Stoichiometric relations in an ant-treehopper mutualism

Carbon : nitrogen : phosphorus (C : N : P) stoichiometry can underlie physiological and life history characteristics that shape ecological interactions. Despite its potential importance, there is much to learn about the causes and consequences of stoichiometric variation in terrestrial consumers. Here we show that treehoppers (Publilia modesta) tended by ants (Formica obscuripes) contained lower N concentrations than treehoppers on plants from which ants were excluded. Ant presence also affected nutrient concentrations in host plants: on plants with ants, leaves contained uniformly low concentrations of N; on plants without ants, N concentrations were low only in the few leaves fed upon by treehoppers at the time of collection. We suggest treehopper feeding reduces leaf nutrient levels and ants positively affect treehopper abundance, producing a top–down effect on plant quality. Determining the causes of these stoichiometric changes should help elucidate factors guiding the dynamics of conditional mutualisms between ants and homopterans.     

Independent cerebral vasoconstrictive effects of hyperoxia and accompanying arterial hypocapnia at 1 ATA.

Breathing 100% O2 at 1 atmosphere absolute (ATA) is known to be associated with a decrease in cerebral blood flow (CBF). It is also accompanied by a fall in arterial Pco2 leading to uncertainty as to whether the cerebral vasoconstriction is totally or only in part caused by arterial hypocapnia. We tested the hypothesis that the increase in arterial Po2 while O2 was breathed at 1.0 ATA decreases CBF independently of a concurrent fall in arterial Pco2. CBF was measured in seven healthy men aged 21-62 yr by using noninvasive continuous arterial spin-labeled-perfusion MRI. The tracer in this technique, magnetically labeled protons in blood, has a half-life of seconds, allowing repetitive measurements over short time frames without contamination. CBF and arterial blood gases were measured while breathing air, 100% O2, and 4 and 6% CO2 in air and O2 backgrounds. Arterial Po2 increased from 91.7 +/- 6.8 Torr in air to 576.7 +/- 18.9 Torr in O2. Arterial Pco2 fell from 43.3 +/- 1.8 Torr in air to 40.2 +/- 3.3 Torr in O2. CBF-arterial Pco2 response curves for the air and hyperoxic runs were nearly parallel and separated by a distance representing a 28.7-32.6% decrement in CBF. Regression analysis confirmed the independent cerebral vasoconstrictive effect of increased arterial Po2. The present results also demonstrate that the magnitude of this effect at 1.0 ATA is greater than previously measured.     

Bacteria Associated with Cysts of the Soybean Cyst Nematode (Heterodera glycines)

The soybean cyst nematode (SCN), Heterodera glycines, causes economically significant damage to soybeans (Glycine max) in many parts of the world. The cysts of this nematode can remain quiescent in soils for many years as a reservoir of infection for future crops. To investigate bacterial communities associated with SCN cysts, cysts were obtained from eight SCN-infested farms in southern Ontario, Canada, and analyzed by culture-dependent and -independent means. Confocal laser scanning microscopy observations of cyst contents revealed a microbial flora located on the cyst exterior, within a polymer plug region and within the cyst. Microscopic counts using 5-(4,6-dichlorotriazine-2-yl)aminofluorescein staining and in situ hybridization (EUB 338) indicated that the cysts contained (2.6 ± 0.5) × 10⁵ bacteria (mean ± standard deviation) with various cellular morphologies. Filamentous fungi were also observed. Live-dead staining indicated that the majority of cyst bacteria were viable. The probe Nile red also bound to the interior polymer, indicating that it is lipid rich in nature. Bacterial community profiles determined by denaturing gradient gel electrophoresis analysis were simple in composition. Bands shared by all eight samples included the actinobacterium genera Actinomadura and Streptomyces. A collection of 290 bacteria were obtained by plating macerated surface-sterilized cysts onto nutrient broth yeast extract agar or on actinomycete medium. These were clustered into groups of siblings by repetitive extragenic palindromic PCR fingerprinting, and representative isolates were tentatively identified on the basis of 16S rRNA gene sequence. Thirty phylotypes were detected, with the collection dominated by Lysobacter and Variovorax spp. This study has revealed the cysts of this important plant pathogen to be rich in a variety of bacteria, some of which could presumably play a role in the ecology of SCN or have potential as biocontrol agents.     

Characterisation of Antibodies Specific for Chick Brain Neural Cell Adhesion Molecules Which Cause Amnesia for a Passive Avoidance Task

Abstract: Antisera were prepared against six postsynaptic density glycoprotein fractions (150–180, 62–80, 50, 41, 33, and 28 kDa) that show enhanced fucosylation during memory formation after training day-old chicks in a one-trial passive avoidance task. Each antiserum was tested for its possible effect on memory retention. Bilateral intracranial injections of two of the antisera, R-1 and R-6, or their IgGs (IgG-1 and IgG-6), resulted in amnesia for the passive avoidance task when chicks were tested 24 h later. IgG-1 and IgG-6 antibodies were amnestic only when injected 5.5 h after training, and had no effect when injections were made 30 min before training, thus resembling an effect previously observed with polyclonal or monoclonal anti-N-CAM antibodies. IgG-1 and IgG-6 antibodies were found to be specific for protein epitopes of glycoproteins that contain a high amount of N-linked mannose and fucose, and a very low amount of polysialic acid and O-linked galactose. Absorption of IgG-6 antibodies with neural cell adhesion molecule (N-CAM) isolated from synaptic plasma membranes derived from day-old chick brain resulted in loss of amnestic effect. As we have previously shown that long-term memory for the passive avoidance task requires two waves of glycoprotein synthesis, the first occurring immediately after training and the second 5–8 h later, the present results suggest strongly that isoforms of N-CAM molecules with a low level of sialic acid are involved specifically in the establishment of an enduring memory for the experience of the passive avoidance task in chicks, possibly by stabilising changes in synaptic connectivity that encode the memory.     

