Photosynthesis of herbaceous plants from nutrient-poor tropical forests

Photosynthetic characteristics, specific leaf mass, chlorophyll and total leaf nitrogen concentrations of four herbaceous plants (Dicranopteris linearis, Hanguana malayana, Pentaphragma ellipticum, Tacca integrifolia) from nutrient-poor tropical forests showed that all these plants were well-adapted to their natural growth environments. No photoinhibition was observed even in the understorey plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Modela-r as a Froude and Strouhal dimensionless numbers combination for dynamic similarity in running

The aim of this study was to test the hypothesis that running at fixed fractions of Froude (Nfr) and Strouhal (Str) dimensionless numbers combinations induce dynamic similarity between humans of different sizes. Nineteen subjects ran in three experimental conditions, (i) constant speed, (ii) similar speed (Nfr) and (iii) similar speed and similar step frequency (Nfr and Str combination). In addition to anthropometric data, temporal, kinematic and kinetic parameters were assessed at each stage to measure dynamic similarity informed by dimensional scale factors and by the decrease of dimensionless mechanical parameter variability. Over a total of 54 dynamic parameters, dynamic similarity from scale factors was met for 16 (mean r=0.51), 32 (mean r=0.49) and 52 (mean r=0.60) parameters in the first, the second and the third experimental conditions, respectively. The variability of the dimensionless preceding parameters was lower in the third condition than in the others. This study shows that the combination of Nfr and Str, computed from the dimensionless energy ratio at the center of gravity (Modela-r) ensures dynamic similarity between different-sized subjects. The relevance of using similar experimental conditions to compare mechanical dimensionless parameters is also proved and will highlight the study of running techniques, or equipment, and will allow the identification of abnormal and pathogenic running patterns. Modela-r may be adapted to study other abilities requiring bounces in human or animal locomotion or to conduct investigations in comparative biomechanics.     

A study on in vitro glycation processes by matrix-assisted laser desorption ionization mass spectrometry

The number of glucose molecules condensed on glycated bovine serum albumin have been easily determined by means of matrix-assisted laser desorption/ionization mass spectrometry. Measurements were carried out on samples from incubation of the proteins with glucose at different concentrations (0.02 M, 0.2 M, 2 M and 5 M). A clear increase in molecular mass of BSA with respect to incubation time is detected. In contrast to what is observed with fluorescence, the plots of molecular mass increase vs. incubation time show tha occurrence of a steady state, corresponding to the complete saturation of all the protein sites against glucose. Comparison of fluorescence and molecular mass data reveals that some further reactions, different from condensation, must take place, which could be in principle either intramolecular or originated by reactivity of modified condensed gluocse moieties vs. free glucose.     

Evaluation of automated analysis of 15N and total N in plant material and soil

Simultaneous determination of ¹⁵N and total N using an automated nitrogen analyser interfaced to a continuous-flow isotope ratio mass spectrometer (ANA-MS method) was evaluated. The coefficient of variation (CV) of repeated analyses of homogeneous standards and samples at natural abundance was lower than 0.1%. The CV of repeated analyses of ¹⁵N-labelled plant material and soil samples varied between 0.3% and 1.1%. The reproductibility of repeated total N analyses using the automated method was comparable to results obtained with a semi-micro Kjeldahl procedure. However, the automated method gave results which were 3% to 5% higher than those obtained with the Kjeldahl procedure. Since only small samples can be analysed, careful sample homogenization and fine grinding are very important. Evaluation of a diffusion method for preparing nitrate and ammonium in solution for automated ¹⁵N analysis showed that the recovery of inorganic N in the NH₃ trap was lower when the N was diffused from water than from 2 M KCl. The results also indicated that different proportions of the NO₃ ^- and the NH₄ ⁺ in aqueous solution were recovered in the trap after combined diffusion. The method is most suited for diffusing either NO₃ ^- or NH₄ ⁺ alone, but can be used for combined diffusion of the two ions.     

Cation export from Alaskan arctic watersheds

The concentrations and stream fluxes of Na, K, Ca and Mg were determined in 1978, 1980 and 1981 in the Toolik Lake watershed and in 1978 in the upper Kuparuk River watershed. The annual export of K was strongly influenced by high K concentrations at the initiation of spring melt. Potassium concentrations were positively correlated with concentrations of particulate and dissolved organic carbon, particulate and dissolved phosphorus, and particulate, dissolved organic and ammonium nitrogen, suggesting a common origin in the decomposition of tundra plants. Calcium and Mg stream concentrations were generally highest in July and August when the depth of the soil active layer reached a maximum of ∼ 0.5 m. Precipitation-derived Na and K accounted for up to half of the Na and K stream export while chemical weathering supplied > 85 % of exported Ca and Mg. Cation export rates in these arctic foothill watersheds are among the lowest recorded.     

Optimization of protocols for microinjection-based delivery of cryoprotective agents into Japanese whiting Sillago japonica embryos

Microinjection has proven useful for introduction of low-permeability cryoprotective agents (CPAs) into fish eggs or embryos for cryopreservation. In this work, we examined the suitable conditions for single or combined microinjection into the perivitelline space (PS) and the yolk mass (YM) of embryos of the Japanese whiting, an alternative marine fish model for embryo cryopreservation studies. The parameters examined were injection volume, CPA type and concentration, vehicle (diluent), and suitable developmental stage. Somites and tail elongation embryos tolerated single or combined injection with 2.1 and 15.6 nl in the PS and YM, respectively, whereas earlier embryonic stages tolerated only up to 8.2 nl in the YM. The injected solutions diffused rapidly throughout the PS and YM and remained contained within each compartment unless in the case of structural damage caused by injection of larger volumes. Yamamoto solution was marginally better as a vehicle for microinjection of CPAs than fish Ringer and phosphate buffer saline whereas ¼ artificial sea water was clearly unsuitable. Ethylene glycol was well tolerated by embryos in all developmental stages whereas 1, 2-propylene glycol was suitable only for early embryonic stages. Overall, microinjection was efficient in delivering high loads of CPAs inside whiting embryos more swiftly than previously obtained for this species by immersion-based impregnation protocols. Embryos microinjected with CPAs showed a decrease in embryo nucleation temperature and an increase in chilling tolerance. CPA-microinjected embryos will provide valuable materials to optimize the remaining parameters that are critical for successful cryopreservation such as cooling and warming strategies.