Symbiogenesis,natural selection,and the dynamic Earth

One century ago, Constantin S. Mereschkowsky introduced the symbiogenesis theory for the origin of chloroplasts from ancient cyanobacteria which was later supplemented by Ivan E. Wallin’s proposal that mitochondria evolved from once free-living bacteria. Today, this Mereschkowsky–Wallin principle of symbiogenesis, which is also known as the serial primary endosymbiosis theory, explains the evolutionary origin of eukaryotic cells and hence the emergence of all eukaryotes (protists, fungi, animals and plants). In 1858, the concept of natural selection was described independently by Charles Darwin and Alfred R. Wallace. In the same year, Antonio Snider-Pellegrini proposed the idea of shifting continents, which was later expanded by Alfred Wegener, who published his theory of continental drift eight decades ago. Today, directional selection is accepted as the major cause of adaptive evolution within natural populations of micro- and macro-organisms and the theory of the dynamic Earth (plate tectonics) is well supported. In this article, I combine the processes and principles of symbiogenesis, natural selection and the dynamic Earth and propose an integrative ‘synade-model’ of macroevolution which takes into account organisms from all five Kingdoms of life.     

In-vivo measurement of cell-wall extensibility in maize coleoptiles: Effects of auxin and abscisic acid

Plastic and elastic in-vivo extensibilities (E_pl and E_el, respectively) of cell walls of growing maize (Zea mays L.) coleoptile segments were measured by stretching living tissue at constant force (creep test) in an extensiometer. The linear displacement transducer used as a measuring device permits the determination of load-induced extensions in the range of 0–1% of the segment's length, leading to a minimal disturbance of the hydraulic parameters of the tissue and allowing the measurement of unidirectional cell-wall creep at virtually unchanged turgor and metabolic activity. A rein-vestigation of the time-course of indole-3-acetic acid-promoted and abscisic acid-inhibited wall loo-sening revealed that the in-vivo creep test yields results very similar to those obtained previously with the in-vitro creep test [Kutschera and Schopfer, 1986, Planta 167, 527–535]. The hormones affect elongation rate and E_pl in a closely correlated manner both in step-up as well as step-down growth changes whereas E_el remains unaltered. It is argued that both hormones influence growth by modifying E_pl of the outer epidermis and that this effect can be quantitatively measured, in relative units, by either the in-vivo or the in-vitro creep test.Abbreviations ABA ±abscisic acid - E_el, E_pl elastic and plastic in-vivo cell-wall extensibility, respectively - E_tot E_el+E_pl - IAA indole-3-acetic acid; m, cell-wall yielding coefficient     

On periodic cohort solutions of a size-structured population model

 We consider a size-structured population model with discontinuous reproduction and feedback through the environmental variable ‘substrate’. The model admits solutions with finitely many cohorts and in that case the problem is described by a system of ODEs involving a bifurcation parameter β. Existence of nontrivial periodic n-cohort solutions is investigated. Moreover, we discuss the question whether n cohorts (n≧2) with small size differences will tend to a periodic one-cohort solution as t→∞. Received 16 March 1995; received in revised form 7 January 1997     

Conditions and mutations affecting the maintenance and replication of plasmid DNA in Escherichia coli 15

Summary An Escherichia coli 15 strain has been constructed which contains, in addition to the plasmids inherent to E. coli 15 (P 1-like DNA and minicircular DNA), the colicinogenic factor E₁ (Col E₁). Whereas the P 1-like DNA of E. coli 15 is unaffected by the uptake of the colicin plasmid, the number of copies of minicircular DNA of E. coli 15 decreases and an equivalent amount of Col E₁ DNA becomes established in the cell. The ratio between these two small plasmids is dependent on the growth temperature. The mode of replication of minicircular DNA and Col E₁ DNA is very similar, but is different in various respects from that of the P 1-like plasmid: 1. Both small plasmids continue to replicate in the presence of chloramphenicol, whereas the replication of P 1-like DNA stops like the chromosomal DNA. 2. Rifampicin inhibits the synthesis of both small plasmids rather rapidly. The replication of P 1-like DNA continues during the remaining replication cycle of the chromosome in the presence of rifampicin. 3. The replication of Col E₁ DNA and of the minicircular DNA still proceeds at elevated temperatures (45–50°C), whereas little or no incorporation of ³H-thymidine into P 1-like DNA is observed at these temperatures. 4. Mutants have been obtained, which show altered properties in the maintenance and replication of the plasmids without being affected in the replication of the chromosomal DNA. In all these mutants the replication and (or) maintenance of the minicircular DNA of E. coli 15 and Col E₁ DNA is affected in the same way, but not that of the P 1-like plasmid.     

