The electric generator in photosynthesis of green plants. I. Vectorial and protolytic properties of the electron transport chain

Light induces the generation of an electrochemical potential difference across the functional membrane of photosynthesis of green plants. Experimental results on the electrochemical phenomena have been largely interpreted in terms of a vectorial alternating electron hydrogen transport system as originally hypothesized by Mitchell.We asked whether or not the reaction coordinate of the electron transport crosses the membrane, and whether or not the protolytic reactions at either side of the membrane can be understood from the protolytic properties of the redox components involved. For this we studied the flash-light-induced protolytic reactions in the outer and the inner aqueous phase of the chloroplast inner disk membranes. Four sites of protolytic reactions were identified, two at either side of the membrane. One of these sites had to be attributed to the reduction of the terminal electron acceptor at the outer side of the membrane. Evidence is presented for the coupling of the other sites to the oxidation of water at the inner side of the membrane, to the reduction of plastoquinone at the outer side and its oxidation at the inner side, respectively. These results support Mitchell's hypothesis for the generation of an electrochemical potential difference by a vectorial electron transport system.     

Agglutination and glycosyltransferase activity of isolated gametic flagella from Chlamydomonas reinhardii

Isolated flagella from gametes of both mating types (mt⁺ and mt^-) of Chlamydomonas reinhardii were suspended in buffer containing 7% sucrose. After mixing instantaneous agglutination occurred, giving rise to clumps which seem to be stable for at least 24 h. Control experiments show that no aggregates are formed when gametic flagella of one mating type are mixed with flagella prepared from vegetative cells of the other mating type.This in vitro agglutination is inhibited by a number of salt solutions in the same concentration range in which the agglutination of live gametes is affected. Moreover the clumps of flagella tend to disaggregate completely when the salt solutions are added after agglutination has occurred, or by treatment with trypsin. These observations suggest that the in vitro agglutination of isolated gametic flagella indeed reflects their physiological role in the recognition step of the mating process, which appears to be possible without participation of live gametes.We have also investigated the activity of glycosyl transferases on isolated gametic flagella before and during the in vitro agglutination reaction. As there was no detectable increase in the activity of glycosyl transferases, our results do not favour the hypothesis that these enzymes are involved in the primary step of recognition between gametic flagella.Dedicated to Prof. Dr. Otto Kandler on the occasion of his 60th birthday     

Molecular AFM imaging of Hsp70-1A association with dipalmitoyl phosphatidylserine reveals membrane blebbing in the presence of cholesterol

Hsp70-1A—the major stress-inducible member of the HSP70 chaperone family—is being implicated in cancer diseases with the development of resistances to standard therapies. In normal cells, the protein is purely cytosolic, but in a growing number of tumor cells, a significant fraction can be identified on to the cell surface. The anchoring mechanism is still under debate, as Hsp70-1A lacks conventional signaling sequences for translocation from the cytosol to exoplasmic leaflet of the plasma membrane and common membrane binding domains. Recent reports propose a lipid-mediated anchoring mechanism based on a specific interaction with charged, saturated lipids such as dipalmitoyl phosphatidylserine (DPPS). Here, we prepared planar supported lipid bilayers (SLBs) to visualize the association of Hsp70-1A directly and on the single molecule level by atomic force microscopy (AFM). The single molecule sensitivity of our approach allowed us to explore the low concentration range of 0.05 to 1.0 μg/ml of Hsp70-1A which was not studied before. We compared the binding of the protein to bilayers with 20% DPPS lipid content both in the absence and presence of cholesterol. Hsp70-1A inserted exclusively into DPPS domains and assembled in clusters with increasing protein density. A critical density was reached for incubation with 0.5 μg/ml (7 nM); at higher concentrations, membrane defects were observed that originated from cluster centers. In the presence of cholesterol, this critical concentration leads to the formation of membrane blebs, which burst at higher concentrations supporting a previously proposed non-classical pathway for the export of Hsp70-1A by tumor cells. In the discussion of our data, we attempt to link the lipid-mediated plasma membrane localization of Hsp70-1A to its potential involvement in the development of resistances to radiation and chemotherapy based on our own findings and the current literature.     

Detection of toxic phytoplankton species by immunochemical particle analysis based on flow cytometry

Particulate suspended matter in oceanic, coastal, and estuarine regions can be specifically marked immunochemically with a fluorescent probe using antisera recognizing antigens present on their surface. Of the particulate matter, phytoplankton is a major component. Toxic species that may form harmful blooms can be a direct threat to aquaculturing tourism, sea-life and man. In order to detect such species in natural fixed phytoplankton populations, immunochemical tagging has been combined with flow cytometric evaluation Microalgal cells can be labeled with a fluorescent probe (fluorescein isothiocyanate, FITC, is recommended). Labeled cells are counted using a flow cytometer. This method has proved to be applicable in a monitoring programme in the North Sea.     

