endosperm development. The genetic basis of diplospory, which is inherited as a single dominant factor, has been previously elucidated. To uncover the genetic basis of the remaining components, a cross between a diploid sexual seed parent and a triploid apomictic pollen donor was made. The resulting 95 triploid progeny plants were genotyped with co-dominant simple-sequence repeat (SSR) markers and phenotyped for apomixis as a whole and for the individual apomixis components using Nomarski Differential Interference Contrast (DIC) microscopy of cleared ovules and seed flow cytometry. From this, a new SSR marker allele was discovered that was closely linked to parthenogenesis and unlinked to diplospory. The segregation of apomixis as a whole does not differ significantly from a three-locus model, with diplospory and parthenogenesis segregating as unlinked dominant loci. Autonomous endosperm is regularly present without parthenogenesis, suggesting that the parthenogenesis locus does not also control endosperm formation. However, the high recovery of autonomous endosperm is inconsistent with this phenotype segregating as the third dominant locus. These results highlight the genetic complexity underlying apomixis in the dandelion and underline the challenge of introducing autonomous apomixis into sexual crops.

Surface Polishing of 2-Inch 4H-SiC Wafer Using Fe Abrasive Particles

Ultra smooth and defect-free 4H-SiC wafers are strongly demanded in the next-generation power semiconductor devices. However, such SiC substrates are relatively difficult to machine because of their mechanical hardness and marked chemical inertness. In this study, we attempt to polish 2-inch 4H-SiC wafers by our proposed method, which utilizes Fe particles and a hydrogen peroxide solution. The processed surface was observed by phase shift interferometric microscopy, Nomarski differential interference contrast microscopy and atomic force microscopy. These observational results show that the surface roughness was improved over the entire 2-inch wafer by our proposed method. These results offer useful information for preparing a smooth SiC wafer.

Advanced Lapping and Polishing Methods for Planarizing a Single-Crystal 4H-Sic Utilizing Fe Abrasive Particles

We have developed advanced lapping and polishing methods for silicon carbide (SiC) substrates using an Fe abrasive particles and hydrogen peroxide (H2O2) solution. In this method, a SiC surface is oxidized by hydroxyl radicals (OH*), which was generated by Fe catalyst reactions, and the oxide layer on the SiC is mechanically and/or chemically removed by Fe abrasive particles and solution [1-4]. In this study, we applied this planarization method for lapping and polishing SiC surface, in which catalytically generated hydroxyl radicals were utilized to oxidize the surface of a SiC wafer. The processed surfaces were observed by optical interferometric microscope, Nomarski differential interference contrast. These observations showed that surface roughness and flatness of a SiC substrate were markedly improved and scratch-free SiC surface was obtained. These results provide useful information for preparing a high-efficiency and high-accuracy SiC substrate.

Significance of Enhanced Morphological Detection of Cryptosporidium sp. Oocysts in Water Concentrates Determined by Using 4′,6′-Diamidino-2-Phenylindole and Immunofluorescence Microscopy

ABSTRACT Of 2,361 water concentrates analyzed for the presence of Cryptosporidium spp. oocysts between January 1992 and May 1998, 269 (11.4%) were positive, of which 235 (87.4%) were raw and 34 were final water concentrates. Of 740 oocysts enumerated in positive samples, 656 oocysts (88.7%) were detected in raw and 84 oocysts (11.3%) were detected in final water concentrates by using a commercially available fluorescein isothiocyanate-labeled anti-Cryptosporidium sp. monoclonal antibody and the nuclear fluorogen 4′,6′-diamidino-2-phenylindole (DAPI). Of raw water positive samples, 66.8% had oocysts that contained nuclei, while 58.8% of final water samples had oocysts that contained nuclei. The most frequently identified oocysts had either no DAPI-positive nuclei and no internal morphology according to Nomarski differential interference-contrast microscopy (DIC) or four DAPI-positive nuclei together with internal contents according to DIC (39.5 and 32.8% of raw and 42.9 and 30.9% of final water positives, respectively). By use of the presence of DAPI-stained nuclei to support oocyst identification based upon oocyst wall fluorescence, 56.5% of oocysts were identified when at least one nucleus was present, while increasing the number of nuclei necessary for identification to four reduced the percentage identifiable to 32.8% in raw water concentrates. In final water concentrates, 51% of oocysts were identified using oocyst wall fluorescence and the presence of at least one nucleus, while increasing the number of nuclei necessary for identification to four reduced the percentage identifiable to 30.9%. By consolidating our identification criteria from the presence of at least one nucleus to the presence of four nuclei, we excluded approximately 20% of oocysts in either water type. Approximately 40% of oocysts detected in these United Kingdom samples were empty and could not be detected by alternative methods, including the PCR and fluorescence in situ hybridization.

Photoreceptor inner segments in monkey and human retina: Mitochondrial density, optics, and regional variation

The present work quantifies aspects of photoreceptor structure related to mitochondria, inner segment dimensions, and optical properties, as a basis for furthering our understanding of rod and cone function. Electron-microscopic analyses were performed on the retina of one stumptail macaque (Macaca arctoides) to obtain stereological measurements of ellipsoid mitochondrial density, and sizes and shapes of outer and inner segments. In addition, the distribution of mitochondria and the optical properties of human foveal cones were examined with electron microscopy and Nomarski differential interference contrast (NDIC) imaging. Mitochondria comprised 74–85% of cone ellipsoids and 54–66% of rod ellipsoids in macaque. Ellipsoid volume increased with eccentricity by 2.4-fold for rods and more than 6-fold for cones over eccentricities to 12.75 mm, while the volume of the outer segment supported by the ellipsoid was essentially constant for both rods and cones. Per unit volume of outer segment, cones contained ten times as much mitochondria as rods. In human fovea, as in the rest of the retina, most cone mitochondria were located in the distal inner segment. In the foveal center, however, there are also mitochondria in the myoid, as well as in the outer fiber, proximal to the external limiting membrane (ELM). Analyses of the optical aperture of human foveal cones, the point at which their refractive index clearly differs from the extrareceptoral space, showed that it correlated well with the location of mitochondria, except in the foveal center, where the aperture appeared proximal to the ELM. While mitochondria have an important metabolic function, we suggest that the striking differences between rods and cones in mitochondrial content are unlikely to be determined by metabolic demand alone. The numerous cone mitochondria may enhance the waveguide properties of cones, particularly in the periphery.

DIFFERENTIAL INTERFERENCE CONTRAST FOR X-RAY MICROSCOPY: FABRICATION AND CHARACTERIZATION OF TWIN ZONE PLATE OPTICS

A novel X-ray technique for converting the phase information of weakly absorbing specimen into strong image contrast similar to Nomarski differential interference contrast (DIC) is presented. DIC for X-rays is accomplished by the fabrication of a novel X-ray optic (TZP) consisting of two zone plates (ZPs) on both sides of the same substrate, laterally shifted by about one outermost zone width. The feasibility of DIC for X-rays was proven at the ID 21 X-ray microscopy beamline at the ESRF using a full-field imaging microscope and a scanning transmission X-ray microscope, which were operated at 4 keV photon energy. In both microscopes, we observe a tremendous contrast enhancement of up to a factor of 25. Though first experiments were carried out at 4 keV photon energy, this X-ray DIC technique can be adapted to any photon energy where ZPs with appropriate parameters and imaging performance can be designed and manufactured.