Further Evidence against a Momentum Explanation for IOR

Reaction times to targets presented in the same location as a preceding cue are greater than those to targets presented opposite the cued location. This observation can be explained as a result of inhibition at the attended location (IOR), or as facilitation at the location opposite the cue (opposite facilitation effect or OFE). Past research has demonstrated that IOR is observed reliably, whereas OFE is observed only occasionally. The present series of four experiments allows us to determine whether or not OFE can be explained by eye movements as suggested by previous authors. Participants'' eye movements were monitored as they were presented with an array of four placeholders aligned with the four cardinal axes. Exogenous cues and targets were presented successively. Participants (N=37) completed either: i.) cue-manual and cue-saccade experiments, ignoring the cue and then responding with a keypress or saccade, respectively, or ii.) manual-manual and saccade-saccade experiments, responding to both the cue and the target with a keypress or saccade respectively. Results demonstrated a reliable IOR effect in each of the four experiments (reaction time greater for same versus adjacent and opposite cue-target trials). None of the four experiments demonstrated evidence of an OFE (reaction times were not significantly lower for opposite versus adjacent cue-target trials). These results are inconsistent with a momentum-based account of cue-target task performance, and furthermore suggest that the OFE cannot be attributed to occasional eye movements to the cue and/or target in previous studies.     

Materia Melanica: Further Dark Thoughts

The view is advanced that melanogenesis arose evolutionarily as a detoxification pathway for intrinsically-generated orthoquinones. The primary impetus for the production of orthoquinones may have been their general antibiotic properties and the utility of these chemical species in forming covalent crosslinks between proteins, as illustrated by cuticular sclerotization in insects. It is argued that polymerization to give rise to visible pigments may have originated as a pathway for the inactivation of orthoquinones. The possible evolutionary advantages accruing from the generation of melanin are discussed with special reference to acuity of photoreceptors and the physico-chemical properties of melanin, as well as the contribution of melanin to protective colouration or display.     

Further Evidence for a Growth-Promoting and Flower-Inhibiting Hormone in Strawberry

Further experiments with runner plants of the cultivated strawberryjoined in pairs as donor/receptor units are reported. Stolonproduction was promoted in receptor plants in short days bylong-day treatment of donor plants. This was a photoperiodiceffect induced by low intensity light. Again, as previously,petiole length was increased and flower induction inhibitedby these, or similar treatments. An attempt to demonstrate thetranslocation and activity of a vegetative-growth-inhibiting,flower-promoting hormone gave negative results. It is argued that the photoperiodic control of the growth habitis mediated mainly by a transmissible vegetative-growth-promotingand flower-inhibiting hormone, which is produced in leaves andacts at the growing regions.     

Anaerobic Growth of Purple Nonsulfur Bacteria Under Dark Conditions

Purple nonsulfur photosynthetic bacteria were cultured anaerobically in the absence of light by a modification of the Hungate technique. Growth was slow and resembled that of fastidious anaerobes; on yeast extract-peptone-agar medium, each cell produced about 16 descendants in 15 to 20 days. Growth was stimulated by addition of ethyl alcohol, acetate and H₂, or pyruvate and H₂. Cells grown in the presence of pyruvate and H₂ produced acetate and CO₂; each cell produced approximately 10 descendants in 24 hr under anaerobic, dark conditions. Spectrophotometric evidence obtained from cells which were the product of five generations suggests no difference between the bacteriochlorophyll and carotenoids synthesized by cells grown anaerobically under dark or light conditions. Likewise, the ultrastructure of the photosynthetic apparatus in cells grown anaerobically in the dark and in the light appears similar.     

