Associational plant refuges: convergent patterns in marine and terrestrial communities result from differing mechanisms

Summary An associational plant refuge occurs when a plant that is susceptible to herbivory gains protection from herbivory when it is associated with another plant. In coastal North Carolina, the abundance of the palatable red alga Gracilaria tikvahiae is positively correlated with the abundance of the unpalatable brown alga Sargassum filipendula during times of increased herbivore activity. To see if grazing by the sea urchin Arbacia punctulata could generate this pattern, controlled experiments were conducted in out-door microcosms and in the laboratory. Gracilaria beneath a canopy of Sargassum was eaten significantly less than Gracilaria alone. When Arbacia were excluded, Gracilaria alone grew significantly more than Gracilaria beneath Sargassum, demonstrating that Sargassum is a competitor of Gracilaria. Experiments investigating Sargassum's deterrent role indicated that Sargassum decreased the foraging range of Arbacia and the rate at which it fed on Gracilaria. Additional experiments with plastic Sargassum mimics indicated that the decreased grazing on Gracilaria was not a result of Sargassum morphology, but was probably attributable to some chemical characteristic of Sargassum. The pattern of increased grazing in monocultures (only Gracilaria present) versus polycultures (both Gracilaria and Sargassum present) demonstrated in this study also has been demonstrated for plant-insect interactions in terrestrial communities. In these communities, insect density is higher in monocultures than in polycultures because insects find and immigrate to monocultures more rapidly, and once in a monoculture, they emigrate from them less often than from polycultures. In this study, urchins did not find and immigrate to monocultures more rapidly, nor did they tend to stay in them once they were found; in fact, they emigrated from monocultures of Gracilaria more rapidly than from Gracilaria and Sargassum polycultures. Increased grazing in Gracilaria monocultures resulted from increased rates of movement and feeding of individual herbivores, not from increased herbivore density as has been reported for terrestrial systems.     

The role of transmembrane cationic gradients in immune complex stimulation of human polymorphonuclear leukocytes

The role of monovalent cationic gradients in human polymorphonuclear leukocyte (PMNL) stimulation was investigated by monitoring immune complex-stimulated transmembrane depolarization and superoxide production, events which accompany--and have been used as indicators of --PMNL activation. Abolishing only the Na+ gradient by substitution of choline for extracellular Na+ did not affect the resting membrane potential but reduced the rate of stimulus-induced transmembrane depolarization to 50% of control. In contrast, collapsing both Na+ and K+ gradients by suspension in K+ buffer (high K-PRK) depolarized the cells and reduced the stimulus-induced rate of depolarization to 11% of control. Pretreatment of cells suspended in Na+ buffers with 5-(N,N-dimethyl)amiloride hydrochloride (DMA) or with valinomycin reduced by one-half the rate of immune complex induced membrane depolarization. Conversely, in the absence of either or of both Na+ or K+ gradients, or in the presence of valinomycin, immune complex elicited an enhanced rate of superoxide production. However, PMNL prepared via NH4Cl (NH4Cl-PMNL) instead of H2O (H2O-PMNL) lysis of residual red blood cells exhibited an absolute requirement for an intact Na+ gradient in cell stimulation. The present results thus demonstrate that: 1) both Na+ and K+ gradients participate equally in the membrane depolarization elicited by immune complex; 2) neither a Na+ or a K+ gradient is required for immune complex activation, or for activity of the respiratory burst; and 3) an artifactual requirement for an intact Na+ gradient occurs in neutrophils prepared by the NH4Cl lysis technique.     

Characterization of a delayed rectifier K+ channel in NG108-15 neuroblastomaX glioma cells: Gating kinetics and the effects of enrichment of membrane phospholipids with arachidonic acid

Summary The calcium sensitivity of exocytosis from electroper-meabilized chromaffin cells is increased by activators of protein kinase C, such as TPA and certain phorbol esters, diacylglycerols, and mezerein. A range of putative inhibitors of protein kinase C block both the phorbol ester-sensitive component of secretion and also the underlying insensitive component. These inhibitors are also shown to inhibit medulla protein kinase C activity in vitro. The extent of secretion is reduced when electropermeabilized cells are exposed to Ca²⁺ levels much in excess of 50 m. The onset of inhibition is faster than the relatively slow rate of Ca-dependent exocytosis and is insensitive to inhibitors of proteolysis. Adrenal medulla protein kinase C activity is also irreversibly inhibited by high Ca²⁺ concentrations. Both the secretory response and the protein kinase C activity in vitro have similar nucleotide and cation specificities. Although these data do not definitely establish an involvement of protein kinase C in exocytosis, none argue against it.Deceased     

