Development of Grossensee (Holstein,Germany): variations in trophic status from the analysis of subfossil microfauna

Microfossil analysis was carried out on 90 samples of a sediment core from Grossensee. The diversity of subfossil Cladocera, Chironomidae, Chaoborus, and Ostracoda reflects at least five different stages of development. Three extended cycles correspond to different climatic periods in the first 10 000 years of the lake's history, while during the last 2 000 years, two shorter cycles can be identified which correlate with proofs or even historical events for human activity in the catchment area. During this time the profundal fauna changed from stenoxibiontic to euryoxibiontic species. In the planktonic fauna a succession of three Eubosmina types, B. longispina, B. coregoni kessleri, and B. coregoni coregoni, was observed. The chydorid and ostracod assembly of the littoral showed no clear change.     

Struktur und quantitatives Verhalten des perimitochondrialen granulären endoplasmatischen Retikulums der Mäuseleber

Zusammenfassung In normalen Leberzellen der Maus wurde das quantitative Verhalten des perimitochondrialen granulären endoplasmatischen Retikulums untersucht. 74% der Mitochondrien zeigen Beziehungen zum granulären endoplasmatischen Retikulum. Die einzelnen Mitochondrien werden zu 52%19,5 von den Membranen des granulären endoplasmatischen Retikulums bedeckt. Je Mikrometer Membranstrecke sind auf der mitochondriennahen Seite des granulären endoplasmatischen Retikulums 21 und auf der mitochondrienfernen Seite 20 Ribosomen zu finden, was der Zahl im übrigen granulären endoplasmatischen Retikulum entspricht. Die Befunde stellen die Grundlage für Untersuchungen des perimitochondrialen granulären endoplasmatischen Retikulums unter pathologischen Bedingungen dar.

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Structure and quantitative behaviour of the perimitochondrial granular endoplasmic reticulum in the liver cells of the mouse

Summary The perimitochondrial granular endoplasmic reticulum in normal mouse liver cells has been investigated quantitatively. 74% of the mitochondria are in association with the granular endoplasmic reticulum. The individual mitochondrion is covered by the membranes of the granulated E. R. in 52%19.5. The outer surface of the endoplasmic membrane, facing the mitochondrion, is occupied by 21 ribosomes per m; the corresponding surface of the membrane facing the free cytoplasm is occupied by 20 ribosomes per m. These data are in agreement with those of that fraction of the E. R., which is not in association with mitochondria. These findings represent a basis for investigations of the perimitochondrial endoplasmic reticulum under pathological conditions.

     

A microtest system for the serial assay of phytotoxic compounds using photoautotrophic cell suspension cultures of Chenopodium rubrum

Chenopodium rubrum photoautotrophic cell suspensions were grown in plastic tissue culture dishes under photoautotrophic conditions. Growth was monitored by measuring cell number, packed cell volume, chlorophyll content and oxygen production. Such microtiter dishes are suitable systems for the serial assay of growth inhibition and various physiological effects (i.e. chlorophyll fluorescence, cell viability, oxygen production) of photoautotrophic cells as caused by herbicides and fungal phytotoxins. The applicability of the test system is discussed.Abbreviations pcv packed cell volume - fr.w. fresh weight - rpm revol. per minute - DMSO dimethyl sulfoxide - PMS phenazine methosulfate - NBT nitro-blue tetrazolium chloride     

Synthesis of [6″-H]-, (6″-H)- and (2-H)-maltotriose

To prepare labeled precursors for biosynthetic studies, methods for the specific introduction of tritium and deuterium into the reducing and the terminal glucose unit of maltotriose were developed. Thus [6″-³H]- and (6″-²H)-maltotriose (17) and (18) were prepared via selective methoxytritylation, deprotection and subsequent modified Pfitzner-Moffatt oxidation, followed by reduction with sodium borotritiide or sodium borodeuteride, respectively. A simple two step procedure utilizing the Lobry de Bruyn/van Ekenstein transformation gave (2-²H)maltotriose (20).     

