Untersuchungen zur Pollenentwicklung und Pollenschlauchbildung bei höheren Pflanzen

Zusammenfassung In reifen Pollenkörnern der beiden Sommergerstensorten Amsel und Wisa sowie der F₁-Pflanzen, die aus den Sorten-Kreuzungen Impala X Wisa und Union X Wisa hervorgegangen sind, wurde die DNS-Menge der Kerne cytophotometrisch bestimmt. Die Messungen wurden zugleich bei Spermakernen und vegetativen Kernen eines Pollenkorns vorgenommen. Außerdem wurde der DNS-Gehalt von Kernen von Wurzelspitzen-Zellen der Sorten Amsel und Wisa ermittelt.Amsel und Wisa unterscheiden sich signifikant im DNS-Gehalt der Kerne von Wurzelspitzen-Zellen.Die Befunde der Messungen des DNS-Gehalts von vegetativen und Sperma-Kernen bei vier Gerstenformen zeigen, daß zum Zeitpunkt der Anthese die DNS-Replikationsphase bei vegetativen und Sperma-Kernen noch nicht abgeschlossen ist. Der DNS-Gehalt vegetativer Kerne von Wisa ist signifikant niedriger als die entsprechenden Werte der übrigen drei Gerstenformen. Der Verlauf der DNS-Replikation erfolgt bei beiden Spermakernen synchron. Hingegen verläuft die DNS-Replikation bei vegetativen und Sperma-Kernen mit großer Wahrscheinlichkeit nicht gleichsinnig.Im Diskussionsteil wird erstens erläutert, daß bei allen bisher analysierten Pflanzenarten des zwei- oder dreikernigen Pollenkorn-Typs zum Zeitpunkt der Pollenreife die DNS-Replikation der generativen bzw. Sperma-Kerne eingesetzt hat, aber je nach Pflanzenart noch nicht beendet sein muß. Zum gleichen Zeitpunkt der Pollenkornentwicklung kann der vegetative Kern in Abhängigkeit von der Pflanzenart auf dem C-Niveau verharren, eine teilweise oder bereits abgeschlossene DNS-Replikation erfahren haben oder schon teilweise oder ganz degeneriert sein, ohne zuvor eine DNS-Replikation vollzogen zu haben. Zweitens wird in diesem Abschnitt diskutiert, daß mit großer Wahrscheinlichkeit im Ablauf der DNS-Replikation zwischen zwei- und dreikernigen Pollenkorn-Typen keine Unterschiede bestehen. Drittens wird die Hypothese vertreten, daß nur auf einem sehr frühen Stadium die normale Pollenkornentwicklung einschließlich des Ablaufs der DNS-Replikation insbesondere des vegetativen Kerns so abgewandelt werden kann, daß aus Pollenkörnern haploide Pflanzen erzeugt werden können.

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The development of pollen grains and formation of pollen tubes in higher plantsIII. DNA-replication of vegetative and sperm nuclei in mature pollen grains of barley

Summary The DNA-content of vegetative and sperm nuclei in mature pollen grains of the barley varieties Amsel and Wisa and the F₁-plants of crossings of the barley varieties Impala X Wisa and Union X Wisa was determined by cytophotometry. In addition, the DNA-content of nuclei of root tips of Amsel and Wisa was cytophotometrically measured.The DNA contents of the nuclei in root tips of Amsel and Wisa differed significantly.The data obtained from the measurements of the vegetative and sperm nuclei of the four types of barley show that DNA-replication continues in the nuclei of mature pollen grains. The DNA values of vegetative nuclei of Wisa are significantly lower than the values of Amsel and of the F₁ plants. The DNA values of the different nuclei indicate that DNA replication of both types of sperm nuclei is synchronous, whereas it probably is not synchronous in vegetative and sperm nuclei respectively.In the discussion it is pointed out that a survey of the literature shows that in all of the plant species having binucleate or trinucleate pollen DNA replication of generative and of sperm nuclei has started at the time of pollen grain maturation. Depending on the plant species, replication may or may not be completed in the mature pollen grain. At a given stage of development of the pollen grain the vegetative nucleus may be arrested at the C-stage, may have partially or completely finished its DNA replication or may be partially or completely degenerated without prior replication of DNA.In the second part of the discussion it is stated that the course of DNA replication is likely to be similar in binucleate and trinucleate pollen grains. Thirdly, the hypothesis is discussed that in order to get haploid plants from pollen grains, changes in the normal development of the pollen grain and in the pattern of DNA replication must occur at a very early stage of pollen grain development.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.

