Antioxidative protection in the inducible CAM plant Sedum album L. following the imposition of severe water stress and recovery

The antioxidative protection during the C₃-CAM shift induced by water stress was investigated in the temperate succulent Sedum album L. The C₃-CAM shift was characterized in terms of CO₂ exchange, titratable acidity and phosphoenolpyruvate carboxylase activity. Well-watered plants displayed C₃-like patterns of gas exchange and exhibited a mild day-night acid fluctuation indicating that those plants were performing CAM-cycling metabolism. Imposed drought highly stimulated CAM cycling, decreasing the net CO₂ uptake during the day, eliminating net CO₂ efflux at night and stimulating tissue acid fluctuations. As water deficit developed, chlorophyll fluorescence measurements showed a decrease in the Fv/Fm ratio, indicating that photoinhibition could follow after severe drought. Protection might be performed by the increased activity of enzymes involved in the destruction of free radicals and oxidants, but their response depended on the water status of the plant. Ascorbate peroxidase and superoxide dismutase activities increased in plants subjected to mild stress but declined during severe water stress. Catalase activity, however, was quite stable under mild water stress and was clearly inhibited under severe water stress. At this stage, glutathione reductase and monodehydroascorbate reductase seemed to be very important in the protection against oxidants, both increasing considerably their activities under severe water stress. Even if recycling has been shown to alleviate photoinhibition, our results clearly demonstrate that antioxidative enzymes play an important role in the protection of plants from oxidants during the C₃-CAM shift induced by water stress.     

Chemical soil conditions in pristineNothofagus forests of New Zealand as compared to German forests

In many German forest soils low base saturation of CEC in deeper soil layers was reported and acidic deposition is seen as the major cause of these findings. To test this hypothesis we sampled 5 New Zealand forest soils from pristine beech (Nothofagus fusca, N. menziesii, N. solandri) sites under climatic and geological conditions comparable to higher elevations in Germany. The soils developed from granite and greywacke. Soil samples were analyzed for pH and the exchangeable cations were extracted with 1M NH₄Cl. The base saturation of all soil profiles was very low, even in deeper layers and was thus similar to the patterns found in many German forest soils. The pH was generally higher in the New Zealand soils as compared to Germany. The reason for the depletion of base cations in deeper soil layers of New Zealand forest soils is most likely the leaching of base cations with HCO₃ ^- resulting from the dissociation of carbonic acid in connection with high amounts of seepage. Thus, under high rainfall conditions, the low base saturation found in deeper layers of forest soils cannot exclusively be attributed to the effects of acidic depositions and land use. ei]Section editor: R F Huettl     

Characterization of esophageal desalination in the seawater eel,Anguilla japonica

To characterize mechanisms of esophageal desalination, osmotic water permeability and ion fluxes were measured in the isolated esophagus of the seawater eel. The osmotic permeability coefficient in the seawater eel esophagus was 2·10^-4 cm·s^-1. This value was much lower than those in tight epithelial, although the eel esophagus is a leaky epithelium with a tissue resistance of 77 ohm·cm^-2. When the esophagus was bathed in normal Ringer solutions on both sides no net ion and water fluxes were observed. However, when mucosal NaCl concentration was increased by a factor of 3, Na⁺ und Cl^- ions were transferred from mucosa to serosa (desalination). If only Na⁺ or Cl^- concentration in the mucosal fluid was increased by a factor of 3, net Na⁺ and Cl^- fluxes were reduced to 30–40%, indicating that 60–70% of the net Na⁺ and Cl^- fluxes are coupled mutually. The coupled NaCl transport seems to be effective in desalting the luminal high NaCl. The remaining 30–40% of the total Na⁺ and Cl^- fluxes seems to be due to a simple diffusion, because these components are independent of each other and follow their electrochemical gradients, and also because these fluxes remain even after treatment with NaCN or ouabain. A half of the coupled NaCl transport could be explained by a Na⁺/H⁺–Cl^-/HCO ₃ ^- double exchanger on the apical membrane of the esophageal epithelium, because mucosal amiloride and 4.4-diisothiocyanatostilbene-2,2-disulphonic acid inhibited the net Na⁺ and Cl^- fluxes by approximately 30%. The other half of the coupled NaCl transport, which follows their electrochemical gradients, still remains to be explained.Abbreviations DIDS 4,4-diisothiocyanatostilbene-2,2-disulphonic acid - NMDG N-methyl-d-glucosamine - P _Cl Cl^- permeability coefficient - PD transepithelial potential difference - P _Na Na⁺ permeability coefficient - P _osm osinotic permeability coefficient - TALH thick ascending limb of Henle's loop     

