Fungal disease incidence along tree diversity gradients depends on latitude in European forests

European forests host a diversity of tree species that are increasingly threatened by fungal pathogens, which may have cascading consequences for forest ecosystems and their functioning. Previous experimental studies suggest that foliar and root pathogen abundance and disease severity decrease with increasing tree species diversity, but evidences from natural forests are rare. Here, we tested whether foliar fungal disease incidence was negatively affected by tree species diversity in different forest types across Europe. We measured the foliar fungal disease incidence on 16 different tree species in 209 plots in six European countries, representing a forest‐type gradient from the Mediterranean to boreal forests. Forest plots of single species (monoculture plots) and those with different combinations of two to five tree species (mixed species plots) were compared. Specifically, we analyzed the influence of tree species richness, functional type (conifer vs. broadleaved) and phylogenetic diversity on overall fungal disease incidence. The effect of tree species richness on disease incidence varied with latitude and functional type. Disease incidence tended to increase with tree diversity, in particular in northern latitudes. Disease incidence decreased with tree species richness in conifers, but not in broadleaved trees. However, for specific damage symptoms, no tree species richness effects were observed. Although the patterns were weak, susceptibility of forests to disease appears to depend on the forest site and tree type.     

Potent inhibitors of farnesyltransferase and geranylgeranyltransferase-I

Compound 1 has been shown to be a dual prenylation inhibitor with FPTase (IC50=2 nM) and GGPTase-I (IC50=95 nM). Analogues of 1, which replaced the cyanophenyl group with various biaryls, led to the discovery of highly potent dual FPTase/GGPTase-I inhibitors. 4-trifluoromethylphenyl, trifluoropentynyl, and trifluoropentyl were identified as good p-cyano replacements.     

Response of field-grownCasuarina equisetifolia to inoculation withFrankia strain ORS 021001 entrapped in alginate beads

A large scale field experiment (ca 1 ha) was carried out in Senegal, to evaluate the response ofCasuarina equisetifolia to inoculation withFrankia strain ORS 021001 entrapped in alginate beads. Biomasses (expressed as dry weight or total nitrogen) of assimilatory branchlets, wood and roots, and nodules were measured in uninoculated and inoculated trees, randomly sampled 1,2 and 3 years after transplantation in the field. When biomasses were expressed as dry weight, increases due to inoculation were similar at the three sampling dates, 45, 36 and 40%, respectively. When biomasses were expressed as total nitrogen, the response to inoculation with time was much higher in the 2nd year than in the 1st and 3rd year. N₂ fixation, estimated using the difference method reached 2.48, 12.25 and 13.44 g N₂ fixed annually per tree. Correspondingly, nodule dry weights, expressed in g per tree, were 2.5, 12.18 and 22.75 at the end of the 1 st, 2nd and 3rd year, respectively. In spite of the positive response of field-grownCasuarina equisetifolia to inoculation, the decrease of N₂ fixation observed in the third year was probably due to unfavorable climatic conditions coupled with insect attacks at the beginning of the third year.     

Activation of glycogenolysis in perfused rat livers by glucagon and metabolic inhibitors

The activation of hepatic glycogenolysis by glucagon and metabolic inhibitors was studied in isolated perfused livers from fed rats. Glucose production rates and phosphorylase activity were increased by all these agents. If iodoacetate (1 mM) and cyanide (1 mM) were infused simultaneously, glycogenolysis was activated to the same extent as by glucagon (1 nM). The effects of the hormone were additive to those of cyanide, but not to those of iodoacetate. When glycogen breakdown was maximally activated by cyanide plus glucagon, additional iodoacetate was inhibitory. The glucagon-induced release of cyclic AMP into the perfusate was partially suppressed by iodoacetate. The inhibitors caused various degrees of depletion of the tissue ATP content and parallel augmentation of the AMP levels. ADP rose to a lesser extent. Indirect evidence suggested that of a progressive lowering of the cellular ATP levels was accompanied by an inhibition of enzyme dephosphorylation as well as of phosphorylation processes. However, dephosphorylation appeared to be more sensitive to changes of the energy balance, resulting in an activation of phosphorylase in response to the metabolic inhibitors.     

