Thorns as induced defenses: experimental evidence

Summary We report evidence from controlled experiments that long straight thorns deter herbivory by browsers. Cut branches of three woody species that had their thorns removed suffered significantly greater herbivory by a tethered goat than did paired intact branches. Branches on living Acacia seyal plants that had their thorns removed suffered significantly greater herbivory by a wild population of free-ranging giraffes than did intact branches on the same plants. These differences in herbivory resulted in long term losses of branch length in clipped as opposed to control branches. In addition, branches within reach of giraffes produced longer thorns and a greater density of thorns than did higher branches. These results imply that increased thorn length is an induced defense.No significance should be attached to order of authorship     

Ozone inhibits endothelial cell cyclooxygenase activity through formation of hydrogen peroxide

We have previously demonstrated that a 2H exposure of cultured pulmonary endothelial cells to ozone (0.0–1.0 ppm) resulted in a concentration-dependent reduction of endothelial prostacyclin production (90% decrease at the 1.0 ppm level). Ozone-exposed endothelial cells, incubated with 20 uM arachidonate, also demonstrated a significant inhibition of prostacyclin synthesis. To further examine the mechanisms of the inhibition of prostacyclin synthesis, bovine pulmonary endothelial cells were exposedto 1.0 ppm ozone for 2H. A significant decease in protacyclin synthesis was found within 5 min of exposure (77 ± 36% of air-exposed control values, p < 0.05). Endothelial prostacyclin synthesis returned to baseline levels by 12H after ozone exposure, a time point which was similar to the recovery time of unexposed endothelium treated with 0.5 uM acetylsalicylic acid. Incubation of endothelial cells, previously exposed to 1.0 ppm ozone for 2 hours, with 4 uM PGH₂ resulted in restoration of essentially normal prostacyclin synthesis. When endothelial cells were co-incubated with catalase (5U/ml) during ozone exposure, no inhibition of prostacycline synthesis was observed. Co-incubation with either heat-inactivated catalase or superoxide dismutase (10U/ml) did not affect the ozone-induced inhibition of prostacycline synthesis. These data suggest that H₂O₂ is a major toxic species produced in endothelial cells during ozone exposure and responsible for the inhibiton of endothelial cyclooxygenase activity.     

Comparison of serotonin uptake by dense bodies inside and outside human platelets

ATP-dependent proteolysis in reticulocyte extracts is stimulated by ubiquitin, a polypeptide which is covalently conjugated to proteins. It has been proposed that ATP and ubiquitin act by repressing an inhibitor of an ATP-independent protease, rather than by conjugation to substrate proteins [Speiser, S. and Etlinger, J.D. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 3577-3580]. We find that the inhibitor preparation used by these authors contains a positively required factor of the ATP-ubiquitin proteolytic system, which can be separated from two types of protease inhibitors by gel filtration chromatography. The following observations indicate that the "inhibitors" are endogenous protease substrates which compete with the labeled substrate: (a) inhibition is competitive with exogenous substrate; (b) inhibition is abolished by a preincubation of "inhibitor" with protease prior to the addition of labeled substrate. These findings are not consistent with the notion that the inhibitors play a regulatory role in the ATP-ubiquitin proteolytic pathway.     

Resonance Raman studies of Escherichia coli sulfite reductase hemoprotein. 1. Siroheme vibrational modes

