Urea and water permeability in dogfish (Squalus acanthias) gills

We used a perfused gill preparation from dogfish to investigate the origin of low branchial permeability to urea. Urea permeability (14C-urea) was measured simultaneously with diffusional water permeability (3H2O). Permeability coefficients for urea and ammonia in the perfused preparation were almost identical to in vivo values. The permeability coefficient of urea was 0.032 x 10(-6) cm/sec and of 3H2O 6.55 x 10(-6) cm/sec. Adrenalin (1 x 10(-6) M) increased water and ammonia effluxes by a factor of 1.5 and urea efflux by a factor of 3.1. Urea efflux was almost independent of the urea concentration in the perfusion medium. The urea analogue thiourea in the perfusate had no effect on urea efflux, whereas the non-competitive inhibitor of urea transport, phloretin, increased efflux markedly. The basolateral membrane is approximately 14 times more permeable to urea than the apical membrane. We conclude that the dogfish apical membrane is extremely tight to urea, but the low apparent branchial permeability may also relate to the presence of an active urea transporter on the basolateral membrane that returns urea to the blood and hence reduces the apical urea gradient.     

Expression of a chitinase transgene in rose (Rosa hybrida L.) reduces development of blackspot disease (Diplocarpon rosae Wolf)

Blackspot, caused by the Ascomycete fungus Diplocarpon rosae, is the most widespread and pernicious disease of cultivated roses. While some species of rose possess resistance to D. rosae, none of the modern-day rose cultivars are fully resistant to the pathogen. In the current study, Biolistic gene delivery was used to introduce a rice gene, encoding a basic (Class I), chitinase into embryogenic callus of the blackspot-susceptible rose (Rosa hybrida L.) cv. Glad Tidings. The plasmid used for transformation carried the neomycin phosphotransferase (nptII) gene facilitating the selection and regeneration of transgenic plants on medium containing 250 mg/l kanamycin. Southern analysis confirmed integration of 2–6 copies of the chitinase gene into the rose genome; gene expression was confirmed by enzyme assay. Bioassays demonstrated that expression of the chitinase transgene reduced the severity of blackspot development by 13–43%. This degree of resistance to the pathogen correlated with the level of chitinase expression in the transgenic rose plants. The introduction of disease defence genes into rose provides a method of producing blackspot-resistant rose cultivars sought by breeders and growers.     

The effects of arginine vasotocin and catecholamines on nitrogen excretion and the cardio-respiratory physiology of the gulf toadfish, Opsanus beta

Simultaneous measurements of cardio-respiratory variables, oxygen uptake and whole body urea/ammonia/tritiated water effluxes were performed on cannulated gulf toadfish, Opsanus beta, before and after intra-arterial injection of the vasoactive agents, adrenaline, isoproterenol and arginine vasotocin. These experiments were conducted to test the hypothesis that the phenomenon of pulsatile urea excretion might reflect sudden changes in the general diffusive properties of the gill for solute transfer. Injection of isoproterenol (final nominal circulating level = 10⁻⁶ mol l⁻¹), was used as a tool to maximise the diffusive and perfusive conditions for branchial solute transfer. This protocol caused a pronounced reduction in arterial blood pressure, an elevation of cardiac frequency and associated increases in whole body urea and tritiated water effluxes; ammonia excretion and oxygen uptake were unaffected. Injection of adrenaline (final nominal circulating level=10⁻⁶ mol l⁻¹), caused a significant increase in arterial blood pressure and a tachycardia, yet nitrogen excretion and oxygen uptake were unaffected. Injection of arginine vasotocin, caused a dose-dependent (final nominal circulating levels = 10⁻¹¹–10⁻⁹ mol l⁻¹) increase in arterial blood pressure without affecting cardiac or ventilation frequency. At the two higher concentrations, arginine vasotocin caused large and transient increases in urea excretion without significantly affecting ammonia, water or oxygen fluxes. These results suggest that increased gill diffusive or perfusive conductance, while capable of augmenting urea efflux, cannot fully explain the sudden and massive increases in urea transfer associated with pulsatile urea excretion in toadfish. It is suggested that pulsatile urea excretion in this species may reflect a specific enhancement of urea excretion under the control of the neurohypophyseal hormone, arginine vasotocin. Accepted: 21 April 1998     

Evaluation of oat bran as a soluble fibre source. Characterization of oat β-glucan and its effects on glycaemic response

