Land use legacy effects on woody vegetation in agricultural landscapes of south‐western Ethiopia

Aim

Past land use legacy effects—extinction debts and immigration credits—might be particularly pronounced in regions characterized by complex and dynamic landscape change. The aim of this study was to evaluate how current woody plant species distribution, composition and richness related to historical and present land uses.

Location

A smallholder farming landscape in south‐western Ethiopia.

Methods

We surveyed woody plants in 72 randomly selected 1‐ha sites in farmland and grouped them into forest specialist, generalist and pioneer species. First, we investigated woody plant composition and distribution using non‐metric multidimensional scaling. Second, we modelled species richness in response to historical and current distance from the forest edge. Third, we examined diameter class distributions of trees in recently converted vs. permanent farmland.

Results

Historical distance was a primary driver of woody plant composition and distribution. Generalist and pioneer species richness increased with historical distance. Forest specialists, however, did not respond to historical distance. Only few old individuals of forest specialist species remained in both recently converted and permanent farmlands.

Main conclusions

Our findings suggest that any possible extinction debt for forest specialist species in farmland at the landscape scale was rapidly paid off, possibly because farmers cleared large remnant trees. In contrast, we found substantial evidence of immigration credits in farmland for generalist and pioneer species. This suggests that long‐established farmland may have unrecognized conservation values, although apparently not for forest specialist species. We suggest that conservation policies in south‐western Ethiopia should recognize not only forests, but also the complementary value of the agricultural mosaic—similar to the case of European cultural landscapes. A possible future priority could be to better reintegrate forest species in the farmland mosaic.

     

Flagella-driven chemotaxis towards exudate components is an important trait for tomato root colonization by Pseudomonas fluorescens

Motility is a major trait for competitive tomato root-tip colonization by Pseudomonas fluorescens. To test the hypothesis that this role of motility is based on chemotaxis toward exudate components, cheA mutants that were defective in flagella-driven chemotaxis but retained motility were constructed in four P. fluorescens strains. After inoculation of seedlings with a 1:1 mixture of wild-type and nonmotile mutants all mutants had a strongly reduced competitive root colonizing ability after 7 days of plant growth, both in a gnotobiotic sand system as well as in nonsterile potting soil. The differences were significant on all root parts and increased from root base to root tip. Significant differences at the root tip could already be detected after 2 to 3 days. These experiments show that chemotaxis is an important competitive colonization trait. The best competitive root-tip colonizer, strain WCS365, was tested for chemotaxis toward tomato root exudate and its major identified components. A chemotactic response was detected toward root exudate, some organic acids, and some amino acids from this exudate but not toward its sugars. Comparison of the minimal concentrations required for a chemotactic response with concentrations estimated for exudates suggested that malic acid and citric acid are among major chemo-attractants for P. fluorescens WCS365 cells in the tomato rhizosphere.     

Heat shock protein 27 is the major differentially phosphorylated protein involved in renal epithelial cellular stress response and controls focal adhesion organization and apoptosis

We used two-dimensional difference gel electrophoresis to determine early changes in the stress-response pathways that precede focal adhesion disorganization linked to the onset of apoptosis of renal epithelial cells. Treatment of LLC-PK1 cells with the model nephrotoxicant 1,2-(dichlorovinyl)-L-cysteine (DCVC) resulted in a >1.5-fold up- and down-regulation of 14 and 9 proteins, respectively, preceding the onset of apoptosis. Proteins included those involved in metabolism, i.e. aconitase and pyruvate dehydrogenase, and those related to stress responses and cytoskeletal reorganization, i.e. cofilin, Hsp27, and alpha-b-crystallin. The most prominent changes were found for Hsp27, which was related to a pI shift in association with an altered phosphorylation status of serine residue 82. Although both p38 and JNK were activated by DCVC, only inhibition of p38 with SB203580 reduced Hsp27 phosphorylation, which was associated with accelerated reorganization of focal adhesions, cell detachment, and apoptosis. In contrast, inhibition of JNK with SP600125 maintained cell adhesion as well as protection against apoptosis. Active JNK co-localized at focal adhesions after DCVC treatment in a FAK-dependent manner. Inhibition of active JNK localization at focal adhesions did not prevent DCVC-induced phosphorylation of Hsp27. Overexpression of a phosphorylation-defective mutant Hsp27 acted as a dominant negative and accelerated the DCVC-induced changes in the focal adhesions as well as the onset of apoptosis. Our data fit a model whereby early p38 activation results in a rapid phosphorylation of Hsp27, a requirement for proper maintenance of cell adhesion, thus suppressing renal epithelial cell apoptosis.     

Enrichment for enhanced competitive plant root tip colonizers selects for a new class of biocontrol bacteria

Our group studies tomato foot and root rot, a plant disease caused by the fungus Forl (Fusarium oxysporum f.sp. radicis-lycopersici ). Several bacteria have been described to be able to control the disease, using different mechanisms. Here we describe a method that enables us to select, after application of a crude rhizobacterial mixture on a sterile seedling, those strains that reach the root tip faster than our best tomato root colonizer tested so far, the Pseudomonas fluorescens biocontrol strain WCS365. Of the five tested new isolates, four appeared to be able to reduce the number of diseased plants. Analysis of one of these strains, P. fluorescens PCL1751, suggests that it controls the disease through the mechanism 'competition for nutrients and niches', a mechanism novel for biocontrol bacteria. Moreover, this is the first report describing a method to enrich for biocontrol strains from a crude mixture of rhizobacteria. Another advantage of the method is that four out of five strains do not produce antifungal metabolites, which is preferential for registration as a commercial product.     

