Foraminifera may structure meiobenthic communities

The cosmopolitan benthic foraminiferan, Ammonia beccarii, is a fervent microfloral predator which often forms densely-populated 2–4 cm² aggregates in the field. Sediments within aggregate patches become extensively pelletized, mucus bound and depleted in microfloral food. On a West German Wattenmeer mudflat, copepodite and naupliar densities of a predominant harpacticoid copepod, Amphiascoides limicola, were significantly depressed in sediments containing>100 A. beccarii·3 cm^-2 suggesting a possible foraminiferal: copepod amensalism. Therefore, I cultured A. beccarii and A. limicola separately in sediment microcosms and then tested if A. limicola's seemingly negative reaction to sediments containing A. beccarii occurs under controlled conditions, how various life stages of A. limicola are affected, and what the repulsive mechanisms of A. beccarii may be. In natural field sediments seeded with a latin-square dispersion of sterile sediment patches containing 0 or 100 A. beccarii, mean A. limicola naupliar and copepodite densities were 2 to 6 times lower in Ammonia-rich patches than Ammonia-poor patches (i.e. patches containing <100 A. beccarii·3 cm^-2). Choice experiments directly testing potential A. beccarii inhibitory mechanisms were conducted with A. limicola copepodites: Cubic microcosms containing a latin-square patch dispersion of (1) sterile sediments (SS) seeded with 100 A. beccarii (low microflora), (2) SS bound with sterile mucus (0.0001%) (low microflora), (3) SS seeded with pelletized sediments (high microflora), and (4) SS seeded with mucus and pellets (high microflora), showed that copepodites colonized 12 & 3, but 1 & 4 were not significantly different. Mucus addition by itself, in the absence of pelletization and microflora, strongly facilitated colonization—as did addition of microfloral-rich pelletized sediments. Pelletization and mucousbinding combined, but with low microflora, were least attractive to A. limicola. Pelletization and mucous-binding combined, but with high microflora, were more attractive to A. limicola than its complement, but not significantly so. Thus A. beccarii's inhibition of A. limicola is probably not caused by sediment pelletization and simple mucous exudates but by local microfloral depletion within aggregate foraminiferal patches.Contribution No 774 of the Belle W. Baruch Institute for Marine Biology and Coastal Research     

Seed Development in Phaseolus vulgaris L. cv Seminole: I. Developmental Independence of Seed Maturation

Phaseolus vulgaris L. cv Seminole pods removed from the plant continued their development when incubated in suitable conditions. Seeds continued to grow and develop and pods and seeds passed through an apparently normal developmental sequence to dryness. Seed growth was at the expense of pod dry weight (DW) reserves. Losses of pod DW paralleled DW gains by seeds in detached pods and in pod cylinders containing a seed. The transfer activity was apparent only within the period 10 to 30 days after anthesis (DAA) with maximal activity between 15 to 20 DAA. This period corresponds to maximum pod growth and the attainment of maximal DW. Seeds are in only the early phase of seed growth at this time. No DW transfer was observed at developmental stages beyond 30 to 35 DAA when normal senescence DW losses in pods became evident and seeds were in the later phase of seed fill. Pods or pod cylinders remained green and succulent over the transfer period, later passing through yellowing and drying phases characteristic of normal development. DW transfer was dependent on funicle integrity and was readily detectable in pod cylinders after 7 days incubation. The DW transfer activity may contribute to continuing nutrition of seeds under conditions where the normal assimilate supply to seeds becomes limiting. Defoliation and water stress treatments applied to Phaseolus plants reduced seed yields but allowed persistence of seed maturation processes such that all seeds developing to dryness were capable of germination.     

Effects of continuous nitrogen application and nitrogen preconditioning on nodulation and growth ofCeanothus griseus varhorizontalis

Rooted cuttings ofCeanothus griseus varhorizontalis were irrigated with 0, 10, 20, 50, 75 or 100ppm nitrogen as NH₄NO₃ for eight weeks prior to inoculation with infectiveFrankia. After inoculation, half of the plants for each treatment nitrogen level continued to be irrigated with the preconditioning nitrogen level and half were given no more supplemental nitrogen. For plants continuously receiving nitrogen, nodule initiation (nodule number) was inversely correlated with increasing supplemental nitrogen levels, and suppressed above 50 ppm N. Leaf nitrogen above 2% in continuous-N plants correlated with greatly reduced or suppressed nodulation. Plants maintained after inoculation without supplemental nitrogen showed influence of the prior nitrogen treatment on nodulation. Preconditioning at 50 ppm and above greatly reduced the number of nodules formed. The evidence suggests that stored internal nitrogen can regulate nodulation.Plant biomass accumulated maximally when nodulation was suppressed, at 75 and 100 ppm supplemental N applied continuously. Internode elongation during the nodulation period occurred only on nodulated plants, or in the presence of supplemental N (10 ppm and above).     

