A model for light adaptation: Producing Weber's law with bleaching-type kinetics

An adaptation model having two stages is introduced and its mathematical properties are examined. The two stages are the adaptive process (parameter K _b), which has bleaching-type kinetics, and the response function (parameters K _r and n), which incorporates response saturation. In order to study the increment threshold functions generated by the adaptation model the concept of a detector is required. It is demonstrated that without an adaptive process the compression hypothesis, in the form of the difference equation, produces increment threshold functions which saturate and do not obey Weber's law. It is then shown that an adaptive process with bleaching-type kinetics can prevent saturation and produce Weber's law behavior provided that the adaptive strength of the system exceeds the detector sensitivity.     

Bcl-2 blocks apoptotic signal of transforming growth factor-β in human hepatoma cells

Transforming growth factor- (TGF-) has been shown to induce apoptosis on normal hepatocytes and hepatoma cells both in vitro and in vivo. However, how the TGF- induces apoptosis is still not clear. We examined the expression of anti-apoptosis proteins and sensitivity to TGF- in three well differentiated human hepatoma cell lines. Two TGF- sensitive cell lines Hep3B and HuH7 totally lacked Bcl-2. In contrast, the TGF- resistant HepG2 cells expressed a substantial amount of Bcl-2. All three cell lines expressed equal amounts of Bcl-X_L, Bcl-X_S and Bax. Overexpression of Bcl-2 in Hep3B and HuH7 cells protected them from TGF--induced apoptosis. TGF- treatment increased intracellular peroxide production and suppressed the expression of glutathione-S-transferase in the Hep3B cells, and these effects were partially suppressed by the overexpression of Bcl-2. These results suggest that Bcl-2 may protect cell from TGF--F-induced apoptosis by interfering TGF- generated signals leading to induce reactive oxygen species production.     

Optimizing development time in a seasonal environment: The ‘ups and downs’ of clinal variation

Summary This paper explores the problem of adapting development time to changes in the length of time conditions are favourable for growth and reproduction (season length). It is shown that systematic changes in season length along some gradient such as latitude can generate either simple clines in development time or saw-tooth clines. The relationship between development time and body size gives rise to a corresponding variation in body size. The generation of a saw-tooth cline does not require sharp environmental changes. Both types of clinal variation are observed in insects.     

Endogenous phosphorylation of rat brain synaptosomal plasma membranes in vitro: Some methodological aspects

The time course of endogenous phosphorylation in vitro of total or separted synaptic plasma membrane proteins (SPM) has been correlated with that of hydrolysis of the phosphate donor (ATP) in the incubation medium. The ATP/SPM ratio in the medium was varied. In a low-ratio medium (7.5 M ATP; 2.2 g SPM/l) a complete hydrolysis of ATP occurred almost instantaneously as was measured by the release of free phosphate in and the disappearance of ATP from the medium. As a consequence, only a very short peak of phosphorylation, followed by dephosphorylation was observed. However, when higher ATP/SPM ratios were used (200 M ATP; 0.4 g SPM/l and 500 M ATP; 0.4 g SPM/l), the incorporation of phosphate into SPM proteins was linear for 20 sec, and the maximum level of phosphate incorporation was increased. Similar results were obtained after separation of³²P-labeled phosphoproteins by slab gel electrophoresis. However, analysis of the autoradiographs obtained fromone SPM preparation under different ATP/SPM ratios revealed dependence of phosphorylation of individual protein bands on the conditions used.     

RNA polymerase sigma-related proteins in Escherichia coli: detection by antibodies against a synthetic peptide

Summary Antibodies were raised against a synthetic tetradecameric peptide with an amino acid sequence, DLIQEGNIGLMKAV, which corresponds to the most highly conserved region of bacterial RNA polymerase factors. In a Western-blot analysis of total Escherichia coli proteins, the antiserum reacted specifically with at least three proteins with apparent molecular weights of 75 kDa, 27 kDa and 23 kDa, in addition to the known factors (⁷⁰ and ³²). The majorities of ⁷⁰ and ³² were recovered as associated forms with the RNA polymerase on glycerol gradient centrifugation, while the other cross-reacting proteins were not. Unambiguous evidence was obtained which indicated that the intracellular level of ³² increased rapidly upon heatshock, at least in the strain containing high copy numbers of the rpoH gene.     

On age morphological changes of males of Chydoridae (Cladocera)

Summary Young and adult males of 11 species of Chydoridae are studied, their figures being published here (fig. 1–15). The necessity is stressed to distinguish young forms of males and gynandromorphic individuals.Pleuroxus balatonicus is considered to be described from the population ofPleuroxus unicatus having under Balaton Lake conditions retarded transformation of young males into adult form, and accordingly having unusually numerous young males. \qO\qs\qn\qo\qv\qn\qy\ye \qr\ye\qz\qu\ql\Qj\qt\qa\qt\qy 11 (. 1–15). . , Pleuroxus uncinatus , Pleuroxus balatonicus.     

