Digestive enzymes in midgut cells,endo-and ectoperitrophic contents,and peritrophic membranes of Spodoptera frugiperda (lepidoptera) larvae

In the midgut of Spodoptera frugiperda larvae, subcellular fractionation data suggest that aminopeptidase and part of amylase, carboxypeptidase A, dipeptidase, and trypsin are bound to the microvillar membranes; that major amounts of soluble dipeptidase, cellobiase, and maltase are trapped in the cell glycocalyx; and finally that soluble carboxypeptidase, amylase, and trypsin occur in intracellular vesicles. Most luminal acetylglucosaminidase is soluble and restricted to the ectoperitrophic contents. Aminopeptidase occurs in minor amounts bound to membranes both in the ectoperitrophic contents and incorporated in the peritrophic membrane. Amylase, carboxypeptidase A, and trypsin are found in minor amounts in the ectoperitrophic contents (both soluble and membrane-bound) and in major amounts in the peritrophic membrane with contents. Part of the activities recovered in the last mentioned contents corresponds to enzyme molecules incorporated in the peritrophic membrane. The results suggest that initial digestion is carried out in major amounts by enzymes in the endoperitrophic space and, in minor amounts, by enzymes immobilized in the peritrophic membrane. Intermediate and final digestion occur at the ectoperitrophic space or at the surface of midgut cells. The results also lend support to the hypothesis that amylase and trypsin are derived from membrane-bound forms, are released in soluble form by a microapocrine mechanism, and are partly incorporated into the peritrophic membrane. © 1994 Wiley-Liss, Inc.     

Inspection and evaluation of host plant by the butterfly Mechanitis lysimnia (Nymph., Ithomiinae) before laying eggs: a mechanism to reduce intraspecific competition

Parasites of all kinds affect the behaviour of their hosts, often making them more susceptible to predators. The associated loss in expected future reproductive success of infected hosts will vary among individuals, with younger ones having more lose than older ones. For this reason, young hosts would benefit more by opposing the effects of parasites than old ones. In a laboratory study, the effects of the trematode Telogaster opisthorchis on the anti-predator responses of the upland bully (Gobiomorphus breviceps) and of the common river galaxias (Galaxias vulgaris) were examined in relation to fish age. In a bully population where parasites were very abundant, the magnitude of the fish's anti-predator responses decreased as the number of parasites per fish increased, and this effect was significantly more pronounced in age 2 + and, to a lesser extent, age 3 + fish than in age 1 + fish. In another bully population where parasites were 10 times less abundant, similar effects were noticeable but not significant, whereas no effects of parasites on the responses of galaxiids to predators were apparent. Differences in the abundance of parasites and in their sites of infection in fish may explain the variability among host populations or species. However, in the bully population with high parasite abundance, parasitism has age-dependent effects on responses to predators, providing some support for the prediction that young fish with high expected future reproductive success invest more energy into opposing the effects of parasites than do older fish.     

Calcium exchanges in Anodonta cygnea: barriers and driving gradients

Electrical potential differences between the haemolymph and the extrapallial fluid, and between the haemolymph and the mantle cavity fluid, and ionic concentrations of calcium in the haemolymph and in extrapallial fluid were measured in vivo in Anodonta cygnea. The electrochemical potential of ionic calcium in the haemolymph is clearly above the electrochemical potential of ionic calcium in the environment and is very nearly in equilibrium with that of the extrapallial fluid. Simultaneous measurements of carbon dioxide partial pressure and pH in the extrapallial fluid showed that in this compartment ionic calcium is clearly above saturation. It is proposed that calcium deposition is regulated through the secretion of the organic matrix and by controlling the pH and the carbon dioxide partial pressure of the extrapallial fluid. An estimation of the minimum positive balance of calcium required to sustain shell growth together with the electrophysiological characterization of the mantle cavity epithelium showed that this tissue is not the route of entry of calcium into the animal.Abbreviations BW body weight - DW dry weight - E_EPF-S chemical potential difference - EPF extrapallial fluid - G_tot total conductance - I_sc short-circuit current - K_sp solubility product - MCE mantle cavity epithelium - MCF mantle cavity fluid - OME outer mantle epithelium - PCO₂ partial pressure of carbon dioxide - PVC Poly(vinyl chloride) - S shell - SEM standard error of mean - V _ic intracellular electrical potential - V _oc open-circuit voltage     

