Genetic control of male fertility in Arabidopsis thaliana : structural analysis of postmeiotic developmental mutants

Seven new male-sterile mutants (ms7–ms13) of Arabidopsis thaliana (L.) Heynh. (ecotype columbia) are described that show a postmeiotic defect of microspore development. In ms9 mutants, microspores recently released from the tetrad appear irregular in shape and are often without exines. The earliest evidence of abnormality in ms12 mutants is degeneration of microspores that lack normal exine sculpturing, suggesting that the MS12 product is important in the formation of pollen exine. Teratomes (abnormally enlarged microsporocytes) are also occasionally present and each has a poorly developed exine. In ms7 mutant plants, the tapetal cytoplasm disintegrates at the late vacuolate microspore stage, apparently causing the degeneration of microspores and pollen grains. With ms8 mutants, the exine of the microspores appears similar to that of the wild type. However, intine development appears impaired and pollen grains rupture prior to maturity. In ms11 mutants, the first detectable abnormality appears at the mid to late vacuolate stage. The absence of fluorescence in the microspores and tapetal cells after staining with 4′,6-diamidino-2-phenylindole (DAPI) and the occasional presence of teratomes indicate degradation of DNA. Viable pollen from ms10 mutant plants is dehisced from anthers but appears to have surface abnormalities affecting interaction with the stigma. Pollen only germinates in high-humidity conditions or during in-vitro germination experiments. Mutant plants also have bright-green stems, suggesting that ms10 belongs to the eceriferum (cer) class of mutants. However, ms10 and cer6 are non-allelic. The ms13 mutant has a similar phenotype to ms10, suggesting is also an eceriferum mutation. Each of these seven mutants had a greater number of flowers than congenic male-fertile plants. The non-allelic nature of these mutants and their different developmental end-points indicate that seven different genes important for the later stages of pollen development have been identified.

Genetic control of male fertility in Arabidopsis thaliana : structural analysis of premeiotic developmental mutants

We have taken a mutational approach to identify genes important for male fertility in Arabidopsis thaliana and have isolated a number of nuclear male/ sterile mutants in which vegetative growth and female fertility are not altered. Here we describe detailed developmental analyses of four mutants, each of which defines a complementation group and has a distinct developmental end point. All four mutants represent premeiotic developmental lesions. In ms3, tapetum and middle layer hypertrophy result in the degeneration of microsporocytes. In ms4, microspore dyads persist for most of anther development as a result of impaired meiotic division. In ms5, degeneration occurs in all anther cells at an early stage of development. In ms15, both the tapetum and microsporocytes degenerate early in anther development. Each of these mutants had shorter filaments and a greater number of inflorescences than congenic male-fertile plants. The differences in the developmental phenotypes of these mutants, together with the non-allelic nature of the mutations indicate that four different genes important for pollen development, have been identified.

Floristic and structural characteristics of a coastal heathland exhibiting symptoms of Phytophthora cinnamomi infestation in the eastern Otway Ranges, Victoria

The floristics and structure of heathland vegetation exhibiting symptoms of Phytophthora cinnamomi Rands infestation was assessed at two sites in heathlands at Anglesea, Victoria. There were significant effects in both floristics and structure. Thirteen heathland species were significantly less abundant in diseased areas and 23 species were more abundant. Diseased (infested) vegetation, when compared with non-diseased areas, had less cover of Xanthorrhoea australis and shrub species and a greater cover of sedges, grasses and open ground. Structural differences were observed between heights 0 and 0.6 m, with a decline in cover recorded in diseased vegetation. Non-metric multidimensional scaling ordination of the floristic data showed a clear separation of diseased and non-diseased vegetation and that changes in floristic composition post-infestation were similar at both sites. Although there was some evidence of regeneration of X. australis, the recovery capacity of other susceptible species at Anglesea is unknown. The long-term consequences of loss of species and structure in the eastern Otways mean that the vegetation is unlikely to return to former status, especially if the pathogen continues to reinfect.

