Plant phylogeny drives arboreal caterpillar assemblages across the Holarctic

1. Assemblages of insect herbivores are structured by plant traits such as nutrient content, secondary metabolites, physical traits, and phenology. Many of these traits are phylogenetically conserved, implying a decrease in trait similarity with increasing phylogenetic distance of the host plant taxa. Thus, a metric of phylogenetic distances and relationships can be considered a proxy for phylogenetically conserved plant traits and used to predict variation in herbivorous insect assemblages among co‐occurring plant species.
2. Using a Holarctic dataset of exposed‐feeding and shelter‐building caterpillars, we aimed at showing how phylogenetic relationships among host plants explain compositional changes and characteristics of herbivore assemblages.
3. Our plant–caterpillar network data derived from plot‐based samplings at three different continents included >28,000 individual caterpillar–plant interactions. We tested whether increasing phylogenetic distance of the host plants leads to a decrease in caterpillar assemblage overlap. We further investigated to what degree phylogenetic isolation of a host tree species within the local community explains abundance, density, richness, and mean specialization of its associated caterpillar assemblage.
4. The overlap of caterpillar assemblages decreased with increasing phylogenetic distance among the host tree species. Phylogenetic isolation of a host plant within the local plant community was correlated with lower richness and mean specialization of the associated caterpillar assemblages. Phylogenetic isolation had no effect on caterpillar abundance or density. The effects of plant phylogeny were consistent across exposed‐feeding and shelter‐building caterpillars.
5. Our study reveals that distance metrics obtained from host plant phylogeny are useful predictors to explain compositional turnover among hosts and host‐specific variations in richness and mean specialization of associated insect herbivore assemblages in temperate broadleaf forests. As phylogenetic information of plant communities is becoming increasingly available, further large‐scale studies are needed to investigate to what degree plant phylogeny structures herbivore assemblages in other biomes and ecosystems.

     

Evidence against an abnormal hepatic microsomal lipid matrix as the primary genetic defect in the jaundiced Gunn rat

The congenitally jaundiced Gunn rat does not conjugate bilirubin but does conjugate bilirubin dimethyl diester. Partial defects in conjugating p-nitrophenol and demethylating aminopyrine are also evident. A proposed mechanism to explain this combination of findings is a defective microsomal membrane. To examine the 'matrix' of Gunn microsomal membranes, hepatic microsomes were isolated from Gunn (jj) and outbred Wistar (JJ) rats and were studied by electron paramagnetic resonance spectroscopy of 7-doxylstearic and 12-doxylstearic acid probes, fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene, glucose-6-phosphatase activity vs. temperature, and lipid analysis. The data indicate several factors related to lipid bilayer order do not differ in microsomes from jj and JJ.     

Thyroid hormones selectively modulate human alcohol dehydrogenase isozyme catalyzed ethanol oxidation

Thyroid hormones are potent, instantaneous, and reversible inhibitors of ethanol oxidation catalyzed by isozymes of class I and II human alcohol dehydrogenase (ADH). None of the thyroid hormones inhibits class III ADH. At pH 7.40 the apparent Ki values vary between 55 and 110 microM for triiodothyronine, 35 and greater than 200 microM for thyroxine, and 10 and 23 microM for triiodothyroacetic acid. The inhibition is of a mixed type toward both NAD+ and ethanol. The binding of the thyroid hormone triiodothyronine to beta 1 gamma 1 ADH is mutually exclusive with 1,10-phenanthroline, 4-methylpyrazole, and testosterone, identifying a binding site(s) for the thyroid hormones, which overlap(s) both the 1,10-phenanthroline site near the active site zinc atom and the testosterone binding site, the latter being a regulatory site on the gamma-subunit-containing isozymes and distinct from their catalytic site. The inhibition by thyroid hormones may have implications for regulation of ADH catalysis of ethanol and alcohols in the intermediary metabolism of dopamine, norepinephrine, and serotonin and in steroid metabolism. In concert with other hormonal regulators, e.g., testosterone, the rate of ADH catalysis is capable of being fine tuned in accord with both substrate and modulator concentrations.     