Further Evidence for an Intrinsic Neuraminidase in CNS Myelin

An intrinsic neuraminidase activity in rat brain CNS myelin has been demonstrated and compared with the neuraminidase activity in rat brain microsomes. With use of ganglioside GM3 as a substrate, the myelin-associated neuraminidase exhibited a shallow pH curve with an optimum at pH 4.8 whereas the microsomal activity had a marked optimum at pH 4-4.3. Neuraminidase activity in both fractions was optimized in 0.3% Triton CF-54 but activation was much greater in the microsomes. When the neuraminidase activities were examined at 60 degrees C, the myelin neuraminidase activity was more than sevenfold of that observed at 37 degrees C and was linear for at least 2 h; the microsomal activity increased only fivefold initially and exhibited a continual loss in activity. Addition of excess microsomes to the total homogenate prior to myelin isolation resulted in no change in myelin neuraminidase activity. When the two membrane fractions were examined at equivalent protein concentrations in the presence of additional cations or EDTA (1 mM), similar but not identical effects on neuraminidase activity were seen. The microsomal neuraminidase was considerably more susceptible to inhibition by divalent copper ion. Activity in both fractions was markedly inhibited by Hg2+ and Ag+ whereas EDTA had no effect on either activity. The myelin-associated neuraminidase activity was the highest in cerebral hemispheres, followed by brainstem, cerebellum, and spinal cord and was extremely low in sciatic nerve. In fact, the myelin neuraminidase activity was higher than the microsomal enzyme activity in the cerebral hemispheres.(ABSTRACT TRUNCATED AT 250 WORDS)     

Further Evidence for Selective Differences between Isoalleles in Drosophila

A number of separate strains of Drosophila pseudoobscura were inbred for 38 generations of brother-sister mating with forced heterozygosity for two alleles of either the octanol dehydrogenase or esterase-5 locus. Crosses were set up within each of these inbred lines such that simple mendelian ratios were expected, and eggs from these crosses were placed on media with additions of simple chemicals likely to interact with alleles of the two loci—octanol and ethanol for the ODH locus and tributyrin and triacetin for the E-5 locus. Similar crosses were set up involving parental flies with normally heterozygous genetic background as a control.—Significant deviations from mendelian expectation were observed in inbred E-5 flies grown on tributyrin, inbred ODH males grown on octanol, and inbred ODH females grown on ethanol. There was also a strong effect of octanol medium on males of one of the inbred E-5 lines, and a weak effect of tributyrin medium on ODH inbred females.—The probability that these results reflect interactions between these loci and the environment is assessed in the light of differences between the present results and those obtained at earlier stages of inbreeding.     

Further Evidence Supporting a Role for Gs Signal Transduction in Severe Malaria Pathogenesis

With the functional demonstration of a role in erythrocyte invasion by Plasmodium falciparum parasites, implications in the aetiology of common conditions that prevail in individuals of African origin, and a wealth of pharmacological knowledge, the stimulatory G protein (Gs) signal transduction pathway presents an exciting target for anti-malarial drug intervention. Having previously demonstrated a role for the G-alpha-s gene, GNAS, in severe malaria disease, we sought to identify other important components of the Gs pathway. Using meta-analysis across case-control and family trio (affected child and parental controls) studies of severe malaria from The Gambia and Malawi, we sought evidence of association in six Gs pathway candidate genes: adenosine receptor 2A (ADORA2A) and 2B (ADORA2B), beta-adrenergic receptor kinase 1 (ADRBK1), adenylyl cyclase 9 (ADCY9), G protein beta subunit 3 (GNB3), and regulator of G protein signalling 2 (RGS2). Our study amassed a total of 2278 cases and 2364 controls. Allele-based models of association were investigated in all genes, and genotype and haplotype-based models were investigated where significant allelic associations were identified. Although no significant associations were observed in the other genes, several were identified in ADORA2A. The most significant association was observed at the rs9624472 locus, where the G allele (∼20% frequency) appeared to confer enhanced risk to severe malaria [OR = 1.22 (1.09–1.37); P = 0.001]. Further investigation of the ADORA2A gene region is required to validate the associations identified here, and to identify and functionally characterize the responsible causal variant(s). Our results provide further evidence supporting a role of the Gs signal transduction pathway in the regulation of severe malaria, and request further exploration of this pathway in future studies.     

