Beiträge zur Frage der lichtmikroskopischen Sichtbarkeit des endoplasmatischen Retikulums in Pflanzenzellen

Zusammenfassung Die an Innenepidermiszellen der Zwiebelschuppe vonAllium cepa zu beobachtenden schlauchförmigen intraplasmatischen Vakuolen, in der vorliegenden Arbeit kurz als Schläuche bezeichnet, werden näher untersucht. Sie heben sich im Protoplasma im Phasenkontrast als nichtkontrastierte, massearme Zonen ab. Diese Gebilde werden als Elemente des endoplasmatischen Retikulums (ER) angesprochen. Vergleichende Literaturstudien bekräftigen diese Ansicht.An tierischen Zellen wurden mehrfach im positiven Phasenkontrast dunkle, längliche oder netzförmige Gebilde als Elemente des ER erkannt. Die bei Pflanzenzellen auftretenden, äußerlich sehr ähnlichen Gebilde sind dagegen Plasmaleisten. Sie entstehen zwischen vergrößerten vakuolenartigen Elementen des ER.In jedem Fall ist es notwendig, streng zwischen dem ER sensu strictu, welches aus den Membranen und der von diesen umschlossenen intrazisternalen Phase (IZP) besteht, und dem Grundplasma, der extrazisternalen Phase (EZP), in der die Organellen liegen, zu unterscheiden. Im Lichtmikroskop (Phasenkontrast) werden an erwachsenen Pflanzenzellen die Membranen des ER nicht aufgelöst. Wenn die Membranen aber auseinanderweichen und die IZP durch Wasseraufnahme ein größeres Volumen einnimmt, kann man den Kontrastunterschied zwischen IZP und EZP sehen.Wir danken den optischen Werken C. Reichert A. G., Wien, für die leihweise Überlassung einer phasenoptischen Ausrüstung und der Firma Werfft-Chemie, Wien, für das Tetracyclin-Präparat Achromycin- Lederle.     

Karyologische Anatomie der Samenanlage vonPinus silvestris

Zusammenfassung In der Samenanlage vonPinus silvestris zeigen das Volumen und die Struktur der Ruhekerne sowie die Größe und Form der Metaphasechromosomen nicht nur gewebespezifische Unterschiede, sondern auch eine große Variabilität in Abhängigkeit von der Lage innerhalb ein und desselben Gewebes und vom Entwicklungsstadium. Große Kerne können lockerer gebaut sein als kleine, aber auch ungefähr gleich dicht, manchmal sogar dichter; aus den großen, dicht gebauten gehen in der Mitose Chromosomen hervor, die ein vielfaches Volumen von denen aus kleinen Kernen aufweisen (bis 132).Im Makrosporen-Tapetum treten normale und gehemmte Mitosen nebeneinander auf, in deren Folge mehrkernige Zellen bzw. Restitutionskerne mit teilweise aneuploiden Chromosomenzahlen entstehen. Der Gesamtpolyploidiegrad einer Tapetumzelle beträgt maximal 16n.     

Distribution,properties, and functions of midgut carboxypeptidases and dipeptidases from Musca domestica larvae

Dipeptidase and carboxypeptidase A activities were determined in cells and luminal contents of the fore-, mid-, and hind-midgut of Musca domestica larvae. Dipeptidase activity was found mainly in hind-midgut cells, whereas carboxy-peptidase activity was recovered in major amounts in both cells and in luminal contents of hind-midguts. The subcellular distribution of dipeptidase and part of the carboxypeptidase A activities is similar to that of a plasma membrane enzyme marker (aminopeptidase), suggesting that these activities are bound to the microvillar membranes. Soluble carboxypeptidase A seems to occur both bound to secretory vesicles and trapped in the cell glycocalyx. Based on density-gradient ultracentrifugation and thermal inactivation, there seems to be only one molecular species of each of the following enzymes (soluble in water or solubilized in Triton X-100): membrane-bound dipeptidase (pH optimum 8.0; Km 3.7 mM GlyLeu, M_r 111,000), soluble carboxypeptidase (pH optimum 8.0; Km 1.22 mM N-carbobenzoxy-glycyl-L-phenylalanine (ZGlyPhe), M_r45,000) and membrane-bound carboxypeptidase (pH optimum 7.5, Km 2.3 mM ZGlyPhe, M_r58,000). The results suggest that protein digestion is accomplished sequentially by luminal trypsin and luminal carboxypeptidase, by membrane-bound carboxypeptidase and aminopeptidase, and finally by membrane-bound dipeptidase.     

