Die submikroskopische Struktur der Assimilatleitbahnen von Polytrichum commune

Summary In the young part of the stem of Polytrichum commune the protoplasts of the two types of conducting cells, the leptoids and parenchyma cells, are nearly identically equipped with cell organelles and cytoplasmic structures. Both types contain a nucleus, chloroplasts, mitochondria, and dictyosomes. The endoplasmic reticulum builds characteristic cisterns in form of hollow cylinders extending from one end wall to the other. The cisterns are connected with many plasmodesmata, which occur only in the end walls. Leptoids have oblique end walls with 16 to 20 plasmodesmata per m², and parenchyma cells show cross walls perpendicular to the axis with 9 to 12 plasmodesmata per m².Since the leptoids are supposed to be the pathways for the longitudinal transport of assimilates (Eschrich and Steiner, 1967, 1968), it is of interest that early in their development these elements undergo a change in their protoplasmatic structure. Two to 3 cm below the apical cell the protoplasts degenerate and show lysosome-like structures. The endoplasmic reticulum and other structures are deformed or dissolved; the plasmodesmata are constricted by callose deposits. At the same level the parenchyma cells still retain the original structure of their protoplasts.Thus, assimilates moving upward in one row of leptoids may penetrate the whole lumen of the leptoids at lower levels, but they are restricted to the cisterns of the endoplasmic reticulum at higher levels of the stem.     

Mathematical models for mixing in deep-jet bioreactors: Calculation of parameters

The macroscopic mathematical model based on compartments with ideal mixing zones and tanks-in series was evaluated. Based on the experimental data obtained in a 300 dm³ pilot reactor and the dependence of mixing time on the volume of liquid phase, we have found mathematical relations between the ratio of vessel diameter to liquid level, adjustable parameters of model and the mixing time.List of Symbols V dm³ total volume of bioreactor - V _g dm³ total volume of liquid - V ₁ dm³ volume of ideally mixed zone in the vessel - V ₂ dm³ volume of macromixer in inner circulation flows - V ₃ dm³ volume of liquid phase in the pump - V ₄ dm³ volume of liquid phase in the pipe between the vessel and the pump - V ₅ dm³ volume of liquid phase in the pipe between the pump and air input system included falling jet - V _LT dm³ volume of liquid in the tank - V _LC dm³ volume of liquid in the circulation system - F _E dm³/s inner volumetric circulation flow rate across the macromixers - F _cir dm³/s external volumetric circulation flow rate, pumping capacity - t _A s time interval of the pulse application - t _AA s time point of the pulse application related to the free choosen starting point of the experiment - t _m s mixing time - t _c s circulation time - t _end s end time of simulation - C _*,* kg/m³ concentration of tracer in the indicated compartment - C ₀ kg/m³ concentration of the tracer before the injection - C _t kg/m³ concentration of the tracer at the indicated time - C kg/m³ theoretical concentration of the full mixed tracer - C _sim kg/m³ calculated concentration of tracer during numerical integration method - i index of an arbitrary tank - D _T m diameter of bioreactor - D 1/s dilution rate - H _L m level of liquid in the unaerated vessel - vector of inhomogenities     

Reassessment of structural characteristics of the d(CGCG)2:actinomycin D complex from complete 1H and 31P NMR

Complexes formed between Actinomycin D (ActD) and the tetranucleotides d(AGCT)2 and d(CGCG)2 were studied in detail by one and two-dimensional 1H and 31P NMR. The 31P two dimensional chemical exchange experiment, at room temperature on saturated complexes (1:1), showed unambiguously that the asymmetrical phenoxazone ring binds to the unique GC site under the two possible orientations in the d(AGCT)2 tetranucleotide but adopts a single orientation in the d(CGCG)2 tetranucleotide. For the d(CGCG)2:Act D saturated complex, complete assignments of all protons and phosphorus signals of the two-nucleotide strands, as well as of the two cyclic pentapeptide chains has allowed us to study in details the conformational features of the complex from NOE and coupling constants analysis. The tetranucleotide remains in a right-handed duplex, but the sugar puckers are modified for residues at the intercalation site. A uniform C2' endo pucker is observed for residues on the strand facing the quinoid side of the phenoxazone ring while a C2' endo-C3-endo equilibrium about 60% of C2' endo is proposed for the two residues on the strand facing the benzenoid side of the phenoxazone ring. In contrast to previous studies on ActD-DNA interactions, we have been able to measure the 3J phosphorus-proton coupling constants at the intercalation site but also adjacent to it, showing that 31P chemical shifts are not simply related to the backbone conformation. Molecular mechanics calculations, using empirical distances deduced from NOE effects as restrained distances during minimizations, led to a model differing mainly from those previously published by orientation of the N methyl groups of both N-Methyl-Valines.     