Molecular dissection of isolated disease features in mosaic neurofibromatosis type 1

Elucidation of the biological framework underlying the development of neurofibromatosis type 1 (NF1)-related symptoms has proved to be difficult. Complicating factors include the large size of the NF1 gene, the presence of several NF1 pseudogenes, the complex interactions between cell types, and the NF1-haploinsufficient state of all cells in the body. Here, we investigate three patients with distinct NF1-associated clinical manifestations (neurofibromas only, pigmentary changes only, and association of both symptoms). For each patient, various tissues and cell types were tested with comprehensive and quantitative assays capable of detecting low-percentage NF1 mutations. This approach confirmed the biallelic NF1 inactivation in Schwann cells in neurofibromas and, for the first time, demonstrated biallelic NF1 inactivation in melanocytes in NF1-related cafe-au-lait macules. Interestingly, both disease features arise even within a background of predominantly NF1 wild-type cells. Together, the data provide molecular evidence that (1) the distinct clinical picture of the patients is due to mosaicism for the NF1 mutation and (2) the mosaic phenotype reflects the embryonic timing and, accordingly, the neural crest-derived cell type involved in the somatic NF1 mutation. The study of the affected cell types provides important insight into developmental concepts underlying particular NF1-related disease features and opens avenues for improved diagnosis and genetic counseling of individuals with mosaic NF1.     

Evidence-based underwriting in the molecular age: the politics of reinsurance companies towards the genetics issue

One of the most contentious topics in public policy debates on genetics has been the use of genetic information by private insurance companies. Confronted with legislation prohibiting the use of genetics in private insurance, the insurance industry has been prompted to deal proactively with the issue. One central feature of this change in tactics is the investment in “evidence-based underwriting”, currently promoted by transnational reinsurance companies. This strategy should contribute to de-politicizing the genetics issue in insurance. Drawing on fieldwork in reinsurance companies and in the broader field of insurance, this article analyzes how reinsurance companies deal with this strategy of evidence-based underwriting and whether it has delivered on its promises. Making use of the theoretical work of Barry and others on the politics of calculation in transnational technical zones, we show how the explicit goal of evidence-based underwriting by reinsurance companies helps to reveal uncertainty in life underwriting, which in turn stimulates new contestation and discussion over the issue of genetics and, more generally, the life underwriting process. In fact, it seems that the turn towards evidence-based underwriting standards has provoked new sources of politicization. While the intentions of evidence-based underwriting strategies are to de-politicize the genetics issue, the effects of this politics of calculation may appear to be political (again).     

Inhibition of α-synuclein aggregation by small heat shock proteins

The fibrillization of α-synuclein (α-syn) is a key event in the pathogenesis of α-synucleinopathies. Mutant α-syn (A53T, A30P, or E46K), each linked to familial Parkinson's disease, has altered aggregation properties, fibril morphologies, and fibrillization kinetics. Besides α-syn, Lewy bodies also contain several associated proteins including small heat shock proteins (sHsps). Since α-syn accumulates intracellularly, molecular chaperones like sHsps may regulate α-syn folding and aggregation. Therefore, we investigated if the sHsps αB-crystallin, Hsp27, Hsp20, HspB8, and HspB2B3 bind to α-syn and affect α-syn aggregation. We demonstrate that all sHsps bind to the various α-syns, although the binding kinetics suggests a weak and transient interaction only. Despite this transient interaction, the various sHsps inhibited mature α-syn fibril formation as shown by a Thioflavin T assay and atomic force microscopy. Interestingly, HspB8 was the most potent sHsp in inhibiting mature fibril formation of both wild-type and mutant α-syn. In conclusion, sHsps may regulate α-syn aggregation and, therefore, optimization of the interaction between sHsps and α-syn may be an interesting target for therapeutic intervention in the pathogenesis of α-synucleinopathies.     

Isolation and identification of a cAMP generating peptide from the flesh fly,Neobellieria bullata (Diptera: Sarcophagidae)

The Manduca sexta Malpighian tubule assay system, developed to monitor adenylate cyclase activity, was used in combination with HPLC to isolate a novel cAMP generating peptide from 350,000 whole flesh flies, Neobellieria bullata. Mass spectrometry revealed a molecular mass of 5,047 daltons, and Edman degradation the following sequence: AGAEAEKLSGLSKYFNGTTMAGRANVAKATYAVIGLIIAYNVMKPKKK. This 48-mer peptide, called Neb-cGP, does not belong to the corticotropin releasing factor family of insect diuretic peptides. Electrophoresis and subsequent immunoblotting of peptides immunoprecipitated from a homogenate of entire flies showed that one fly contained approximately 0.003 to 0.03 μg Neb-cGP and that 10 μg represents the lowest immunostainable amount on a Western blot. © 1996 Wiley-Liss, Inc.