The V-ATPase in Paramecium:functional specialization by multiple gene isoforms

The vacuolar H(+)-ATPase (V-ATPase), a multisubunit, adenosine triphosphate (ATP)-driven proton pump, is essential for numerous cellular processes in all eukaryotes investigated so far. While structure and catalytic mechanism are similar to the evolutionarily related F-type ATPases, the V-ATPase's main function is to establish an electrochemical proton potential across membranes using ATP hydrolysis. The holoenzyme is formed by two subcomplexes, the transmembraneous V(0) and the cytoplasmic V(1) complexes. Sequencing of the whole genome of the ciliate Paramecium tetraurelia enabled the identification of virtually all the genes encoding V-ATPase subunits in this organism and the studying of the localization of the enzyme and roles in membrane trafficking and osmoregulation. Surprisingly, the number of V-ATPase genes in this free-living protozoan is strikingly higher than in any other species previously studied. Especially abundant are V(0)-a-subunits with as many as 17 encoding genes. This abundance creates the possibility of forming a large number of different V-ATPase holoenzymes by combination and has functional consequences by differential targeting to various organelles.

Development and growth of the lichen Rhizocarpon geographicum

The development of new areolae on the marginal hypothallus of the lichen Rhizocarpon geographicum (L.) DC was studied after complete or partial removal of the central areolae. New areolae developed slowly on the isolated hypothalli over two years. Development was similar when the areolae were completely removed and when the central areolae were separated from the marginal hypothallus by ‘moats’ 2 to 5 mm in width. However, in intact thalli, the marginal areolae developed rapidly during Jan. – June 1986 but showed periods of retreat from the margin during Oct. - Dec. 1985 and July – Sept. 1986. These results suggested that primary areolae may develop from free-living algal cells trapped by the hypothallus while secondary areolae may develop from zoospores produced by the thallus. Complete removal of the areolae resulted in no measurable radial growth of the marginal hypothallus over 18 months. Removal of the central areolae to within 1 and 2 mm of the hypothallus significantly reduced growth. These results suggest that the areolae may supply the hypothallus with carbon for growth. When the marginal hypothallus was experimentally removed a new hypothallus developed within one year. Regeneration occurred initially by retreat of the marginal areolae and later by new hyphal growth. The concentration of ribitol, arabitol and mannitol was measured in the areolae and marginal hypothallus on four occasions in 1985/6 in a population growing on a steep south facing rock surface. The three carbohydrates were present in significantly higher concentration in the areolae than in the hypothallus. Hence, the slow growth of this species may result from inhibited transport of carbohydrate from areolae to hypothallus.

The biology of the crustose lichen Rhizocarpon geographicum

The crustose lichen Rhizocarpon geographicum (L.) DC. comprises yellow-green lichenized areolae which develop and grow on the surface of a non-lichenized fungal hypothallus, the latter extending beyond the edge of the areolae to form a marginal ring. The hypothallus advances very slowly and the considerable longevity of R. geographicum, especially in Arctic and Alpine environments, has been exploited by geologists in dating the exposure age of rock surfaces (lichenometry). This review explores various aspects of the biology of R. geographicum including: (1) structure and symbionts, (2) lichenization, (3) development of areolae, (4) radial growth rates (RaGR), (5) growth physiology, (6) changes in RaGR with thallus size (growth ratesize curve), (7) maturity and senescence, and (8) aspects of ecology. Lichenization occurs when fungal hyphae become associated with a compatible species of the alga Trebouxia, commonly found free-living on the substratum. Similarly, 'primary' areolae develop from free-living algal cells trapped by the advancing hypothallus. The shape of the growth rate-size curve of R. geographicum is controversial but may exhibit a phase of decreasing growth in larger thalli. Low rates of translocation of carbohydrate to the hypothallus together with allocation for stress resistance results in very slow RaGR, a low demand for nutrients, hence, the ability of R. geographicum to colonize more extreme environments. Several aspects of the biology of R. geographicum have implications for lichenometry including early development, mortality rates, the shape of the growth-rate size curve, and competition. © The Author(s) 2012.

