Distance-dependent pollen limitation of seed set in some insect-pollinated dioecious plants

By applying hand pollination, we studied pollen limitation of seed set of female plants in four dioecious plant species with insect-pollination. The effect of hand pollination increased with distance to the nearest male plant. Distances at which seed set was 50% of its maximal value (after hand pollination) were: 2.3 m for Valeriana dioica, 5.3 m for Salix repens, 8.5 m for Asparagus officinale and 10.6 m for Bryonia dioica. We discuss to what extent the reduced seed set was caused by either fewer visits or by visits of a lower quality. We argue that quantifying distance-dependent seed set in dioecious plants may be a good way of studying effects of habitat fragmentation on the breakdown of mutualistic pollination systems.     

Evidence for multiple modes of neutrophil serine protease recognition by the EAP family of Staphylococcal innate immune evasion proteins

Neutrophils contain high levels of chymotrypsin‐like serine proteases (NSPs) within their azurophilic granules that have a multitude of functions within the immune system. In response, the pathogen Staphylococcus aureus has evolved three potent inhibitors (Eap, EapH1, and EapH2) that protect the bacterium as well as several of its secreted virulence factors from the degradative action of NSPs. We previously showed that these so‐called EAP domain proteins represent a novel class of NSP inhibitors characterized by a non‐covalent inhibitory mechanism and a distinct target specificity profile. Based upon high levels of structural homology amongst the EAP proteins and the NSPs, as well as supporting biochemical data, we predicted that the inhibited complex would be similar for all EAP/NSP pairs. However, we present here evidence that EapH1 and EapH2 bind the canonical NSP, Neutrophil Elastase (NE), in distinct orientations. We discovered that alteration of EapH1 residues at the EapH1/NE interface caused a dramatic loss of affinity and inhibition of NE, while mutation of equivalent positions in EapH2 had no effect on NE binding or inhibition. Surprisingly, mutation of residues in an altogether different region of EapH2 severely impacted both the NE binding and inhibitory properties of EapH2. Even though EapH1 and EapH2 bind and inhibit NE and a second NSP, Cathepsin G, equally well, neither of these proteins interacts with the structurally related, but non‐proteolytic granule protein, azurocidin. These studies expand our understanding of EAP/NSP interactions and suggest that members of this immune evasion protein family are capable of diverse target recognition modes.     

Parasites of fishes in the recently inundated ephemeral Lake Liambezi,Namibia

Lake Liambezi forms the periodic connection between the upper Zambezi, Kwando and Okavango rivers. A full parasitological assessment was conducted on 86 fish, representing 14 species in six families sampled in August 2011. Parasite diversity was low and dominated by species with complex life cycles involving intermediate hosts. Most prevalent were larval nematodes (Contracaecum sp.) infecting 12 and Trypanasoma sp. infecting nine of the 14 host species. The intra-erythrocytic parasite Babesiosoma mariae was found in the blood of Coptodon rendalli and Oreochromis andersonii with prevalence of 50% and 60%, respectively. The host-specific monogenean Annulotrema hepseti was recorded only from H. cuvieri with a prevalence of 100%. Notable absences were the copepod and branchiuran parasites that have direct lifecycles and usually occur in high prevalence and abundance in the region. Because parasites with direct life cycles can only be transported into the lake on the host fish, their absence suggests limited immigration of infected fishes into the lake. This suggests that internal recruitment dominates over immigration in the fish population dynamics in Lake Liambezi.     

Holling's “hungry mantid” model for the invertebrate functional response considered as a Markov process. Part I: The full model and some of its limits

In this paper we give an analytical reformulation of Holling's (1966) simulation model for invertebrate predatory behaviour. To this end we represent a population of predators as a frequency distribution over a space of (physiological) states. The functional response of a predator is calculated from the (stable) equilibrium distribution of its state as a function of prey density.Starting from the general model various other models are obtained by limit processes, some of them new and some of them old. The more interesting of which will be studied in further papers in this series.List of Notation a rate constant of digestion - b maximum of rate constant of prey encounter in the mantid - b maximum pursuit duration in the mantid (_p(0)) - c satiation threshold for search - c satiation threshold for pursuit in the mantid: c=c(b-D_s/v)/b - D _m maximum sighting distance - D _p pursuit distance - D _s strike distance - expectation operator - f, f ₀ rate of change of satiation during search - f ₁ rate of change of satiation during prey handling - F functional response: number of prey eaten per unit of time by one predator - g rate constant of effective prey encounter in the gobbler and sucker - g₀ rate constant of prey encounter - g₁ probability of no prey loss from pursuit - g₂ probability of no prey escaping during pursuit - H Holling secretary correction factor in the sucker: fraction of the time spent searching - k _R density of R - k_T probability density of maximum prey handling time - K probability that maximum prey handling time is _e, i.e. pursuit duration is zero - K _R distribution function of R - N number of prey caught - p (marginal) density of S - p₀ density of S in search - p₁ simultaneous density of S and T - P probability - p ₁ marginal density of S in handling prey - q probability of strike success - R ratio of realized to maximum sighting distance - s, S satiation - satiation axis - t time - handling time axis - u eating speed - U homogeneous(0,1) random variable - v pursuit speed - V exponential(1) random variable - w prey weight - W exponential(_m) random variable - x prey density - ratio of maximum successful pursuit duration to meal duration (_pm/_e) - _pm - relative duration of successful pursuit (_p/_pm) - ratio of shortest to largest sighting distance - x_e - time already spent handling a prey item - rate of prey loss during prey handling - prey escape rate during pursuit - prey biomass density (xw) - , T maximum time still to be spent handling a prey item - _e meal duration - _m maximum handling time ( _e+ _p) - _p duration of successful pursuit - _pm maximum duration of successful pursuit (_p(0)) - hazard rate - _m maximum of hazard rate - scaled functional response (wF) - minimal i-state space     

