Book Reviews

Book reviewed in this article:
Applied Anthropology: The Aboriginal Arts and Crafts Industry . Jon Altman
Marketing Aboriginal Art in the 1990s . Jon Altman and Luke Taylor     

The biogeochemical cycle of the adsorbed template

Experimental results are presented for the verification of the first adsorption step of the ‘adsorbed template’ biogeochemical cycle, a simple model for a primitive prebiotic replication system. The adsorption of Poly-C, Poly-U, Poly-A, Poly-G, and 5′-AMP, 5′-GMP, 5′-CMP and 5′-UMP onto gypsum was studied. It was found that under the conditions of the experiment, the polymers have a very high affinity for the mineral surface, while the monomers adsorb much less efficiently.     

Growth Inhibition, Turgor Maintenance, and Changes in Yield Threshold after Cessation of Solute Import in Pea Epicotyls

The dependence of stem elongation on solute import was investigated in etiolated pea seedlings (Pisum sativum L. var Alaska) by excising the cotyledons. Stem elongation was inhibited by 60% within 5 hours of excision. Dry weight accumulation into the growing region stopped and osmotic pressure of the cell sap declined by 0.14 megapascal over 5 hours. Attempts to assay phloem transport via ethylenediaminetetraacetate-enhanced exudation from cut stems revealed no effect of cotyledon excision, indicating that the technique measured artifactual leakage from cells. Despite the drop in cell osmotic pressure, turgor pressure (measured directly via a pressure probe) did not decline. Turgor maintenance is postulated to occur via uptake of solutes from the free space, thereby maintaining the osmotic pressure difference across the cell membrane. Cell wall properties were measured by the pressure-block stress relaxation technique. Results indicate that growth inhibition after cotyledon excision was mediated primarily via an increase in the wall yield threshold.     

Human recombinant insulin-like growth factor I. I. Development of a serum-free medium for clonal density assay of growth factors using balb/c 3T3 mouse embryo fibroblasts

Summary A serum-free clonal density growth assay was developed for the quantification of the biological activity of human recombinant insulin-like growth factor I (IGF-I). The assay measures IGF-I stimulated growth of Balb/c 3T3 cells cultured over 4 d on poly-d-lysine-coated plastic surfaces in a serum-free medium formulation composed of a 1∶1 (vol/vol) mixture of Ham's F12 and Dulbecco's modified Eagle's media, supplemented with 3.0 ng/ml bovine basic fibroblast growth factor (bFGF), 10 μg/ml human transferrin, 100 μg/ml ovalbumin, and 1.0 μM dexamethanose. Low-temperature trypsinization of serum-supplemented stock cultures combined with the use of poly-d-lysine-coated plates made it unnecessary to use serum or fibronectin to promote cell attachment and survival. Serum-free growth conditions were optimized with respect to the concentrations of the supplements. Addition of IGF-I resulted in 3.5-fold more cells than control cultures without IGF-I after 4 d. Deletion of bFGF resulted in no IGF-I stimulation of growth. The concentrations of various preparations of IGF-I required to achieve one-half maximal stimulation of cell number (ED₅₀), ranged between 1.25 and 4.7 ng/ml. In parallel assays, IGF-I was 6.6 times more potent than human recombinant insulin-like growth factor II and 32 times more potent than insulin. When cells were seeded into medium containing IGF-I, transferrin, ovalbumin, and dexamethasone but no bFGF, growth was minimal. Dose-response addition of bFGF showed an ED₅₀, of 0.9 ng/ml. The methods reported are useful to monitor the biological potency of recombinant and natural-source growth factors as well as providing a new means of studying the multiple growth factor requirements of Balb/c 3T3 cells in cultures. This work was supported by a contract from IMCERA Bioproducts, Inc.     

Structure-from-motion based on information at surface boundaries

Existing computational models of structurefrom-motion — the appearance of three-dimensional motion generated by moving two-dimensional patterns — are all based on variations of optical flow or feature point correspondence within the interior of single objects. Three separate phenomena provide strong evidence that in human vision, structure-from-motion is significantly affected by surface boundary cues. In the first, a rotating cylinder is seen, though no variation in optical flow exists across the apparent cylinder. In the second, the shape of the bounding contour of a moving pattern dominates the actual differential motion within the pattern. In the third, the appearance of independently moving objects changes significantly when the boundary between them becomes indistinct. We describe a simple computational model sufficient to account for these effects. The model is based on qualitative constraints relating possible object motions to patterns of flow, together with an understanding of the patterns of flow that can be discriminated in practice.     

Effect of Zeitgeber Intensity Reduction on a Simulated Dual-Oscillator Human Circadian System: Classical and Dynamic Analysis

The two-oscillator model of human circadian rhythmicity was analyzed when a zeitgeber relative intensity of 1, 0.5, or 0.1 was introduced into the equations. Fourier analysis was compared with dynamic analysis such as attractor reconstruction or Liapunov exponent calculation. After a 50 or 90% reduction in zeitgeber intensity, the dynamics of the system became equivalent and differed significantly from those of a system with maximal zeitgeber intensity. When 10% aleatory noise was added to the data, the analysis was still applicable, and the results obtained were essentially the same as in the absence of noise. Dynamic analysis could thus provide a distinct classification for periodic data, based on the type of analysis.     

