Biology of Australian seagrasses: Pollen development and submarine pollination in Amphibolis antarctica and Thalassodendron ciliatum (Cymodoceaceae)

1978 ◽  
Vol 26 (3) ◽  
pp. 265 ◽  
Author(s):  
SC Ducker ◽  
JM Pettitt ◽  
RB Knox

Development of the filiform pollen of the sea nymph Arnphibolis antarctica (Labill.) Sonder & Aschers. ex Aschers. has been characterized by high resolution light and electron microscopic methods. First pollen mitosis occurs at the end of the young spore period immediately preceding the vacuolate period, in contrast to many terrestrial pollens. Mature pollen is trinucleate, and is spirally coiled within the anther. The mature pollen wall shows a positive reaction for acid phosphatase like the intine of terrestrial pollens but is devoid of the outer exine layer, as judged by light and electron microscopic evidence. Development and arrangement of Thalassodendron ciliatum (Forssk.) Den Hartog pollen are similar. The adaptation of the pollen of aquatic plants for submarine pollination is reviewed in the light of evidence from 18th and 19th century work.

2008 ◽  
Vol 389 (7) ◽  
Author(s):  
Jaroslav Matoušek ◽  
Lidmila Orctová ◽  
Josef Škopek ◽  
Karel Pešina ◽  
Gerhard Steger

Abstract Hop latent viroid (HLVd) is not transmissible through hop generative tissues and seeds. Here we describe the process of HLVd elimination during development of hop pollen. HLVd propagates in uninucleate hop pollen, but is eliminated at stages following first pollen mitosis during pollen vacuolization and maturation. Only traces of HLVd were detected by RT-PCR in mature pollen after anthesis and no viroid was detectable in in vitro germinating pollen, suggesting complete degradation of circular and linear HLVd forms. The majority of the degraded HLVd RNA in immature pollen included discrete products in the range of 230–100 nucleotides and therefore did not correspond to siRNAs. HLVd eradication from pollen correlated with developmental expression of a pollen nuclease and specific RNAses. Activity of the pollen nuclease HBN1 was maximal during the vacuolization step and decreased in mature pollen. Total RNAse activity increased continuously up to the final steps of pollen maturation. HBN1 mRNA, which is abundant at the uninucleate microspore stage, encodes a protein of 300 amino acids (34.1 kDa, isoeletric point 5.1). Sequence comparisons revealed that HBN1 is a homolog of S1-like bifunctional plant endonucleases. The developmentally activated HBN1 and pollen ribonucleases could participate in the mechanism of HLVd recognition and degradation.


Author(s):  
Glen B. Haydon

High resolution electron microscopic study of negatively stained macromolecules and thin sections of tissue embedded in a variety of media are difficult to interpret because of the superimposed phase image granularity. Although all of the information concerning the biological structure of interest may be present in a defocused electron micrograph, the high contrast of large phase image granules produced by the substrate makes it impossible to distinguish the phase ‘points’ from discrete structures of the same dimensions. Theory predicts the findings; however, it does not allow an appreciation of the actual appearance of the image under various conditions. Therefore, though perhaps trivial, training of the cheapest computer produced by mass labor has been undertaken in order to learn to appreciate the factors which affect the appearance of the background in high resolution electron micrographs.


Author(s):  
J. A. Pollock ◽  
M. Martone ◽  
T. Deerinck ◽  
M. H. Ellisman

Localization of specific proteins in cells by both light and electron microscopy has been facilitate by the availability of antibodies that recognize unique features of these proteins. High resolution localization studies conducted over the last 25 years have allowed biologists to study the synthesis, translocation and ultimate functional sites for many important classes of proteins. Recently, recombinant DNA techniques in molecular biology have allowed the production of specific probes for localization of nucleic acids by “in situ” hybridization. The availability of these probes potentially opens a new set of questions to experimental investigation regarding the subcellular distribution of specific DNA's and RNA's. Nucleic acids have a much lower “copy number” per cell than a typical protein, ranging from one copy to perhaps several thousand. Therefore, sensitive, high resolution techniques are required. There are several reasons why Intermediate Voltage Electron Microscopy (IVEM) and High Voltage Electron Microscopy (HVEM) are most useful for localization of nucleic acids in situ.


