Competitive hierarchies in marine benthic communities

Summary Patterns of competitive displacement by over-growth were examined in communities of sessile organisms in the low intertidal zone at three sites in Washington state and Alaska. Cruotose invertebrates and algae can be arranged into a hierarchy such that species of lower competitive rank rarely overgrow any higher ranking species. Erect and solitary species show a wide range of competitive abilities, but whether they fall into a strict hierarchy is unknown. Few of the solitary or erect species occupy substantial amounts of space in the communities examined.An approximate competitive hierarchy is well established in middle to high intertidal areas dominated by mussels, fleshy algae, and barncles, and has been an important concept in developing both an intuitive understanding and specific mathematical models of the dynamics of benthic marine communities. In particular, lower ranking species in such communities are thought to depend upon predation or chronic disturbance to the dominants to avoid competitive displacement. An alternative viewpoint, proposed on the basis of nonstransitive competitive relationships observed in cryptic encrusting communities on the undersides of coral plates, is that specific competitive loops or networks allow the coexistence of a number of competitors. Although the growth forms and higher taxa represented in the low intertidal bear some similarity to those in the cryptic coral reef community, there is little evidence of ecologically important competitive loops in the intertidal. A reanalysis of data from cryptic reef communities suggests that they also do not depart substantially from a competitive hierarchy, although there appear to be many more cases of local reversals in the outcome of competition. It is suggested that the ecological importance of departures from a strict hierarchy depends upon the competitive rankings of the participants, with departures involving competitively dominant species likely to contribute much more to community structure than those involving opportunistic species.     

High Specific Binding of [3H]GABA and [3H]Muscimol to Membranes from Dendrodendritic Synaptosomes of the Rat Olfactory Bulb

Olfactory bulbs contain dendrodendritic synapses, which occur between granule cells and mitral cells, and gamma-aminobutyric acid (GABA) is thought to act as an inhibitory neurotransmitter at these synapses. Synaptosomes derived from the dendrodendritic synapses of the olfactory bulb were shown previously to contain considerable L-glutamate decarboxylase activity. The subcellular distribution and binding parameters of [3H]GABA and [3H]muscimol binding sites have now been determined in the rat olfactory bulb. Of all fractions examined, crude synaptic membranes (CSM) prepared from the dendrodendritic synaptosomes were shown to have the highest specific binding activity and accounted for nearly all of the total binding activity for both ligands. The specific binding activities for [3H]GABA and for [3H]muscimol were greatly increased after treating the CSM with 0.05% Triton X-100. Binding was shown to be Na+-independent, reversible, pharmacologically specific, and saturable. High- and low-affinity sites were detected for both ligands, and both classes of sites had appreciably lower KD values for muscimol (KD1 = 3.1 nM, KD2 = 25.1 nM) than for GABA (KD1 = 8.6 nM; KD2 = 63.7 nM). The amounts of the high-affinity binding sites for muscimol and GABA were similar (Bmax = 1.7 and 1.5 pmol/mg protein, respectively). The results of the present experiments indicate that the GABA and muscimol binding sites represent the GABA postsynaptic receptor, presumably on mitral cell dendrites, and provide further support for the hypothesis that GABA functions as a neurotransmitter at the dendrodendritic synapses in the olfactory bulb.     

Use of formylated yeast initiator Met tRNA to define the NH2-terminal residues of rat preproinsulin and pregrowth hormone

A method for unambiguously determining the initiator methionine residue and the adjacent NH2-terminal amino acid sequence of cell-free translation products of eukaryotic messenger RNA is described. In this procedure, the NH2 termini of nascent peptides are blocked by incorporating labeled formylmethionine instead of methionine, using yeast initiator tRNA in the wheat germ cell-free system. After immunoprecipitation of the desired product the radiolabeled material is treated with dansyl-Cl to irreversibly block all remaining free amino groups. The material is then deformylated by mild acid hydrolysis and subjected to automated Edman degradation. Only those products that had been synthesized with formylmethionine residues at their NH2-termini can then give rise to labeled phenylthiohydantoin derivatives during degradation. Using this method, we have defined the initiation sites in both rat preproinsulin and pregrowth hormone messenger RNAs.     

Effect of neurotensin on pancreatic function in man

The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs.     

Biflavones of Dacrydium sensu lato

A survey of the biflavonyls in the leaves and branchlets of all three sections of the genus Dacrydium s.l. revealed a complex mixture of amentoflavone and its partial methyl ethers and hinokiflavone in most species. A group of three species in section C, however, were characterised by cupressuflavone derivatives as the major biflavone constituents. The results are used to discuss proposals for revised generic boundaries.     

