DNA homology and adsorption specificity of Pseudomonas aeruginosa virulent bacteriophages

Summary The DNA homology and adsorption specificity of newly isolated virulent bacteriophages of P. aeruginosa have been studied. On the basis of this analysis all phages were divided into four groups: k, m, mnP78-like and mnF82-like bacteriophages. DNA's of k as well as m phages were shown to possess different restriction patterns although they have an extensive homology. Unlike other groups, k phages were characterized by the presence of T4 DNA ligase-repaired, single-chain breaks.Abbreviations kbp kilobase pairs - EM electron microscopy     

Phenogenetic Characterization of a Group of Giant φKZ-like Bacteriophages of Pseudomonas aeruginosa

A comparative study was made of a group ofPseudomonas aeruginosa virulent giant DNA bacteriophages similar to phage KZ in several genetic and phenotypic properties (particle size, particle morphology, genome size, appearance of negative colonies, high productivity, broad spectrum of lytic activity, ability to overcome the suppressing effect of plasmids, absence of several DNA restriction sites, capability of general transduction, pseudolysogeny). We have recently sequenced the phage KZ genome (288 334 bp) [J. Mol. Biol., 2002, vol. 317, pp. 1–19]. By DNA homology, the phages were assigned to three species (represented by phages KZ, Lin68, and EL, respectively) and two new genera (KZ and EL). Restriction enzyme analysis revealed the mosaic genome structure in four phages of the KZ species (KZ, Lin21, NN, and PTB80) and two phages of the EL species (EL and RU). Comparisons with respect to phage particle size, number of structural proteins, and the N-terminal sequences of the major capsid protein confirmed the phylogenetic relatedness of the phages belonging to the KZ genus. The origin and evolution of the KZ-like phages are discussed. Analysis of protein sequences encoded by the phage KZ genome made it possible to assume wide migration of the KZ-like phages (wandering phages) among various prokaryotes and possibly eukaryotes. Since the phage KZ genome codes for potentially toxic proteins, caution must be exercised in the employment of large bacteriophages in phage therapy.     

Isolation and characterization of lytic phages fromBacterioides ruminicola ssbrevis

Two bacteriophages (Brb01 and Brb02), lytic toBacteroides ruminicola ssbrevis AR20, were isolated from sewage water. Both phages possessed polyhedral heads and long noncontractile tails, and were classified as Siphoviridae of morphotype B1. Bacteria resistant to phages Brb01 and Brb02 arose following lysis of broth cultures. Survivors of Brb01 infection were capsulated but remained susceptible to Brb02 infection. Survivors of Brb02 infection were noncapsulated and were resistant to attack by both Brb01 and Brb02. Neither phage lysogenized the host. Both phages contained double-stranded DNA, and their restriction endonuclease digestion patterns indicated that the phage genomes were circularly permuted and terminally redundant. Phage Brb01 genome was examined in greater detail and confirmed to be circularly permuted, of size 33 kb, with a terminal redundancy of 2 kb, or 6% of the length of the genome. Circularly permuted genomes in phages of rumen bacteria do not appear to have been reported previously.At present, there is considerable interest in the genetic manipulation of rumen bacteria. The characterization of the phages described herein provides the basic information required for their use in the construction of vectors for the transfer of genetic material.     

Determination of a molecular torsional angle in the metarhodopsin-I photointermediate of rhodopsin by double-quantum solid-state NMR

We present a solid-state NMR study of metarhodopsin-I, the pre-discharge intermediate of the photochemical signal transduction cascade of rhodopsin, which is the 41 kDa integral membrane protein that triggers phototransduction in vertebrate rod cells. The H-C10-C11-H torsional angles of the retinylidene chromophore in bovine rhodopsin and metarhodopsin-I were determined simultaneously in the photo-activated membrane-bound state, using double-quantum heteronuclear local field spectroscopy. The torsional angles were estimated to be || = 160 ± 10° for rhodopsin and = 180 ± 25° for metarhodopsin-I. The result is consistent with current models of the photo-induced conformational transitions in the chromophore, in which the 11-Z retinal ground state is twisted, while the later photointermediates have a planar all-E conformation.     

Determination of the torsion angles of alanine and glycine residues of model compounds of spider silk (AGG)(10) using solid-state NMR methods

Spiders synthesize several kinds of silk fibers. In the primary structure of spider silk, one of the major ampullate (dragline, frame) silks, spidroin 1, and flagelliform silk (core fibers of adhesive spiral), there are common repeated X-Gly-Gly (X = Ala, Leu, Pro, Tyr, Glu, and Arg) sequences, which are considered to be related to the elastic character of these fibers. In this paper, two dimensional spin diffusion solid-state NMR under off magic angle spinning (OMAS), ¹³C chemical shift contour plots, and Rotational Echo DOuble Resonance (REDOR) were applied to determine the torsion angles of one Ala and two kinds of Gly residues in the Ala-Gly-Gly sequence of ¹³C=O isotope-labeled (Ala-Gly-Gly)₁₀. The torsion angles were determined to be (, ) = (–90°, 150° ) within an experimental error of ±10° for each residue. This conformation is characterized as 3₁ helix which is in agreement with the structure proposed from the X-ray powder diffraction pattern of poly(Ala-Gly-Gly). The 3₁ helix of (Ala-Gly-Gly)₁₀ does not change by formic acid treatment although (Ala-Gly)₁₅ easily changes from the silk I conformation (the structure of Bombyx mori silk fibroin before spinning in the solid state) to silk II conformation (the structure of the silk fiber after spinning) by such treatment. Thus, the 3₁ helix conformation of (Ala-Gly-Gly)₁₀ is considered very stable. Furthermore, the torsion angles of the 16th Leu residue of (Leu-Gly-Gly)₁₀ were also determined as (, ) = (–90°, 150° ) and this peptide is also considered to take 3₁ helix conformation.     

