Isolation and characterization of <Emphasis Type="Italic">Arabidopsis</Emphasis> mutants with enhanced tolerance to oxidative stress

We have previously reported a method for isolation of mutants with enhanced tolerance to the fungal AAL toxin and given a detailed characterization of atr1 (AAL toxin resistant, Gechev et al. in Biochem Biophys Res Commun 375:639–644, 2008). Herewith, we report eight more mutants with enhanced tolerance to the AAL toxin. Phenotypic analysis showed that six of the mutants were reduced in size compared with their original background loh2. Furthermore, atr2 showed delayed flowering and senescence. The mutants were also evaluated for oxidative stress tolerance by growing them on ROS-inducing media supplemented with either aminotriazole or paraquat, generating, respectively, H₂O₂ or superoxide radicals. Oxidative stress, confirmed by induction of the marker genes, HIGH AFFINITY NITRATE TRANSPORTER At1G08090 and HEAT SHOCK PROTEIN 17 At3G46230, inhibited growth of all lines. However, while the original background loh2 developed necrotic lesions and died rapidly on ROS-inducing plant growth media, atr1, atr2, atr7 and atr9 remained green and viable. The tolerance against oxidative stress-induced cell death was confirmed by fresh weight and chlorophyll measurements. Real-time PCR analysis revealed that the expression of the EXTENSIN gene At5G46890, previously shown to be downregulated by aminotriazole in atr1, was repressed in all lines, consistent with the growth inhibition induced by oxidative stress. Taken together, the data indicate a complex link between growth, development and oxidative stress tolerance and indicates that growth inhibition can be uncoupled from oxidative stress-induced cell death.     

Inferring temperature adaptation from thermal performance curves of somatic growth rate: The importance of growth measurements and mortality

When comparing somatic growth thermal performance curves (TPCs), higher somatic growth across experimental temperatures is often observed for populations originating from colder environments. Such countergradient variation has been suggested to represent adaptation to seasonality, or shorter favourable seasons in colder climates. Alternatively, populations from cold climates may outgrow those from warmer climates at low temperature, and vice versa at high temperature, representing adaptation to temperature. Using modelling, we show that distinguishing between these two types of adaptation based on TPCs requires knowledge about (i) the relationship between somatic growth rate and population growth rate, which in turn depends on the scale of somatic growth (absolute or proportional), and (ii) the relationship between somatic growth rate and mortality rate in the wild. We illustrate this by quantifying somatic growth rate TPCs for three populations of Daphnia magna where population growth scales linearly with proportional somatic growth. For absolute somatic growth, the northern population outperformed the two more southern populations across temperatures, and more so at higher temperatures, consistent with adaptation to seasonality. In contrast, for the proportional somatic growth TPCs, and hence population growth rate, TPCs tended to converge towards the highest temperatures. Thus, if the northern population pays an ecological mortality cost of rapid growth in the wild, this may create crossing population growth TPCs consistent with adaptation to temperature. Future studies within this field should be more explicit in how they extrapolate from somatic growth in the lab to fitness in the wild.     

Thyroxine as a Mediator of Metamorphosis of Atlantic Halibut, Hippoglossus Hippoglossus

The response of morphological, histological and endocrinological development to exogenous 1-thyroxine (T₄) and to water depth during metamorphosis in Atlantic halibut, Hippoglossus hippoglossus, was investigated. Exogenous T₄ was given in daily doses of 0.1, 0.05 ppm or a control treatment to halibut larvae at 550 daydegrees (posthatch, premetamorphic) for 14 days. Water depths of 40 cm, 10 cm or 1.5 cm were used to rear halibut larvae from 590 daydegrees for 21 days. Halibut larvae given exogenous T₄ at 0.1 ppm had accelerated eye migration relative to MH in fish given 0.05 ppm and in control fish. Pigmentation was correlated with dosage after 14 days. The volume of thyroid tissue was expressed in a dose-dependent manner and exhibited a size-dependency within each treatment. However, the follicles were atypical with reduced colloid, increased lumen and low epithelial cells even in the control group. The results indicate that T₄ is a mediator in halibut metamorphosis. In the water depth experiment, only cortisol levels of larvae reared in 1.5 cm water were significantly affected after 21 days, but this was not correlated with metamorphic rate. Hormone profiles, morphological changes and size suggest the existence of a window of opportunity for metamorphosis in halibut extending from about 16 mm and tapering off about 21 mm SL. The pooled hormone profiles indicate the commencement of a hormonal cascade similar to that of other flatfishes during metamorphosis. The results indicate that growth, neural and skeletal transformation, and pigmentation are biochemically separate processes in the metamorphosis of Atlantic halibut.     