Biochemical studies of soluble atrial natriuretic peptide (ANP) receptors from rat olfactory bulb and vascular smooth muscle cells

1. Aim. The biochemical characteristics of atrial natriuretic peptide receptors (ANP-R) derived from rat vascular smooth muscle (A-10 cell line) and central nervous system (CNS; olfactory bulb) tissue were compared. 2. Method and Results. ANP-Rs from each source were solubilized with 40 to 65% efficiency utilizing the nonionic detergent Lubrol-PX. Upon solubilization, the ANP-R from each source maintained the ability to bind 125I-ANP (99-126) with a high affinity; Scatchard analysis indicated that the VSMC ANP-R displayed a Kd for the radioligand of approximately 10 pM, whereas the olfactory receptor possessed a Kd of about 165 pM. The Bmax values for the soluble VSMC and olfactory ANP-Rs were 285 and 30 fmol/mg protein, respectively. Competition binding studies indicated that the VSMC ANP-R bound ANP(99-126), ANP(103-126), and ANP(103-123) with similar affinities, whereas the olfactory ANP-R was much more sensitive to changes in the COOH-terminal structure of the competing peptide. The soluble ANP-Rs from VSMC and olfactory were chromatographically indistinguishable on phenyl-, DEAE-, and wheat germ agglutinin-agarose columns. However, the ANP-Rs could be distinguished using GTP-agarose; the olfactory ANP-R was capable of binding to the resin, whereas the VSMC ANP-R was not. 3. Conclusions. Coupled with other studies, these data suggest that the A10 VSMC ANP-R observed in this study may not be coupled to guanylate cyclase and may represent a receptor serving a clearance function, whereas a significant proportion of the olfactory CNS ANP-R appears to be associated with GTP-binding proteins, likely particulate guanylate cyclase, and probably represents a coupled form of the receptor.     

Production of alkaline phosphatase by immobilized growing cells of Escherichia coli excretory mutants

Summary In continuous cultures, alkaline phosphatase was synthesised and excreted for more than 250 h by immobilized growing cells in contrast to free cells for which the excretion decreased after 150 h of culture. This observed increase in alkaline phosphatase synthesis and excretion by immobilized cells may have resulted from growing conditions within the gel beads.Offprint requests to: C. Manin     

The interplay of electrostatic fields and binding interactions determining catalytic-site reactivity in actinidin. A possible origin of differences in the behaviour of actinidin and papain.

1. The pH-dependence of the second-order rate constant (k) for the reaction of actinidin (EC 3.4.22.14) with 2-(N'-acetyl-L-phenylalanylamino)ethyl 2'-pyridyl disulphide was determined and the contributions to k of various hydronic states were evaluated. 2. The data were used to assess the consequences for transition-state geometry of providing P2/S2 hydrophobic contacts in addition to hydrogen-bonding opportunities in the S1-S2 intersubsite region. 3. The P2/S2 contacts (a) substantially improve enzyme-ligand binding, (b) greatly enhance the contribution to reactivity of the hydronic state bounded by pKa 3 (the pKa characteristic of the formation of catalytic-site-S-/-ImH+ state) and pKa 5 (a relatively minor contributor in reactions that lack the P2/S2 contacts), such that the major rate optimum occurs at pH 4 instead of at pH 2.8-2.9, and (c) reveal the kinetic influence of a pKa approx. 6.3 not hitherto observed in reactions of actinidin. 4. Possibilities for the interplay of electrostatic effects and binding interactions in both actinidin and papain (EC 3.4.22.2) are discussed.     

Vascular relaxation mediated by hydroxylamines and oximes: their conversion to nitrites and mechanism of endothelium dependent vascular relaxation

Hydroxylamines (R-NHOH) and oximes (R = NOH) relax rat aortic rings independent of the presence of the endothelium. The relaxation is inhibited by methylene blue, an inhibitor of soluble guanylate cyclase and by hemoglobin, an inhibitor of the endothelium dependent relaxing factor (EDRF). Both the oximes and hydroxylamines generate NO/NO2- ions on treatment with iodine in glacial acetic acid. However, there is no correlation between relaxation and NO/NO2- formation. Compared to hydroxylamines, the oximes are less potent relaxing agents and not efficiently converted to NO/NO2- ions. We suggest that endothelium dependent relaxation is associated with a hydroxylamine like compound and is not directly related to NO.     

Performance profiles of topical antimicrobials in vitro

The in-vitro efficacy of commercially available topical antimicrobial products against control strains and those from clinical material are compared with an agar diffusion model. The MICs of the constituent antimicrobial compounds have been determined for the same organisms. Plotting the inhibition zone diameters produced by the topical products against the log10 MICs of their constituent antimicrobial compound(s) gives overall product performance profiles for a range of organisms. These profiles confirm that the formulation of a topical product clearly modifies the response obtained with a specific antimicrobial compound.