Oogenesis in the Apogamous Fern Pteris cretica

The events that characterize egg formation and maturation inPteris cretica were investigated using transmission electronmicroscopy and electron microscope microprobe analysis. Theydid not differ significantly from those described for sexuallyreproducing ferns. The significance of these findings is discussedin relation to current theories concerning phase change in ferns. Pteris cretica, fern, apogamy, agamospory, transmission electron microscopy, oogenesis     

Experimental studies of rapid bioerosion of coral reefs in the Galápagos Islands

Experimental carbonate blocks of coral skeleton,Porites lobata (PL), and cathedral limestone (LS) were deployed for 14.8 months at shallow (5–6 m) and deep (11–13m) depths on a severely bioeroded coral reef, Champion Island, Galápagos Islands, Ecuador. Sea urchins (Eucidaris thouarsii) were significantly more abundant at shallow versus deep sites.Porites lobata blocks lost an average of 25.4 kg m^–2yr^–1 (23.71 m^–2yr^–1 or 60.5% decrease yr^–1). Losses did not vary significantly at depths tested. Internal bioeroders excavated an average of 2.6 kg m^–2 yr^–1 (2.41 m^–2 yr^–1 or 0.6% decrease yr^–1), while external bioeroders removed an average of 22.8 kg m^–2 yr^–1). (21.31 m^–2 yr^–1). or 59.9% decrease yr^–1). few encrusting organisms were observed on the PL blocks. Cathedral limestone blocks lost an average of 4.1 kg m^–2 yr^–1). (1.81 m^–2 yr^–1). or 4.6% decrease yr-'), also with no relation to depth. Internal bioeroders excavated an average of 0.6 kg m^–2 yr^–1). (0.31 m^–2 yr^–1). or 0.7% decrease yr^–1). and external bioeroders removed an average of 3.5 kg m^–2 yr^–1). (1.51 m^–2 yr^–1). or 3.9% decrease yr^–1). from the LS blocks. Most (57.6%) encrustation occurred on the bottom of LS blocks, and there was more accretion on block bottoms in deep (61.4 mg cm^–2 yr^–1). versus shallow (35.0 mg cm^–2 yr^–1) sites. External bioerosion reduced the average height of the reef framework by 0.2 cm yr^–1). for hard substrata (represented by LS) and 2.3 cm yr^–1). for soft substrata (represented by PL). The results of this study suggest that coral reef frameworks in the Galápagos Islands are in serious jeopardy. If rates of coral recruitment do not increase, and if rates of bioerosion do not decline, coral reefs in the Galápagos Islands could be eliminated entirely.     

Genotype and phenotype associations with drought tolerance in barley tested in North Africa

A review is presented of genetic strategies deployed in a 3-yr project on drought tolerance in barley. Data were collected on genetic, physiological and agronomic traits in non-irrigated and irrigated field trials in Egypt, Morocco and Tunisia. A wide range of barley germplasm (developed from African and European cultivars, adapted landraces and wild barleys) was tested, and positive traits were found in each gene pool. The contrasting environments of the three North African countries had major effects on plant/genotype performance. Genetic effects were also detected, as were genotype × environment interactions. A range of strategies were deployed to investigate the physiology and genetics of quantitative traits associated with field performance. Quantitative trait locus (QTL) analysis was performed using backcross lines, recombinant inbred lines and doubled haploid mapping populations. A detailed genetic map was generated in the Tadmor × (ER/Apm) recombinant inbred lines, an important mapping population specifically developed by ICARDA (Centre for Agricultural Research in Dry Areas) and CIMMYT (International Maize and Wheat Improvement Center) to study drought. Quantitative trait loci (QTLs) for grain yield and other important morphological and physiological traits were also identified in a population of doubled haploids derived from F2BCj plants from a cross between a cultivar and a wild barley accession. Significantly, the wild parental line was found to contribute a number of positive alleles for yield. Effects of major developmental genes could explain many of the responses observed. QTLs were found to cluster around major genes controlling flowering time (sghI), plant stature (sdwI and arie.GP) and ear type (vrsl), and it is highly likely that the associations represent pleiotropic effects. Some QTLs were associated with candidate genes such as dehydrins and rubisco activase. One of the most significant results was the identification and generation of material that out performed the best local standards in the three participating North African countries; the selected lines have now entered local breeding programmes. The strategies adopted provided information on physiological traits, genotypes and genetic markers that could be used for marker-assisted selection. Target QTLs and their associated genetic markers may be deployed in marker assisted selection programmes to match crop phenology to the field environment.     

