Zur Feinstruktur der Plasmodesmen und Plasmakanäle bei Pollenmutterzellen

Zusammenfassung Bei Tomate (Lycopersicum esculentum) und Kürbis (Cucurbita maxima) wurde der Feinbau der zwischen den Pollenmutterzellen bestehenden Plasmaverbindungen elektronenmikroskopisch untersucht.Neben feinen, den Verhältnissen in meristematischen somatischen Zellen entsprechenden Plasmaverbindungen (Plasmodesmen im engeren Sinne, Durchmesser im geometrischen Mittel 253,3 Å) wurden relativ breite, fast durchweg gröbere Cytoplasmaeinschlüsse (Mitochondrien, Vesikel, Potocytose-Bläschen, Dictyosomen usw.) aufweisende Verbin-dungen (Plasmakanäle, Durchmesser im geometrischen Mittel 0,175 ) festgestellt. Elemente des Endoplasmatischen Reticulums finden sich regelmäßig in den Plasmakanälen. Sie lassen sich jedoch häufig auch in größeren Plasmodesmen nachweisen.Weder über den Zeitpunkt der Entstehung, noch über die Entstehungsweise der Plasmakanäle lassen sich bei unserem Pflanzenmaterial konkrete Angaben machen. Gleiches gilt hinsichtlich des Zeitpunktes und der Art, wie die Plasmakanäle schließlich schwinden.Unbekannt ist auch die Art und Weise, wie die Plasmodesmen in Verbindung mit der Bildung der die Pollenmutterzellen bzw. auch die einzelnen Tetradenzellen umhüllenden dicken Callosemembranen schwinden.Bei der Tomate sind die Plasmakanäle bereits vor Aufgabe der Plasmodesmen vorhanden. Andererseits lassen sie sich in späteren Phasen der Tetradenentwicklung nicht mehr nachweisen.Die Beobachtungen werden in Verbindung mit bereits vorliegenden Angaben in der Literatur, insbesondere im Hinblick auf die Bedeutung der Plasmakanäle und ihre Ähnlichkeit mit Siebporen, diskutiert.

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On the fine structure of plasmodesmata and plasma-channels in pollen mother cells (PMC)

Summary The fine structure of plasmatic connections between PMC has been examined by electron microscopy in tomato (Lycopersicum esculentum) and squash (Cucurbita maxima).In addition to plasmodesmata, of geometrical mean diameter 253.3 Å, which correspond to the plasmodesmata in meristematic somatic cells, there are also to be distinguished plasma-channels of geometrical mean diameter 0.175 , which frequently contain cytoplasmic inclusions, such as mitochondria, vesicles, potocytosevesicles, dictyosomata etc. Generally we found elements of the endoplasmic reticulum in the plasma-channels. These elements are also to be found in larger plasmodesmata.We do not know the time nor the manner in which the plasma-channels of our plants originate and disappear. Also it is unknown how the plasmodesmata disappear when the thick callose-membrane is formed around the PMCs and the tetrad-cells.In the tomato the plasma-channels are present before the plasmodesmata disappear. On the other hand they are absent in later stages of tetrad development.The observations are discussed with regard to the possible function of the plasma-channels and their similarity to sievepores.

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Mit 17 Textabbildungen     

Prediction of sequential antigenic regions in proteins

Prediction of antigenic regions in a protein will be helpful for a rational approach to the synthesis of peptides which may elicit antibodies reactive with the intact protein. Earlier methods are based on the assumption that antigenic regions are primarily hydrophilic regions at the surface of the protein molecule. The method presented here is based on the amino acid composition of known antigenic regions in 20 proteins which is compared with that of 314 proteins [(1978) Atlas of Protein Sequence and Structure, vol. 5, suppl. 3, 363-373]. Antigenicity values were derived from the differences between the two data sets. The method was applied to bovine ribonuclease, the B-subunit of cholera toxin and herpes simplex virus type 1 glycoprotein D. There was a good correlation between the predicted regions and previously determined antigenic regions.     

Identification of bacteria with beta-galactosidase activity in faeces from lactase non-persistent subjects

Previous studies suggest that, besides the maldigestion of lactose in the small intestine, the colonic processing of lactose might play a role in lactose intolerance. beta-Galactosidase is the bacterial enzyme which catalyzes the first step of lactose fermentation in the colon. We propose a practical method to differentiate and identify bacteria with beta-galactosidase activity in faeces which combines a colony-lift filter assay with X-gal (5-bromo-4-chloro-3-indolyl-beta-d-galactopyranoside) as substrate for differentiation and the fluorescent in situ hybridization technique for identification. The method was applied to faeces from lactase non-persistent subjects. After 28 subjects had undergone one glucose and two lactose challenges, consistent intolerant (n=5) and tolerant (n=7) groups were defined according to their symptom scores. Of the 28 faecal samples, 80.6% (mean, SD: 12.1, range: 47.8-100%) of the total cultured bacteria were found to possess beta-galactosidase activity, which indicates that the bacterial beta-galactosidase is abundant in the colon. The tolerant and intolerant groups did not differ in the percentage or composition of the bacteria with beta-galactosidase activity or beta-galactosidase activity in faeces. Results suggest that the percentage or composition of the bacteria with beta-galactosidase activity in faeces do not play a role in lactose intolerance.