Significance of stromatoporoids in Jurassic reefs and carbonate platforms—concepts and implications

Although many case studies describe stromatoporoid-rich Jurassic reefs, there are only few reliable data as to their distribution pattern. This is in part due to a largely taxonomic and systematic focus on the enigmatic stromatoporoids which now are interpreted as a polyphyletic informal group of demosponges by most specialists. The common co-occurrence of Jurassic scleractinian corals and stromatoporoids might, at first hand, point to very similar environmental demands of both organismic groups, but autecological considerations as well as evaluation of stromatoporoid distribution patterns should allow for a much more refined interpretation. This study concludes that Jurassic corals and stromatoporoids show a relatively broad overlap of environmental demands but their maximum ecological tolerances appear to differ considerably. Jurassic corals were dominating in mesotrophic to mildly oligotrophic, slightly deeper settings, where they largely outcompeted stromatoporoids. On the other hand, stromatoporoid growth was particularly favoured in very shallow water, strongly abrasive, high-energy settings as well as in possibly overheated waters. Many taxa and growth forms were very tolerant towards frequent reworking and redistribution, a feature which is compatible with the sponge nature of the stromatoporoids. As such, stromatoporoid facies may be common in low-accommodation regimes, giving rise to frequent “shelf shaving” and redistribution across wide shelf areas. The mixed coral-stromatoporoid reefs from the margins of isolated Intra-Tethys platforms are interpreted to be indicative of oligotrophic normal marine waters. This is corroborated by statistical cluster analysis of stromatoporoid taxa from representative areas. In addition, Arabian stromatoporoid occurrences might have been adapted to overheated and slightly hypersaline waters. There also are a few exceptional stromatoporoid taxa which might have had environmental tolerances different from the bulk tolerances of other Jurassic stromatoporoids. Part of our interpretations are preliminary and should stimulate further research. However, the present results already help explain the observed compositional differences between Jurassic North Tethys/North Atlantic, Intra-Tethys, and South Tethys shallow-water reefs and platforms.     

In Vitro Localization of Hydroxyproline O-Glycosyl Transferases in Chlamydomonas reinhardii

The intracellular location of the two major O-glycosylatingenzymes (hydroxyproline-arabinosyl and -galactosyl transferases)involved in the synthesis of the cell wall glycoproteins ofChlamydomonas reinhardii was determined by isopycnic sucrosedensity gradient centrifugation. A comparison of gradients preparedunder low and high Mg²⁺-conditions has enabled us to clearlyallocate the galactosyl transferase to membranes of the Golgiapparatus. In contrast, the membranes which bear the arabinosyltransferase respond to a change in Mg²⁺-concentration in justthe same way as the endoplasmic reticulum does. Analysis ofthe product formed in vitro from UDP-[¹⁴C]arabinose and microsomalmembranes has confirmed the synthesis of an arabinose-containinghydroxyproline-rich glycoprotein. Our results indicate thatwhilst the Golgi apparatus is responsible for some of the glycosylationreactions in hydroxyproline-rich glycoprotein biosynthesis anappreciable portion of the arabinosylation is accomplished whilethe polypeptide is still in the lumen of the endoplasmic reticulum. ³This paper is dedicated to Professor Lothar Jaenicke on theoccasion of his 65th birthday. (Received July 2, 1988; Accepted March 8, 1989)     

Life history,sexual dimorphism and ‘ornamental’ feathers in the mesozoic bird Confuciusornis sanctus

The life history of Confuciusornis sanctus is controversial. Recently, the species’ body size spectrum was claimed to contradict osteohistological evidence for a rapid, bird-like development. Moreover, sexual size dimorphism was rejected as an explanation for the observed bimodal size distribution since the presence of elongated rectrices, an assumed ‘male’ trait, was uncorrelated with size. However, this interpretation (i) fails to explain the size spectrum of C. sanctus which is trimodal rather than bimodal, (ii) requires implausible neonate masses and (iii) is not supported by analogy with sexual dimorphisms in modern birds, in which elongated central rectrices are mostly sex-independent. Available information on C. sanctus is readily reconciled if we assume a bird-like life history, as well as a pronounced sexual size dimorphism and sexually isomorphic extravagant feathers as frequently observed in extant species.