Further Evidence to Support a Nutritional Interpretation of Sclerophylly

A statistical analysis is made of published data on the leafcomposition of eighty-nine species, covering both sclerophyllousand mesophytic types of leaves, from North and Central America,Africa, and India. Expressing degree of sclerophylly by theratio crude fibre dry weight x 100/crude protein dry weight,the analysis shows: (1) that in terms of organic matter an increasein sclerophylly is associated with a decrease in percentageprotein content and with an increase in percentage fibre content,and (2) that in terms of mineral matter a decrease in phosphoruscontent below about 0.3 per cent. results in a proportionalincrease in degree of sclerophylly. These two results are consideredcomplementary. Since phosphorus is essential for protein synthesis,the observed protein deficiency of sclerophyllous leaves canbe correlated with their low phosphorus content. It is alsoreasonable to expect the observed reciprocal relationship betweenprotein content and fibre content on the basis of a common poolof intermediate metabolites. The above conclusions support the author's hypothesis, suggestedin a previous paper, that a sclerophyllous leaf is the expressionof a metabolism found in plants that can tolerate low levelsof phosphate. Strong circumstantial evidence is also providedby the fact that phosphate deficiency is characteristic of thesoils, either wet or dry, which carry sclerophyllous vegetation.The hypothesis thus provides a ready answer to the apparentparadox of why the same specialized type of leaf should occurin both wet and dry habitats.     

Further Evidence for a Role of Carbohydrates in Insulin Binding : Studies in Lectin-Purified Receptors

Abstract

Purification of liver membrane insulin receptors on concanavalin A-and ricin I-lectin columns gave a 15-fold enrichment in the insulin binding capacity per milligramm of protein. Final receptor and protein recoveries were 53 and 3.8 % respectively. Lectin-purification increased the receptor affinity for insulin, as indicated by a left-ward shift in the binding competition curve and a steeper slope in the Scatchard plot. Lectin-purification increased the receptor sensitivity towards the glycosidic probes. The maximal effects of β-galactosidase, ricin I (galactose-binding lectin) and α-mannosidase were markedly amplified : 80, 90 and 60 % inhibition, versus 45, 40 and 15 % with particulate membranes. The limulus polyphemus (LPA) and wheat germ (WGA) agglutinins (sialic acid- and N-acetyl-glucosaminyl-binding lectins) became effective in modifying the insulin binding : 45 and 80 % inhibition, respectively. The effects were dose-dependent, reversed by the monosaccharide competitors (lectin effects) and unrelated to the state of receptor occupancy. These findings indicate that, within the hormone recognition area, peptide chains containing galactose, mannose and N-acetyl-glucosamine are strictly required for insulin-receptor interaction and suggest that change in the receptor affinity is related to the role of carbohydrate in insulin binding.     

Evidence for Detachment of Indigenous Bacteria from Aquifer Sediment in Response to Arrival of Injected Bacteria

Two bacterial strains isolated from the aquifer underlying Oyster, Va., were recently injected into the aquifer and monitored using ferrographic capture, a high-resolution immunomagnetic technique. Injected cells were enumerated on the basis of a vital fluorescence stain, whereas total cell numbers (stained target cells plus unstained target and antigenically similar indigenous bacteria) were identified by cell outlines emanating from fluorophore-conjugated antibodies to the two target strains. The arrival of injected bacteria at the majority of monitored sampling ports was accompanied by simultaneous temporary increases in unstained cell counts that outnumbered the injected bacteria by 2- to 100-fold. The origin and mechanism of appearance of the unstained cells are considered.     

Saturation of Dark Repair Synthesis: Accumulation of Strand Breaks

Reversal of ultraviolet light damage to DNA by the dark repair system is limited. Experiments utilizing density and radioactive labels demonstrated that repair synthesis is not proportional to dose at doses above 200 ergs/mm². In addition, the number of residual excision induced gaps in Escherichia coli B/r hcr⁺ DNA increases with higher UV doses. The extent of repair is apparently limited by saturation of the repair synthesis step.     

