Concurrent measurement of (Na+,K+)-ATPase activity and lipid peroxides in rat brain following reversible global ischemia

Lipid peroxides, quantitated as lipid conjugated dienes, and (Na⁺,K⁺)-ATPase activity were assayed concurrently in brains of control rats and in three groups subjected to 30 min of reversible forebrain ischemia followed by 0, 1, and 4 hr of recirculation. Multiple small samples were taken from lateral, dorsolateral and medial cortex, hippocampus, thalamus and striatum following in situ freezing. (Na⁺,K⁺)-ATPase activity was elevated in hippocampus, dorsolateral and lateral cortex (P<0.10) and in thalamus (P<0.05) following 30 min ischemia. ATPase activity in medial cortex continued to increase during the first 1 hr of recirculation (P<0.10). Following 4 hr of recirculation, decreased enzyme activities were observed in all of these regions (lateral cortex and hippocampus,P<0.10). No changes in ATPase activity were observed in samples from striatum. Of the regional samples assayed for lipid peroxide content, the incidence of conjugated dienes as a function of recirculation time was 6% (0 hr), 23% (1 hr), and 17% (4 hr). For these samples, plots of normalized ATPase activity vs. tissue conjugated diene concentration revealed that normalized ATPase activity varied with recirculation time, but was independent of the magnitude of the lipid peroxidative process (expressed in terms of tissue conjugated diene concentration). These results suggest that disturbances in membrane structure and function presumed to arise from lipid peroxidation are not responsible for the behavior of the ATPase under the current in vivo conditions.     

The mechanistic,genetic and evolutionary causes of bird eye colour variation

Birds display a rainbow of eye colours, but this trait has been little studied compared with plumage coloration. Avian eye colour variation occurs at all phylogenetic scales: it can be conserved throughout whole families or vary within one species, yet the evolutionary importance of this eye colour variation is under-studied. Here, we summarize knowledge of the causes of eye colour variation at three primary levels: mechanistic, genetic and evolutionary. Mechanistically, we show that avian iris pigments include melanin and carotenoids, which also play major roles in plumage colour, as well as purines and pteridines, which are often found as pigments in non-avian taxa. Genetically, we survey classical breeding studies and recent genomic work on domestic birds that have identified potential ‘eye colour genes’, including one associated with pteridine pigmentation in pigeons. Finally, from an evolutionary standpoint, we present and discuss several hypotheses explaining the adaptive significance of eye colour variation. Many of these hypotheses suggest that bird eye colour plays an important role in intraspecific signalling, particularly as an indicator of age or mate quality, although the importance of eye colour may differ between species and few evolutionary hypotheses have been directly tested. We suggest that future studies of avian eye colour should consider all three levels, including broad-scale iris pigment analyses across bird species, genome sequencing studies to identify loci associated with eye colour variation, and behavioural experiments and comparative phylogenetic analyses to test adaptive hypotheses. By examining these proximate and ultimate causes of eye colour variation in birds, we hope that our review will encourage future research to understand the ecological and evolutionary significance of this striking avian trait.     

Seagrass-salinity interactions: Physiological mechanisms used by submersed marine angiosperms for a life at sea