A literature review of the blood chemistry of rainbow trout, Salmo gairdneri Rich.

The literature on the blood chemistry of rainbow trout, Salmo gairdneri Rich., is reviewed from the aspects of experimental methods, electrophoresis, normal values, environmental and endogenous factors including toxic substances and diseases.     

Triiodothyronine (T3)-mediated toxicity and induction of apoptosis in insulin-producing INS-1 cells

Thyroid hormones reduce glucose tolerance in humans and animals. This effect is related to a decrease of glucose-induced insulin secretion following a reduction of pancreatic beta cell mass due to beta cell loss. The aim of this study was to analyze in vitro the mechanisms underlying the effects of triiodothyronine (T(3)) on the cell viability and cell cycle caused by changes of cell death or proliferation rate of insulin-producing INS-1 cells. 72-h Exposure of INS-1 cells to increasing T(3) concentrations up to 500 microM resulted in a significant viability reduction. This T(3) toxicity was caused by an increased apoptotic cell death rate, which was accompanied by a decreased proliferation rate. Inhibitory effects of T(3) on glucose-induced insulin secretion were already seen after 24 h of incubation, indicating that the deleterious effects of T(3) were time-dependent, changing from specific cellular dysfunctions to a severe and extended disturbance of the cellular survival program. Only T(3) concentrations higher than 250 microM were able to decrease cell viability and proliferation rate, to increase the rate of apoptosis and to reduce glucose-induced insulin secretion. These micromolar T(3) concentrations were significantly higher than the concentration range of T(3) receptor binding, indicating that other non-receptor-mediated mechanisms beyond the receptor level must be responsible for the observed toxic effects of T(3) in vitro.     

Differential effects of proinflammatory cytokines on cell death and ER stress in insulin-secreting INS1E cells and the involvement of nitric oxide

Proinflammatory cytokines produced by immune cells destroy pancreatic beta cells in type 1 diabetes. The aim of this study was to investigate the cytokine network and its effects in insulin-secreting cells. INS1E cells were exposed to different combinations of proinflammatory cytokines. Cytokine toxicity was estimated by MTT assay and caspase activation measurements. The NFκB-iNOS pathway was analyzed by a SEAP reporter gene assay, Western-blotting and nitrite measurements. Gene expression analyses of ER stress markers, Chop and Bip, were performed by real-time RT-PCR. Cytokines tested in this study, namely IL-1β, TNFα and IFNγ, had deleterious effects on beta cell viability. The most potent toxicity exhibited IL-1β and its combinations with other cytokines. The toxic effects of IL-1β towards cell viability, caspase activation and iNOS activity were dependent on nitric oxide and abolished by an iNOS blocker. IL-1β was the strongest inducer of the NFκB activation. An iNOS blocker inhibited IL-1β-mediated NFκB activation in the first, initial phase of cytokine action, but did not affect significantly NFκB activation after prolonged incubation. Interestingly iNOS protein expression was induced predominantly by IL-1β and decreased in the presence of an iNOS blocker in the case of a short time exposure. The changes in the expression of ER stress markers were also almost exclusively dependent on the IL-1β presence and counteracted by iNOS blockade. Thus cytokine-induced beta cell death is primarily IL-1β mediated with a NO-independent enhancement by TNFα and IFNγ. The deleterious effects on cell viability and function are crucially dependent on IL-1β-induced nitric oxide formation.     

Das Moorschneehuhn (Lagopus lagopus subspec.) im Winter in Transkaukasien

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