Identification of site-types important for rare ferns in an area of deciduous woodland in northwest Spain

The Eume woods in northwest Spain are an important refuge for a number of endangered ferns, including Culcita macrocarpa, Cystopteris diaphana, Dryopteris aemula, Dryopteris guanchica, Hymenophyllum tunbrigense and Woodwardia radicans. Because some of these species are inconspicuous or difficult to identify in the field, we attempted to develop simple floristic criteria to identify sites important or potentially important for these species (high-value sites). Having drawn up field-layer vascular plant inventories for 44 plots in the study area, we considered two major strategies. Under strategy 1, we looked for those conspicuous species which best discriminated between plots containing the endangered species (current-high-value plots) and all other plots. Under strategy 2, we first carried out a global plots-by-species classification using indicator species analysis (Hill et al. 1975) and then looked for those conspicuous species which best discriminated between groups containing current-high-value plots and all other groups. For our data set, the second strategy proved more effective. The best criterion identified was If two or more of Luzula sylvatica, Viola riviniana and Rubus spp. are present, then that plot is high-value. We include a listing of a BASIC program for the discriminant analysis algorithm, which we consider to have a number of potential applications in vegetation science and biogeography.     

Gross Damage Accumulation in Frozen Rabbit Liver Due to Mechanical Stress at Cryogenic Temperatures

The second phase of a pilot study dealing with the mechanical response of frozen biological tissues to external compressive load is presented. This stage deals with histological observations of the damage accompanying mechanically induced permanent deformation in frozen rabbit liver. No significant gross histological damage was observed in the liver samples due to either processing the tissue in the frozen state, due to slow cooling of the liver tissues down to −20°C, or due to rapid cooling of the samples down to −196°C. No histological changes were observed in tissue samples that were loaded within the elastic regime, that is, below the yield strength of the material. Therefore, it is concluded that histological changes due to mechanical stresses are associated with plastic (permanent) deformations. Histological observations indicate that linear cracks which appear to have no preferred orientation develop due to mechanical stress beyond the yield strength of the frozen tissue. These cracks accumulate until final failure of the frozen tissue, when the tissue sample collapses to rubble. Based on histological observations and concepts from solid mechanics, an interaction between crack formation and irregularities in the frozen medium is suggested. Significant sources for such irregularities, in an homogeneous tissue such as the liver, are blood vessels and bile ducts. These irregularities may either initiate crack formation or, on the other hand, may also arrest propagating cracks.     

Serine synthesis in cyanobacteria by a nonphotorespiratory pathway

The pathway of serine synthesis was investigated in six species of cyanobacteria: Anabaena cylindrica, A. variabilis, A. flos-aquae, Coccochloris peniocystis, Gleo-capsa alpicola and Phormidium molle . Activity of the enzymes phosphoglycerate (PGA) dehydrogenase (EC 1.1.1.95), phosphoserine transaminase (EC 2.6.1.52) and phosphoserine phosphatase (EC 3.1.3.3) was detected in vitro in all species, but no PGA phosphatase (EC 3.1.3.20) or hydroxypyruvate reductase (EC 1.1.1.26) activity could be detected. Metabolism of [1-¹⁴C]PGA by cell-free extracts of C. peniocystis resulted in the labelling of serine, alanine and aspartate, which represented 84, 11 and 4% of the labelled amino acid pool, respectively, Labelled serine isolated from these experiments was 100% carboxyl-labelled indicating that it was formed directly from PGA. The labelling of serine was markedly reduced by 5 mM phosphoserine. These in vitro findings indicate that cyanobacteria are capable of synthesizing serine directly from PGA, independent of ribulose-1.5-bisphosphate oxidation, and that the route of serine synthesis via phosphohydroxypyruvate and phosphoserine is the predominant pathway in these organisms.     

The carotenoid-deficient mutant, C-6E, of Scenedesmus obliquus is blocked at the site of phytoene synthase

In contrast to the wild type strain of Scenedesmus , mutant C-6E synthesized only trace amounts of the carotenoids violaxanthin and lutein during prolonged heterotrophic growth. All other carotenoids and carotenoid precursors, such as phytoene, were undetectable. Additionally, only reduced levels of chlorophyll a and no chlorophyll b were formed. To evaluate the potential site of inhibition in the pathway for carotenoid biosynthesis the enzymatic activities of geranylgeranyl pyrophosphate synthase and phytoene synthase were assayed in cell-free extracts. Both enzymes were highly active in extracts of the wild type but only geranylgeranyl pyrophosphate synthase was active in comparable extracts from mutant C-6E . This observation strongly indicates that the phenotype of C-6E results from either a mutation of the phytoene synthase structural gene or of a regulatory gene involved in expression of this enzyme. Other phenotypic effects on composition and structure of the photosynthetic apparatus are discussed as a secondary consequence of the carotenoid deficiency in the thylakoid membranes.     