Standing biomass and production in water drainages of the foothills of the Philip Smith Mountains, Alaska

In the foothills of the Philip Smith Mountains, Brooks Range, Alaska, tussock tundra is the most widely distributed vegetation, and it occurs on rolling hills and in valleys that were shaped by a sequence of Pleistocene glaciations. In this study, aboveground standing biomass and production were compared in "intertrack tundra" areas that were relatively homogenous with respect to downslope drainage and adjacent "water tracks" that acted to channel water flow to the valley bottom stream. Comparisons of biomass, leaf area index, and specific leaf weight were also made between upper and lower slope positions. Similarities and differences of vegetation structure are examined with respect to graminoid, deciduous shrub, evergreen shrub, herbaceous, and bryophyte components.
Water tracks were found to have 1.5–1.7 times the biomass of intertrack tundra, and production (excluding secondary growth) in water tracks was 40% greater than in intertrack tundra. The aboveground biomass for all areas studied and the annual production values were similar to those found in other studies of tussock tundra. While only slight differences in depth of thaw occurred in water tracks and intertrack tundra during June and early July, water tracks thawed more deeply with the onset of summer rains. Warmer temperatures at 40 cm depth in July and August may have increased nutrient availability, whereas greater rooting depth and movement of water may have increased nutrient capture in water tracks as compared with the intertrack areas. Greater biomass and a deeper thaw depth occurred at upper slope locations.     

Structural basis for variations in the sensitivity of human decay accelerating factor to phosphatidylinositol-specific phospholipase C cleavage.

Human decay-accelerating factor (DAF) proteins expressed on E and nucleated cells differ in their susceptibility to phosphatidylinositol (PI)-specific phospholipase C (PLC) cleavage/release. To investigate the mechanism of this difference, the glycoinositol-phospholipid anchoring moieties of E DAF, and of HeLa cell, polymorphonuclear cell, and lymphocyte DAF were structurally compared. Labeling of PI-PLC-resistant E DAF with 3-(trifluoromethyl)-3-(m-[125I]-iodophenyl)-diazirine ([125I]TID) and TLC analysis of nitrous acid deamination anchor fragments showed a predominant phospholipid species with less polar migration than the 125I-TID-labeled PI. Gas chromatographic analyses of methanolyzed E protein revealed 2.20 +/- 0.16 mol of fatty acids [16:0, 18:0, 18:1, 20:4, 22:4, and 22:5 (0.76, 0.36, 0.25, 0.15, 0.40, 0.28 mol, respectively)] and 0.86 +/- 0.05 mol of inositol per mol of N-terminal Asp. Gas chromatography-mass spectroscopy demonstrated principally myo-inositol but also variable amounts of the chiro-isomer. Nondenaturing polyacrylamide gel electrophoresis of 14C-radiomethylated E protein revealed that pretreatment with hydroxylamine, a reagent which removes ester-linked lipids, rendered it PI-PLC susceptible. In contrast, parallel analyses of 35S-cys-labeled PI-PLC-sensitive HeLa DAF protein revealed only minor amounts of the hydroxylamine-sensitive phospholipid species. Similar results were obtained with 125I-surface-labeled DAF from polymorphonuclear cells, as well as from unstimulated peripheral blood and anti-CD3-activated lymphocytes. These findings demonstrate that, rather than PI, the E DAF anchor contains an inositol alkylacylglycerol-phospholipid which is heterogeneous with respect to acyl groups and inositol isomers, that an ester-linked substitution in this inositolphospholipid underlies the resistance of E DAF protein to PI-PLC cleavage/release, and that this structural modification is cell-specific.