Lindane degradation by cell-free extracts of Clostridium rectum

For lindane degradation, a cell suspension of Clostridium rectum strain S-17 demands the addition of substrates such as leucine, alanine, pyruvate, a leucine-proline mixture, and molecular hydrogen. In the presence of leucine-proline mixture, lindane decomposed in parallel with isovaleric acid formation, and both lindane degradation and isovaleric acid formation were inhibited by monoiodoacetic acid, suggesting a close relation between lindane degradation and the Stickland reaction. Lindane was degraded by cell-free extracts of C. rectum in the presence of dithiothreitol (DTT). Radiogaschromatograms of n-hexane soluble metabolites from [¹⁴C] lindane showed the presence of monochlorobenzene and -3,4,5,6-tetrachlorocyclohexene, Leucine, NADH, and NADPH were somewhat less active than DTT for lindane degradation in cell-free extracts. Reductive dechlorination seemed the major route of lindane degradation in cell-free extracts as well as in the intact cells of C. rectum.Abbreviations Lindane (-HCH) -1,2,3,4,5,6-hexachlorocyclohexane - -HCH -1,2,3,4,5,6-hexachlorocyclohexane - -TCH -3,4,5,6-tetrachlorocyclohexene - -PCH -1,3,4,5,6-pentachlorocyclohexene - DTT 1,4-dithiothreitol     

Stable isotope ratio as a tracer of mangrove carbon in Malaysian ecosystems

Summary The ratio of stable carbon isotopes (¹³C) in plants and animals from Malaysian mangrove swamps, coastal inlets, and offshore waters was determined. Vascular plants of the swamps were isotopically distinct ( x±s.d.=-27.1±1.2) from plankton (-21.0±0.3) and other algae (-18.7±2.2). Animals from the swamps (-20.9±4.1) and inlets (-19.8±2.5) had a wide range of isotope ratios (-28.6 to-15.4), indicating consumption of both mangrove and algal carbon. Several commercially important species of bivalves, shrimp, crabs, and fish obtained carbon from mangrove trees. Mangrove carbon was carried offshore as detritus and was isotopically distinguishable in suspended particulate matter and sediments. Animals collected from 2 to 18 km offshore, however, showed no isotopic evidence of mangrove carbon assimilation, with ratios (-16.5±1.1, range-19.1 to-13.1) virtually identical to those reported for similar animals from other plankton-based ecosystems. Within groups of animals, isotope ratios reflected intergencric and interspecific differences in feeding and trophic position. In particular, there was a trend to less negative ratios with increasing trophic level.     

Anaerobic dechlorination and degradation of hexachlorocyclohexane isomers by anaerobic and facultative anaerobic bacteria

Screening studies with strict and facultative anaerobic bacteria showed that Clostridium app. and several other representatives of Bacillaceae and Enterobacteriaceae actively degraded -hexachlorocyclohexane (-HCH) under anaerobic conditions. Representatives of Lactobacillaceae and Propronibacterium were inactive. With ³⁶Cl-labelled -HCH a nearly complete dechlorination was shown to occur in 4–6 days by Clostridium butyricum, C. pasteurianum and Citrobacter freundii, while other facultative anaerobic species were less active.Aerobically grown facultative anaerobes also dechlorinated actively -HCH during subsequent anaerobic incubation with glucose, pyruvate or formate as substrates. The -, - and -HCH isomers were also, but more slowly, dechlorinated (>>-HCH). All species active in anaerobic degradation of -HCH formed -tetrachlorocyclohexene (TCH) as the main intermediate metabolite and no -pentachlorocyclohexene (PCH) or other isomers of TCH or PCH have been found. Small amounts of tri- and tetrachlorinated benzenes have been found too. The mechanism of dechlorination is discussed.Non-Common Abbreviations Used -HCH -hexachlorocyclohexane - -TCH -2,3,4,5-tetrachlorocyclohexene - -PCH -1,2,3,4,5-pentachlorocyclohexene - GLC gas liquid chromatography     

