The effect of stocking rate and supplementary selenium on the fatty acid composition and subsequent peroxidisability of poultry muscle tissues

Selenium (Se) plays a crucial role in protecting biological materials from oxidative damage through the action of the selenoprotein glutathione peroxidase (GSH-Px), and the effectiveness of this protection is often dependent upon Se supply. Recent evidence has indicated that GSH-Px mRNA expression can be upregulated in response to potential oxidative damage risk, and that this upregulation is independent of Se supply. The current study aimed to determine the effect of Se supplementation, stocking rate and tissue fatty acid profile on GSH-Px activity in breast and thigh tissue of commercial broilers. A total of 168 Ross 308 broiler chicks were enrolled onto the study. Prior to enrolment, birds were brooded as a single group and received a starter diet containing no additional Se. The study was a 2 × 2 factorial design comprising of two levels of dietary Se (high Se, 0.5 mg/kg total Se, low Se background Se only), and two stocking rates (high, 30 kg/m², and low, 15 kg/m²). At 15 days of age, birds were blocked by live weight and randomly allocated to one of the four treatments, with six pen replicates per treatment. At 42 days of age, one bird was randomly selected from each pen replicate, euthanased and breast and thigh tissue harvested. GSH-Px activity, thiobarbituric acid reactive substances (TBARS), and fatty acid (FA) content of these tissues were determined. There was no effect (P > 0.05) of stocking rate on GSH-Px activity or TBARS. GSH-Px activity did not differ between tissue types but was greater in high Se birds (P < 0.001) compared to low Se. TBARS concentrations were greater in thigh tissue (P < 0.001), and these thigh concentrations were greater in high Se birds (P < 0.05). There were marked differences between breast and thigh tissue in most FAs (P < 0.001), with breast generally containing greater proportions of polyunsaturated FA, so that breast tissue had a higher (P < 0.001) peroxidisability index (PI) than thigh. A positive correlation between GSH-Px activity and PI in the thigh tissue of high Se birds (Pearson Correlation 0.668; P = 0.025) may indicate that increasing susceptibility to peroxidisation in lipid-rich tissues may also upregulate GSH-Px activity in Se-replete birds. This study suggests that ensuring adequate dietary selenium could be a useful tool to mitigate adverse effects on meat quality caused by oxidation, particularly in lipid-rich meat.     

Some speculations on the possible roles of the plasmodesmata in the control of differentiation

Most plasmodesmata are formed across the cell plate at cytokinesis. Most of them persist until the cell is mature. Depending upon the pattern of elongation of the cell in differentiation, the frequency of plasmodesmata per unit area will suffer dilution to a greater or lesser extent. This dilution effect is now well understood and results commonly in high concentrations of plasmodesmata across transverse walls which have undergone little elongation and low concentrations on the longitudinal walls.Apart from their obvious role in cell to cell communication it is now believed that some plasmodesmata may offer preferential sites from which endogenous wall lytic enzymes may attack some or all of the constituent polymers of the surrounding wall. The effects of the asymmetrical distribution of large numbers of plasmodesmata, leading to the asymmetrical penetration of the wall by lytic enzymes are described and a hypothesis concerning the later stages of cell differentiation is constructed. In addition the late stage differentiation of individual plasmodesmata based on the same proposed lytic action, is described and re-interpreted.     

Hydrothermal vent protistan distribution along the Mariana arc suggests vent endemics may be rare and novel

Elucidation of the potential roles of single-celled eukaryotes (protists) in ecosystem function and trophodynamics in hydrothermal vent ecosystems is reliant on information regarding their abundance, distribution and preference for vent habitats. Using high-throughput 18S rRNA gene sequencing on a diverse suite of hydrothermally influenced and background water samples, we assess the diversity and distribution of protists and identify potential vent endemics. We found that 95% of the recovered sequences belong to operational taxonomic units (OTUs) with a cosmopolitan distribution across vent and non-vent habitats. Analysis of ‘vent only’ OTUs found in more than one vent sample and co-occurrence network analysis comparing protist groups to extremophilic reference organisms suggest that the most likely vent endemics are infrequently encountered, potentially in low abundance, and belong to novel lineages, both at the phylum level and within defined clades of Rhizaria and Stramenopila. Potential endemism is inferred for relatives of known apusomonads, excavates and some clades of Syndiniales. Similarity in community composition among samples was low, indicating a strong stochastic component to protist community assembly and suggesting that rare endemics may serve as a reservoir poised to respond to changing environmental conditions in these dynamic systems.     