Methodological considerations in the measurement of institutional and structural forms of HIV discrimination

The systematic measurement of HIV/AIDS-related discrimination is imperative within the current rhetoric that holds discrimination as one of the two ‘biggest' barriers to HIV/AIDS pandemic intervention. This paper provides a methodological critique of the UNAIDS (2000b) Protocol for the Identification of Discrimination against People Living with HIV (the Protocol) . Specifically, the paper focuses on the Protocol's capacity to accurately identify and measure institutional levels of HIV-related discrimination that allows data that are reliable and comparable across time and contexts. Conceptual issues including the Protocol's objective as an indicator versus a direct measure of discrimination and the role of the Protocol as a tool of research versus a tool of advocacy are explored. Design issues such as the operationalization of discrimination, appropriateness of indicator content, sampling and data collection strategies and issues of scoring are also evaluated. It is hoped that the matters outlined will provide readers with ways of critically reflecting and evaluating the findings of the research papers presented in this Special Issue, as well as pointing to ways of improving research design.

Institutional and structural forms of HIV-related discrimination in health care : a study set in Beijing

This paper presents key findings of a situational analysis of institutional and structural levels of HIV/AIDS-related discrimination in Beijing, China, with a focus on the area of health care. Initially slow to respond to the presence of HIV, China has altered its approach and enacted strict legislative protection for people living with HIV/AIDS (PLWHA). In order to determine whether this has altered discrimination against PLWHA, this study examined existing legislation and policy, and interviewed key informants working in health care and PLWHA. The overall findings revealed that discrimination in its many forms continued to occur in practice despite China's generally strong legislative protection, and it is the actual practice that is hindering PLWHAs' access to health services. A number of legislative and policy gaps that allow discrimination to occur in practice were also identified and discussed. The paper concludes with a call to rectify specific gaps between legislation, policy and practice. An understanding of the underlying factors that drive discrimination will also be necessary for effective strategic interventions to be developed and implemented.

Structural characterization of rare intramolecularly (1,4-Te· · ·N) bonded diorganotellurides and their monomeric complexes with mercury(II) halides: metal assisted C-H· · ·X (Hg) interactions leading to supramolecular architecture

Monomeric tellurides 4-RC₆H₄(SB)Te [SB = 2-(4,4'-N0₂C₆H₄CH=NC₆H₃-Me); R = H, 1a; Me,1b; OMe, 1c], which incidentally represent the first example of a telluride with 1,4-Te···N intramolecular interaction, have been prepared and characterized by solution and solid-state ¹²⁵Te NMR, ¹³C NMR and X-ray crystallography. Interplay of weak C-H···O and C-H-··π{ interactions in the crystal lattice of 1b and1c are responsible for the formation of supramolecular motifs. These tellurides undergo expected oxidative addition reactions with halogens and interhalogens and also interact coordinatively with mercury(II) halides to give 1:2 complexes, HgX₂[4-RC₆H₄(SB)Te]₂ (X = CI, R = H, 2a; Me, 2b; OMe, 2c and X = Br, R = H, 3a; Me, 3b; and OMe, 3c) with no sign of Te-C bond cleavage, as has been reported for some 1,5-Te·· ·N(O) intramolecularly bonded tellurides. The complexes 2a and 3c are the first structurally characterized monomeric 1:2 adducts of mercury(II) halides with Te ligands. The 1,4-Te···N intramolecular interactions in the solid-state are retained in the complexes highlighting simultaneously the Lewis acid and base character of the Te(lI) atom. Packing of molecules in the crystal lattice of 2a
and 3c reveals that non-covalent C-H· . ·Cl/Br interactions involving metal-bound halogen atoms possess significant directionality and in
combination with coordinative covalent interactions may be of potential use in creating inorganic supramolecular synthons.