Maturational steps of bone marrow-derived dendritic murine epidermal cells. Phenotypic and functional studies on Langerhans cells and Thy-1+ dendritic epidermal cells in the perinatal period

The adult murine epidermis harbors two separate CD45+ bone marrow (BM)-derived dendritic cell systems, i.e., Ia+, ADPase+, Thy-1-, CD3- Langerhans cells (LC) and Ia-, ADPase-, Thy-1+, CD3+ dendritic epidermal T cells (DETC). To clarify whether the maturation of these cells from their ill-defined precursors is already accomplished before their entry into the epidermis or, alternatively, whether a specific epidermal milieu is required for the expression of their antigenic determinants, we studied the ontogeny of CD45+ epidermal cells (EC). In the fetal life, there exists a considerable number of CD45+, Ia-, ADPase+ dendritic epidermal cells. When cultured, these cells become Ia+ and, in parallel, acquire the potential of stimulating allogeneic T cell proliferation. These results imply that CD45+, Ia-, ADPase+ fetal dendritic epidermal cells are immature LC precursors and suggest that the epidermis plays a decisive role in LC maturation. The day 17 fetal epidermis also contains a small population of CD45+, Thy-1+, ADPase-, CD3- round cells. Over the course of 2 to 3 wk, they are slowly replaced by an ever increasing number of round and, finally, dendritic CD45+, Thy-1+, CD3+ EC. Thus, CD45+, Thy-1+, ADPase-, CD3- fetal EC may either be DETC precursors or, alternatively, may represent a distinctive cell system of unknown maturation potential. According to this latter theory, these cells would be eventually outnumbered by newly immigrating CD45+, Thy-1+, CD3+ T cells--the actual DETC.     

Collagen fiber arrangement of the human shoulder joint capsule--an anatomical study

The polariscopic examination of isolated shoulder joint capsules shows that the entire capsule does not have a homogeneous collagen structure. Most of the capsule is characterized by regular collagen fibers which cross at an obtuse angle in the area of the musculus supraspinatus and at an acute angle in the area of the m. infraspinatus. The density of the collagen network increases from the medial to the lateral part. Deviating from this basic pattern of the joint capsule, there is a different collagen texture in the area between the m. supraspinatus and the m. subscapularis. This texture has dissociated, rarefied and irregular collagen fibers. This means that the area--in comparison with the remainder of the capsule--is characterized not only by missing reinforcing ligaments but also by a deviating pattern of the collagen fibers. This different collagen structure is already existent in the fetus.     

Modulation of calmodulin levels, calmodulin methylation, and calmodulin binding proteins during carrot cell growth and embryogenesis.

Carrot cell cultures were used to study the dynamics of calmodulin protein levels, calmodulin methylation, and calmodulin-binding proteins during plant growth and development. Comparisons of proliferating and nonproliferating wild carrot cells show that, while calmodulin protein levels does not vary significantly, substantial variation in post-translational methylation of calmodulin on lysine-115 is observed. Calmodulin methylation is low during the lag and early exponential stages, but increases substantially as exponential growth proceeds and becomes maximal in the postexponential phase. Unmethylated calmodulin quickly reappears within 12 h of reinoculation of cells into fresh media, suggesting that the process is regulated according to the cell growth state. Calmodulin and calmodulin-binding proteins were also analyzed during the formation and germination of domestic carrot embryos in culture. Neither calmodulin methylation nor calmodulin protein levels varied significantly during somatic embryogenesis. However, upon germination of embryos, the level of calmodulin protein doubled. By calmodulin overlay analysis, we have detected a major 54,000 M(r) calmodulin-binding protein that also increased during embryo germination. This protein was purified from carrot embryo extracts by calmodulin-Sepharose chromatography. Overall, the data suggest that calmodulin methylation is regulated depending upon the state of cell growth and that calmodulin and its target proteins are modulated during early plant development.     

Suppression and Restoration of Lesion Formation in Arabidopsis lsd Mutants

Systemic acquired resistance (SAR) is a broad-spectrum, systemic defense response that is activated in many plant species after pathogen infection. We have previously described Arabidopsis mutants that constitutively express SAR and concomitantly develop lesions simulating disease (lsd). Here, we describe two new mutants, lsd6 and lsd7, that develop spontaneous necrotic lesions and possess elevated levels of salicylic acid (SA) as well as heightened disease resistance, similar to the previously characterized lsd and accelerated cell death (acd2) mutants. Genetic analysis of lsd6 and lsd7 showed that the mutant phenotypes segregated as simple dominant traits. When crossed with transgenic Arabidopsis plants containing the SA-degrading enzyme salicylate hydroxylase, the F1 progeny showed suppression of both SAR gene expression and resistance. In addition, salicylate hydroxylase suppressed lesion formation in the F1 progeny, suggesting that SA or some SA-dependent process may have a role in pathogen-associated cell death. Surprisingly, lesions were restored in the lsd6 F1 progeny after the application of either 2,6-dichloroisonicotinic acid or SA. Lesions were not restored by treatment with either compound in the lsd7 F1 plants. Our findings demonstrate that steps early in the signal transduction pathway leading to SAR and disease resistance are potentiated by later events, suggesting feedback control of lesion formation.