Phosphate transport in mitochondria: Past accomplishments,present problems,and future challenges

The requirement of inorganic phosphate (P_i) for oxidative phosphorylation in eukaryotic cells is fulfilled through specific P_i transport systems. The mitochondrial proton/phosphate symporter (P_ic) is a membrane-embedded protein which translocates P_i from the cytosol into the mitochondrial matrix. P_ic is responsible for the very rapid transport of most of the P_i used in ATP synthesis. During the past five years there have been advances on several fronts. Genomic and cDNA clones for yeast, bovine, rat, and human P_ic have been isolated and sequenced. Functional expression of yeast P_ic in yeast strains deficient in P_i transport and expression inEscherichia coli of a chimera protein involving P_ic and ATP synthase subunit have been accomplished. P_ic, in contrast to other members of the family of transporters involved in energy metabolism, was demonstrated to have a presequence, which optimizes the import of the precursor protein into mitochondria. Six transmembrane segments appear to be a structural feature shared between P_ic and other mitochondrial anion carriers, and recent-site directed mutagenesis studies implicate structure-functional relationships to bacteriorhodopsin. These recent advances on P_ic will be assessed in light of a more global interpretation of transport mechanism across the inner mitochondrial membrane.     

Molecular cloning and analysis of CDC28 and cyclin homologues from the human fungal pathogen Candida albicans

In the budding yeast Saccharomyces cerevisiae, progress of the cell cycle beyond the major control point in G1 phase, termed START, requires activation of the evolutionarily conserved Cdc28 protein kinase by direct association with GI cyclins. We have used a conditional lethal mutation in CDC28 of S. cerevisiae to clone a functional homologue from the human fungal pathogen Candida albicans. The protein sequence, deduced from the nucleotide sequence, is 79% identical to that of S. cerevisiae Cdc28 and as such is the most closely related protein yet identified. We have also isolated from C. albicans two genes encoding putative G1 cyclins, by their ability to rescue a conditional GI cyclin defect in S. cerevisiae; one of these genes encodes a protein of 697 amino acids and is identical to the product of the previously described CCN1 gene. The second gene codes for a protein of 465 residues, which has significant homology to S. cerevisiae Cln3. These data suggest that the events and regulatory mechanisms operating at START are highly conserved between these two organisms.     

Lipase catalyzed esterification of glycidol in organic solvents

We studied the resolution of racemic glycidol through esterification with butyric acid catalyzed by porcine pancreatic lipase in organic media. A screening of seven solvents (log P values between 0.49 and 3.0, P being the n-octanol-water partition coefficient of the solvent) showed that neither log P nor the logarithm of the molar solubility of water in the solvent provides good correlations between enantioselectivity and the properties of the organic media. Chloroform was one of the best solvents as regards the enantiomeric purity (e. p.) of the ester produced. In this solvent, the optimum temperature for the reaction was determined to be 35 degrees C. The enzyme exhibited maximum activity at a water content of 13 +/- 2% (w/w). The enantiomeric purity obtained was 83 +/- 2% of (S)-glycidyl butyrate and did not depend on the alcohol concentration or the enzyme water content for values of these parameters up to 200 mM and 25% (w/w), respectively. The reaction was found to follow a BiBi mechanism. (c) 1993 John Wiley & Sons, Inc.     