A berberine-aniline blue fluorescent staining procedure for suberin,lignin, and callose in plant tissue

Summary A fluorescent staining procedure to detect suberin, lignin and callose in plants has been developed. This procedure greatly improves on previous methods for visualizing Casparian bands in root exodermal and endodermal cells, and performs equally well on a variety of other plant tissues. Berberine was selected as the most suitable replacement forChelidonium majus root extract after comparing the staining properties of the extract with those of four of its constituent alkaloids. Aniline blue counterstaining efficiently quenched unwanted background fluorescence and nonspecific berberine staining, while providing a fluorochrome for callose. When used with multichambered holders which allow simultaneous processing of freehand sections, this efficient staining procedure facilitates morphological studies involving large numbers of samples.Abbreviations ISCC-NBS Inter-Society Color Council-National Bureau of Standards - UV ultraviolet light     

Glyphosate tolerant flax plants from Agrobacterium mediated gene transfer

Agrobacterium tumefaciens carrying a disarmed Ti-plasmid vector containing a chimeric NPT-II gene and a glyphosate resistance plant-derived 5-enolpyruvylshikimate-3-phosphate synthase gene was used to transform flax hypocotyl tissues. Transformed shoots could be regenerated from the inoculated tissue and were proven to be transgenic by the combination of leaf callus assays, nopaline assays and progeny tests. Co-segregation was observed in the progeny for kanamycin and glyphosate resistance.     

Twelve loci form a continuous linkage map for human chromosome 18

We have constructed a primary genetic map of human chromosome 18 consisting of 11 DNA markers and one serological marker (JK). Two of these loci define highly polymorphic VNTR systems. The markers define a continuous genetic linkage map of 97 cM in males and 205 cM in females; female genetic distances in a panel of 59 three-generation families were consistently about twice those observed in males. The high odds in support of the linear order of the markers on this recombination map, and the extent of coverage of chromosome 18, indicate that this map will permit efficient linkage studies of human genetic diseases that may be segregating on chromosome 18 and will provide anchor points for development of high-resolution maps for this chromosome.     

Long-term vegetation change in the Juncus squarrosus grassland at Moor House,northern England

Data from the long-term experiment on sheep grazing versus zero sheep grazing (i.e. in an enclosure) on the composition of the Juncus squarrosus grassland at the Moor House NNR are presented. The data have been analysed to assess change in (1) the abundance of individual species, (2) higher plant and bryophyte communities, and (3) vegetation structure. The higher plant data suggested that both the enclosed-and grazed plots were changing in the same direction, but the enclosed plot was moving much faster. The general tendency was towards a blanket bog vegetation dominated by Eriophorum vaginatum and Calluna vulgaris. Juncus squarrosus has declined very quickly in the enclosed plot, but there has also been a slower decline in the grazed one. A significant increase in Calluna vulgaris has occurred only in the enclosed plot. In contrast, the bryophyte data showed completely different successional trajectories in the two treatment plots.The vegetation structure changed markedly after release from grazing, with a decrease in phytomass, but increase in necromass in the lowest height strata. There was no noticeable change in structure over the 18 year period in the grazed plot.Particular problems found in this study were that some species either fluctuated widely in response, or changed in a curvilinear manner.     

Ultrastructural and morphometric analysis of long-term peripheral nerve regeneration through silicone tubes

Brain Cell Biology - Light and electron microscopy were used to investigate long-term regeneration in peripheral nerves regenerating across a 10 mm gap through silicone tubes. Schwann cells and...     

Characterization oftrans-acting regulatory elements affecting the expression of Mn-superoxide dismutase (sodA) inEscherichia coli

Escherichia coli strains harboringtrans-acting mutations affecting the expression of Mn-superoxide dismutase (SOD) gene (sodA) were used to studysodA regulation. Complementation studies revealed that eitherarc (aerobic respiratory control) orfur (ferric uptake regulation) loci independently complemented anaerobic expression of asodA::lacZ protein fusion in one mutant strain (UV16). This mutant exhibited phenotypes (i.e., elevated outer membrane proteins, enzyme activity, and dye sensitivity) typical offur andarc mutants. When these mutations were introduced into an otherwise wild-type background, anaerobicsodA expression occurred only when botharc andfur mutations were present simultaneously, suggesting cooperative roles of Fur and Arc insodA repression. The reconstructedfur arcA andfur arcB double mutants were still inducible by iron chelators, suggesting the possible involvement of another iron-containing repressor protein. A second independent mutant strain harboring atrans-acting regulatory mutation (UV14) was only partially complemented by multicopy plasmids carryingfur ⁺ orarc ⁺ genes, implicating other genetic elements insodA regulation.