Lack of causal relationship between clusterin expression and photoreceptor apoptosis in light-induced retinal degeneration

Induction of apoptosis in the retina leads to cellular death by molecular mechanisms that are not well understood. Clusterin expression is increased in tissues undergoing apoptosis, including retinal neurodegenerative states, but the causal relationships remain to be clarified. To gain insight into clusterin's role in photoreceptor apoptosis, the cellular distribution of clusterin mRNA was compared with the pattern of apoptotic nuclear labelling in a rat model of light-induced retinal degeneration. In control retinal sections, clusterin mRNA was localized to the retinal pigment epithelium cells, photoreceptor inner segments, inner nuclear layer, and ganglion cell layer. Clusterin expression decreased in photoreceptors and retinal pigment epithelium cells, which progressively degenerated, and increased in preserved inner nuclear layer, in proportion to the duration of light exposure in both cyclic light- and dark-reared animals. These results suggest that clusterin is not causally involved in apoptotic mechanisms of photoreceptor death, but may relate to cytoprotective functions.     

Superhelical DNA studied by solution scattering and computer models

We present here recent results on the structure of superhelical DNA and its changes with salt concentration between 0.01 and 1.5 M NaCl. Scattering curves of two different superhelical DNAs were determined by static light scattering. The measured radii of gyration do not change significantly with salt concentration. Small-angle neutron scattering, together with calculations from a Monte Carlo model, allows to determine the superhelix diameter. Measured and simulated scattering curves agreed almost quantitatively. Experimentally we find that the diameter decreases from 16.0±0.9 nm at 10 mM to 9.0±0.7 nm at 100 mM NaCl. The superhelix diameter from the simulated conformations decreased from 18.0±1.5 nm at 10 mM to 9.4±1.5 nm at 100 mM NaCl. At higher salt concentrations up to 1.5 M NaCl, the diameter stays constant at 9 nm.This revised version was published online in October 2005 with corrections to the Cover Date.     

Factors affecting the dissociation and aggregation of human interferon gamma

The biologically active form of interferon γ (IFN-γ) is a dimer consisting of two identical non-covalently bound polypeptide chains. We have studied spectroscopically the dimer–monomer dissociation equilibrium of human recombinant IFN-γ and have found that the monomers possess approximately 50% lower Trp quantum yield than the dimers [Boteva et al. Biochemistry 1996;35:14825]. In the present study we characterise the conformational properties of the two states — monomeric and dimeric, and analyse the effects of the salt composition of human blood plasma, physiological cations K⁺, Na⁺, Ca²⁺ and Mg²⁺ and mechanical stress on the dimer–monomer equilibrium. A medium with electrolyte composition of human blood plasma increases both the association and dissociation rate constants without shifting significantly the dimer–monomer equilibrium. The physiological cations shift the equilibrium towards dissociation of dimers into monomers by lowering the activation energy and the free energy of the process thus decreasing the stability of IFN-γ. Mechanical stress caused by stirring of the protein solution reduces irreversibly the Trp fluorescence by 75–80% and decreases significantly the -helical content and favours the aggregation.     

Thermoregulatory responses in humans during exercise after exposure to two different light intensities

The effects after exposure to two different light intensities (dim, 50 lx and bright, 5000 lx) on thermoregulatory responses during exercise in a climatic chamber (27 degrees C, 60% relative humidity) were studied in nine untrained female subjects, aged 19-22 years. The subjects were in either the dim or bright light intensities from 0600 hours to 1200 hours. They were then instructed to exercise on a cycle ergometer at an intensity of 60% maximal oxygen uptake from 1200 hours to 1300 hours in a light intensity of 500 Ix. The main results can be summarized as follows. Firstly, exercise-induced increases of core temperature were significantly smaller, after exposure to the bright than after the dim light intensities, although both tests were performed in the same light intensity. Secondly, body mass loss after exercise was significantly greater after exposure to the bright light intensity. Thirdly, an increase in salivary lactic acid during exercise was significantly lower after the bright intensity. Fourthly although the salivary melatonin level was not different between the two light intensities both before and after the exercise, it increased significantly during exercise only after the bright intensity. These results are discussed in terms of the establishment of a lower set-point in the core temperature after exposure to a bright light intensity.     

Modeling the vertical foliage distribution of an individual <Emphasis Type="Italic">Castanopsis cuspidata</Emphasis> (Thunb.) Schottky,a dominant broad-leaved tree in Japanese warm-temperate forest

The vertical foliage distribution of Castanopsis cuspidata (Thunb.) Schottky was examined in trees of various sizes to clarify its variation in relation to tree size and the light environment in a stand. As indices of these parameters, we analyzed crown social position (CSP: percent of stand height) and specific leaf area (SLA). The vertical foliage distribution of trees was expressed by a Weibull function. The variation in the vertical foliage distribution of C. cuspidata could be categorized into three types using crown social position and light environment. In the first type, leaves were concentrated to the top 20% of the tree; such trees are canopy trees that can receive full sunlight. The second type had a large relative crown depth and an asymmetric distribution with the maximum foliage located near the top of the tree; such trees are suppressed trees whose crowns do not receive sufficient light. The third type had a large relative crown depth and a symmetric distribution; such trees occur in high light environments, although their crowns are in the understory layer. The differences in the vertical foliage distribution are related to the strategies used to capture light. Multiple regression analysis showed that CSP and SLA at the top layer of the tree explained successive changes in the vertical foliage distribution. These results will contribute to scaling-up the vertical foliage distribution to the community level in pure stands of C. cuspidata using an individual-based model.     

