Plant species diversity, plant biomass and responses of the soil community on abandoned land across Europe: idiosyncracy or above-belowground time lags

We examined the relationship between plant species diversity, productivity and the development of the soil community during early secondary succession on former arable land across Europe. We tested the hypothesis that increasing the initial plant species diversity enhances the biomass production and consequently stimulates soil microbial biomass and abundance of soil invertebrates. We performed five identical field experiments on abandoned arable land in five European countries (CZ, NL, SE, SP and UK) which allowed us to test our hypothesis in a range of climate, soil and other environmental factors that varied between the experimental sites. The initial plant diversity was altered by sowing seed mixtures of mid-successional grassland species with two or five grass species, one or five legumes and one or five forbs. The results of low and high sown diversity treatments were compared with plots that were naturally colonized by species present in the seed bank. In three out of the five field sites, there was no correlation between plant species number and plant biomass production, one site had a positive and the other a negative relation. Treatments with a high diversity seed mixture had a higher biomass than the naturally colonized plots. However, there was no significant difference between high and low sown diversity plots at four out of five sites. The three-year study did not give any evidence of a general bottom-up effect from increased plant biomass on biomass of bacteria, saprophytic fungi or abundance of microarthropods. The biomass of arbuscular mycorrhizal was negatively related to plant biomass. The abundance of nematodes increased after abandonment and was related to plant biomass at four sites. Our results support the hypothesis that plant species diversity may have idiosyncratic effects on soil communities, even though studies on a longer term could reveal time lags in the response to changes in composition and biomass production of plant communities.     

Gene targeting and instability of Agrobacterium T-DNA loci in the plant genome

To develop a model system for studies of homologous recombination in plants, transgenic Nicotiana tabacum and Nicotiana plumbaginifolia lines were generated harbouring a single target T-DNA containing the negative selective codA gene encoding cytosine deaminase (CD) and the β-glucuronidase (GUS) gene. Subsequently, the target lines were transformed with a replacement-type T-DNA vector in which the CD gene and the GUS promoter had been replaced with a kanamycin-resistance gene. For both Nicotiana species kanamycin-resistant lines were selected which had lost the CD gene and the GUS activity. One tobacco line was the result of a precise gene targeting event. However, most other lines were selected due to a chromosomal deletion of the target locus. The deletion frequency of the target locus varied between target lines, and could be present in up to 20% of the calli which were grown from leaf protoplasts. T-DNA transfer was not required for induction of the deletions, indicating that the target loci were unstable. A few lines were obtained in which the target locus had been deleted partially. Sequence analysis of the junctions revealed deletion of DNA sequences between microhomologies. We conclude that T-DNAs, which are stable during plant development as well as in transmission to the offspring, may become unstable during propagation in callus tissue. The relationships between callus culture, genetic instability and the process of T-DNA integration and deletion in the plant genome are discussed.     

A simple method to change geometrical proportions of muscles by means of a tibial lengthening osteotomy in the rat

A method is designed to change geometrical proportions of muscles in the rat. After a tibial osteotomy, the application of a stainless steel prosthesis resulted in an elongation of about 8% of the tibia. In 23 out of 28 operated rats a correct application of the prosthesis was maintained till the rats were sacrificed. The operation caused hardly any muscle tissue damage. No disuse of the manipulated leg was observed in the operated rats.     

A three-step screening procedure to identify the mode of phloem loading in intact leaves

A three-step screening method was developed to identify the mode of phloem loading in intact leaves. Phloem loading of ¹⁴CO₂-derived photosynthate was challenged by p-chloromercuribenzenesulfonic acid (PCMBS) in leaves of dicotyledons with either a symplasmic (type 1, with intermediary cells as companion cells) or apoplasmic (type 2b, with transfer cells as companion cells) minor-vein configuration. Firstly, photosynthate export as the result of phloem loading was measured by collection of phloem exudate from the petiole. The PCMBS had virtually no effect on photosynthate export in representatives of type-1 families (Lamiaceae, Lythraceae, Onagraceae, Saxifragaceae). In contrast, photosynthate export was strongly reduced by PCMBS in representatives of type-2b families (Asteraceae, Balsaminaceae, Dipsacaceae, Linaceae, Tropaeolaceae, Valerianaceae) and type-2b members of polytypical families (Fabaceae, Scrophulariaceae). Secondly, densitometric measurements of leaf autoradiographs demonstrated that the contrast between the mesophyll and the lower-order veins was hardly affected by PCMBS treatment in type-1 species, whereas PCMBS strongly reduced the contrast in type-2b species. Thirdly, separate ¹⁴C-radioassays of vein and mesophyll tissues confirmed this observation. The three-step procedure thus revealed a strong and consistent reduction of phloem loading by PCMBS in type-2b species which was absent in type-1 species. In conclusion, phloem loading in type-2b species occurs via the apoplast and type-1 species execute an alternative — most likely symplasmic — mode of phloem loading.Abbreviations PCMBS p-chloromercuribenzenesulfonic acid - SE/CC-complex sieve element/companion cell complex We gratefully acknowledge the expert help of Dr. Maarten Terlou, Department of Image Processing and Design, University of Utrecht, in carrying out the densitometric measurements.     

Electron transfer between the hydrogenase from Desulfovibrio vulgaris (Hildenborough) and viologens. 2. Investigations by chronoamperometry

The electron transfer kinetics between the hydrogenase from Desulfovibrio vulgaris (strain Hildenborough) and the mediators methyl viologen, di-(n-aminopropyl) viologen and propyl viologen sulfonate have been investigated by chronoamperometry. Second-order rate constants were calculated on basis of the theory for a simple catalytic mechanism and are compared with the results obtained before by cyclic voltammetry (preceding paper in this journal). From the ionic-strength dependence and the observed differences in the rate constants for the differently charged viologens, the existence of an electrostatic interaction between mediator and a negatively charged part of the protein is confirmed. Chronoamperometry (computer-controlled) was found to possess advantages over cyclic voltammetry in the determination of homogeneous rate constants (faster, more accurate, and better reproducibility).     

A rapid method for obtaining monomeric glutaraldehyde

Summary A new method for the distillation of glutaradlehyde to obtain the monomeric form is presented. The monomer is obtained after only one distillation and it has a purification index (P_i) smaller than 0.20.