Spring-associated limestones of the Eastern Alps: overview of facies,deposystems, minerals,and biota

In the Eastern Alps, both fossil spring limestones and actively limestone-depositing springs are common. The geological context and a few radiometric age data of fossil spring-associated limestones (SAL) mentioned herein indicate that they accumulated subsequent to the Last Glacial Maximum in the Eastern Alps (24–21 ka BP). Prevalent facies of the SAL deposits, active and fossil, including phytoclastic tufa, microbialites s.l., springstone, and moss tufa form, or formed, from (a) waterfall/creek systems, (b) hillslope-paludal systems, (c) moss-tufa systems, and from (c) foreland-type systems. Precipitated minerals include calcite and, at springs of elevated Mg/Ca ratio, magnesian calcite and aragonite. In a few limestone-depositing, oxygen-deficient springs with dissolved Fe²⁺, downstream, iron oxide precipitates ahead of CaCO₃ (mineralogical zonation). Biota associated with calcium-carbonate deposition include cyanobacteria, green micro-algae, macro-algae, and mosses. Calcium-carbonate precipitation may be speeded by biological mediation, but mineralogy and polymorphy of precipitated CaCO₃ are not biotically controlled. In the Eastern Alps, SAL deposits in total range from 190 to 2,520 m a.s.l., corresponding to mean annual temperatures of 10°C to less than 0°C. In altitudes below the continuous permafrost line (about 2,600–3,000 m a.s.l., depending on location), SAL deposition is chiefly controlled by proper balance between water supply and sufficient supersaturation for CaCO₃, rather than by mean annual temperature.     

Photophysiology of turion germination inSpirodela polyrhiza (L.)Schleiden. The cause of germination inhibition by overcrowding

Red-light-induced (via phytochrome) germination decreased with increasing numbers of turions per germination flask (overcrowding). Three hypotheses concerning the mechanism of this germination inhibition were tested, related to abscisic acid, ethylene, and oxygen deficiency: (i) Although abscisic acid is a powerful inhibitor of turion germination it had to be excluded as a cause, because abscisic acid was not secreted from turions into the nutrient solution, (ii) Ethylene (ethrel) strongly inhibited growth of newly formed sprouts, but germination response itself was not inhibited, (iii) Germination inhibition did not appear if short light pulses were substituted by continuous irradiation. It reappeared in the presence of the photosynthesis inhibitor 3-(3, 4-dichlorophenyl)-l, 1-dimethylurea, but it was not observed in aerated nutrient solutions, or when Petri dishes instead of Erlenmeyer flasks were used. Decreased oxygen concentrations in the nutrient solution were produced by turion respiration. Consequently, anaerobiosis within the nutrient solution caused by turion respiration was the reason for germination inhibition by overcrowding.     

PEG-mediated plastid transformation in higher plants

Summary Plastids are surrounded by an envelope consisting of a double membrane. This barrier has to be penetrated or overcome by the DNA when transforming the plastome. Both the biolistic and polyethylene glycol-mediated transformation techniques accomplish this task, albeit by different mechanisms. We were the first laboratory to successfully use the polyethylene glycol (PEG)-method for plastid transformation, yet we use the particle gun when appropriate. In this report we compare the two methods and discuss their shortcomings and advantages. Plastid transformations with various constructs, mainly using theaadA gene as a selective marker, were performed. We point to potential problems likely to be encountered during the transformation and selection processes and offer possibilities for improvement. We give further examples of the successful application of plastome transformation and show its merits in addressing biological questions concerning the elucidation of plastid sequences of unknown function and the control of plastid gene expression. Based on a presentation in the symposium “Organelle Transformation” during the 1997 SIVB Congress held in Washington, DC June 14–18, 1997. An erratum to this article is available at .