Acidification of small mountain lakes in the High Tatra Mountains,Poland

A hydrochemical investigation was carried out on eight small High Tatra mountain lakes (Poland). When comparing recent data with those from the period 1935–1965, a constant process of acidification of the lakes is found. The average pH of precipitation is 4.8 in the study area, but the lakes are in two stages of acidification: weak (pH 6.0–6.5) and intermediate (pH 5.5–5.8). The differences are due to differences in water sources.     

Paleolirnnological records of carotenoids and carbonaceous particles in sediments of some lakes in Southern Alps

Stratigraphic analyses of organic carbon, organic nitrogen and algal and bacterial carotenoids in short cores of profundal sediments of four alpine lakes (Tovel, Leit, Paione superiore and Tom) were used to reconstruct their trophic history. In addition, depth distribution of carbonaceous particle concentrations provided information on lake contamination from atmospheric deposition. In three lakes (Tovel, Leit and Tom), sedimentary carotenoids unique to sulfur photosynthetic bacteria (okenone and isorenieratene) provide evidence of changes in the oxygen, light and sulfide conditions in the water column. All the lakes are oligotrophic or moderately productive, and the algal community is dominated by Chlorophyta, Pyrrhophyta and Cryptophyta. Cyanobacteria are rather poorly represented. The steep increase of carbonaceous particles in the uppermost sediment layers of all the lakes suggests that lake contamination by atmospheric transport of pollutants began in the 1940s to 1950s. These data, coupled with those from a parallel study on Chrysophycean scale-inferred pH, indicate recent acidification in those which are poorly buffered (Paione superiore and Leit).     

The effects of nutrient addition and pH manipulation in bag experiments on the phytoplankton of a small acidic lake in West Virginia,USA

In situ bag experiments were performed during summer and autumn in a small acidic lake, Tibbs Run Lake, West Virginia, USA. The objective was to evaluate phytoplankton responses to pH manipulation and nutrient addition. Increasing the pH from below 4.5 to over 6.3 resulted in great declines in phytoplankton biovolume. There was also a succession from dinoflagellates (Peridinium inconspicuum to small chlorophytes. The trend was more rapid where phosphorus (P) additions were made along with pH enhancement. During summer, P limitation was indicated, while nitrogen (N) appeared to limit production in autumn. In both seasons, nutrient additions greatly altered the phytoplankton composition in high pH treatments, but had no discernable effects at (the natural) low pH. A low pH, P addition treatment in autumn was the single exception. When N was subsequently added, phytoplankton composition changed dramatically, probably because the proceeding P additions caused severe secondary N-limitation. In general, however, the results supported the view that phytoplankton compositional responses to nutrient additions are suppressed in low pH, relative to high pH lake water.     

Dynamic properties of water at phosphatidylcholine lipid-bilayer surfaces as seen by deuterium and pulsed field gradient proton NMR

The dynamic properties of water in phosphatidylcholine lipid/water dispersions have been studied, applying a combination of ²H-NMR techniques (quadrupole splitting and spin-lattice relaxation time) and self-diffusion measurements using pulsed field gradient (PFG) ¹H-NMR. The hydration properties of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine) were compared with those of DOPC (1,2-dioleoyl-sn-glycero-3-phosphatidylcholine) and EYL (egg yolk phosphatidylcholine (lecithin)). A model is presented that assumes an exponentially decaying influence of the bilayer surface on water dynamics as well as on water orientation with increasing hydration. This assumption is based on an exponentially decaying hydration potential which results from direct lipid-water and water-water interactions. The model describes successfully the experimental data for a large water concentration range, especially at low hydration, where other models failed. With the exception of a small fraction of water which is significantly influenced by the surface in slowing down the mobility, the interbilayer water has isotropic, free water characteristics in terms of correlation times and molecular order. Hydration properties of POPC are comparable with those of EYL but differ from DOPC. At very low water content the correlation times of headgroup segmental reorientation and water are similar, indicating a strong coupling of this water to the lipid lattice. The hydration properties of the three lipids studied are explained in terms of slightly different headgroup conformations due to different lateral packing of the molecules by their fatty-acid chain composition.     

