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Notes: Abstract During the last few years increasing evidence has shown that sphingolipid metabolites are highly bioactive compounds that play important roles in cellular regulation. The induction of ceramide signalling in primary human keratinocytes and HaCaT keratinocytes has recently been demonstrated using 1·,25-dihydroxyvitamin D3. The data obtained indicate that approximately one-third of the proapoptotic effect of 1·,25-dihydroxyvitamin D3 is mediated by an intracellular ceramide increase induced via tumor necrosis factor · expression and autocrine stimulation of sphingomyelin hydrolysis. In the present study the role of bcl-2 in this process was investigated. HaCaT keratinocytes were transfected with bcl-2 and the effects of C2-ceramide, tumor necrosis factor · and 1·,25-dihydroxyvitamin D3 on HaCaT keratinocytes stably overexpressing bcl-2 were determined. Apoptosis was measured by detection of soluble DNA-histone complexes using the ELISA technique. In situ analysis of apoptotic cells was also carried out by detecting phosphatidylserine flip using the annexin V method and by detecting DNA fragmentation using the TUNEL assay. The results obtained showed that apoptosis induced by C2-ceramide, tumor necrosis factor · or 1·,25-dihydroxyvitamin D3 occurred in a vector-transfected clone but not in a bcl-2-transfected HaCaT clone. This indicates the important role of bcl-2 in the regulation of ceramide-mediated signalling pathways in human keratinocytes and supports the involvement of ceramide as a signalling molecule in 1α,25-dihydroxyvitamin D3-induced biological responses.

Notes: Abstract Monthly uptake rates and the annual deposition of gaseous SO2 via the stomata of six Norway spruce canopies (Picea abies (L.) Karst.) in Germany (Königstein im Taunus, Witzenhausen, Grebenau, Frankenberg, Spessart, Fürth im Odenwald) were calculated (i) from statistical response functions of stomatal aperture depending on meteorological data, and (ii) from the synchronously measured SO2 immission at these stands. The stomatal response functions had been derived on the basis of thorough stomatal water conductance measurements in the field. Calculations of the SO2 conductance of spruce twigs and SO2 uptake rates via stomata need continuously measured complete data sets of the (i) light intensity, (ii) air temperature, (iii) air humidity and (iv) SO2 concentration in spruce forests from all the year. These data were recorded half hourly in different German spruce forests. The apparent needle water vapour pressure difference and transpiration rates were calculated from meteorological data. Additional use of canopy through flow data in dry years allowed the estimation of the mean stomatal conductance for H2O and SO2 of whole spruce canopies. The annual SO2 uptake of a mean unit needle surface in spruce forests was 32% of the SO2 uptake rate of exposed needles at the top of spruce crowns. There is significant SO2 uptake all the year. The mean SO2 dose at all sites and years received through the stomata was (0.25±0.07) μmol SO2 m-2 (total needle surface) (nPa Pa-1)-1 (annual mean of SO2 immission; 1 nPa (SO2) Pa-1 (air) = 1 ppb) day-1 (vegetation period per year). Comparison of calculated SO2 uptake rates into needles with measured SO4 2- accumulation rates in needles from the mentioned sites and additionally from Würzburg, Schneeberg (Fichtelgebirge) and from three sites in the eastern Erzgebirge (Höckendorf, Kahleberg, Oberbärenburg) revealed that oxidative SO2 detoxification (SO4 2- formation) dominates only at sites with high SO2 immission and short vegetation periods. Under these conditions 70 to 90% of the annual stomatal SO2 uptake is detoxified via SO4 2- accumulation in needles. Cations are needed for neutralization of accumulating SO4 2- which are inavailable to support growth. Thus, SO2 induces a dominant and competitive additional nutrient cation demand, cation deficiency symptoms and enhanced needle loss (“spruce decline symptoms”) mainly at sites, where the ratio R=(SO2 immission): (length of the vegetation period) is higher than R=0.07 nPa Pa-1 day-1. Correlation analysis of the relative needle loss versus the SO2-dependent SO4 2- formation rate revealed a significant increase of needle loss at the 98% level (Student). At sites with small SO2 immission and long vegetation periods (R〈0.07 nPa Pa-1 day-1) reductive SO2 detoxification via growth (and/or phloem export of SO4 2-) is not kinetically overburdened. Under these conditions only 30% of the annual SO2 uptake is detoxified via SO4 2- formation and spruce decline is small or absent. On the basis of the critical value R≈0.07 nPa Pa-1 day-1 recommended SO2 immission limits can be deduced on a mere ecophysiological basis. These deduced values are close to the proposed SO2 immission limits of the IUFRO, WHO and the UNECE.