The Receptor for Urokinase-Type Plasminogen Activator of a Human Keratinocyte Line (HaCaT)

It is assumed that plasmin participates in pericellular proteolysis in the epidermis. Plasmin is generated by keratinocyte-associated plasminogen activators from the proenzyme plasminogen; plasminogen activation can proceed at the keratinocyte surface. The resultant plasmin interferes with cell to matrix adhesion and does possibly contribute to keratinocyte migration during reepithelialization. Here we describe the receptor for urokinase-type plasminogen activator (uPA-R) in the human keratinocyte cell line HaCaT, which serves to direct plasminogen activation to the cell surface; we relate the receptor to the uPA-R previously described in human myclo-/monocytes. Binding of uPA to the receptor accelerated plasminogen activation by a factor of ≈10, compared to uPA in solution. Receptor-bound uPA was susceptible to inhibition by the plasminogen activator inhibitors 1 and 2. uPA and uPA-R antigen, as well as uPA activity, were localized to the leading front of expanding sheets of HaCaT cells. Exposure of HaCaT cells to plasminogen was followed by detachment of the cells. Detachment was prevented by an anti-catalytic anti-uPA antibody, by the plasmin-specific inhibitor aprotinin, and by the lysine analogue tranexamic acid, the latter of which prevents plasmin(ogen) binding to the cell surface. Our findings support the hypothesis that uPA-mediated plasminogen activation is characteristic of mobile rather than sessile keratinocytes. Moreover, the uPA-R seems to focalize plasminogen activation to the surface of cells at the site of keratinocyte migration.     

Indirect versus direct effects of grasses on growth of a cactus (Opuntia fragilis): insect herbivory versus competition

Variation in plant performance between microhabitats is usually attributed to direct mechanisms, such as plant physiological tolerances or competitive interactions. However, indirect mechanisms, such as differences in herbivore pressure mediated by microhabitat differences, could create the same pattern of variation. In this study, we investigated the effect of insect herbivore pressure on the growth of the grassland cactus Opuntia fragilis under different regimes of grassland canopy cover. Our purpose was to establish the extent to which canopy cover plays a direct, competitive role versus an indirect, mediatory role in cactus growth. We manipulated aboveground microhabitat, specifically the cover of adjacent grasses. The three treatments were: (1) open canopy, with grass pinned down away from the cactus; (2) shaded canopy, with a partial mesh cage staked over the cactus; and (3) ambient grass canopy. We measured seasonal plant growth and recorded changes in insect herbivore occurrence and damage in relation to cover. Cactus growth, defined as the change in number of live cladodes, was higher in the open than under either treatment where the plant was more shaded (P<0.05). However, allocation to new growth, measured as the proportion of new segments (cladodes) in a patch, did not differ among cover treatments. Thus, the hypothesis that physiological constraints, or competition for light, limited cactus performance in grass is rejected. Instead, we found that both cladode mortality, caused by the larvae of a cactus moth borer (Melitara dentata), and occurrence of the moth were lower in the open microhabitat than in either shaded microhabitat. Thus, higher net growth in the open, unshaded treatment, rather than representing a release from competition for light with grasses, was better explained as an indirect effect of grass cover on the activity and impact of the cactus moth. These results show that indirect effects can lead to a misinterpretation of experimental data on direct effects. These data also contribute to an improved understanding of mixed results in the biological control of weedy cacti. Clearly, future evaluations of the relative importance of physiology, competition, and insect herbivory in plant performance must be environmentally explicit.     

