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.     

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.     

In vitro effects of arachidonic acid on the prostaglandin synthesizing system in gastric mucosa

Self-destruction of the prostaglandin cyclooxygenase has been suggested to be an important factor in the regulation of endogenous prostaglandin synthesis. The present study was done in order to define the role of this substrate-induced inactivation in the regulation of prostaglandin synthesis in gastric mucosa. In tissue homogenate, the prostaglandin synthesizing capacity is rapidly inactivated at 37 degrees C, even in the absence of exogenous arachidonic acid. It was shown that this inactivation can be prevented both by EDTA as a chelator of calcium-ions and by tetracaine, a specific inhibitor of the phospholipase A2. Additional exogenous arachidonic acid again inactivated prostaglandin synthesis in a dose dependent manner. In contrast, the prostaglandin synthesizing capacity in organ cultured mucosal biopsies is well preserved, although the release of endogenous substrate was activated by extracellular calcium and Ca-ionophore A23187. Furthermore, even at high concentrations of exogenous arachidonic acid present in the culture medium, the synthesizing capacity in intact biopsies was only slightly and reversibly reduced. These large differences between intact biopsies and cell free tissue preparations point to very efficient mechanisms controlling the substrate availability for the cyclooxygenase system both from endogenous and exogenous sources in intact gastric mucosa.     

Influence of mefluidide on growth,development, and cell wall digestibility of sorghum

Application of mefluidide (N-[2,4-dimethyl-5-([(trifluoromethyl)sulfonyl]amino) phenyl]acetamide) inhibits plant development in perennial grasses. This study examined the effect of mefluidide on the morphological development and digestibility of sorghum. In the greenhouse, 5.9 × 10^–5 g active ingredient (a.i.) plant^–1 applied at the seedling, eight-leaf and boot stages reduced mean plant height 70%, 59%, and 2%, respectively. Heights were also reduced 14%, 15% and 35% by 5.9 × 10^–8, 5.9 × 10^–7 and 5.9 × 10^–6 gram a.i. plant^–1 applied at the eight-leaf stage. Field application of 0.26 or 0.52 kg ha^–1 mefluidide at either the eight-leaf or flagleaf stage reduced mean plant height of all cultivars. Basal tiller numbers increased 319% 28 d, and dry matter production was reduced 65% 42 d following mefluidide application at the eight-leaf stage. Treated stems were 34% higher and treated leaves were 7% higher in cellulase dry matter digestibility than control plants following mefluidide application at the eight-leaf stage. These results indicate that mefluidide application to vegetative stages in sorghum may enhance the forage value of the plants while it inhibits normal plant growth.     

Deregulation of arginine biosynthesis in Synechococcus sp. PCC7942

Summary In order to deregulate arginine biosynthesis in Synechococcus sp. PCC7942, d-arginine-resistant cell lines were selected following ethyl methanesulfonate mutagenesis of wild-type (WT) cells. Three of these arginine-producing mutant (APM) cell lines, APM1, APM31 and APM40, were putative regulatory mutants based upon secretion of l-arginine into their growth medium. HPLC of lyophilized post-harvest supernatants of APM 31 and 40 resolved two predominant amino acids, arginine and citrulline. In-vitro activity of N-acetylglutamate kinase (NAGK), the proposed regulatory enzyme of the arginine pathway, was about 100-fold less sensitive to l-arginine inhibition in extracts from APM 31 and 40 than the enzyme in WT extracts. The enzyme from APM 1 was 20-fold less sensitive to l-arginine inhibition than WT. The most likely site of mutation in each of the APM cell lines is in the gene for NAGK, rendering the enzymes insensitive to l-arginine feedback control. These strains can be utilized for the phototrophic production of arginine. Offprint requests to: S. E. Bingham     

Consumption of leaf detritus by a stream shredder: Influence of tree species and nutrient status

Four species of riparian vegetation (alder, birch, willow and poplar) were fertilized with nitrogen, phosphorus, nitrogen + phosphorus, or no fertilizer (control). The resulting leaf detritus (leached but not microbially colonized) was offered to a stream shredder, Hydatophylax variabilis (Trichoptera: Limnephilidae). In one experiment, shredder consumption of leaf detritus from different nutrient treatments (within tree species) was compared, and in a second experiment, consumption of different tree species (within nutrient treatments) was compared. Larvae preferred leaf detritus from nitrogen + phosphorus treatments (except in poplar where nitrogen treatment was preferred). Alder was preferred over other tree species for all treatments. Chemical and physical analyses of leaf litter showed differences between tree species and nutrient treatments in nutrient content, tannins and leaf toughness. Leaf consumption by larvae was positively associated with nitrogen content and negatively associated with condensed tannin content. Species composition and nutrient status of riparian vegetation may strongly influence detrital food webs in streams.     

