Laser absorption spectroscopy with an ATR prism--noninvasive in vivo determination of glucose.

The use of lasers as light sources in IR spectroscopy allows an improvement in measuring sensitivity by a factor of about 100 as compared with the conventional technique. In addition, the monochromaticity of lasers appreciably improves the resolution. Combining lasers with an ATR plate acting as test prism gets rid of transmission cells without impairing the measuring sensitivity. It also considerably reduces the thermal load on the test sample; in vivo measurements on biological tissue can thus be made simply.     

The effect of hydrogen peroxide on CO2 fixation of isolated intact chloroplasts

Low concentrations of hydrogen peroxide strongly inhibit CO₂ fixation of isolated intact chloroplasts (50% inhibition at 10⁻⁵ M hydrogen peroxide). Addition of catalase to a suspension of intact chloroplasts stimulates CO₂ fixation 2–6 fold, indicating that this process is partially inhibited by endogenous hydrogen peroxide formed in a Mehler reaction.

The rate of CO₂ fixation is strongly increased by addition of Calvin cycle intermediates if the catalase activity of the preparation is low. However, at high catalase activity addition of Calvin cycle intermediates remains without effect. Obviously the hydrogen peroxide formed at low catalase activity leads to a loss of Calvin cycle substrates which reduces the rate of CO₂ fixation.

3-Phosphoglycerate-dependent O₂-evolution is not influenced by hydrogen peroxide at a concentration (5 · 10⁻⁴ M) which inhibits CO₂ fixation almost completely. Therefore the inhibition site of hydrogen peroxide cannot be at the step of 3-phosphoglycerate reduction. Dark CO₂ fixation of lysed chloroplasts in a hypotonic medium is not or only slightly inhibited by hydrogen peroxide (2.5 · 10⁻⁴ M), if ribulose-1,5-diphosphate, ribose 5-phosphate or xylulose 5-phosphate were added as substrates. However, there is a strong inhibition of CO₂ fixation by hydrogen peroxide, if fructose 6-phosphate together with triose phosphate are used as substrates. This indicates that hydrogen peroxide interrupts the Calvin cycle at the transketolase step, leading to a reduced supply of the CO₂-acceptor ribulose 1,5-diphosphate.     

Model for external influences on cellular signal transduction pathways including cytosolic calcium oscillations

Experiments on the effects of extremely-low-frequency (ELF) electric and magnetic fields on cells of the immune system, T-lymphocytes in particular, suggest that the external field interacts with the cell at the level of intracellular signal transduction pathways. These are directly connected with changes in the calcium-signaling processes of the cell. Based on these findings, a theoretical model for receptor-controlled cytosolic calcium oscillations and for external influences on the signal transduction pathway is presented. We discuss the possibility that the external field acts on the kinetics of the signal transduction between the activated receptors at the cell membrane and the G-proteins. It is shown that, depending on the specific combination of cell internal biochemical and external physical parameters, entirely different responses of the cell can occur. We compare the effects of a coherent (periodic) modulation and of incoherent perturbations (noise). The model and the calculations are based on the theory of self-sustained, nonlinear oscillators. It is argued that these systems form an ideal basis for information-encoding processes in biological systems. © 1995 Wiley-Liss, Inc.     

From gene to phenotype in Drosophila and other organisms

The growing number of cloned eukaryotic genes lacking a defined or proven biological function poses a major challenge in 'reverse genetics'. A method is described here that permits efficient screening for new lesions in, or close to, genes corresponding to cloned DNA sequences of interest. The technique involves transposon mutagenesis, followed by screening of DNA isolated from a population of mutagenised individuals (or their progeny) for evidence that the population contains at least one individual in which transposon insertion has occurred at the target locus. Detection of rare individuals within the population is facilitated by the use of the polymerase chain reaction (PCR). Once recognised, specific individuals (or their progeny) are isolated from the population by a process of sib-selection. In cases where insertion of the transposon has occurred close to, but not within, the target locus, secondary events involving imprecise excision of the transposon will nonetheless allow the isolation of mutant individuals. Though the method was developed specifically for the transposon-mutagenesis of Drosophila, extensions to other organisms and to other mutagenic strategies are feasible and some of the possibilities are discussed.     