First isolation and structural determination of cyclic β-(1→2)-glucans from an alga, Chlorella pyrenoidosa

The aqueous extract of the edible green microalgae Chlorella pyrenoidosa is of interest because of its immunostimulatory activity. Some components in the extract have been identified previously, namely a unique type of arabinogalactan and a galactofuran. Further fractionation of this extract was accomplished by treating the aqueous solution of the fraction precipitated by addition of 1.5vol of 95% ethanol with cetyltrimethylammonium bromide. The residue obtained by concentration of the supernatant was fractionated further by anion-exchange chromatography and size-exclusion chromatography on Sephadex G-100. Two fractions from the latter column were retained, of which one was a starch-like alpha-(1-->4)-linked d-glucan with some alpha-(1-->6) branches, and the other contained a starch plus a mixture of beta-(1-->2)-d-glucans. ESI mass spectrometry was used to show that the mixture contained both cyclic and linear beta-(1-->2)-d-glucans in a cyclic:linear ratio of 64:36, based on intensities of mass spectral peaks. For the cyclic beta-(1-->2)-d-glucans, ring sizes ranged from 18 to 35 monosaccharides with the ring containing 21 glucose units (54% of the cyclic glucans) being greater than three times more abundant than the next most abundant component, the ring containing 22 glucose units (15%). No rings containing 20 glucose units were present. This is the first observation of cyclic beta-(1-->2)-d-glucans in algae, as far as we are aware. For the linear beta-(1-->2)-d-glucans, the component containing 20 glucoses was most abundant (35% of the linear glucans), while the component containing 21 glucose units was the next most abundant (17%). These relatively low-molecular-weight glucans had low immunostimulatory activity.

Corporate codes of ethics in Australia, Canada and USA : measurement and structural properties of a cross-cultural model

The objective is to test the consistency of measurement and structural properties in a model of corporate codes of ethics (CCE) on an aggregated level and across multiple samples derived from three countries, namely Australia, Canada and the USA. The properties of four constructs of CCE are described and tested, these being: surveillance/training, internal communication, external communication, and guidance. The conclusion is that the measurement and structural models on an aggregated level have a satisfactory fit, validity and reliability. Furthermore, they are consistent when tested on each of the three samples (i.e. cross-validated). The cross-cultural model makes a contribution in addition to previous mostly descriptive studies and theory in the field using confirmatory factor analysis and structural equation modeling.

Isolation, characterization and structural determination of a unique type of arabinogalactan from an immunostimulatory extract of Chlorella pyrenoidosa

An arabinogalactan was isolated from a hot water extract of freeze-dried cells of the green microalga, Chlorella pyrenoidosa. This hot water extract is a proprietary immunomodulator, with the trademark Respondin™ (ONC-107). The arabinogalactan was recovered from the ethanol-soluble fraction of the supernatant resulting from a process that involved controlled ethanol precipitation followed by size exclusion chromatography on Sephadex G-100, then Cetavlon precipitation. Sugar analyses, GC–MS data for (S)-2-octyl glycosides, and 1D and 2D NMR experiments established unambiguously that the repeating unit was →2)-α-l-Araf-(1→3)-[α-l-Araf-(1→4)]-β-d-Galp-(1→. This structure does not fit into any of the known classes of arabinogalactans. SEC/MALS experiments gave a molecular mass for the arabinogalactan isolated as 47 ± 4 kDa but the original structure was probably larger.

Comparative structural analyses of purified glycogen particles from rat liver, human skeletal muscle and commercial preparations

Glycogen is a cellular energy store that is crucial for whole body energy metabolism, metabolic regulation and exercise performance. To understand glycogen structure we have purified glycogen particles from rat liver and human skeletal muscle tissues and compared their biophysical properties with those found in commercial glycogen preparations. Ultrastructural analysis of commercial liver glycogens fails to reveal the classical α-rosette structure but small irregularly shaped particles. In contrast, commercial slipper limpet glycogen consists of β-particles with similar branching and chain lengths to purified rat liver glycogen together with a tendency to form small α-particles, and suggest it should be used as a source of glycogen for all future studies requiring a substitute for mammalian liver glycogen.