Seasonal and diurnal variations in ultraviolet-B and ultraviolet-A irradiances at and below the sea surface at Helgoland (North Sea) over a 6-year period

Ultraviolet (UV) radiation at four wavelengths (305, 320, 340 and 380 nm) and photosynthetically active radiation (PAR) were measured from May 1994 to October 1999 using Biospherical UV radiometers. A surface reference sensor located on the roof of the Marine Station at Helgoland recorded values every 5 min, and an equivalent profiling underwater sensor was used for measurements in the sea at approximately monthly intervals. The ratio of 305-nm radiation to PAR varied seasonally, with a 14-fold increase from winter to summer. A much weaker seasonal trend (ca. 1.5-fold) was apparent in the ratio of 320-nm radiation to PAR, but there was no seasonal trend in the ratios of 340- or 380-nm radiation to PAR. The year-to-year variations in 305-nm radiation were also much greater relative to PAR than for the other UV wavelengths, but there was no evidence of a change in the 305 nm:PAR ratio over the study period. The ratios of both 305- and 320-nm radiation to PAR increased from dawn to midday, but those of 340- and 380-nm radiation were almost constant through the day, except shortly before sunrise and after sunset when the proportions of 340- and 380-nm radiation increased. Underwater measurements of PAR and UV suggest that the 1% depth for 305-nm radiation was little more than 1 m, but this estimate is valid only for summer and autumn because, in other seasons, few reliable readings for 305-nm radiation could be obtained underwater, and no attenuation coefficient could be calculated. The 1% depths recorded for the other UV wavelengths in the middle 6 months of the year were 2.0 m for 320 nm, 2.6 m for 340 nm and 4.6 m for 380 nm, compared with 12 m for PAR, but the attenuation of all wavebands increased sharply in October and remained higher until March. An analysis of the influence of sun angle, total column ozone concentration, the proportion of skylight, and cloud cover on the ratio of UV wavelengths to PAR in surface irradiance demonstrated that solar angle has a greater influence than ozone concentration on the irradiance at 305 nm, and that the typical occurrence of ozone "holes" in spring may not result in higher UV-B irradiances than occur under higher ozone concentrations in summer. The implications of the data for attempts to model the biological effects of natural UV radiation on marine organisms are considered. Received in revised form: 3 July 2000 Electronic Publication     

The EF-Hand Ca2+ Binding Protein MICU Choreographs Mitochondrial Ca2+ Dynamics in Arabidopsis

Plant organelle function must constantly adjust to environmental conditions, which requires dynamic coordination. Ca²⁺ signaling may play a central role in this process. Free Ca²⁺ dynamics are tightly regulated and differ markedly between the cytosol, plastid stroma, and mitochondrial matrix. The mechanistic basis of compartment-specific Ca²⁺ dynamics is poorly understood. Here, we studied the function of At-MICU, an EF-hand protein of Arabidopsis thaliana with homology to constituents of the mitochondrial Ca²⁺ uniporter machinery in mammals. MICU binds Ca²⁺ and localizes to the mitochondria in Arabidopsis. In vivo imaging of roots expressing a genetically encoded Ca²⁺ sensor in the mitochondrial matrix revealed that lack of MICU increased resting concentrations of free Ca²⁺ in the matrix. Furthermore, Ca²⁺ elevations triggered by auxin and extracellular ATP occurred more rapidly and reached higher maximal concentrations in the mitochondria of micu mutants, whereas cytosolic Ca²⁺ signatures remained unchanged. These findings support the idea that a conserved uniporter system, with composition and regulation distinct from the mammalian machinery, mediates mitochondrial Ca²⁺ uptake in plants under in vivo conditions. They further suggest that MICU acts as a throttle that controls Ca²⁺ uptake by moderating influx, thereby shaping Ca²⁺ signatures in the matrix and preserving mitochondrial homeostasis. Our results open the door to genetic dissection of mitochondrial Ca²⁺ signaling in plants.     

Dual Targeting of MEK and PI3K Pathways Attenuates Established and Progressive Pulmonary Fibrosis

Pulmonary fibrosis is often triggered by an epithelial injury resulting in the formation of fibrotic lesions in the lung, which progress to impair gas exchange and ultimately cause death. Recent clinical trials using drugs that target either inflammation or a specific molecule have failed, suggesting that multiple pathways and cellular processes need to be attenuated for effective reversal of established and progressive fibrosis. Although activation of MAPK and PI3K pathways have been detected in human fibrotic lung samples, the therapeutic benefits of in vivo modulation of the MAPK and PI3K pathways in combination are unknown. Overexpression of TGFα in the lung epithelium of transgenic mice results in the formation of fibrotic lesions similar to those found in human pulmonary fibrosis, and previous work from our group shows that inhibitors of either the MAPK or PI3K pathway can alter the progression of fibrosis. In this study, we sought to determine whether simultaneous inhibition of the MAPK and PI3K signaling pathways is a more effective therapeutic strategy for established and progressive pulmonary fibrosis. Our results showed that inhibiting both pathways had additive effects compared to inhibiting either pathway alone in reducing fibrotic burden, including reducing lung weight, pleural thickness, and total collagen in the lungs of TGFα mice. This study demonstrates that inhibiting MEK and PI3K in combination abolishes proliferative changes associated with fibrosis and myfibroblast accumulation and thus may serve as a therapeutic option in the treatment of human fibrotic lung disease where these pathways play a role.     

