Biodiversity and ecosystem functioning: It is time for dispersal experiments

The experimental study of the relationship between biodiversity and ecosystem function has mainly addressed the effect of species and number of functional groups. In theory, this approach has mainly focused on how extinction affects function, whereas dispersal limitation of ecosystem function has been rarely discussed. A handful of seed introduction experiments, as well as numerous observations of the effects of long‐distance dispersal of alien species, indicate that ecosystem function may be strongly determined by dispersal limitation at the local, regional and/or global scales. We suggest that it is time to replace biodiversity manipulation experiments, based on random draw of species, with those addressing realistic scenarios of either extinction or dispersal. Experiments disentangling the dispersal limitation of ecosystem function should have to take into account the probability of arrival. The latter is defined as the probability that a propagule of a particular species will arrive at a particular community. Arrival probability depends on the dispersal ability and the number of propagules of a species, the distance a species needs to travel, and the permeability of the matrix landscape. Current databases, in particular those in northwestern and central Europe now enable robust estimation of arrival probability in plant communities. We suggest a general hypothesis claiming that dispersal limitation according to arrival probability will have ecosystem‐level effects different from those arising due to random arrival. This hypothesis may be rendered more region‐, landscape‐ or ecosystem‐specific by estimating arrival probabilities for different background conditions.     

A Search for Discrete Cholinergic Nuclei in the Human Ventral Forebrain

Abstract: Slices cut from five frozen human brains were dissected into 2-mm cubes and assayed for choline acetyltransferase (ChAT) activity and protein content. A pattern of enrichment of ChAT activity was found ventral to the anterior commissure; this finding is consistent with the location of the enzyme in the cells of the nucleus basalis of Meynert. The region beneath the anterior commissure was the only place a discrete enrichment of activity could be found, and the precise topography of the enrichment was somewhat variable from brain to brain. The results are discussed in the light of recent knowledge concerning the source of the cortical cholinergic innervation.     

Evidence for carrier-mediated,energy-dependent uptake of urea in some bacteria

Evidence for the existence of an energy-dependent urea permease was found for Alcaligenes eutrophus H16 and Klebsiella pneumoniae M5a1 by studying uptake of ¹⁴C-urea. Since intracellular urea was metabolized immediately, uptake did not result in formation of an urea pool. Evidence is based on observations that the in vivo urea uptake and in vitro urease activity differ significantly with respect to kinetic parameters, temperature optimum, pH optimum, response towards inhibitors and regulation. The K _m for urea uptake was 15–20 times lower (38 M and 13 M urea for A. eutrophus and K. pneumoniae, respectively) than the K _m of urease for urea (650 M and 280 M urea), the activity optimum for A. eutrophus was at pH 6.0 and 35°C for the uptake and pH 9.0 and 65°C for urease. Uptake but not urease activity in both organisms strongly decreased upon addition of inhibitors of energy metabolism, while in K. pneumoniae, potent inhibitors of urease (thiourea and hydroxyurea) did not affect the uptake process. Significant differences in the uptake rates were observed during growth with different nitrogen sources (ammonia, nitrate, urea) or in the absence of a nitrogen source; this suggested that a carrier is involved which is subject to nitrogen control. Some evidence for the presence of an energy-dependent uptake of urea was also obtained in Pseudomonas aeruginosa DSM 50071 and Providencia rettgeri DSM 1131, but not in Proteus vulgaris DSM 30118 and Bacillus pasteurii DSM 33.Non-standard abbreviations CCCP Carbonylcyanide-m-chlorphenylhydrazone - DCCD dicyclohexylcarbodiimide - DNP 2,4-dinitrophenole     

Muscarinic Agonists Evoke Neurotransmitter Release: Possible Roles for Phosphatidyl Inositol Bisphosphate Breakdown Products in Neuromodulation

Carbachol (CCh), a muscarinic agonist that elicits the formation of inositol trisphosphate (IP3) and diacylglycerol (DG), induces a calcium-dependent [3H]norepinephrine ([3H]NE) release [IC50 = (2.7 +/- 0.5) X 10(-4) M] in rat brain slices. Similarly, other muscarinic agonists evoke [3H]NE release which is specifically inhibited by muscarinic antagonists such as 3-quinuclidinyl benzilate, atropine, and N-methyl-4-piperidyl benzilate. The atropine-sensitive evoked release is effectively inhibited by neomycin (IC50 = 50 microM), a phospholipase C inhibitor that interferes with IP3-dependent cellular processes. In addition, polymyxin B, a rather selective inhibitor of protein kinase C (PK-C), abolishes the agonist-mediated release with a half-maximal effective concentration of 0.53 microM (750 ng/ml). These results have a significant implication for the mechanism by which agonists generating IP3 and DG act as inducers of neurotransmitter release in the CNS. However, since both neomycin and polymyxin B act also as N-calcium-channel blockers, other possible mechanisms are discussed. The CCh-induced release suggests that in the CNS an agonist-receptor interaction leads to a calcium-dependent neurotransmitter release, most likely via promoting the IP3/DG as second messengers followed by activation of PK-C.     