Due to the nature of coastal and estuarine systems, seagrasses must be able to tolerate short-term salinity fluctuations including both hyposaline and hypersaline conditions. Salt tolerance can be achieved, in part, through vacuolar ion sequestering (mostly Na⁺, K⁺, and Cl⁻) and cytosolic osmolyte accumulation (K⁺ and organic osmolytes), with differences in cellular ion levels attributed to selective ion flux and ion partitioning between the cytoplasm and vacuole (with lower cytoplasmic-to-vacuolar ratios favoring higher cellular Na⁺ concentrations). The hydrophilic nature of organic compounds such as organic acids, soluble carbohydrates, and free amino acids allow them to serve as osmoprotectants and low-molecular-weight chaperones which diminishes the inhibitory effects of potentially harmful ions on metabolic processes. Nevertheless, some carbohydrate studies on seagrasses have shown decreased soluble sugar content with increased salinities. During salt stress, carbohydrates are likely converted to other organic compounds that would better facilitate osmotic adjustment in these plants. This is further supported by observed decreases in sucrose-P synthase (a key enzyme involved in sucrose synthesis) activities in seagrass exposed to higher salinities. While modifications in ion flux and organic solute levels often follow changes in environmental salinities, these adjustments are relatively slow (hours to days). Therefore, the initial response to sudden salinity change will include rapid alterations in turgor pressure driven by water flux in the direction of the osmotic gradient. The rate of water movement depends largely on the hydraulic conductivity of the plasmalemma and the elastic properties of the cell wall (bulk elastic modulus; Є). Observations on cell wall elasticity indicate that some seagrasses maintain fairly rigid walls (high Є values), thereby limiting the amount of water influx during hypoosmotic stress. Although high Є would be beneficial to open-water coastal plants living in relatively stable saline environments, in estuaries where salinities fluctuate considerably over shorter intervals, high Є could promote flaccid cells with no turgor pressure during hyperosmotic conditions. Hypo- and hyperosmotic conditions also inhibit photosynthesis in seagrasses. Decreases in photosynthesis have been attributed to declines in chlorophyll content, changes in chloroplast ultrastructure, disruptions of electron flow through photosystems, and inhibitions of key photosynthetic enzymes. The uptake of nutrients can also be strongly influenced by salinity. High affinity Na⁺-dependent nutrient transport systems (for NO₃⁻, H₂PO₄⁻, and HPO₄⁻²) which benefit from the inwardly driving force for Na⁺ have been observed in seagrasses. Nitrate reductase, the key enzyme involved in nitrate reduction/ assimilation, also has elevated activities at higher salinities which would agree with Na⁺-dependent NO₃⁻ transport. While our basic understanding of how seagrasses survive in saline environments is increasing, it still lags well behind marine algae and terrestrial halophytes. It is likely that further investigations will reveal unique physiological adaptations that have not been observed in other plants.     

Hidden Structural Modules in a Cooperative RNA Folding Transition

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More than 1000 ultraconserved elements provide evidence that turtles are the sister group of archosaurs

We present the first genomic-scale analysis addressing the phylogenetic position of turtles, using over 1000 loci from representatives of all major reptile lineages including tuatara. Previously, studies of morphological traits positioned turtles either at the base of the reptile tree or with lizards, snakes and tuatara (lepidosaurs), whereas molecular analyses typically allied turtles with crocodiles and birds (archosaurs). A recent analysis of shared microRNA families found that turtles are more closely related to lepidosaurs. To test this hypothesis with data from many single-copy nuclear loci dispersed throughout the genome, we used sequence capture, high-throughput sequencing and published genomes to obtain sequences from 1145 ultraconserved elements (UCEs) and their variable flanking DNA. The resulting phylogeny provides overwhelming support for the hypothesis that turtles evolved from a common ancestor of birds and crocodilians, rejecting the hypothesized relationship between turtles and lepidosaurs.     

An investigation of pectin and pectic acid in dilute aqueous solution

Light-scattering measurements have been carried out on carefully clarified aqueous solutions of pectin and pectic acid. The strong dependence of the inverse excess scattering intensity on angle yields pectin chain dimensions that are inconsistent with the complete molecular dispersion of pectin molecules possessing the degrees of polymerization indicated by the measured osmotic molecular weights. Negligible or negative concertration dependences of the inverse scattering intensities coupled with the centrifugation, filtration, and gel permeation chromatography behavior of the samples likewise suggest nonequilibrium aggregation of the pectin molecules in solution. It is shown that the measured mean polymer chain dimensions can be rationalized in terms of the presence of a very small proportion of aggregated material.