Chemiosmotic coupling of ion transport in the yeast vacuole: Its role in acidification inside organelles

Acidification inside the vacuo-lysosome systems is ubiquitous in eukaryotic organisms and essential for organelle functions. The acidification of these organelles is accomplished by proton-translocating ATPase belonging to the V-type H⁺-ATPase superfamily. However, in terms of chemiosmotic energy transduction, electrogenic proton pumping alone is not sufficient to establish and maintain those compartments inside acidic. Current studies have shown that thein situ acidification depends upon the activity of V-ATPase and vacuolar anion conductance; the latter is required for shunting a membrane potential (interior positive) generated by the positively charged proton translocation. Yeast vacuoles possess two distinct Cl^– transport systems both participating in the acidification inside the vacuole, a large acidic compartment with digestive and storage functions. These two transport systems have distinct characteristics for their kinetics of Cl^– uptake or sensitivity to a stilbene derivative. One shows linear dependence on a Cl^– concentration and is inhibited by 4,4-diisothiocyano-2,2-stilbenedisulfonic acid (DIDS). The other shows saturable kinetics with an apparentK _m for Cl^– of approximately 20 mM. Molecular mechanisms of the chemiosmotic coupling in the vacuolar ion transport and acidification inside are discussed in detail.     

Variations in stream water uptake by Eucalyptus camaldulensis with differing access to stream water

The stable isotopes ²H and ¹⁸O were used to determine the water sources of Eucalyptus camaldulensis at three sites with varying exposure to stream water, all underlain by moderately saline groundwater. Water uptake patterns were a function of the long-term availability of surface water. Trees with permanent access to a stream used some stream water at all times. However, water from soils or the water table commonly made up 50% of these trees' water. Trees beside an ephemeral stream had access to the stream 40–50% of the time (depending on the level of the stream). No more than 30% of the water they used was stream water when it was available. However, stream water use did not vary greatly whether the trees had access to the stream for 2 weeks or 10 months prior to sampling. Trees at the third site only had access to surface water during a flood. These trees did not change their uptake patterns during 2 months inundation compared with dry times, so were not utilising the low-salinity flood water. Pre-dawn leaf water potentials and leaf ¹³C measurements showed that the trees with permanent access to the stream experienced lower water stress and had lower water use efficiencies than trees at the least frequently flooded site. The trees beside the ephemeral stream appeared to change their water use efficiency in response to the availability of surface water; it was similar to the perennial-stream trees when stream water was available and higher at other times. Despite causing water stress, uptake of soil water and groundwater would be advantageous to E. camaldulensis in this semi-arid area, as it would provide the trees with a supply of nutrients and a reliable source of water. E. camaldulensis at the study site may not be as vulnerable to changes in stream flow and water quality as previously thought.     

Water relations,gas exchange,and growth of resprouts and mature plant shoots of Arbutus unedo L. and Quercus ilex L.

Resprout and mature plant shoot growth, leaf water status and gas exchange behavior, tissue nutrient content, flowering, and production were studied for co-occurring shallow-rooted (Arbutus unedo L.) and deeprooted (Quercus ilex L.) Mediterranean tree species at the Collserola Natural Park in Northeast Spain Resprouts showed higher growth rates than mature plant shoots. During fall, no differences in eco-physiological performance of leaves were found, but mobilization of carbohydrates from burls strongly stimulated growth of fall resprouts compared to spring resprouts, despite low exposed leaf area of the fall shoots. During summer drought, resprouts exhibited improved water status and carbon fixation compared to mature plant shoots. Shoot growth of Q. ilex was apparently extended due to deep rooting so that initial slower growth during spring and early summer as compared to A. unedo was compensated. Tissue nutrient contents varied only slightly and are postulated to be of minor importance in controlling rate of shoot growth, perhaps due to the relatively fertile soil of the site. Fall flowering appeared to inhibit fall shoot growth in A. unedo, but did not occur in Q. ilex. The results demonstrate that comparative examinations utilizing vegetation elements with differing morphological and physiological adaptations can be used to analyze relatively complex phenomena related to resprouting behavior. The studies provide an important multi-dimensional background framework for further studies of resprouting in the European Mediterranean region.