Cryptophytes: An emerging algal group in the rapidly changing Antarctic Peninsula marine environments

The western Antarctic Peninsula (WAP) is a climatically sensitive region where foundational changes at the basis of the food web have been recorded; cryptophytes are gradually outgrowing diatoms together with a decreased size spectrum of the phytoplankton community. Based on a 11-year (2008–2018) in-situ dataset, we demonstrate a strong coupling between biomass accumulation of cryptophytes, summer upper ocean stability, and the mixed layer depth. Our results shed light on the environmental conditions favoring the cryptophyte success in coastal regions of the WAP, especially during situations of shallower mixed layers associated with lower diatom biomass, which evidences a clear competition or niche segregation between diatoms and cryptophytes. We also unravel the cryptophyte photo-physiological niche by exploring its capacity to thrive under high light stress normally found in confined stratified upper layers. Such conditions are becoming more frequent in the Antarctic coastal waters and will likely have significant future implications at various levels of the marine food web. The competitive advantage of cryptophytes in environments with significant light level fluctuations was supported by laboratory experiments that revealed a high flexibility of cryptophytes to grow in different light conditions driven by a fast photo-regulating response. All tested physiological parameters support the hypothesis that cryptophytes are highly flexible regarding their growing light conditions and extremely efficient in rapidly photo-regulating changes to environmental light levels. This plasticity would give them a competitive advantage in exploiting an ecological niche where light levels fluctuate quickly. These findings provide new insights on niche separation between diatoms and cryptophytes, which is vital for a thorough understanding of the WAP marine ecosystem.     

Litter and soil biodiversity jointly drive ecosystem functions

The decomposition of litter and the supply of nutrients into and from the soil are two fundamental processes through which the above- and belowground world interact. Microbial biodiversity, and especially that of decomposers, plays a key role in these processes by helping litter decomposition. Yet the relative contribution of litter diversity and soil biodiversity in supporting multiple ecosystem services remains virtually unknown. Here we conducted a mesocosm experiment where leaf litter and soil biodiversity were manipulated to investigate their influence on plant productivity, litter decomposition, soil respiration, and enzymatic activity in the littersphere. We showed that both leaf litter diversity and soil microbial diversity (richness and community composition) independently contributed to explain multiple ecosystem functions. Fungal saprobes community composition was especially important for supporting ecosystem multifunctionality (EMF), plant production, litter decomposition, and activity of soil phosphatase when compared with bacteria or other fungal functional groups and litter species richness. Moreover, leaf litter diversity and soil microbial diversity exerted previously undescribed and significantly interactive effects on EMF and multiple individual ecosystem functions, such as litter decomposition and plant production. Together, our work provides experimental evidence supporting the independent and interactive roles of litter and belowground soil biodiversity to maintain ecosystem functions and multiple services.     

Calcineurin is associated with the cytoskeleton of cultured neurons and has a role in the acquisition of polarity.

Calcineurin is a calmodulin-dependent serine-threonine phosphatase found in many cell types but most abundant in neurons. To determine its localization in developing neurons, dissociated cultures from embryonic day 15 rat cerebellum were analyzed immunocytochemically after treatment with cytoskeletal-disrupting drugs. During the initial outgrowth of neurites, calcineurin is enriched in growth cones where its localization depends upon the integrity of both microtubules and actin filaments. Treatment with cytochalasin shifts calcineurin from the growth cone to the neurite shaft, and with nocadozole calcineurin translocates to the cell body. Therefore calcineurin is well positioned to mediate interactions between cytoskeletal systems during neurite elongation. By 14 d in culture, when the neurons have developed extensive neuronal contacts and synapses are present, calcineurin is predominantly in the neurite shaft. Incubation of cultured cells with Cyclosporin A or a specific peptide, both of which selectively inhibit calcineurin's phosphatase activity, prevented axonal elongation. Because the microtubule-associated protein tau appears to play a key role in asymmetric neurite elongation, we examined modifications in its phosphorylation state resulting from calcineurin inhibition. In contrast to the normal development of cerebellar macroneurons in which reactivity with the phosphorylation-dependent antibody, tau-1, progressively increases, there was a persistent inhibition of tau-1 reactivity in cells exposed to Cyclosporin A. These findings suggest a role for calcineurin in regulating tau phosphorylation and possibly modulating other steps required for the determination of polarity.