Author(s):  
H. Takaoka ◽  
M. Tomita ◽  
T. Hayashi

High resolution transmission electron microscopy (HRTEM) is the effective technique for characterization of detailed structure of semiconductor materials. Oxygen is one of the important impurities in semiconductors. Detailed structure of highly oxygen doped silicon has not clearly investigated yet. This report describes detailed structure of highly oxygen doped silicon observed by HRTEM. Both samples prepared by Molecular beam epitaxy (MBE) and ion implantation were observed to investigate effects of oxygen concentration and doping methods to the crystal structure.The observed oxygen doped samples were prepared by MBE method in oxygen environment on (111) substrates. Oxygen concentration was about 1021 atoms/cm3. Another sample was silicon of (100) orientation implanted with oxygen ions at an energy of 180 keV. Oxygen concentration of this sample was about 1020 atoms/cm3 Cross-sectional specimens of (011) orientation were prepared by argon ion thinning and were observed by TEM at an accelerating voltage of 400 kV.


Author(s):  
Ralph M. Albrecht ◽  
Scott R. Simmons ◽  
Marek Malecki

The development of video-enhanced light microscopy (LM) as well as associated image processing and analysis have significantly broadened the scope of investigations which can be undertaken using (LM). Interference/polarization based microscopies can provide high resolution and higher levels of “detectability” especially in unstained living systems. Confocal light microscopy also holds the promise of further improvements in resolution, fluorescence studies, and 3 dimensional reconstruction. Video technology now provides, among other things, a means to detect differences in contrast difficult to detect with the human eye; furthermore, computerized image capture, processing, and analysis can be used to enhance features of interest, average images, subtract background, and provide a quantitative basis to studies of cells, cell features, cell labelling, and so forth. Improvements in video technology, image capture, and cost-effective computer image analysis/processing have contributed to the utility and potential of the various interference and confocal microscopic instrumentation.Electron microscopic technology has made advances as well. Microprocessor control and improved design have contributed to high resolution SEMs which have imaging capability at the molecular level and can operate at a range of accelerating voltages starting at 1KV. Improvements have also been seen in the HVEM and IVEM transmission instruments. As a whole, these advances in LM and EM microscopic technology provide the biologist with an array of information on structure, composition, and function which can be obtained from a single specimen. Corrrelative light microscopic analysis permits examination of living specimens and is critical where the “history” of a cell, cellular components, or labels needs to be known up to the time of chemical or physical fixation. Features such as cytoskeletal elements or gold label as small as 0.01 μm, well below the 0.2 μm limits of LM resolution, can be “detected” and their movement followed by VDIC-LM. Appropriate identification and preparation can then lead to the examination of surface detail and surface label with stereo LV-HR-SEM. Increasing the KV in the HR-SEM while viewing uncoated or thinly coated specimens can provide information from beneath the surface as well as increasing Z contrast so that positive identification of surface and subsurface colloidal gold or other heavy metal labelled/stained material is possible. Further examination of the same cells using stereo HVEM or IVEM provides information on internal ultrastructure and on the relationship of labelled material to cytoskeletal or organellar distribution, A wide variety of investigations can benefit from this correlative approach and a number of instrumentational configurations and preparative pathways can be tailored for the particular study. For a surprisingly small investment in time and technique, it is often possible to clear ambiguities or questions that arise when a finding is presented in the context of only one modality.


Development ◽  
1974 ◽  
Vol 32 (1) ◽  
pp. 133-145
Author(s):  
Par Claude Chapron

Evidence for the role of an apical cap glycoprotein in amphibian regeneration: cytochemical and autoradiographic electron-microscopic studies Early during limb regeneration in the newt, an ectodermal apical cap covering a mesodermal blastema is formed. High-resolution autoradiography of these tissues has been carried out after incorporation of [3H]fucose, which is a precursor of glycoproteins. Autoradiography shows that silver particles are located at first on epithelial cells, then on mesenchymatous cells. This observation is consistent with a hypothesis in which the apical cap would elaborate a glycoprotein acting on the blastema. Substructural autoradiography and cytochemistry also show the importance of cellular surfaces for both cells producing glycoprotein and those which are target cells.


2005 ◽  
Vol 38 (2) ◽  
pp. 260-265 ◽  
Author(s):  
Leonore Wiehl ◽  
Jens Oster ◽  
Michael Huth

Epitaxially grown Mo films on a faceted corundum (α-Al2O3)mplane were investigated by transmission electron microscopy. Low- and high-resolution images were taken from a cross-section specimen cut perpendicular to the facets. It was possible to identify unambiguously the crystallographic orientation of these facets and explain the considerable deviation (∼10°) of the experimental interfacet angle, as measured with atomic force microscopy (AFM), from the expected value. For the first time, proof is given for a smooth \{10\bar{1}1\} facet and a curvy facet with orientation near to \{10\bar{1}\bar{2}\}. Moreover, the three-dimensional epitaxial relationship of an Mo film on a faceted corundummsurface was determined.


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