Pollination biology and outcrossing rates in hermaphroditic Schiedea lydgatei (Caryophyllaceae)

The influence of outcrossing and pollination biology on the maintenance of hermaphroditism was studied for Schiedea lydgatei (Caryophyllaceae: Alsinoideae), a species endemic to Moloka`i in the Hawaiian Islands. Schiedea lydgatei is the only hermaphroditic species in an otherwise dimorphic clade and hermaphroditism is likely the result of a reversal from a gynodioecious ancestor. Both wind and native moths in the family Pyralidae are responsible for pollination in S. lydgatei. Outcrossing rates were generally high (0.80), especially in years when the greatest number of plants were flowering. The combination of high outcrossing rates and substantial inbreeding depression indicates that at present females would not be favored in the population. Pollination by both wind and insects is consistent with the hypothesis that hermaphroditism is the result of a relatively recent reversal, as the ancestor of S. lydgatei was probably wind pollinated and gynodioecious with few females in the populations. A shift from wind to predominately insect pollination on Moloka`i may have resulted in increased outcrossing rates and prevented the expression of high inbreeding depression among progeny of hermaphrodites, a condition that would select against females and favor a reversal to hermaphroditism. Because few females were likely to have been present in ancestral populations that colonized Moloka`i, founder effect is another potential explanation for loss of females. In either case, current high levels of outcrossing prevent re-establishment of females in populations of S. lydgatei.     

Double Coupling Edman Chemistry for High-Sensitivity Automated Protein Sequencing

Capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) is a promising new method for the analysis of protein sequencing products. It gives 10 zmol (1 zmol = 10^–21 mol) limits of detection (3) for fluorescein thiohydantoin (FTH) amino acids. We have developed a separation for the (FTH)-amino acid products generated from 18 of the 20 coded amino acids. The extremely low volume requirement associated with CE-LIF makes it incompatible with commercial sequencers. For this reason, we have also been developing a miniaturized sequencer that can be more easily coupled to our detection system. Both the CE-LIF system and the miniaturized sequencer are described.     

Airway thermal volume in humans and its relation to body size

Serikov, Vladimir B., E. Heidi Jerome, Neal W. Fleming,Peter G. Moore, Frederick A. Stawitcke, and Norman C. Staub.Airway thermal volume in humans and its relation to body size.J. Appl. Physiol. 83(2): 668-676, 1997.The objective of this study was to investigate the influence ofvolume ventilation(E) andcardiac output () on the temperature of the expiredgas at the distal end of the endotracheal tube in anesthetized humans.In 63 mechanically ventilated adults, we used a step decrease in thehumidity of inspired gas to cool the lungs. After change from humid todry gas ventilation, the temperature of the expired gas decreased. Weevaluated the relationship between the inverse monoexponential timeconstant of the temperature fall (1/) and eitherE or . WhenE wasincreased from 5.67 ± 1.28 to 7.14 ± 1.60 (SD) l/min(P = 0.02), 1/ did not changesignificantly [from 1.25 ± 0.38 to 1.21 ± 0.51 min¹,P = 0.81]. In the 11 patients in whom changed during the study period(from 5.07 ± 1.81 to 7.38 ± 2.45 l/min,P = 0.02), 1/ increasedcorrespondingly from 0.89 ± 0.22 to 1.52 ± 0.44 min¹(P = 0.003). We calculated the airwaythermal volume (ATV) as the ratio of the measured values to 1/ and related it to the body height (BH):ATV (liters) = 0.086 BH (cm)  9.55 (r = 0.90).

     

Studies of the action of ceramide-like substances (d- andl-PDMP) on sphingolipid glycosyltransferases and purified lactosylceramide synthase

We have studied the effects ofD-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP) and itsL-enantiomer on glycosphingolipids in cultured normal human kidney proximal tubular cells. We found thatD-PDMP exerted a concentration-dependent reduction in the metabolic labelling and cellular levels of glucosylceramide (GlcCer), lactosylceramide (LacCer), and the globo-series glycosphingolipids, GbOse₃Cer and GbOse₄Cer. It also directly inhibited the activity of UDP-glucose:ceramide 1 4-glucosyltransferase (GlcT-1) and UDP-galactose: GlcCer 1 4 galactosyltransferase (GalT-2). In contrast,L-PDMP had opposite effects on the metabolic labelling of GlcCer, LacCer, and GbOse₃Cer. The levels of GlcCer and LacCer were increased, while the labelling and level of GbOse₄Cer were strongly reduced. Purified GalT-2 from human kidney was inhibited byD-PDMP and stimulated byL-PDMP. It appears likely that the different glycosphingolipid glycosyltransferases possess similar binding sites for the ceramide moiety, which are blocked by binding toD-PDMP and, in the case of GbOse₄Cer synthase, byL-PDMP as well. The stimulatory effects ofL-PDMP on GlcCer and LacCer synthases may be the result of binding to a modulatory site on the glycosyltransferases; in intact cells, the enzyme-analog complex may afford protection against the normal catabolic inactivation of the enzymes.Abbreviations GalT-2 UDP-galactose:GlcCer -galactosyltransferase - GbOse₃Cer Gal1 4Gal1 GlcCer - GbOse₄Cer GalNAc1 3Gal1 4Gal1 GlcCer - GlcCer glucosylceramide - GlcT-1 UDP-glucose:ceramide -glucosyltransferase - GSLs glycosphingolipids - LacCer lactosylceramide - PDMP threo-1-phenyl-2-decanolyamino-3-morpholino-1-propanol