The decolorization of the polymeric dye Poly-Blue (polyvinalamine sulfonate-anthroquinone) by lignin degrading fungi

Summary In this work we have investigated the decolorization of the polymeric dye Poly-B411 by several fungi. Only fungi with known lignin degrading ability were able to decolorize the dye. Pleurotus ostreatus sp. florida decolorized the dye both in solid and liquid media. Decolorizing ability developed in the absence of the dye but only when the fungus had been previously cultivated on lignin containing substrates.The work was supported by a grant from the Charles Wolfson Trust     

Relationships between macroalgal functional form groups and substrata stability in a subtropical rocky-intertidal system

The general hypothesis that morphological, physiological, and ecological adaptations of macro algal functional-form groups can be related to the level of disturbance encountered in a natural environment was examined. Two articulated calcareous coralline algae (Amphiroa van-bosseae Lemoine, 24% cover and Corallina frondescens Post. & Rupr. 20%) and one non-articulated coralline alga (Lithophyllum sp., 16%), all late-successional predation-tolerant strategists, comprise most of the community cover on stable bedrock substrata at Punta Las Cuevitas, Sonora, Mexico. Conversely, Ulva rigida C. ag. (26% cover) and a ralfsioid crust (23%), shows to be early-successional opportunistic strategists, cover more of the disturbed boulder habitat. Porolithon sonorense Daws., a stress-tolerant strategist, is uniquely abundant on both substratum types (13% cover on boulders, 10% on bedrock). The sheet-like and filamentous algae, prevalent in the temporally unstable habitat, generally show greater productivity (>2×) than the thicker and calcareous forms conspicuous in the more constant environment. It appears that selection for delicate thalli with high productivities, as well as selection for tougher morphologies having lower photosynthetic rates due to greater proportions of structural tissues, are widespread, divergent evolutionary forces among marine algae. Experiments with captive sea urchins (Echinometra vanbrunti Agassiz), in conjunction with fish-preference data published for some of the same algae studied here, offer strong support for the functional-form model. Parrotfishes, rudderfishes, surgeonfishes, damselfishes and E. vanbrunti, in the Gulf of California, preferentially feed on delicate, early-successional, sheet-like, and filamentous algae, while rejecting or ignoring the more structured, late-successional and calcareous algae. There is no significant (P > 0.05) gradation in calorific content between the first four of the six functional groups (i.e., Sheet-, Filamentous-, Coarsely Branched- and Thick Leathery-Groups), but the mean value for these fleshy forms (2.6 kcal · g ash-free dry wt^?1) is significantly greater than that for the last two groups (0.3 kcal, Jointed Calcareous- and Crustose-Groups). The approach used in this study demonstrates a realistic technique for predicting macrophyte community composition from knowledge of the disturbance levels in a given habitat or the reverse. The form group-disturbance relationship has important implications for future biological monitoring of rocky-inter-tidal and subtidal systems.     

The effects of prey size, predator size, and sediment composition on the rate of predation of the blue crab, Callinectes Sapidus Rathbun, on the hard clam, MercenariaMercenaria (Linné)

Sediment preferences of blue crabs, Callinectes sapidus Rathbun, and predation rates on various size classes of the hard clam, Mercenaria mercenaria (Linné), in a variety of sediment types were studied in the laboratory. Blue crabs of all size classes exhibited a preference for sand, mud, and sand/mud rather than crushed oyster shell or granite gravel. Clams were more vulnerable to predation by crabs in sand and sand/mud than in crushed oyster shell or granite gravel. When crabs were given a choice of clam sizes based on carapace width (CW), small crabs (<75 mm CW) consumed 5- and 10-mm shell length (SL) clams. Medium crabs (75–125 mm CW) preferentially consumed 10-mm SL clams. Large crabs (> 125 mm CW) consumed 10- and 25-mm SL clams equally. Blue crabs did not eat clams that were >40-mm SL.