Effect of light on the organogenic ability of garlic roots using a one-step in vitro system

A simple and efficient garlic in vitro shoot regeneration protocol has been developed. This system uses axenic root tips cultivated from the beginning in the presence of light and does not require any change or refreshing of the original medium during the entire process. The application of light from the beginning of the culture process did not affect the callus formation rate but did significantly improve the explant regeneration ability. In a 2-month period it was possible to obtain up to 250 shoots per gram of callus.Abbreviations BAP: 6-Benzylaminopurine - 2,4-D: 2,4-Dichlorophenoxyacetic acid - NAA: -Naphthaleneacetic acid Communicated by L. Peña     

Photoinhibition and recovery in a herbicide-resistant mutant from<Emphasis Type="Italic"> Glycine max</Emphasis> (L.) Merr. cell cultures deficient in fatty acid unsaturation

Photoinhibition and recovery were studied in two photosynthetic cell suspensions from soybean (Glycine max L. Merr): the wild type (WT) and the herbicide-resistant D1 mutant STR7. This mutant also showed an increase in saturated fatty acids from thylakoid lipids. STR7 was more sensitive to photoinhibition under culture conditions. In vivo photoinhibition experiments in the presence of chloramphenicol, in vitro studies in isolated thylakoid membranes, and immunoblot analysis indicated that the process of light-induced degradation of the D1 protein was not involved in the response of STR7 to light. At growth temperature (24°C), the recovery rate of photoinhibited photosystem II (PSII) was slower in STR7 relative to WT. Photoinhibition and recovery were differentially affected by temperature in both cell lines. The rates of photoinhibition were faster in STR7 at any temperature below 27°C. The rates of PSII recovery from STR7 were more severely affected than those of WT at temperatures lower than 24°C. The photoinhibition and recovery rates of WT at 17°C mimicked those of STR7 at 24°C. In organelle translation studies indicated that synthesis and elongation of D1 were substantially similar in both cell lines. However, sucrose gradient fractionation of chloroplast membranes demonstrated that D1 and also other PSII proteins such as D2, OEE33, and LCHII had a reduced capability to incorporate into PSII to yield a mature assembled complex in STR7. This effect may become the rate-limiting step during the recovery of photoinhibited PSII and may explain the increased sensitivity to high light found in STR7. Our data may hint at a possible role of fatty acids from membrane lipids in the assembly and dynamics of PSII.Abbreviations DCBQ 2,6-Dichloro p-benzoquinone - DM Dodecyl--d-maltoside - DTT Dithiothreitol - HL High light - LHCII Light-harvesting complex II - LL Low light - OEE Oxygen-evolving extrinsic proteins - PAGE Polyacrylamide gel electrophoresis - PG Phosphatidylglycerol - PSII Photosystem II - Q_A and Q_B Secondary quinone electron acceptors from PSII - RC Reaction center - SDS Sodium dodecyl sulfate - WT Wild type     

In vitro assay and light regulation of nitrate reductase in red alga Gracilaria chilensis

Nitrate reductase (NR) is the first enzyme in the nitrogen assimilation pathway. The in vitro NR activity of Gracilaria chilensis was assayed under different conditions to reveal its stability and biochemical characteristics, and an optimized in vitro assay is described. Maximal NR activities were observed at pH 8.0 and 15 degrees C. The apparent Km value for NADH was 8 microM and for nitrate 680 microM. Crude extracts of G. chilensis stored at 4 degrees C showed a 50% decrease of NR activity after 24 h. The highest NR activity value (253.20+/-2.60 x 10(-3) U g(-1)) was obtained when 100% von Stosch medium (500 microM NO3-) was added before extraction of apical parts. Algae under light:dark cycles of 12:12h exhibited circadian fluctuation of NR activity and photosynthesis with more than 2 times higher levels in the light phase. No evidence of endogenous diel rhythm controlling NR activity or photosynthesis was observed. Light pulses lasting 10 or 60 min during the darkness increased the NR activity by 30% and 45%, respectively. The results indicate that NR and photosynthesis are regulated mainly by light and not by a biological clock.     

Modulation of pigment profiles of Calothrix elenkenii in response to environmental changes

Cyanobacteria are versatile tetrapyrrole synthesizers that can regulate their tetrapyrrole content and composition in response to environmental signals. The present investigation analyses the interplay between light and dark regimes (continuous light, light-dark cycles (16:8) and continuous darkness) and aerobic, air-tight, and anaerobic environments (argon-enriched), on the relative composition of various pigments and growth attributes of Calothrix elenkenii as a prelude to exploiting C. elenkenii's bioindustrial potential as a source of pigments. Incubation in an anaerobic environment stimulated hormogonia formation and induced colouration/thickening of cells. Aerobically grown cultures of Calothrix, under continuous illumination produced the maximum amount of total phycobiliproteins and sugars, although chlorophyll accumulation and nitrogenase activity were highest in the light-dark environment. However, the beta-carotene content was observed to vary under anaerobic conditions with different light-dark regimes. This C. elenkenii strain can be a valuable source of pigments under optimized environmental conditions.