Indole-3-butyric acid in plants: occurrence, synthesis, metabolism and transport

Indole-3-butyric acid (IBA) was recently identified by GC/MS analysis as an endogenous constituent of various plants. Plant tissues contained 9 ng g^?1 fresh weight of free IBA and 37 ng g^?1 fresh weight of total IBA, compared to 26 ng g^?1 and 52 ng g^?1 fresh weight of free and total indole-3-acetic acid (IAA), respectively. IBA level was found to increase during plant development, but never reached the level of IAA. It is generally assumed that the greater ability of IBA as compared with IAA to promote rooting is due to its relatively higher stability. Indeed, the concentrations of IAA and IBA in autoclaved medium were reduced by 40% and 20%, respectively, compared with filter sterilized controls. In liquid medium, IAA was more sensitive than IBA to non-biological degradation. However, in all plant tissues tested, both auxins were found to be metabolized rapidly and conjugated at the same rate with amino acids or sugar. Studies of auxin transport showed that IAA was transported faster than IBA. The velocities of some of the auxins tested were 7. 5 mm h^?1 for IAA, 6. 7 mm h^?1 for naphthaleneacetic acid (NAA) and only 3. 2 mm h^?1 for IBA. Like IAA, IBA was transported predominantly in a basipetal direction (polar transport). After application of ³H-IBA to cuttings of various plants, most of the label remained in the bases of the cuttings. Easy-to-root cultivars were found to absorb more of the auxin and transport more of it to the leaves. It has been postulated that easy-to-root, as opposed to the difficult-to-root cultivars, have the ability to hydrolyze auxin conjugates at the appropriate time to release free auxin which may promote root initiation. This theory is supported by reports on increased levels of free auxin in the bases of cuttings prior to rooting. The auxin conjugate probably acts as a ‘slow-release’ hormone in the tissues. Easy-to-root cultivars were also able to convert IBA to IAA which accumulated in the cutting bases prior to rooting. IAA conjugates, but not IBA conjugates, were subject to oxidation, and thus deactivation. The efficiency of the two auxins in root induction therefore seems to depend on the stability of their conjugates. The higher rooting promotion of IBA was also ascribed to the fact that its level remained elevated longer than that of IAA, even though IBA was metabolized in the tissue. IAA was converted to IBA by seedlings of corn and Arabidopsis. The K_m value for IBA formation was low (approximately 20 μM), indicating high affinity for the substrate. That means that small amounts of IAA (only a fraction of the total IAA in the plant tissues) can be converted to IBA. It was suggested that IBA is formed by the acetylation of IAA with acetyl-CoA in the carboxyl position via a biosynthetic pathway analogous to the primary steps of fatty acid biosynthesis, where acetyl moieties are transferred to an acceptor molecule. Incubation of the soluble enzyme fraction from Arabidopsis with ³H-IBA, IBA and UDP-glucose resulted in a product that was identified tentatively as IBA glucose (IBGIc). IBGIc was detected only during the first 30 min of incubation, showing that it might be converted rapidly to another conjugate.     

Regeneration from intact and sectioned immature embryos of barley (Hordeum vulgare L.): the scutellum exhibits an apico-basal gradient of embryogenic capacity

Immature zygotic embryos from spring barley cv. Dissa were used to induce somatic embryogenenesis. Up to 158 germinated somatic embryos could be recovered per plated zygotic embryo. Critical factors for obtaining a high yield of regenerants were the size of the explant, the level of 2,4-D used for callus induction and the careful division of callus at each subculture. Use of microsections of immature embryos as explants revealed a pronounced gradient of callus formation and embryogenic response across the scutellum. Sections from the scutellar tissue at the coleoptilar end of the embryo gave the most callus and were highly embryogenic. The regeneration response of sectioned explants was comparable to that recovered from intact embryos of similar size.     

Extracellular Neuroactive Amino Acids in the Rat Striatum During Ischaemia: Comparison Between Penumbral Conditions and Ischaemia with Sustained Anoxic Depolarisation

Abstract: Changes in the extracellular levels of excitatory and inhibitory amino acid transmitters were studied in the rat striatum during penumbral ischaemia using intracerebral microdialysis. Effects of penumbral forebrain ischaemia were compared with those of ischaemia with sustained anoxic depolarisation and K⁺ (100 m M ). Comparisons were also made between different groups of animals at 2 and 24 h after dialysis probe implantation. The K⁺ stimulus did not provoke any release of excitatory amino acids in the 24-h group, probably reflecting a decrease of functional synapses adjacent to the probe. During 30 min of penumbral ischaemia, excitatory amino acids did not reach critical concentrations in the extracellular fluid, and increases in levels of inhibitory/modulatory amino acids were similar. On the other hand, severe transient ischaemia resulted in massive synchronous release of many neuroactive excitatory and inhibitory compounds, in both the 2- and 24-h groups. These and other data suggest that changes during severe ischaemia may arise from both neurotransmitter and metabolic pools. It is concluded that is- chaemic damage in the penumbra may not be related to extracellular neuroactive amino acid changes generated within this region.