A modified dinucleotide motif specifies tRNA recognition by TLR7

RNA can function as a pathogen-associated molecular pattern (PAMP) whose recognition by the innate immune system alerts the body to an impending microbial infection. The recognition of tRNA as either self or nonself RNA by TLR7 depends on its modification patterns. In particular, it is known that the presence of a ribose methylated guanosine at position 18, which is overrepresented in self-RNA, antagonizes an immune response. Here, we report that recognition extends to the next downstream nucleotide and the effectively recognized molecular detail is actually a methylated dinucleotide. The most efficient nucleobases combination of this motif includes two purines, while pyrimidines diminish the effect of ribose methylation. The constraints of this motif stay intact when transposed to other parts of the tRNA. The results argue against a fixed orientation of the tRNA during interaction with TLR7 and, rather, suggest a processive type of inspection.     

Accumulation of germanium (Ge) in plant tissues of grasses is not solely driven by its incorporation in phytoliths

Ge/Si ratios of plant phytoliths have been widely used to trace biogeochemical cycling of Si. However, until recently, information on how much of the Ge and Si transferred from soil to plants is actually stored in phytoliths was lacking. The aim of the present study is to (i) compare the uptake of Si and Ge in three grass species, (ii) localize Ge and Si stored in above-ground plant parts and (iii) evaluate the amounts of Ge and Si sequestrated in phytoliths and plant tissues. Mays (Zea mays), oat (Avena sativa) and reed canary grass (Phalaris arundinacea) were cultivated in the greenhouse on soil and sand to control element supply. Leaf phytoliths were extracted by dry ashing. Total elemental composition of leaves, phytoliths, stems and roots were measured by ICP-MS. For the localization of phytoliths and the determination of Ge and Si within leaf tissues and phytoliths scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) was used. The amounts of Si and Ge taken up by the species corresponded with biomass formation and decreased in the order Z. mays > P. arundinacea, A. sativa. Results from LA-ICP-MS revealed that Si was mostly localized in phytoliths, while Ge was disorderly distributed within the leaf tissue. In fact, from the total amounts of Ge accumulated in leaves only 10% was present in phytoliths highlighting the role of organic matter on biogeochemical cycling of Ge and the necessity for using bulk Ge/Si instead of Ge/Si in phytoliths to trace biogeochemical cycling of Si.

     

Quantitative trait loci involved in the reproductive success of a parasitoid wasp

Dissecting the genetic basis of intraspecific variations in life history traits is essential to understand their evolution, notably for potential biocontrol agents. Such variations are observed in the endoparasitoid Cotesia typhae (Hymenoptera: Braconidae), specialized on the pest Sesamia nonagrioides (Lepidoptera: Noctuidae). Previously, we identified two strains of C. typhae that differed significantly for life history traits on an allopatric host population. To investigate the genetic basis underlying these phenotypic differences, we used a quantitative trait locus (QTL) approach based on restriction site‐associated DNA markers. The characteristic of C. typhae reproduction allowed us generating sisters sharing almost the same genetic content, named clonal sibship. Crosses between individuals from the two strains were performed to generate F2 and F8 recombinant CSS. The genotypes of 181 clonal sibships were determined as well as the phenotypes of the corresponding 4,000 females. Informative markers were then used to build a high‐quality genetic map. These 465 markers spanned a total length of 1,300 cM and were organized in 10 linkage groups which corresponded to the number of C. typhae chromosomes. Three QTLs were detected for parasitism success and two for offspring number, while none were identified for sex ratio. The QTLs explained, respectively, 27.7% and 24.5% of the phenotypic variation observed. The gene content of the genomic intervals was investigated based on the genome of C. congregata and revealed 67 interesting candidates, as potentially involved in the studied traits, including components of the venom and of the symbiotic virus (bracovirus) shown to be necessary for parasitism success in related wasps.