β-Globin gene polymorphism in the Saudi Arab population

Summary DNA mapping with the restriction endonucleases, Hpa I and Mst II, has been used to investigate -globin gene polymorphism in the Saudi Arab population. Using Hpa I digestion, 13.0kb and 7.6kb fragments were found in association with the ^A and ^S genes. The frequency of the polymorphic forms in two regions investigated vary significantly. In Al-Hafouf and the surrounding villages, situated in the Eastern Province of Saudi Arabia, the frequencies of association of the ^S gene with the Hpa I 7.6kb, 7.0kb, and 13.0kb fragments were 0.866, 0.043, and 0.071, respectively. The frequency of association of ^A with the 7.6kb and 13.0kb fragments resulting from the Hpa I digestion were 0.875 and 0.125. In Khaiber, Tehamat-Aseer, and surrounding villages, in the Western Province, the frequency of association of ^S with 7.6kb, 7.0kb, and 13.0kb fragments were 0.836, 0.027, and 0.0136, respectively, while that of ^S was 0.250 and 0.750 with 7.0kb and 13.0kb Hpa I fragments, respectively. Using Mst II digestion, ^A was found to be linked to a 1.15kb fragment, while ^s was linked to a 1.35kb fragment. The normal (Hb AA), heterozygotes (Hb AS), and homozygotes (Hb SS) gave 1.15, 1.15/1.35, and 1.35kb fragments, respectively. The results of this study show extensive polymorphism at the Hpa I restriction site of the ^A and ^S globin genes with the different polymorphic forms existing at a variable frequency in different regions of Saudi Arabia.     

Degradation of alpha, beta, gamma and delta-hexachlorocyclohexanes by Sphingomonas paucimobilis

Sphingomonas paucimobilis degrades aerobically , , and -hexachlorocyclohexane. With -HCH, complete degradation occurred after 3 days but with and , and with -HCH, 98 and 56 % degradation occurred after 12 and 8 days of incubation, respectively. Pentachlorocyclohexene was formed as the primary metabolite during the degradation of all the HCH isomers. © Rapid Science Ltd. 1998     

Bacterial regeneration of ammonium and phosphate as affected by the carbon:nitrogen:phosphorus ratio of organic substrates

The effect of carbonnitrogenphosphorus (CNP) ratio of organic substrates on the regeneration of ammonium and phosphate was investigated by growing natural assemblages of freshwater bacteria in mineral media supplemented with the simple organic C, N, and P sources (glucose, asparagine, and sodium glycerophosphate, respectively) to give 25 different substrate CNP ratios. Both ammonium and phosphate were regenerated when CN and NP atomic ratios of organic substrates were 101 and 161, respectively. Only ammonium was regenerated when CN and NP ratios were 101 and 10–201, respectively. On the other hand, neither ammonium nor phosphate was regenerated when CN and NP ratios were 151 and 51, respectively. In no case was phosphate alone regenerated. As bacteria were able to alter widely the CNP ratio of their biomass, the growth yield of bacteria appeared primarily dependent on the substrate carbon concentration, irrespective of a wide variation in the substrate CNP ratio.     

Ganglioside-cholera toxin interactions: a binding and lipid monolayer study

Summary On t.l.c. plates ¹²⁵I-cholera toxin binds to a disialoganglioside tentatively identified as GD_lb with about 10 times less capacity than to ganglioside GM₁. Binding of labeled toxin to both gangliosides was abolished in presence of excess amounts of unlabeled B subunit. Ganglioside extracts from human or pig intestinal mucosa showed toxin binding to gangliosides GM₁ and GD_1b. In ganglioside-containing lipid monolayers the penetration of the toxin was independent of the ganglioside binding capacity.Abbreviations GM₂ Gal-NAc14Gal(3-2NeuAc)14G1c1Cer - GM₁ Gal3Ga1-NAc14Gal(32NeuAc)14G1c11Cer - GD_1a NeuAc23Ga113Gal-NAc14Gal(32NeuAc)14G1c11Cer - GD1b Gall3Gal-NAcl4Gal(32NeuAc82NeuAc)14Glc11Cer - GT_1b NeuAc23Ga113Ga1-NAcal4Gal(3-2NeuAc82NeuAc)14G1c11Cer - dpPC 1,2-hexadecanoyl-sn-glycero-3-phosphocholine - dpPE 1,2-hexadecanoyl-sn-glycero-3-phosphoethanolamine     

Differential susceptibility in some sorghum (Sorghum vulgar) genotypes to zinc deficiency in soil

Summary Nine genotypes of sorghum were screened for their relative susceptibility to zinc deficiency in soil. All the varieties were highly responsive to zinc application, but behaved differently under zinc stress conditions in respect of dry-matter production, zinc concentration and uptake. The varieties, JS-263, 29/1, JS-20 and Son 127×SL-245 and CSH-1 were relatively more susceptible to zinc deficiency than 3677×6352, Son 3×SL 209, CSH-3 and 2077×1151. re]19730102     

Structures of the N-linked sugar chains in the PAS-6 glycoprotein from the bovine milk fat globule membrane

