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.

---

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.

---

---

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.

---

Angenommen durch F. Mechelke

---

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.     

Inhibition by S-adenosyl-L-homocysteine of dopamine dependent adenylate cyclase in rat retina

S-adenosyl-L-homocysteine (S-AH), a potent inhibitor of biological transmethylation, decreased the response of rat retina adenylate cyclase to dopamine and to 2-amino-6, 7-dihydroxytetrahydronaphtalene (ADTN). This effect appeared for 10^?7M of S-adenosyl-L-homocysteine and was linear for concentration ranging to 10^?4M. S-adenosyl-L-homocysteine did not decrease the cyclic AMP accumulation with sodium fluoride, a non specific adenylate cyclase activator. On the other hand, the incorporation of methyl group was reduced in rat retina homogenates by S-adenosyl-L-homocysteine. These findings suggest that the activity of the dopamine dependent adenylate cyclase is linked to a methylation process.     

Nonintegrative transformation in the filamentous fungus Podospora anserina: stabilization of a linear vector by the chromosomal ends of Tetrahymena thermophila.

The effect of the chromosomal ends of Tetrahymena thermophila on the stability of linear transforming molecules in the filamentous fungus Podospora anserina was tested. A derivative of an integrative vector for this fungus has been constructed, so that after linearization, the ends of the plasmid are the telomeric sequences of T. thermophila. After transformation, this linear molecule was maintained as an extrachromosomal plasmid with no integrated copies in about 50% of the transformants. Under selective conditions, there was approximately one linear molecule per 5 to 10 nuclei, and these extrachromosomal molecules were rapidly lost under nonselective conditions. The circular plasmid carrying an inverted repeat of T. thermophila telomeres could be linearized and processed in vivo.     

Osteoarthritis of the hip: an occupational disease in farmers.

OBJECTIVE--To test the hypothesis that farmers are at high risk of hip osteoarthritis and to investigate possible causes for such a hazard. DESIGN--Cross sectional survey. SETTING--Five rural general practices. SUBJECTS--167 male farmers aged 60-76 and 83 controls from mainly sedentary jobs. All those without previous hip replacement underwent radiography of the hip. MAIN OUTCOME MEASURES--Hip replacement for osteoarthritis or radiological evidence of hip osteoarthritis. RESULTS--Prevalence of hip osteoarthritis was higher in farmers than controls and especially in those who had farmed for over 10 years (odds ratio 9.3, 95% confidence interval 1.9 to 44.5). The excess could not be attributed to any one type of farming, and heavy lifting seems the likely explanation. CONCLUSIONS--Manual handling in agriculture should be limited where possible. Consideration should be given to making hip osteoarthritis a prescribed industrial disease in farmers. There may be wider implications for the prevention of hip osteoarthritis in the general population.