Evidence for para Dechlorination of Polychlorobiphenyls by Methanogenic Bacteria

When microorganisms eluted from upper Hudson River sediment were cultured without any substrate except polychlorobiphenyl (PCB)-free Hudson River sediment, methane formation was the terminal step of the anaerobic food chain. In sediments containing Aroclor 1242, addition of eubacterium-inhibiting antibiotics, which should have directly inhibited fermentative bacteria and thereby should have indirectly inhibited methanogens, resulted in no dechlorination activity or methane production. However, when substrates for methanogenic bacteria were provided along with the antibiotics (to free the methanogens from dependence on eubacteria), concomitant methane production and dechlorination of PCBs were observed. The dechlorination of Aroclor 1242 was from the para positions, a pattern distinctly different from, and more limited than, the pattern observed with untreated or pasteurized inocula. Both methane production and dechlorination in cultures amended with antibiotics plus methanogenic substrates were inhibited by 2-bromoethanesulfonic acid. These results suggest that the methanogenic bacteria are among the physiological groups capable of anaerobic dechlorination of PCBs, but that the dechlorination observed with methanogenic bacteria is less extensive than the dechlorination observed with more complex anaerobic consortia.     

Light Breaks and Fruit-Body Maturation in Coprinus congregatus: Dark Inhibitory and Dark Recovery Process

Experiments were conducted to better understand the inhibitoryeffect of lightduring the dark-induced process of fruit-bodysporulation of Coprinus congregatus Bull, ex Fr. Light-initiatedfruit-body primordia were subjected to different dark periodsinterrupted by a short blue light break at different times.The sporulating response depended on the duration of the darkperiod following the light break. For any inductive dark periodlonger than 3.5 h, a period of darkness lasting half as longas the inductive night completely inhibited fruit-body maturationwhen given after the light break (dark inhibitory process).Longer dark periods after the light break causedrecovery ofthe maximal sporulating response (dark recovery process). Theeffects of the dark inhibitory and the dark recovery processwere alternately reversible, the sporulating response dependingon the duration of darkness after the last light break. Studyof the time course of sporulation showed that a new dark-inducedprocess of fruit-body sporulation was initiated by the beginningof the dark period after the light break. (Received August 2, 1982; Accepted May 6, 1983)     

Evidence for Repair Processes in the Invigoration of Seeds by Hydration

Seeds with low vigour as a result of ageing showed a large improvementin seed quality following a 2 h soak in water, reflected inan increased rate of germination, higher emergence in soil,and the retention of high germination after 24 h rapid ageingin a controlled deterioration vigour test. Similar, but smallerimprovements were seen after a priming treatment using polyethyleneglycol. Seeds dried to their initial moisture content aftertreatment retained these beneficial effects. The treatmentshad little effect on high vigour seed. These findings suggestthat seed invigoration by hydration treatments results fromthe repair of previously sustained deterioration. Brussels sprouts, Brassica oleracea var. gemmifera, priming, repair, seed moisture content, ageing     

Further Evidence for Lack of Gene Expression in the Tetrahymena Micronucleus

Certain galA mutations in the ciliated protozoan Tetrahymena thermophila confer an almost total loss of galactokinase activity in homozygotes. Heterokaryons have been constructed that are homogeneous for the galA1 mutation in the (45n) macronucleus, but which contain a galA⁺ (2n) micronucleus. Soluble cell extracts prepared from these heterokaryons have been assayed for galactokinase activity, using a radiometric assay for the conversion of galactose to galactose-1-phosphate (gal-1-P). No galactokinase activity attributable to the micronuclear genes is observed in such heterokaryons. These results, obtained with the galA1 marker, provide the first direct, quantitative evidence for the lack of micronuclear (germ line) gene expression in Tetrahymena during vegetative growth, and substantiate the predictions of previous phenotypic observations on heterokaryons and autoradiographic studies of micronuclear RNA synthesis. The generality of this conclusion will be established in the future when other enzymically assayable mutations become available for similar studies.