The structures of the N-linked sugar chains in the PAS-6 glycoprotein (PAS-6) from the bovine milk fat globule membrane were determined. The sugar chains were liberated from PAS-6 by hydrazinolysis, and the pyridylaminated sugar chains were separated into a neutral (6N) and two acidic chains (6M and 6D), the acidic sugar chains then being converted to neutral sugar chains (6MN and 6DN). 6N was separated into two neutral fractions (6N13 and 6N5.5), while 6MN and 6DN each gave a single fraction (6MN13 and 6DN13). The structure of 6N5.5, which was the major sugar chain in PAS-6, is proposed to be Man16 (Man13) Man14GlcNAc14GlcNAc-PA; 6N13, 6MN13 and 6DN13 are proposed to be Gal13Gal14GlcNAc12Man16 (Gal13Gal14GlcNAc12Man13) Man14GlcNAc14 (Fuc16)GlcNAc-PA;6M and 6D had 1 or 2 additional NeuAc residues at the non-reducing ends of 6MN13 and 6DN13, respectively. © 1998 Rapid Science Ltd     

Mutagen sensitivity and mutability in lentil

Summary Seeds of two cultivars, each of macrosperma and microsperma varietal groups of lentil were mutagenised with gamma-rays and NMU to determine their mutagen sensitivity and mutability. The increasing doeses of gamma-rays and NMU decreased germination, root and shoot length, pollen fertility and plant survival, but increased the occurrence of leaf spots. The root system was found to be more sensitive to both mutagens than the shoot. The macrosperma varietal group was more sensitive to both the mutagens than microsperma group. In microsperma group, variety Pusa-1 was more sensitive to both the mutagens than L-259, while in the macrosperma group L-1491 showed more sensitivity to the mutagens than L-1492. Radio-sensitivity corresponded positively with chemosensitivity in both varietal groups. There was a positive relationship between radio- and chemo-sensitivity of the genotypes and their mutability. The results also revealed the existence of a parallelism between radiomutability and chemo-mutability. Due to saturation in the mutational events and vigour of both diplontic and haplontic selection in the biological material, the mutation frequency either decreased or remained constant at higher doses of the mutagens.     

Genetic analysis of resistance to whitebacked planthopper in twenty-one varieties of rice,Oryza sativa L.

Summary The inheritance of resistance to whitebacked planthopper Sogatella furcifera (Horvath) was studied in 21 rice varieties. Reactions of F₁; F₂ and F₃ progenies of the crosses of 21 resistant varieties with the susceptible variety TN 1 revealed that a single dominant gene governs resistance in Mushkan 41, Santhi, Siahnakidar 195, SM2-34, Tirisurkh 251, Zirijowaian 245, 18, 24A, 39, 76 S, 78, 180, 213 B, 267, 293, CI 6037-4, NP97, S39 JKW and Bansphul. In varieties 65 and 274 A, resistance is governed by one dominant and one recessive gene which segregate independently of each other. Tests for allelism with the Wbph 1 gene originally identified in N 22 revealed that the dominant gene present in all the test varieties is the same as Wbph 1. Further studies are required to determine the allelic relationships of the recessive gene found in varieties 65 and 274 A.     

α-and β-Glycosidases in maize roots

Four glycosidases were analyzed in 10 mm apical segments prepared from growing roots (15 mm) of Zea mays L. The pH optima were found to be 5.8 for -glucosidase, 4.4 for -galactosidase, 6.4 for -glucosidase and 6.0 for -galactosidase. The -glucosidase showed 4-fold higher activity than the -galactosidase. The distribution of the -glucosidase activity was signifcantly different from that of the -galactosidase, -glucosidase and -galactosidase.Abbreviations -Glu -glucosidase - -Gal -galactosidase - -Glu -glucosidase - -Gal -galactosidase     

Partial mispairing and crossing-over between β0 and δ genes as the origin of the δ β0 thalassemia gene

Summary Two double heterozygous ⁰/⁰ thalassemic sibs of Mexican descent were studied. The father had a ⁰/⁰ genotype, while the mother, one sib and several maternal relatives were ⁰/⁰ heterozygotes. Parental consanguinity and an apparently low frequency of thalassemia among Mexicans suggested a possible common origin of both ⁰ and ⁰ genes. A hypothesis to explain such a possibility is proposed on the basis of a partial mispairing between ⁰ and genes followed by a crossing-over which would results in a ⁰ recombinant gene. This hypothesis could also be extended to explain the 22 gluala, 22 alaglu and 116 arghis Hb variants as recombinants from double crossing-over between and mispaired genes for which the name interstitial-Lepore is proposed.