RNA levels in colchicine-resistant mutants of Chlamydomonas reinhardi

A colchicine-resistant mutant of Chlamydomonas reinhardi (col⁻_{10, 12}) which appears blocked in the final stages of the cell division cycle is shown to have an RNA: protein ratio over four times that which is observed in wild-type cultures. This does not appear to be simply a consequence of reduced overall growth rate, because a comparable reduction in the overall growth rate of wild type by caffeine inhibition did not produce such a large rise in RNA content. The RNA levels in six other colchicine-resistant mutants, which have various abnormalities in colchicine-binding activity, has also been investigated. Two of them have elevated RNA levels.     

Collagen synthesis by cultured skin fibroblasts from siblings with hydroxylysine-deficient collagen.

It has been previously shown that dermis from subjects with hydroxylysine-deficient collagen contains approximately 5% of normal levels of hydroxylysine and sonicates of skin fibroblasts contain less than 15% of normal levels of collagen lysyl hydroxylase activity. However, cultures of dermal fibroblasts from two siblings with hydroxylysine-deficient collagen (Ehlers-Danlos Syndrome Type VI) compared to fibroblasts from normal subjects synthesize collagen containing approximately 50% of normal amounts of hydroxylysine. The lysyl hydroxylase deficient cultures synthesize both Type I and Type III collagen in the same proportion as control cultures. Both alpha 1(I) and alpha 2 chains are similarly reduced in hydroxylysine content. Collagen prolyl hydroxylation by normal collagen lysyl hydroxylation is the same with or without ascorbate supplementation. In mutant cells the rate of prolyl hydroxylation measured after release of inhibition by alpha, alpha'-dipyridyl is the same as in control cells. The rate of lysyl hydroxylation is reduced in mutant cells but only to approximately 50% of normal.     

Proteolytic activity in human skin fibroblasts harvested with trypsin and its effect on measurements of collagen hydroxylase activities.

Lysates of human skin fibroblasts harvested without the use of trypsin do not contain detectable proteolytic activity, but when trypsin is used, lysates may contain activity equal to 10 ng of trypsin/10⁷ cells. The amount of cell lysate ordinarily examined for collagen prolyl and lysyl hydroxylase activity is sufficiently small that such amounts of trypsin have no observable effect on the unhydroxylated collagen substrate. Larger amounts of trypsin cause proteolysis of the unhydroxylated collagen substrate and a reduction of both prolyl and lysyl hydroxylation with lysyl hydroxylation more affected at low trypsin concentration than prolyl hydroxylation.     

Biosynthesis of serum albumin in rat liver. Isolation and probable structure of ''proalbumin'' from rat liver.

1. Two methods are described for the preparation of 'proalbumin' in good yields from rat liver. 2. One of the methods does not depend on the use of specific antisera. 3. The product from both methods is identical as judged by electrophoresis on polyacrylamide gel, isoelectric focusing on pH gradients, ion-exchange chromatography and quantitative immunoelectrophoresis. The protein also appears to be radiochemically pure by these criteria. 4. The protein is free from serum albumin as judged by isoelectric focusing and co-chromatography on ion-exchange columns. It is judged to be free from other proteins by these same criteria and by specific precipitation with antibody. 5. It is converted into serum albumin by limited tryptic hydrolysis. The albumin so produced has the same N-terminal (glutamic acid) and C-terminal (alanine) amino acids as reported for rat serum albumin. 6. A hexapeptide is liberated from the N-terminal end of 'proalbumin' simultaneously. It contains three arginine, one phenylalanine, one valine and one glycine residues.     

A comparison of the activity of phosphatidylinositol phosphodiesterase against substrate in dispersions and as monolayers at the air-water interface.

The activity of phosphatidylinositol phosphodiesterase, purified from rat brain, against substrate in three forms, (a) multibilayer liposomes, (b) single bilayer vesicles of phosphatidylinositol and (c) phosphatidylinositol oriented as monolayers at the air-water interface, was examined. The reaction rate was similar against the two substrate dispersions prepared with the same phospholipid concentration, although there was a large difference in substrate surface area available to the enzyme, and this similarity could not be accounted for by any differences in the microviscosity of the hydrocarbon region of the phospholipid bilayers. The reaction showed apparent zero-order reaction kinetics until about 10% of the substrate had been degraded, whereupon the rate decreased. The reaction against monolayers of phosphatidylinositol was linear throughout the entire digestion of the film, provided that more than 0.25 mg of enzyme was present in the subphase. The pH optimum was 6.6. Bivalent ions )Ca2+, Mg2+, Co2+, Ni2+ and Mn2+) facilitated enzyme penetration into substrate monolayers, but the enzyme was only activated by Ca2+ (optimal concentration, 1mM) and to a lesser extent by Mg2+. The reaction rate was independent of initial surface pressures of less than about 22mN-m(-1) but at higher pressures the rate decreased. This decrease could be prevented by the addition of 10mol of octadecylamine/90mol of phosphatidylinositol to the substrate monolayer; the amine did not increase the rate of reaction in films of less than 22mN-m(-1).