Topography strongly affects atmospheric deposition and canopy exchange processes in different types of wet lowland rainforest,Southwest Costa Rica

Bulk precipitation and throughfall were collected in a wet lowland rainforest in SW Costa Rica on an event basis to allow modelling the contributions of dry deposition and canopy exchange to nutrient inputs and internal cycling of nutrients. Estimates based on bulk precipitation underestimated total atmospheric deposition to tropical rainforests by up to 10-fold ignoring the contributions of dry deposition. Canopy exchange contributed most of the aboveground inputs to the forest soil of Na⁺, about half for K⁺, 10% for P and Mg²⁺ and negligible for N, C and other elements. Tree species composition did not account for the differences found in net throughfall between forest sites, and vegetation structure (plant area index) had only a small effect on net throughfall. Forest regrowth affected net throughfall through reduced soil fertility and differences in leaf traits. Topography most significantly affected net throughfall via increased dry deposition at sites of higher elevation and via soil fertility and increased canopy exchange at down slope sites.     

Periodic movements of Dictyostelium discoideum sorocarps

We report periodic movements during erection of Dictyostelium discoideum (Dd) sorocarps. Our observations lead to the working hypothesis that Dd sorocarp erection occurs by two superimposed processes: one periodic, with a modal period of 6 1/2 min, and one continuous. We tentatively identify the periodic process with cell movement into the apex of the Dd stalk, and the continuous process with cell vacuolation, together with stalk sheath extension.     

Combining microdilution with MicroResp™: microbial substrate utilization, antimicrobial susceptibility and respiration

Pharmacological studies focus on susceptibility of pathogenic microbes against specific drugs or combinations of them, ecological studies on substrate utilization efficiency of variable microbial communities. The MicroResp? system was especially developed to study soil microbial communities. It was slightly modified to facilitate exploring of microbial growth efficiency in a concentration-dependent fashion (microdilutions of carbohydrate mixtures or specific toxic chemicals). After turbidimetric growth assessment, colorimetric indicator plates (cresol red agar) were mounted to the assay plates. The substrate utilisation design is illustrated by glucose and a plant carbohydrate mixture, the antimicrobial susceptibility design by the naphthoquinone juglone. Dose-response effects are explored by curve fitting of nonlinear models that especially have been developed to detect hormetic effects that are characterized by stimulation at lower followed by inhibition at higher dosages (U- and inverse U-shaped effects). Multivariate analyses are presented utilizing metavariables that were obtained in the curve fitting process of the measured parameters growth and respiration and the factor growth efficiency.     

Vertebrate caudal gene expression gradients investigated by use of chick cdx-A/lacZ and mouse cdx-1/lacZ reporters in transgenic mouse embryos: evidence for an intron enhancer

The vertebrate caudal proteins, being upstream regulators of the Hox genes, play a role in establishment of the body plan. We describe analysis of two orthologous caudal genes (chick cdx-A and mouse cdx-1) by use of lacZ reporters expressed in transgenic mouse embryos. The expression patterns show many similarities to the expression of endogenous mouse cdx-1. At 8.7 days, cdx/lacZ activity within neurectoderm and mesoderm forms posterior-to-anterior gradients, and we discuss the possibility that similar gradients of cdx gene expression may function as morphogen gradients for the establishment of Hox gene expression boundaries. Our observations suggest that gradients form by decay of cdx/lacZ activity in cells that have moved anterior to the vicinity of the node. The cdx-A/lacZ expression pattern requires an intron enhancer that includes two functional control elements: a DR2-type retinoic acid response element and a Tcf/beta-catenin binding motif. These motifs are structurally conserved in mouse cdx-1.     

cdx4/lacZ and cdx2/lacZ protein gradients formed by decay during gastrulation in the mouse

Expression of the mouse caudal genes cdx4 and cdx2 is examined by use of lacZ reporter constructs expressed in transgenic mouse embryos. During early gastrulation, up to at least 8.5 days of development, reporter mRNA distributions are apparently similar to those of endogenous cdx mRNAs. By 8.25 to 8.8 days, cdx/lacZ protein activities have become distributed as posterior-to-anterior gradients along the neural and mesoderm tissues. The gradients form by decay of activity as cells become distanced from the regressing tailbud. In situ hybridization studies indicate that the decay is primarily in cdx/lacZ protein activities rather than mRNAs. As gastrulation proceeds, the locations of the gradients regress progressively posteriorly along the growing axis. Our results indicate how cdx4 and cdx2 protein gradients might be generated by decay during normal development. The smoothness of the gradients that we detect shows that there cannot be extensive mixing of cells once they leave the tailbud to contribute to the growing axis. An enhancer element located in the first intron of the cdx4 gene is essential for correct transgene expression.