A new null hypothesis for measuring the degree of plant community organization

An attempt is made to derive a measure for the degree of plant community organization, which would not be based on species co-occurrence and co-abundance. The use of the independent random distribution hypothesis (IRDH) is suggested for this purpose. The hypothesis is expected to be valid, if no deterministic phytosociological-structure-generating mechanism is present. If structural variability is used as a statistic for testing the hypothesis, deviances from the conditions of IRDH (species distributions are independent from each other, environmental gradients are lacking) will be attributable either to species interactions (smaller structural variability than expected), or to environmental heterogeneity (greater structural variability than expected). Structural variability is evaluated as the variance of species diversity, the indexN=exp(H') is used for measuring diversity. The precise measure of the degree of community organizationW is computed as the shift between two empirical distributions:D ^* (VN) or Bootstrap distribution of variance of diversity in the community, andD ^o (VN) or the random community variability distribution, which is evaluated after simulating the IRDH conditions.A satisfactory interpretation can be given to the results of evaluatingW for 11 data sets of 10 relevés each.Abbreviation IRDH Independent random distribution hypothesis     

Aeroponics for the culture of organisms, tissues and cells

Characteristics of aeroponics are discussed. Contrast is made, where appropriate, with hydroponics and aero-hydroponics as applies to research and commercial applications of nutrient mist technology. Topics include whole plants, plant tissue cultures, cell and microbial cultures, and animal tissue cultures with regard to operational considerations (moisture, temperature, minerals, gaseous atmosphere) and design of apparati.     

Isolation and characterization of porcine somatotropin containing a succinimide residue in place of aspartate129.

Aspartate129 in porcine somatotropin was converted into a cyclic imide residue (succinimide) under acidic solution conditions. Reversed-phase high performance liquid chromatography was utilized to isolate and quantitate this altered species, which accounted for approximately 30% of the total protein. The molecular mass of this modified species was determined by electrospray mass spectrometry to be 18 Da less than normal porcine somatotropin, indicative of a loss of 1 H2O molecule. Tryptic peptide mapping demonstrated that the peptide composed of residues 126-133 was altered in this modified protein. Amino acid analysis, amino acid sequencing, mass spectrometry, and capillary zone electrophoresis were used to demonstrate that aspartate129 in this peptide had been converted into a succinimide residue. Further confirmation that this peptide contained a succinimide was obtained by hydrolyzing the modified peptide at pH 9.0, which yielded both the aspartate and isoaspartate peptides.     

Effects of Neuronal Activity on Inositol Phospholipid Metabolism in the Rat Autonomic Nervous System

The effect of nerve stimulation on inositol phospholipid hydrolysis in autonomic tissue was assessed by direct measurement of [3H]inositol phosphate production in ganglia that had been preincubated with [3H]inositol. Within minutes, stimulation of the preganglionic nerve increased the [3H]inositol phosphate content of the superior cervical sympathetic ganglion indicating increased hydrolysis of inositol phospholipids. This effect was blocked in a low Ca2+, high Mg2+ medium. It was also greatly reduced when nicotinic and muscarinic antagonists were present together in normal medium. However, neither the nicotinic antagonist nor the muscarinic antagonist alone appeared to be as effective as both in combination. In other experiments, stimulation of the vagus nerve caused dramatic increases in [3H]inositol phosphate in the nodose ganglion but did not increase [3H]inositol phosphate in the nerve itself. This effect was insensitive to the cholinergic antagonists. Thus, neuronal activity increased inositol phospholipid hydrolysis in a sympathetic ganglion rich in synapses, as well as in a sensory ganglion that contains few synapses. In the sympathetic ganglion, synaptic stimulation activated inositol phospholipid hydrolysis and this was primarily due to cholinergic transmission; both nicotinic and muscarinic pathways appeared to be involved.     

Vegetation structure and species coexistence

“Vegetation Structure and Species Co-existence” was the topic of a symposium organized in 1992, in Tartu, Estonia. The symposium was dedicated to the memory of Professor Teodor Lippmaa (1892–1943), who made important contributions, especially to the concept of synusia in community ecology. Current views on relation between vegetation structure and species co-existence vary. This variation is partly due to the traditional opposite views of plant community structure (the individualistic and organismic concept); these views refer both to the strength and role of biotic interactions within a community, and to the community structure.     

The effect of post-hypoxia on roots inSenecio andMyosotis species related to the glutathione system

This paper shows the effect of re-aeration following hypoxic pretreatment on the glutathione system in plants with different flooding tolerance. Re-aeration of hypoxically pretreated roots led to an increase of TBA-rm content indicating an accelerated lipid peroxidation (post-anoxic injury). Re-admission of oxygen resulted in a clear increase in the content of total glutathione in both flooding-intolerant speciesMyosotis arvensis andSenecio jacobaea. Simultaneously, the high ratio between reduced (GSH) and oxidized (GSSG) glutathione decreased in these species upon the onset of re-aeration, while the tolerantMyosotis palustris andSenecio aquaticus showed only little changes in contents of GSH and GSSG. An imbalance in GSH/GSSG ratio reflects oxidative stress. The glutathione reductase (GR) reacted very differently in the investigated genera. The metabolic response to varying oxygen pressure is much stronger in the flooding-intolerant species compared to species naturally growing in wetlands. The present results suggest that glutathione system is an important component in overcoming oxidative stress.