Modifications of anionic-lipid domains preceding membrane fusion in guinea pig sperm

The relationship between anionic-lipid concentration and the functional properties of plasma-membrane domains was explored using the guinea-pig sperm membrane as a model, with polymyxin B (PXB) as a probe. Areas of plasmalemma specialized for fusion during the acrosome reaction had a higher affinity for the probe than adjacent nonfusigenic regions. In addition, capacitation--a process preceding acrosome:plasma-membrane fusion--markedly enlarged the area susceptible to PXB binding over the acrosomal cap. Protease treatment mimicked capacitation by increasing the acrosome-reaction incidence as well as PXB binding, at enzyme concentrations not affecting the surface coat nor altering filipin/sterol localization. Both proteolytic digestion and capacitation failed to augment PXB- or filipin-affinity in nonfusigenic zones, such as the post-acrosomal segment, including its particle-free maculae. Incubation of sperm in capacitating medium supplemented with 32P-labeled phosphate, followed by lipid extraction, thin-layer chromatography, and autoradiography, revealed a radioactive band comigrating with cardiolipin and phosphatidic acid. Vermiform protrusions elicited by PXB in the outer lamellae of cardiolipin- phosphatidylcholine liposomes resembled those seen in fusional regions of sperm membrane. We conclude that (a) differing concentrations of anionic lipids are found in adjacent domains of the sperm plasma membrane; (b) these domains mirror the functional regions of the membrane, with higher anionic-lipid concentrations localized over fusional zones; (c) the surface coat does not participate in the maintenance of such domains; (d) anionic-lipid synthesis may contribute to their formation; and (e) anionic-lipid concentrations increase as the membrane becomes fusionally competent, indicating that cellular modulation of lipid domains accompanies regulation of membrane function.     

Phosphorus-31 nuclear magnetic resonance studies of bioenergetics in wild-type and adenosinetriphosphatase(1-) Escherichia coli cells

By use of 31P NMR, the transmembrane pH gradient (delta pH) and the intracellular levels of phosphorylated metabolites were measured in aerobic suspensions of wild-type Escherichia coli cells in the presence and absence of the adenosinetriphosphatase (ATPase) inhibitor dicyclohexylcarbodiimide (DCCD); the same parameters were also determined in E. coli mutants deficient in ATPase activity under both anaerobic and aerobic conditions. A method is described by which dense suspensions of E. coli cells (approximately 3 X 10(11) cells/mL) were oxygenated so that steady-state O2 levels in the suspensions were far greater than the Km for O2 consumption. Under these conditions, in wild-type MRE600 cells, the intracellular concentrations of PI, NTP, and NDP were measured to be 3.0 +/- 1.5, 8 +/- 1, and 1.2 +/- 1 mM, respectively, while the intracellular pH was approximately 7.5 over the external pH range studied (6 to approximately 7.0). Upon treatment with DCCD, the intracellular NTP level was drastically reduced and intracellular Pi concentration increased in respiring wild-type cells; in the same cells, however, DCCD did not affect the intracellular pH and the delta pH. During respiration in the presence of lactate, ATPase- cells established a delta pH but failed to synthesize any detectable levels of NTP. Conversely, ATPase- cells accumulated high levels of NTP but did not generate a delta pH during glycolysis under anaerobic conditions. These results are in complete agreement with the generally accepted chemiosmotic hypothesis. 31P NMR data on intact ATPase- NR70 cells were in agreement with the previously proposed [Rosen, B. P., Brey, R., & Hasan, S. (1978) J. Bacteriol. 134, 1030] existence of a proton leak in this strain which is sealed by DCCD or by spontaneous mutation into strain NR71. However, the NMR data also indicated that other major differences exist between NR71 and NR70 cells.