The competition of 2 types of epithelial layers in mixed cultures

The interaction of epithelial cells was studied in mixed cultures by phase contrast, time-lapse microcinematography, transmission and scanning electron microscopy. Epithelial cells, united into monolayer sheets with smooth apical surfaces, can be competing for substrate lamellae at the lower surfaces and force out each other from the substrate up to full elimination. The competition of cells for territory may be an important factor in morphogenesis in vivo.     

Study of the chlorosomal antenna of the green mesophilic filamentous bacterium Oscillochloris trichoides

Whole cells, chlorosome-membrane complexes and isolated chlorosomes of the green mesophilic filamentous bacterium Oscillochloris trichoides, representing a new family of the green bacteria Oscillochloridaceae, were studied by optical spectroscopy and electron microscopy. It was shown that the main light-harvesting pigment in the chlorosome is BChl c. The presence of BChl a in chlorosomes was visualized only by pigment extraction and fluorescence spectroscopy at 77 K. The molar ratio BChl c: BChl a in chlorosomes was found to vary from 70:1 to 110:1 depending on light intensity used for cell growth. Micrographs of negatively and positively stained chlorosomes as well as of ultrathin sections of the cells were obtained and used for morphometric measurements of chlorosomes. Our results indicated that Osc. trichoides chlorosomes resemble, in part, those from Chlorobiaceae species, namely, in some spectral features of their absorption, fluorescence, CD spectra, pigment content as well as the morphometric characteristics. Additionally, it was shown that similar to Chlorobiaceae species, the light-harvesting chlorosome antenna of Osc. trichoides exhibited a highly redox-dependent BChl c fluorescence. At the same time, the membrane B805–860 BChl a antenna of Osc. trichoides is close to the membrane B808–866 BChl a antenna of Chloroflexaceae species. This revised version was published online in June 2006 with corrections to the Cover Date.     

Orientation of B798 BChl a Q y transition dipoles in Chloroflexus aurantiacus chlorosomes: polarized transient absorption spectroscopy studies

Photosynthesis Research - Isotropic and anisotropic pump-probe spectra of Cfx. aurantiacus chlorosomes were measured on the fs-through ps-time scales for the B798 BChl a Q y band upon direct...     

Survival strategy of photosynthetic organisms. 1. Variability of the extent of light-harvesting pigment aggregation as a structural factor optimizing the function of oligomeric photosynthetic antenna. Model calculations

In accordance with our concept of rigorous optimization of photosynthetic machinery by a functional criterion, this series of papers continues purposeful search in natural photosynthetic units (PSU) for the basic principles of their organization that we predicted theoretically for optimal model light-harvesting systems. This approach allowed us to determine the basic principles for the organization of a PSU of any fixed size. This series of papers deals with the problem of structural optimization of light-harvesting antenna of variable size controlled in vivo by the light intensity during the growth of organisms, which accentuates the problem of antenna structure optimization because optimization requirements become more stringent as the PSU increases in size. In this work, using mathematical modeling for the functioning of natural PSUs, we have shown that the aggregation of pigments of model light-harvesting antenna, being one of universal optimizing factors, furthermore allows controlling the antenna efficiency if the extent of pigment aggregation is a variable parameter. In this case, the efficiency of antenna increases with the size of the elementary antenna aggregate, thus ensuring the high efficiency of the PSU irrespective of its size; i.e., variation in the extent of pigment aggregation controlled by the size of light-harvesting antenna is biologically expedient.     

Optimal spectral coordination of subantennae in natural antennae as an efficient strategy for light harvesting in photosynthesis

This work continues a series of our investigations on efficient strategies of functioning of natural light-harvesting antennae, initiated by a concept of rigorous optimization of photosynthetic apparatus by functional criterion, and deals with the problem of an optimal spectral coordination of subantennae in photosynthetic superantenna of the green bacterium Oscillochloris trichoides from a new family of green bacteria Oscillochloridaceae based in 2000. At present, two subantennae were identified surely: chlorosomal BChl c subantenna B750 and membrane BChl a subantennae B805-860. Some indirect experiments indicated on the presence of minor amounts of BChl a in isolated chlorosomes which allowed us to propose on the existence of an intermediate-energy subantenna which can connect the chlorosomal BChl c and the membrane BChl a ones. However, in the absorption spectra of isolated chlorosomes, this BChl a subantenna was not visually identified. This promoted us to perform a theoretical analysis of the optimality of spectral coordination of Oscillochloris trichoides subantennae. Using mathematical modeling for the functioning of the natural superantenna, we showed that an intermediate-energy subantenna, connecting B750 and B805-860 ones, allows one to control superantenna efficiency, i.e. to optimize the excitation energy transfer from B750 to B805 by functional criterion, and hence, the existence of such intermediate-energy subantenna is biologically expedient.     

A giant rhinocerotoid (Mammalia, Perissodactyla) from the Late Oligocene of north-central Anatolia (Turkey)

A giant rhinocerotoid is described for the first time south of the Black Sea, in Turkey. The single specimen, a fragmentary radius referred to Paraceratherium sp., originates from conglomerates nearby at Gözükizilli, in the Çankiri–Çorum Tertiary basin. These layers correspond to the Lower member of the Kizilirmak Formation. The same locality (Gözükizilli-2) yields also the small rhinocerotid Protaceratherium sp., cf. P. albigense (Roman, 1912). Three other mammal localities (Gözükizilli-1, in the Lower Member of the formation, with several rodent species; Tepe 641 and Kizilirmak, in the Upper Member, with a diversified micro- and macro-mammal fauna) allow us to refer the Kizilirmak Formation as a whole to the Late Oligocene. All the observed taxa have strong Asian and/or European affinities, which precludes any geographical insulation for this part of Anatolia during the Late Oligocene.  © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 152 , 581–592.