Leaf photosynthetic rate is correlated with biomass and grain production in grain sorghum lines

Significant genetic variation in leaf photosynthetic rate has been reported in grain sorghum [Sorghum biocolor (L.) Moench]. The relationships between leaf photosynthetic rates and total biomass production and grain yield remain to be established and formed the purpose of this experiment. Twenty two grain sorghum parent lines were tested in the field during the 1988 growing season under well-watered and water-limited conditions. Net carbon assimilation rates were measured at mid-day during the 30 day period from panicle initiation to head exertion on upper-most fully expanded leaves using a portable photosynthesis system (LI-6200). Total biomass and grain production were determined at physiological maturity. The lines exhibited significant genetic variation in leaf photosynthetic rate, total biomass production and grain yield. Significant positive correlations existed between leaf photosynthesis and total biomass and grain production under both well-watered and water-limited conditions. The results suggest that leaf photosynthetic rate measured prior to flowering is a good indicator of productivity in grain sorghum.     

Optimization of growth conditions for the production of proteolytically-sensitive proteins in the periplasmic space of Escherichia coli

Summary The expression of many secreted recombinant proteins in Gram-negative bacteria is limited by degradation in the periplasmic space. We have previously shown that the production of protein A--lactamase, a secreted fusion protein highly sensitive to proteolysis in Escherichia coli, can be increased in mutant strains deficient in up to three cell-envelope-associated proteolytic activities. In this work we investigated the effect of fermentation conditions on suppressing any residual proteolytic activity in various protease-deficient strains. Optimal production of the fusion protein was observed in cells grown under mildly acidic conditions (5.5pH6.0) and at low temperatures. These conditios were shown to specifically decrease the rate of proteolysis. In addition, a further increase in production was observed in cultures supplemented with 0.5 to 0.75 mM zinc chloride. This may relate to the inhibition of a cell envelope protease by Zn²⁺ ions. Offsprint requests to: G. Georgiou     

The oral assimilation of radiomanganese by the mouse

The metabolism of orally administered radiomanganese was studied in mice. Assimilation of absorbed manganese (Mn) was determined using whole body counting techniques. When⁵⁴MnCl₂ was administered, 2.7% of the dose was retained after 10 d compared with 1.2% from the⁵⁴Mn-nitrilotriacetate (NTA) complex. However, this difference was accounted for by the rapid and persistent adsorption of the Mn onto the teeth of the lower jaw when fed as the ionic salt at pH 2.0 compared with the NTA-chelate fed at pH 9.0. Once corrected for the amount adsorbed onto the teeth, the biodistribution and relative specific activity of the assimilated radiomanganese into a variety of tissues were similar for both forms of the metal.     

Prevention of stress-induced gastric ulcers by dopamine agonists in the rat

Dopamine (DA) and DA agonists have been shown to exert a protective role against the formation of duodenal ulcers. The effect of stimulation of DA receptors on the development of stress-induced gastric ulcers is currently unknown. Accordingly, we evaluated the effect of several DA agonists on the development of gastric ulcers induced by 3 h of cold + restraint stress (CRS) in rats. Apomorphine, d-amphetamine, methylphenidate, and threo-dl-p-hydroxymethylphenidate (an hydroxylated analog of methylphenidate), significantly reduced both the incidence and severity of CRS-induced gastric ulcers. The gastric cytoprotection afforded by these agents was dose-related, and completely antagonized by pretreatment with the peripheally acting DA antagonist domperidone. Because domperidone blocks peripheral, but not central, DA receptors, and since the entry of threo-dl-p-hydroxymethylphenidate across the blood-brain barrier into the brain is restricted to a great extent, we conclude that stimulation of peripheral DA receptors is primarily involved in the gastric cytoprotection induced by dopamimetics.The pathogenesis of stress-induced gastric ulcers remains largely unknown, and significant efforts have been made over the last decade to functionally characterize some of the factors involved in the etiology of this disease. Considerable attention has been focused on gastric acid secretion, but its primary role in stress-induced gastric ulcer disease remains uncertain. In fact, agents which effectively inhibit or neutralize gastric acid secretion such as cimetidine or antacids do not necessarily exert protection against stress-induced gastric ulcers (1,2). Moreover, in our original studies with neurotensin, a brain and gastrointestinal peptide, we have found that central administration of this neuropeptide, which completely prevents the development of cold + restraint stress (CRS)-induced gastric ulcers, does not appreciably alter gastric acid secretion (2). These findings support the contention that gastric acid secretion may not be an important factor in the development of this type of gastric ulcer.There is, however, considerable evidence that the automatic nervous system plays an intermediary role in the development of these ulcers (3,4). In this regard, surgical or pharmacological blockade of the vagal (cholinergic) division of the autonomic nervous system prevents the appearance of stress-associated gastric ulcers (5,6). Direct stimulation of catecholamine receptors, or indirect activation via increased sympathetic outflow to the periphery (7,4,8–11) appears to produce a salutary effect of stress-induced gastric ulcers.Szabo and his associates (12, 13, 14) have extensively studied the anti ulcer effects of dopamine (DA) in duodenal ulcer formation. Whether DA also modifies the development of stress-induced gastric ulcers is currently unknown.We have therefore evaluated the effect of selected DA receptor agonists and antagonists on CRS-induced gastric ulcer formation in rats.