Effect of resistive loading on ventilatory response to hypoxia.

Ventilatory responses to hypoxia, with and without an inspiratory resistive load, were measured in eight normal subjects, using a rebreathing technique. During the studies, the end-tidal P-CO2 was kept constant at mixed venous level (Pv-CO2) by drawing expired gas through a variable CO2-absorbing bypass. The initial bag O2 concentration was 24% and rebreathing was continued until the O2 concentration in the bag fell to 6% or the subject's arterial oxygen saturation (Sa-O2), monitored continuously by ear oximetry, fell to 70%. Studies with and without the load were performed in a formally randomized order for each subject. Linear regressions for rise in ventilation against fall in Sa-O2 were calculated. The range of unloaded responses was 0.78-3.59 1/min per 1% fall in Sa-O2 and loaded responses 0.37-1.68 1/min per 1% fall in Sa-O2. In each subject, the slope of the response curve during loading fell by an almost constant fraction of the unloaded response, such that the ratio of loaded to unloaded slope in all subjects ranged from 0.41 to 0.48. However, the extrapolated intercept of the response curve on the Sa-O2 axis did not alter significantly indicating that the P-CO2 did not alter between experiments. These results suggest that the change in ventilatory response to hypoxia during inspiratory resistive loading is related to the mechanical load applied, with the loaded slope being directly proportional to the unloaded one.     

The plasma membrane of young Chara internodal cells revealed by rapid freezing

Young elongating internodal cells of Chara globularis var. capillacea (Thuill.) Zanev. were rapidly frozen and freze-fractured in order to observed transient events occurring within the plasma membrane. Several structures have been observed. Relatively small depressions, varying in depth, are prolific and scattered at random over the plasma membrane. Charasomes and clusters of particle rosettes are common. Arrays of intramembrane particle lines are a characteristic feature of the internodal cell plasma membrane. The charasomes and the arrays of particle lines occupy a considerable proportion of the plasma membrane. In these young cells, substantial movement must take place across this membrane and its basic structure must fluctuate accordingly. The innumerable small depressions may represent pinocytotic and secretory processes. The array of intramembrane particle lines may represent stages in fusion between the membranes of vesicles within the cytoplasm and the plasma membrane. The technique of ultra-rapid freezing allows these events and their intermediate stages to be visualised; some features of the membrane may only be seen by this method.     

Directional secretion by the Golgi bodies in maize root cells

Summary In the root caps of many plant species, the outer few layers of cells secrete a polysaccharide mucus. This mucus probably derives from the breakdown of the starch in the amyloplasts. Is then fed through the Golgi bodies and, in vesicular form, reaches and is discharged through the plasmamembrane. Once in the wall it accumulates briefly between the plasmalemma and the wall and finally passes through the wall to the outside of the root. Its function is probably to facilitate the passage of the root through the soil by lubricating the movement of the root tip around and between the soil particles. Our observations show that the pattern of this discharge is not random, but that the mucus accumulates only against that wall which is or will be the outer tangential. The implication of this directional movement and possible suggestions for its control are discussed.     

High voltage electron microscopy of cytoskeletal structures in whole plant cells

During the past decade, work on whole, critical-point dried animal cells has revealed a three-dimensional meshwork, the microtrabecular lattice or cytomatrix, which pervades the ground cytoplasm. This work was carried out on cells which could be spread out into thin layers on support films. Plant cells provide a more difficult problem since their rigid cell walls do not allow them to be spread into thin layers. Nevertheless high-voltage electron microscopy at up to 2.5 MeV permits examination of whole cells up to 30 μm thick, though both preparation and interpretation present problems. In algal cells flagellar roots and associated structures can be seen in three dimensions, while cells of mosses, ferns and lycopods show a cytomatrix of fine interconnecting filaments.