Melittin-induced changes of the macroscopic structure of phosphatidylethanolamines

The binding of melittin to phosphatidylethanolamine model systems and its influence on the supramolecular organization of the lipid were investigated with binding assays, differential scanning calorimetry, 31P NMR, freeze-fracture electron microscopy, and small-angle X-ray scattering. The results are compared with binding to an analogous phosphatidylcholine and structural consequences thereof. Melittin binds with similar affinity to both lipid types in the liquid-crystalline state; at gel-phase temperatures, in contrast, interaction with phosphatidylethanolamine is much weaker and does not lead to the bilayer fragmentation observed for phosphatidylcholines. With regard to phosphatidylethanolamine polymorphism, it is shown that melittin acts as an inhibitor of HII-phase formation and as a stabilizer of the bilayer organization. It is demonstrated that the remarkable variety of effects of melittin on the polymorphism of different membrane phospholipids can be understood in a relatively simple concept, taking into account the relative position and the shape of the interacting components.     

Isolation of alveolar type II cells from fetal rat lung by differential adherence in monolayer culture

Type II alveolar epithelial cells were isolated from fetal rat lung by differential adherence in monolayer culture. The preparation had a high degree of purity, as assessed by phase contrast microscopy and immunocytochemistry. Purity, based on reactivity with specific anti-adult lung serum (SAALS), which recognizes only type II cells, was 91% for cells isolated from 19-day fetal lungs and 79% for cells isolated from 21-day fetal lungs. The lower purity of type II cells in cultures derived from 1-day postnatal rat lungs (51% cells reactive with SAALS) is probably due to a lower tendency of the type II cells from neonatal rats to adhere to culture dishes than of type II cells from fetal rats. Type II cells isolated from 21-day fetal lungs contained a higher percentage phosphatidylglycerol and incorporated [Me-3H]choline faster into phosphatidylcholine (PC) than type II cells isolated from 19-day fetal lungs. Moreover, in cell preparations derived from lungs at fetal day 21, a higher percentage of epithelial cells contained lamellar bodies than in preparations derived from lungs at fetal day 19. The observation of these differences in the stage of maturation indicates that these differences, which are typical features of the original material, are not obliterated by differentiation during the culture. Type II cells isolated according to the present procedure were capable of synthesizing PC with a high percentage of the disaturated species. This method for the isolation of fetal type II cells may be a useful tool in studies concerning surfactant synthesis and its regulation in the fetal lung.     

Crystallization and preliminary X-ray study of a lipase from Pseudomonas glumae.

Lipase from Pseudomonas glumae has been purified and crystallized in two forms, using the hanging drop method of vapour diffusion at 4 degrees C and 15 degrees C. Both forms grew at pH 9.0 from 0.1 M-Tris buffer in the presence of 10% (v/v) acetone. Form 1 was crystallized from 27 to 29% polyethylene glycol in the presence of less than 0.5% (v/v) n-dodecyl-beta-D-glucopyranoside. Form 2 was grown from 17 to 19% ammonium sulphate in the presence of 1% n-octyl-beta-D-glucopyranoside. Form 1 is orthorhombic with space group P2(1)2(1)2(1), and cell dimensions of a = 158.1 A, b = 158.6 A, c = 63.4 A, Form 2 is tetragonal with space group P4(1)2(1)2 (or P4(3)2(1)2) and cell dimensions of a = 89.3 A, c = 180.4 A. Form 1 probably has four molecules per asymmetric unit and diffracts to at least 2.5 A. Form 2 has two molecules per asymmetric unit and diffracts to at least 3.0 A.     

Selective inhibition of prostaglandin biosynthesis by gold salts and phenylbutazone

Gold salts and phenylbutazone selectively inhibit the synthesis of PGF_2α and PGE₂ respectively. Lowered production of one prostaglandin species is accompanied by an increased production of the other. Selective inhibition by these drugs was observed in the presence of adrenaline, reduced glutathione and copper sulphate under conditions when most anti-inflammatory compounds inhibited PGE₂ and PGF_2α syntheses equally. It is postulated that selective inhibitors may have a different mode of action in vivo and beneficial effects may be related to the endogenous ratio of PGE to PGF required for normal function.