Agrobacterium tumefaciens-mediated barley transformation

Genetically transformed barley was produced by eco-cultivating immature embryo explants with Agrobacterium tumefaciens carrying a binary vector coding for chimaeric bacterial genes, bar and gus , and selecting for bialaphos-resistant cultures from which plants were regenerated. Integration of both genes was confirmed by gel blot hybridization analysis of DNA from the transformed plants and their progenies. From 1282 embryos, plants were recovered for 54 independently transformed lines, giving a transformation efficiency of 4.2%. Transgene numbers in the different lines ranged from single copy insertion to at least ten copies. Sixteen out of 18 plants grown to maturity were fully fertile. Both marker genes, bar and gus , were expressed and co-segregated in the T₁ progeny plants. In the majority of cases, the genes showed Mendelian segregation predicted for transgene insertion at a single locus. In one family with multiple transgene insertions, molecular analysis of T₁ and T₂ plants suggested that the T-DNA had inserted at two unlinked loci.     

A defect in synapsis causes male sterility in a T-DNA-tagged Arabidopsis thaliana mutant

Fluorescence microscopy was used to study meiosis in microsporocytes from wild-type Arabidopsis thaliana and a T-DNA-tagged meiotic mutant. Techniques for visualizing chromosomes and β-tubulin in other plant species were evaluated and modified in order to develop a method for analyzing meiosis in A. thaliana anthers. Like most dicots, A. thaliana microsporocytes undergo simultaneous cytokinesis in which both meiotic divisions are completed prior to cytokinesis. However, two unique events were observed in wild-type A. thaliana that have not been reported in other angiosperms: (1) polarization of the microsporocyte cytoskeleton during prophase I prior to nuclear envelope breakdown, and (2) extensive depolymerization of microtubules just prior to metaphase II. The first observation could have implications regarding a previously uncharacterized mechanism for determining the axis of the metaphase I spindle during microsporogenesis. The second observation is peculiar since microtubules are known to be involved in chromosome alignment in other species; possible explanations will be discussed. A T-DNA-tagged meiotic mutant of A. thaliana ( syn1 ), which had previously been shown to produce abnormal microspores with variable DNA content, was also cytologically characterized. The first observable defect occurs in microsporocytes at telophase I, where some chromosomes are scattered throughout the cytoplasm, usually attached to stray microtubules. Subsequent developmental stages are affected, leading to complete male sterility. Based on similarities to synaptic mutants that have been described in other species, it is suggested that this mutant is defective in synaptonemal complex formation and/or cohesion between sister chromatids.     

Roles for Protein Kinase C and Mitogen-Activated Protein Kinase in Nicotine-Induced Secretion from Bovine Adrenal Chromaffin Cells

Abstract: Both the Ca²⁺/phospholipid-dependent protein kinases (protein kinases C, PKCs) and mitogen-activated protein kinases (MAPKs) have been implicated as participants in the secretory response of bovine adrenomedullary chromaffin cells. To investigate a possible role for these kinases in exocytosis and the relationship of these kinases to one another, intact chromaffin cells were treated with agents that inhibited each of the kinases and analyzed for catecholamine release and MAPK/extracellular signal-regulated kinase (ERK) kinase (MEK)/MAPK activation after stimulation with secretagogues of differential efficacy. Of the three secretagogues tested, inactivation of PKCs by long-term phorbol 12-myristate 13-acetate (PMA) treatment or incubation with GF109203X had the greatest inhibitory effect on nicotine-induced catecholamine release and MEK/MAPK activation, a moderate effect on KCl-induced events, and little, if any, effect on Ca²⁺ ionophore-elicited exocytosis and MEK/MAPK activation. These results indicate that PKC plays a significant role in events induced by the optimal secretagogue nicotine and a lesser role in exocytosis elicited by the suboptimal secretagogues KCl and Ca²⁺ ionophore. Treatment of cells with the MEK-activation inhibitor PD098059 completely inhibited MEK/MAPK activation (IC₅₀ 1–5 µM) and partially inhibited catecholamine release induced by all secretagogues. However, PD098059 was more effective at inhibiting exocytosis induced by suboptimal secretagogues (IC₅₀～10 µM) than that induced by nicotine (IC₅₀～30 µM). These results suggest a more prominent role for MEK/MAPK in basic secretory events activated by suboptimal secretagogues than in those activated by the optimal secretagogue nicotine. However, PD098059 also partially blocked secretion potentiated by short-term PMA treatment, suggesting that PKC can function in part by signaling through MEK/MAPK to enhance secretion. Taken together, these results provide evidence for the preferential involvement of MEK/MAPK in basic secretory events activated by the suboptimal secretagogues KCl and Ca²⁺ ionophore and the participation of both PKC and MEK/MAPK in optimal secretion induced by nicotine.