Physiology and ecologic relevance of salt secretion by the salt gland of Glaux maritima L.

Summary The effects of salinity in the root medium, time, and relative humidity on the salt secretion of Glaux maritima were investigated. Both in the greenhouse and in the field increasing salinity stimulated sodium and chloride secretion, whereas the essential elements potassium, calcium, and magnesium remained at low secretion levels, which might be interpreted as efficient mineral economy. The low secretion level of potassium is remarkable, because growing on a nutrient solution containing 6 mM potassium, the concentration of the plant sap increases to 150 mM K⁺ and the secreted quantity amounts to only 2 m mol l^-1 plant sap 24 h^-1.Attempts were made to establish the secretion rate. The maximum secretion rate calculated may be 80 pEq NaCl cm^-2 s^-1, but for long periods (days) the secretion rate will be lower. Measurement of salt secretion unavoidably leads to removal of secreted salt. Salt was removed by rinsing with distilled water, which artificially accelerates the secretion process or parts of it by diffusion of salt from the cuticle cavity or secretory cells. At increasing salinities the amount of secreted ions showed a fivefold increase, whereas the osmotic potential of the plant sap was raised only twofold, indicating the importance of secretion as a rapid regulation mechanism with regard to the salt economy.     

Dynamics of non-linear biochemical systems and the evolutionary significance of time hierarchy

Several non-linear reaction networks are analyzed in order to study the influence of time hierarchy on the dynamics of biochemical systems. The analysis is based on the assumption that the separation of the time constants within metabolic systems is a direct consequence of strong differences of enzyme concentrations. Therefore, as variable system parameters, only the enzyme concentrations are considered. By investigation of the stationary states of various three-component models with feedback-activation bifurcation diagrams within a two-dimensional parameter space, the enzyme simplex, are constructed. The diagrams contain the information about the number of stationary states, their stability properties as well as the type of motion expected at different parameter combinations. The results support the hypothesis that systems with separated time constants generally show a simple dynamic behaviour. Complex motions can be expected mainly for systems without time hierarchy, which are characterized by parameters located within the centre of the enzyme simplex. Quantitative measures for the time hierarchy and the complexity of the dynamics are derived. It is supposed that the separation of time constants is a main feature of the evolution of biochemical systems. The hypothesis is further supported by the consideration of the time hierarchy of the glycolytic pathway.     

Photosynthesieintensität der Stielregionen von Acetabularia mediterranea

Summary The rate of photosynthesis (¹⁴C-incorporation) of cell parts isolated from the stalk of the alga Acetabularia mediterranea is highest in parts derived from the tip region and lowest in parts from the basal region of the stalk (Table 1).Similar results are obtained when whole cells are used for photosynthesis and divided afterwards into tip region, basal region and middle region (Fig. 1, Table 2).There is a gradient of photosynthetic capacity within the stalk which shows a pattern similar to that demonstrated for the morphogenetic capacity of the different stalk regions.     

Selection of scFv Antibody Fragments Binding to Human Blood versus Lymphatic Endothelial Surface Antigens by Direct Cell Phage Display

The identification of marker molecules specific for blood and lymphatic endothelium may provide new diagnostic tools and identify new targets for therapy of immune, microvascular and cancerous diseases. Here, we used a phage display library expressing human randomized single-chain Fv (scFv) antibodies for direct panning against live cultures of blood (BECs) and lymphatic (LECs) endothelial cells in solution. After six panning rounds, out of 944 sequenced antibody clones, we retrieved 166 unique/diverse scFv fragments, as indicated by the V-region sequences. Specificities of these phage clone antibodies for respective compartments were individually tested by direct cell ELISA, indicating that mainly pan-endothelial cell (EC) binders had been selected, but also revealing a subset of BEC-specific scFv antibodies. The specific staining pattern was recapitulated by twelve phage-independently expressed scFv antibodies. Binding capacity to BECs and LECs and differential staining of BEC versus LEC by a subset of eight scFv antibodies was confirmed by immunofluorescence staining. As one antigen, CD146 was identified by immunoprecipitation with phage-independent scFv fragment. This antibody, B6-11, specifically bound to recombinant CD146, and to native CD146 expressed by BECs, melanoma cells and blood vessels. Further, binding capacity of B6-11 to CD146 was fully retained after fusion to a mouse Fc portion, which enabled eukaryotic cell expression. Beyond visualization and diagnosis, this antibody might be used as a functional tool. Overall, our approach provided a method to select antibodies specific for endothelial surface determinants in their native configuration. We successfully selected antibodies that bind to antigens expressed on the human endothelial cell surfaces in situ, showing that BECs and LECs share a majority of surface antigens, which is complemented by cell-type specific, unique markers.