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Angenommen durch F. Mechelke

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Mein Dank grit Herrn Prof. Dr. F. Mechelke fiir die Anregung zu diesen Untersuchungen sowie fiir die Unterstfitzung und die kritischen Diskussionen w/ihrend ihres Verlaufs und Fr/iulein H. Nagel fiir zuverl/issige technische Hilfe.     

Sequence analysis of a 101-kilobase plasmid required for agar degradation by a Microscilla isolate.

An agar-degrading marine bacterium identified as a Microscilla species was isolated from coastal California marine sediment. This organism harbored a single 101-kb circular DNA plasmid designated pSD15. The complete nucleotide sequence of pSD15 was obtained, and sequence analysis indicated a number of genes putatively encoding a variety of enzymes involved in polysaccharide utilization. The most striking feature was the occurrence of five putative agarase genes. Loss of the plasmid, which occurred at a surprisingly high frequency, was associated with loss of agarase activity, supporting the sequence analysis results.     

The role of the cysteine-rich region of the β2 integrin subunit in the leukocyte function-associated antigen-1 (LFA-1, αLβ2, CD11a/CD18) heterodimer formation and ligand binding

The cysteine-rich region (CRR) of the β2 integrin subunit was replaced by that of β1 to give the chimera β2NV1. β2NV1 can combine with αL to form a variant leukocyte-function-associated antigen (LFA)-1 on COS cell surface, suggesting that the specificity of the β2 interaction with αL does not lie in the CRR. Unlike those expressing wild-type LFA-1, COS cells expressing αLβ2NV1 are constitutively active in intercellular adhesion molecule (ICAM)-1 adhesion. These results suggest that activation of LFA-1 involves the release of an intramolecular constraint, which is maintained, in part, by the authentic β2 CRR.     

A putative GDP–GTP exchange factor is required for development of the excretory cell in Caenorhabditis elegans

The Caenorhabditis elegans excretory cell extends tubular processes, called canals, along the basolateral surface of the epidermis. Mutations in the exc-5 gene cause tubulocystic defects in this canal. Ultrastructural analysis suggests that exc-5 is required for the proper placement of cytoskeletal elements at the apical epithelial surface. exc-5 encodes a protein homologous to guanine nucleotide exchange factors and contains motif architecture similar to that of FGD1, which is responsible for faciogenital dysplasia. exc-5 interacts genetically with mig-2, which encodes Rho GTPase. These results suggest that EXC-5 controls the structural organization of the excretory canal by regulating Rho family GTPase activities.     

Lung tissue mechanics and extracellular matrix composition in a murine model of silicosis.

The dynamic mechanical properties of lung tissue and its contents of collagen and elastic fibers were studied in strips prepared from mice instilled intratracheally with saline (C) or silica [15 (S15) and 30 days (S30) after instillation]. Resistance, elastance, and hysteresivity were studied during oscillations at different frequencies on S15 and S30. Elastance increased from C to silica groups but was similar between S15 and S30. Resistance was augmented from C to S15 and S30 and was greater in S30 than in S15 at higher frequencies. Hysteresivity was higher in S30 than in C and S15. Silica groups presented a greater amount of collagen than did C. Elastic fiber content increased progressively along time. This increment was related to the higher amount of oxytalan fibers at 15 and 30 days, whereas elaunin and fully developed elastic fibers were augmented only at 30 days. Silicosis led not only to pulmonary fibrosis but also to fibroelastosis, thus assigning a major role to the elastic system in the silicotic lung.     

Regulation of energy economy in raccoon dogs and blue foxes: a process of dynamic interactions

1. Seasonal regulation of energy economy was studied in farm-raised blue foxes (Alopex lagopus) and raccoon dogs (Nyctereutes procyonoides; Gray, 1834). 2. Both species exhibited marked seasonal changes in body weight, body energy content, food intake and locomotor activity. Seasonal changes in food efficiency were also evident. 3. The results emphasize the important role of both energy intake and energy expenditure in the regulation process. 4. It can be concluded that regulation of seasonal energy balance is a dynamic process with various interactions between different factors.