Oat β-glucan, present in oat bran in greater concentrations than in the whole oat groat, is mainly composed of β-(1 → 3)-linked cellotriosyl and cellotetraosyl units, present at 52 and 34% by weight of the molecule, respectively. The remaining structure consits of β-(1 → 3)-linked blocks composed of four or more consecutive β-(1 → 4)-linked -glucopyranosyl units. Size-exclusion chromatography indicated a molecular weight for oat β-glucan of 2–3 × 10⁶. This was significantly reduced during digestion in the small intestine of rats and chicks. In healthy human volunteers, oat β-glucan reduced the postprandial glucose response to an oral glucose load similarly to guar gum. The effectiveness of oat β-glucan was proportional to the logarithm of the viscosity of the solution fed.     

Gastrointestinal parasites of the chimpanzee population introduced onto Rubondo Island National Park,Tanzania

The release of any species into a novel environment can evoke transmission of parasites that do not normally parasitize the host as well as potentially introducing new parasites into the environment. Species introductions potentially incur such risks, yet little is currently known about the parasite fauna of introduced primate species over the long term. We describe the results of long‐term monitoring of the intestinal parasite fauna of an unprovisioned, reproducing population of chimpanzees introduced 40 years earlier (1966–1969) onto Rubondo Island in Lake Victoria, Tanzania, a non‐native habitat for chimpanzees. Two parasitological surveys (March 1997–October 1998 and October 2002–December 2005) identified Entamoeba spp. including E. coli, Iodamoeba buetschlii, Troglodytella abrassarti, Chilomastix mesnili, Trichuris sp., Anatrichosoma sp., Strongyloides spp., Strongylida fam. gen. sp., Enterobius anthropopitheci, Subulura sp., Ascarididae gen. sp., and Protospirura muricola. The parasite fauna of the Rubondo chimpanzees is similar to wild chimpanzees living in their natural habitats, but Rubondo chimpanzees have a lower prevalence of strongylids (9%, 3.8%) and a higher prevalence of E. anthropopitheci (8.6%, 17.9%) than reported elsewhere. Species prevalence was similar between our two surveys, with the exception of Strongyloides spp. being higher in the first survey. None of these species are considered to pose a serious health risk to chimpanzees, but continued monitoring of the population and surveys of the parasitic fauna of the two coinhabitant primate species and other animals, natural reservoir hosts of some of the same parasites, is important to better understand the dynamics of host–parasite ecology and potential long‐term implications for chimpanzees introduced into a new habitat. Am. J. Primatol. 72:307–316, 2010. © 2009 Wiley‐Liss, Inc.     

QUANTITATIVE GENETIC ANALYSIS OF MORPHOLOGICAL VARIATION IN AN ANTARCTIC DIATOM GROWN AT TWO LIGHT INTENSITIES1

Ten clonal isolates of Thalassiosira tumida (Janisch) Hasle were grown in duplicate semi-continuous batch cultures at 116 and 11.6 μE.m⁻².s⁻¹; acclimated cells were harvested during exponential growth and cleaned for examination by light microscopy (LM) and scanning electron microscopy (SEM). Number of strutted processes surrounding the central annulus (SP) and average number of satellite pores per process (AVSAT) were counted using SEM on 20 valves from each culture grown in high light, for a total of 400 valves examined; number of marginal labiate processes (LP) and overall diameter (DIAM) were measured using LM on 20 valves from each culture grown in both high and low light for a total of 800 valves examined. Univariate analysis of variance showed that bottle effects resulting from microenvironmental differences between replicates were a small but significant source of variation in DIAM, LP, and SP but not AVSAT. Significant differences among clones were observed for all characters. Decreased irradiance resulted in a significant decrease in valve diameter but no significant effect on LP; no light x clone interaction was obsered. Significant covariance between characters among clones was also observed; since valve diameter is known to decrease during asexual growth, the correlation coefficients for SP, AVSAT, and LP with DIAM were used to correct the data for this source of nongenetic differences between clones. Analysis of the size-corrected data showed that the proportion of total phenotypic variance in SP, LP, and AVSAT caused by genetic differences among clones was 0.14, 0.14, and 0.30, respectively. This indicates that the majority of total phenotypic variance was due to environmental or developmental causes, but that sufficient genetic variability exists to support rapid phenotypic evolution in SP, LP, and AVSAT under continued directional selection. Finally, the results of the genetic analysis revealed a high (0.82) genetic correlation between SP and LP.