Local Conformation and Dynamics of Isoleucine in the Collagenase Cleavage Site Provide a Recognition Signal for Matrix Metalloproteinases

The mechanism by which enzymes recognize the “uniform” collagen triple helix is not well understood. Matrix metalloproteinases (MMPs) cleave collagen after the Gly residue of the triplet sequence Gly∼[Ile/Leu]-[Ala/Leu] at a single, unique, position along the peptide chain. Sequence analysis of types I-III collagen has revealed a 5-triplet sequence pattern in which the natural cleavage triplets are always flanked by a specific distribution of imino acids. NMR and MMP kinetic studies of a series of homotrimer peptides that model type III collagen have been performed to correlate conformation and dynamics at, and near, the cleavage site to collagenolytic activity. A peptide that models the natural cleavage site is significantly more active than a peptide that models a potential but non-cleavable site just 2-triplets away and NMR studies show clearly that the Ile in the leading chain of the cleavage peptide is more exposed to solvent and less locally stable than the Ile in the middle and lagging chains. We propose that the unique local instability of Ile at the cleavage site in part arises from the placement of the conserved Pro at the P₃ subsite. NMR studies of peptides with Pro substitutions indicate that the local dynamics of the three chains are directly modulated by their proximity to Pro. Correlation of peptide activity to NMR data shows that a single locally unstable chain at the cleavage site, rather than two or three labile chains, is more favorable for cleavage by MMP-1 and may be the determining factor for collagen recognition.     

Phospholipid methyltransferase activity in pancreatic islets: activation by calcium

Pancreatic islet homogenates contain a Mg2+-requiring phospholipid methyltransferase activity, the activity of which was doubled by calcium (K0.5 less than 5 microM). Other divalent metal ions stimulated the activity from 11 to 35%, but zinc and strontium were inhibitory. Cyclic AMP had no effect on the enzyme activity and cyclic GMP inhibited it slightly. Calcium increased the Vmax of the enzyme without affecting its Km with respect to S-adenosylmethionine (6 microM). Chlorpromazine, trifluoperazine, and dibucaine inhibited the calcium-stimulatable activity without affecting the activity in the absence of calcium. Phosphatidylserine stimulated, and arachidonic acid and palmitic acid inhibited, the basal enzyme activity. The methylated products were found to be primarily mono- and dimethylphosphatidylethanolamine (30%) and phosphatidylcholine (43%) and an, as yet unidentified, nonpolar lipid fraction (27%), as judged by thin-layer chromatography. In the presence of calcium, incorporation of methyl groups into phosphatidylcholine, mono- and dimethylphosphatidylethanolamine, and nonpolar lipids was increased by 131, 60, and 46%, respectively. Based on the localization of the enzyme activity in the insulin secretory granule fraction, it is proposed that phospholipid methylation plays a role in coupling the stimulus to the initial events in insulin secretion, leading to the exocytosis of insulin.     

Bacteriocin-resistant mutants of Erwinia chrysanthemi: possible involvement of iron acquisition in phytopathogenicity.

A series of bacteriocin-resistant mutants of Erwinia chrysanthemi 3937JRH were unable to elicit soft-rot symptoms on saintpaulia plants. The loss of pathogenicity was correlated with the disappearance of one to three outer membrane polypeptides (molecular weights, about 80,000 to 90,000) whose production in wild-type strains was greatly enhanced under iron-limited growth conditions. The mutants did not exhibit altered extracellular pectinolytic or cellulolytic activities.     

Interacting role of thyroxine and growth hormone in the hepatic synthesis of alpha 2u-globulin and its messenger RNA

Hypophysectomy completely abolishes and thyroidectomy results in a 90% reduction in the hepatic content of alpha 2u-globulin and its mRNA in the male rat. Thyroid hormone is also known to be required for the synthesis and secretion of pituitary growth hormone. In the hypothyroid rat either thyroxine or growth hormone was found to increase the activity and number of sequences of the mRNA for alpha 2u-globulin (measured by translational assay and hybridizational analysis with a cloned cDNA probe) to the euthyroid level. Treatment of hypophysectomized rats with a hormone combination containing growth hormone but not thyroxine increased the hepatic level of the mRNA for alpha 2u-globulin to that of normal animals. From these results we conclude that thyroxine indirectly influences the hepatic concentration of the mRNA for alpha 2u-globulin through its effect on pituitary growth hormone. Although administration of growth hormone to hypothyroid animals raised the hepatic concentration of alpha 2u-globulin mRNA to the euthyroid level, synthesis of alpha 2u-globulin remained low (50% of the normal). Complete recovery of alpha 2u-globulin synthesis required thyroxine. Therefore, in addition to an indirect effect on the hepatic level of alpha 2u-globulin mRNA, thyroxine also directly influences the synthesis of this protein. This direct effect of thyroxine on alpha 2u-globulin synthesis seems to be exerted at a step distal to the formation of mature mRNA.