Resonance Raman (RR) spectra are reported for the hemoprotein subunit (SiR-HP) of Escherichia coli NADPH-sulfite reductase (EC 1.8.1.2) in various ligation and redox states. Comparison of the RR spectra of extracted siroheme and the mu-oxo FeIII dimer of octaethylisobacteriochlorin with those of mu-oxo FeIII octaethylchlorin dimer and mu-oxo FeIII octaethylporphyrin dimer demonstrates that many siroheme bands can be correlated with established porphyrin skeletal modes. Depolarization measurements are a powerful tool in this correlation, since the 45 degrees rotation of the C2 symmetry axis of the isobacteriochlorin ring relative to the chlorin system results in reversal of the polarization properties (polarized vs anomalously polarized) of bands correlating with B1g and B2g modes of porphyrin. Various SiR-HP adducts (CO, NO, CN-, SO3(2-] show upshifted high-frequency bands, characteristic of the low-spin state and consistent with the expected core size sensitivity of the skeletal modes. Fully reduced unliganded SiR-HP (both siroheme and Fe4S4 cluster reduced) in liquid solution displays RR features comparable to those of high-spin ferrous porphyrins; on freezing, the RR spectrum changes, reflecting an apparent mixture of siroheme spin states. At intermediate reduction levels in solution a RR species is observed whose high-frequency bands are upshifted relative to oxidized and fully reduced SiR-HP. This spectrum, thought to arise from the "one-electron" state of SiR-HP (siroheme reduced, cluster oxidized), may be due to S = 1 FeII siroheme.     

Resonance Raman studies of Escherichia coli sulfite reductase hemoprotein. 3. Bound ligand vibrational modes

The vibrations of the bound diatomic heme ligands CO, CN-, and NO are investigated by resonance Raman spectroscopy in various redox states of Escherichia coli sulfite reductase hemoprotein, and assignments are generated by use of isotopically labeled ligands. For the fully reduced CO complex (ferrous siroheme, reduced Fe4S4 cluster) at room temperature, nu CO is observed at 1904 cm-1, shifting to 1920 cm-1 upon oxidation of the cluster. The corresponding delta FeCO modes are identified at 574 and 566 cm-1, respectively, by virtue of the zigzag pattern of their isotopic shifts. In frozen solution, two species are observed for the cluster-oxidized state, with nu CO at 1910 and 1936 cm-1 and nu FeC at 532 and 504 cm-1, respectively; nu FeC for the fully reduced species is identified at 526 cm-1 in the frozen state. For the ferrous siroheme-NO complex (cluster oxidized), nu NO is identified at 1555 cm-1 in frozen solution and a low-frequency mode is identified at 558 cm-1; this stretching mode is significantly lower than that observed in Mb-NO. For the ferric siroheme cyanide complexes evidence of two ligand-bonding forms is observed, with modes at 451/390 and 451/352 cm-1; they are distinguished by a reversal of the isotopic shift patterns of the upper and lower modes and could arise from a linear and a bent Fe-C unit, respectively. For the ferrous siroheme cyanide complex isotope-sensitive modes observed at 495 and 452 cm-1 are assigned to the FeCN- bending and FeC stretching vibrations, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Scanning electron microscopy of the lip denticiles of Ascaris suum adults of known ages.

Purebred Hampshire pigs, farrowed and maintained under conditions precluding extraneous helminth infection, were exposed to a single dose of 10,000 Ascaris suum infective eggs. The pigs were killed at intervals of 28, 41, 55, 86, 115, 145, 175, and 206 days after infection. At necropsy, no gross lesions were found in the lungs or livers of infected pigs. The worms were recovered from the small intestine, identified, counted, and fixed. The heads were excised, critical point dried, mounted en face, and examined by scanning electron microscopy. Worms 28 to 115 days old had unworn denticles that were triangular when viewed laterally but blunt when viewed tangentially. Wearing of the denticles was observed first with 145-day-old worms; wearing increased with age both in numbers of denticles affected and in degree of wear so that by 206 days after inoculation, almost all denticles in the center of the lip were worn. Worn denticles appear truncated when viewed from any angle. The denticles outside the central area were not affected by wear. The size of the denticles varies not only between specimens of the same age, but also on each specimen. However, average denticle size is directly related to the size and, accordingly, to the age of the worm. External to each denticle is a corresponding depression that we have called the denticular groove. One 28-day-old specimen had some extra denticles aligned irregularly along the lip; this irregularity gave the appearance of a double row. The denticles of the two subventral lips are similar to those of the dorsal and are equally affected by wear. There was no detectable difference in denticles of male and female worms. Since wear can now be specifically correlated with age, we conclude that the denticles are functional and become worn through use. Consequently, adult A. suum may be an even more injurious pathogen than heretofore supposed.