Growth of crustose lichens: a review

Crustose species are the slowest growing of all lichens. Their slow growth and longevity, especially of the yellow-green Rhizocarpon group, has made them important for surface-exposure dating (‘lichenometry’). This review considers various aspects of the growth of crustose lichens revealed by direct measurement including: 1) early growth and development, 2) radial growth rates (RGR, mm yr-1), 3) the growth rate-size curve, and 4) the influence of environmental factors. Many crustose species comprise discrete areolae that contain the algal partner growing on the surface of a non-lichenised fungal hypothallus. Recent data suggest that ‘primary’ areolae may develop from free-living algal cells on the substratum while ‘secondary’ areolae develop from zoospores produced within the thallus. In more extreme environments, the RGR of crustose species may be exceptionally slow but considerably faster rates of growth have been recorded under more favourable conditions. The growth curves of crustose lichens with a marginal hypothallus may differ from the ‘asymptotic’ type of curve recorded in foliose and placodioid species and the latter are characterized by a phase of increasing RGR to a maximum and may be followed by a phase of decreasing growth. The decline in RGR in larger thalli may be attributable to a reduction in the efficiency of translocation of carbohydrate to the thallus margin or to an increased allocation of carbon to support mature ‘reproductive’ areolae. Crustose species have a low RGR accompanied by a low demand for nutrients and an increased allocation of carbon for stress resistance; therefore enabling colonization of more extreme environments.

Pseudoperiodic "Living" and/or controlled cationic ring-opening copolymerization of oxetane with tetrahydropyran:microstructure of polymers vs kinetics of chain growth

The "living" and/or controlled cationic ring-opening bulk copolymerization of oxetane (Ox) with tetrahydropyran (THP) (cyclic ether with no homopolymerizability) at 35°C was examined using ethoxymethyl-1 -oxoniacyclohexane hexafluoroantimonate (EMOA) and (BF3 · CH3OH)THP as fast and slow initiator, respectively, yielding living and nonliving polymers with pseudoperiodic sequences (i.e., each pentamethylene oxide fragment inserted into the polymer is flanked by two trimethylene oxide fragments). Good control over number-average molecular weight (Mn up to 150000 g mol-1) with molecular weight distribution (MWD ∼ 1.4-1, 5) broader than predicted by the Poison distribution (MWDs > 1 +1/DPn) was attained using EMOA as initiating system, i.e., C 2H5OCH2Cl with 1.1 equiv of AgSbF6 as a stable catalyst and 1.1 equiv of 2,6-di-tert-butylpyridine used as a non-nucleophilic proton trap. With (BF3 · CH 3OH)THP, a drift of the linear dependence M n(GPC) vs Mn(theory) to lower molecular weight was observed together with the production of cyclic oligomers, ∼3-5% of the Ox consumed in THP against ∼30% in dichloromethane. Structural and kinetics studies highlighted a mechanism of chains growth where the rate of mutual conversion between "strain ACE species" (chain terminated by a tertiary 1-oxoniacyclobutane ion, Al) and "strain-free ACE species" (chain terminated by a tertiary 1-oxoniacyclohexane ion, Tl) depends on the rate at which Ox converts the stable species T1 (kind of "dormant" species) into a living "propagating" center A1 (i.e., k aapp[Ox]). The role of the THP solvent associated with the suspension of irreversible and reversible transfer reactions to polymer, when the polymerization is initiated with EMOA, was predicted by our kinetic considerations. The activation -deactivation pseudoequilibrium coefficient (Qt) was then calculated in a pure theoretical basis. From the measured apparent rate constant of Ox (kOxapp) and THP (kTHPapp = ka(endo)app) consumption, Qt and reactivity ratio (kp/kd, k a(endo)/ka(exo), and ks/ka(endo) were calculated, which then allow the determination of the transition rate constant of elementary step reactions that governs the increase of Mu with conversion. © 2009 American Chemical Society.

Fiber grating type dependence of temperature and strain coefficients and application to simultaneous temperature and strain measurement

Although fiber Bragg gratings (FBGs) have been widely used as advanced optical sensors, the cross-sensitivity between temperature and strain has complicated independent measurement procedures for these two measurands. We report here, for the first time to our knowledge, the results of a systematic investigation of the dependence of both temperature and strain sensitivities on the grating type, including the well-known Type I, Type IIA, and a new type which we have designated Type IA, using both hydrogen-free and hydrogenated B/Ge codoped fibers. We have identified distinct sensitivity characteristics for each grating type, and we have utilised them to implement a novel dual-grating, dual-parameter sensor device with performance superior to that of previously reported grating-based structures.

Use of dual-grating sensors formed by different types of fiber Bragg gratings for simultaneous temperature and strain measurements

We report on a systematic investigation of the dependence of both temperature and strain sensitivities on the fiber Bragg grating type, including the well-known Type I, Type IIA, and a new type that we have designated Type IA, using both hydrogen-free and hydrogenated B/Ge codoped fibres. We have identified distinct sensitivity characteristics for each grating type, and we have used them to implement a novel dual-grating, dual-parameter sensor device. Three dual-grating sensing schemes with different combinations of grating type have been constructed and compared, and that of a Type IA-Type IIA combination exhibits the best performance, which is also superior to that of previously reported grating-based structures. The characteristics of the measurement errors in such dual-grating sensor systems is also presented in detail. © 2004 Optical Society of America.