Decreased catalase activity is the underlying mechanism of oxidant susceptibility in glucose-6-phosphate dehydrogenase-deficient erythrocytes

Historically, it has been theorized that the oxidant sensitivity of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes arises as a direct consequence of an inability to maintain cellular gluthione (GSH) levels. This study alternatively hypothesizes that decreased NADPH concentration leads to impaired to catalase activity which, in turn, underlies the observed oxidant susceptibility. To investigate this hypothesis, normal and G6PD-deficient erythrocytes and hemolysates were challenged with a H₂O₂-generating agent. The results of this study demonstrated that catalase activity was severely impaired upon H₂O₂ challenge in the G6PD-deficient cell whiel only decrease was observed in normal cells. Supplmentation of either normal or G6PD-deficient hemolysates with purified NADPH was found to significantly (P < 0.001) inhibit catalase inactivation upon oxidant challenge while addition of NADP⁺ had no effect. Analysis of these results demonstrated direct correlation between NADPH concentration and catalase activity (r = 0.881) and an inverse correlation between catalase activity and erythrocyte oxidant sensitivity (r = 0.906). In contrast, no correlation was found to exist between glutathione concentration (r = 0.170) and oxidant sensitivity. Analysis of NADPH/NADPt ration in acatalasemic mouse erythrocytes demonstrated that NADPH maintenance alone was not sufficient to explain oxidant resistance, and that catalase activity was required. This study supports the hypothesis that impaired catalase activity underlies the enhanced oxidant sensitivity of G6PD-deficient erythrocytes and elucidates the importance of NADPH in the maintenance of normal catalase activity.     

Inter-rater agreement on chromosome 5 breakage in FISH-based mutagen sensitivity assays (MSAs)

In chromosome breakage assays, validated, universal criteria for selection of cells and classification of chromosome aberrations may enhance their utility for cancer susceptibility screening. To standardize a fluorescence in situ hybridization (FISH) modification of the mutagen sensitivity assay (MSA), scoring criteria were evaluated by web-based validation. Two hundred digital FISH images were assigned random identification numbers. With this set of images, criteria for inclusion of cells and measurement of the frequency of abnormal cells were evaluated by eight observers, all of whom had five or more years of experience. Observers included doctoral and MS/BS level cytogeneticists, and were drawn from a randomized pool of 54 volunteers. Questions addressed were: (1) how uniformly were criteria applied to analysis of a standard digital FISH image set and (2) did concordance vary with educational level? These data suggest inter-rater agreement within a factor of 2 for average breakage frequency, but revealed greater variability in cell selection. These results aid in estimating the components of assay variance due to definitions, technical parameters and biological variables.     

Light and temperature regulation of greening in dark‐grown ginkgo (Ginkgo biloba)

The last steps of chlorophyll (Chl) biosynthesis were studied at different light intensities and temperatures in dark‐germinated ginkgo (Ginkgo biloba L.) seedlings. Pigment contents and 77 K fluorescence emission spectra were measured and the plastid ultrastructure was analysed. All dark‐grown organs contained protochlorophyllide (Pchlide) forms with similar spectral properties to those of dark‐grown angiosperm seedlings, but the ratios of these forms to each other were different. The short‐wavelength, monomeric Pchlide forms were always dominating. Etioplasts with small prolamellar bodies (PLBs) and few prothylakoids (PTs) differentiated in the dark‐grown stems. Upon illumination with high light intensities (800 μmol m^?2 s^?1 photon flux density, PFD), photo‐oxidation and bleaching occurred in the stems and the presence of ¹O₂ was detected. When Chl accumulated in plants illuminated with 15 μmol m^?2 s^?1 PFD it was significantly slower at 10°C than at 20°C. At room temperature, the transformation of etioplasts into young chloroplasts was observed at low light, while it was delayed at 10°C. Grana did not appear in the plastids even after 48 h of greening at 20°C. Reaccumulation of Pchlide forms and re‐formation of PLBs occurred when etiolated samples were illuminated with 200 μmol m^?2 s^?1 PFD at room temperature for 24 h and were then re‐etiolated for 5 days. The Pchlide forms appeared during re‐etiolation had similar spectral properties to those of etiolated seedlings. These results show that ginkgo seedlings are very sensitive to temperature and light conditions during their greening, a fact that should be considered for ginkgo cultivation.