Age-dependent changes in extracellular proteins, aminopeptidase and proteinase activities in Frankia isolate BR

To investigate protein secretion by the nitrogen-fixing actinomycete Frankia isolate BR, we designed a rapid DEAE adsorption, salt elution and Biogel P6DG desalination method to concentrate protein from the growth medium. Secreted proteins reached a maximum concentration (5.6 gm l-1) in the medium at growth arrest. Analysis by SDS-PAGE detected up to 63 extracellular polypeptides when Frankia cells were grown under stirred conditions in BAP medium supplemented with phosphatidylcholine and MES buffer and 65 proteins in stirred BAP media alone. The pattern of extracellular polypeptides changed during growth. Several extracellular proteolytic activities were detected and compared with intracellular ones. The substrate specificity of the extracellular and intracellular aminopeptidase activities were the same. Also, the electrophoretic migration patterns of secreted and intracellular aminopeptidases could not be distinguished. Secretion of the proline-specific aminopeptidase FAP proteinase (PF) were secreted: 10 had the same electrophoretic mobility as their intracellular counterparts after SDS-gelatine-PAGE while five (PF - 39.5, PF - 38.5, PF - 36.5, PF - 25.5 and PF - 20.5 kDa) had a different electrophoretic mobility and, therefore, appeared to be exclusively extracellular. At least seven extracellular proteinases appeared to increase coordinately in activity shortly before growth arrest.     

An examination of the potential role of spider digestive proteases as a causative factor in spider bite necrosis

Tissue necrosis following spider bites is a widespread problem. In the continental United States, the brown recluse (Loxosceles reclusa), hobo spider (Tegenaria agrestis), garden spider (Argiope aurantia) and Chiracanthium species, among others, reportedly cause such lesions. The exact mechanism producing such lesions is controversial. There is evidence for both venom sphingomyelinase and spider digestive collagenases. We have examined the role of spider digestive proteases in spider bite necrosis. The digestive fluid of A. aurantia was assayed for its ability to cleave a variety of connective tissue proteins, including collagen. Having confirmed that the fluid has collagenases, the digestive fluid was injected into the skin of rabbits to observe whether it would cause necrotic lesions. It did not. The data do not support the suggestions that spider digestive collagenases have a primary role in spider bite necrosis.     

Coordinate increase in activity of proteinase subunits of the 1300-kDa megaproteinase of Frankia strain BR: role of carbon source depletion and extracellular metabolites

We have recently described the presence of a high molecular mass multicatalytic proteinase complex (megaproteinase; 28 S, 1300 kDa) in Frankia strain BR. The complex dissociates into 11 low molecular mass proteinase subunits (40-19 kDa) when subjected to sodium dodecyl sulfate - gelatin - polyacrylamide gel electrophoresis. We show here that the activity of these proteinase subunits strongly increased after cessation of growth in stirred BAP-PCM mineral medium. Subsequent addition of either BAP medium components or sodium propionate alone, as carbon source, to a Frankia culture at the end of the exponential growth phase was found to prolong growth for 1 additional day, and to delay the increase in activity of the proteinase subunits for 3 days after cessation of growth. Addition of ammonium chloride alone, as nitrogen source, had no effect. On the other hand, when Frankia cells in the late exponential phase (3 days) were resuspended in a culture filtrate recovered from a 5-day-old culture and supplemented with BAP-PCM medium components, the biomass yield decreased to about 50%. Also, the activity of the proteinase subunits increased as soon as growth ceased. The ability of this culture filtrate to inhibit growth and stimulate the activity of proteinase subunits was partially lost by heating or was largely removed by DEAE-cellulose treatment. Thus, our findings indicate an extracellular control of Frankia megaproteinase activity, suggesting that carbon source depletion and probably accumulation of heat-sensitive growth-inhibiting metabolites in the medium are determining factors.     

Potassium,calcium and magnesium antagonism in clones of Populus trichocarpa

Two clones of Populus trichocarpa varying in growth rate were grown in nutrient solutions with a range of K supply. In the leaves an antagonism between the levels of K and Ca+Mg was found, this was most extreme in the older leaves. Analysis of the contents of these elements in leaf vacuoles and cytoplasm suggests that in the vacuoles the total contents of K+Ca+Mg are controlled to maintain ionic and osmotic balance. At low K supply, the K deficit in the cytoplasm is not balance by accumulation of Ca and Mg, and it is suggested that other organic osmotica may accumulate. The regulation of K+Mg+Ca supplied to the leaves seems to be regulated by the roots and is not simple competition of ions for uptake sites at the plasmalemma.