The low-light reduction in the quantum yield of photosynthesis: potential errors and biases when calculating the maximum quantum yield

Photosynthesis-irradiance (P-E) curves are widely used to describe photosynthetic efficiency and potential. Contemporary models assume maximal photosynthetic quantum yield () at low irradiances. But P-E observations made with both oxygen evolution and carbon uptake techniques show that this is not always the case. Using new and published data in conjunction with modeling exercises, we demonstrate that regardless of the mechanism there can be reductions in at low irradiances that are not readily observable using conventional P-E analyses. We also show that analytical errors, such as inaccurate estimation of dark oxygen consumption or carbon uptake, can markedly affect the structure of -E curves with negligible effect on P-E curve structure. Whether from respiration `corrections' or other mechanisms, these deviations in at low light levels from the maximum quantum yield of photosynthesis (_max) can lead to significant errors (> 50%) in the estimation of the linear portion of the P-E curve and ultimately _max. Non-linear models of P-E, such as the rectangular hyperbola, quadratic, exponential and hyperbolic tangent that are commonly used to estimate the initial slope () of the P-E curve assume that is maximal at low light levels and therefore can err in the estimation of _max when is reduced at low light levels. Using a diverse data set of 622 P-E curves with a total of 7623 points, we show that although model skills are high (r ² = 0.96 ± 0.05, 0.97 ± 0.04, 0.97 ± 0.04 and 0.97 ± 0.04, respectively), a large fraction of the model-predicted _max differ by greater than 10% from true _max values (91%, 50%, 82% and 46%, respectively). Data from these observations and modeling exercises lead us to suggest that _max be determined by directly estimating the true maximum of a -E curve rather than using the more conventional methodology employing the initial slope of the P-E curve.This revised version was published online in October 2005 with corrections to the Cover Date.     

The growth of Saccharomyces cerevisiae CBS 426 on mixtures of glucose and ethanol: a model

Saccharomyces cerevisiae CBS 426 was grown in continuous culture in a defined medium with a mixture of glucose and ethanol as carbon source. Growth on ethanol as the sole carbon source was only possible after the addition of a small amount of glutamic acid. The flows of glucose, ethanol, oxygen, carbon dioxide and biomass to and from the system were measured and a model for the growth of the yeast on the carbon sources constructed. The model is shown to allow independent estimation of Y_ATP and P/O. Y_ATP is not independent of the substrate used, but the amount of ATP used in the production of biomass from the monomers is approximately the same for growth on ethanol and on glucose.Nomenclature C chemical state vector - C_i component of the chemical state vector (C-mol) - C_x biomass present in the system (C-mol biomass) - H₂ reduction equivalents (NAD(P)H + H⁺ and FADH₂) - k the amount of ATP required in the production of 1 C-mol of biomass from the monomers (mol ATP/C-mol biomass) - m_ATP maintenance requirement for ATP (mol ATP/C-mol biomass·h) - P/O (=), efficiency of the oxidative phosphorylation (mol ATP/atom O) - r vector of reaction rates - r_i component of the vector of reaction rates (C-mol/h) - r_ATP rate of ATP production (mol ATP/h) - r_x rate of biomass production (C-mol biomass/h) - Y_ATP Y_ATP growth yield on ATP (C-mol biomass/mol ATP) - (Y_ATP)_max maximum growth yield on ATP - stoichiometry matrix - P/O - vector of the flows to the system - _s flow of glucose to the system (C-mol glucose/h) - _o flow of oxygen to the system (mol O₂/h) - _c flow of carbon dioxide to the system (mol CO₂/h) - _x flow of biomass to the system (C-mol biomass/h) - _e flow of ethanol to the system (C-mol ethanol/h) - _w flow of water produced during metabolism (mol H₂O/h)     

Positive φ-angles in proteins by nuclear magnetic resonance spectroscopy

Summary Non-glycine residues with positive -angles have been identified in four proteins, barley serine proteinase inhibitor CI-2, bacterial ribonuclease (barnase) ofBacillus amyloliquefaciens, hen egg white lysozyme and a basic protein from barley seed (barwin) by use of nuclear magnetic resonance spectroscopy. By accurate measurements of the coupling constant and integration of the nuclear Overhauser H^N-H cross peak, positive -angles could be determined reliably to 60°±30°, in full agreement with the crystal structures for lysozyme, barnase and serine proteinase inhibitor CI-2. The work emphasizes that positive -angles can also occur in non-glycine residues and in the four proteins, positive -angles have been observed for the residue types aspartic acid, asparagine, arginine, serine, glutamine, histidine, tyrosine, tryptophan and phenylalanine. The measured coupling constants and the intensity of the intraresidue H^N-H NOEs agree well with the solution structures of three of the proteins, using the existing parametrization of the Karplus curve (Pardi, A., Billeter, M. and Wüthrich, K. (1984)J. Mol. Biol.,180, 741–751; Ludvigsen, S., Andersen, K.V. and Poulsen, F.M. (1991)J. Mol. Biol.,217, 731–736).     

The relationship between CO2 assimilation and electron transport in leaves

The inter-relationships between the quantum efficiencies of photosystems I (_I) and II (_II) and the quantum yield of CO₂ fixation % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaOqaaiabeA8aMnaaBa% aaleaacaWGdbGaam4tamaaBaaameaacaaIYaaaleqaaaqabaaaaa!3BD3!\[\phi _{CO_2 } \] were investigated in pea (Pisum sativum (L)) leaves with differing rates of photosynthesis using both photorespiratory and non-photorespiratory conditions, and in a leaf of Hedera helix (L) under photorespiratory conditions. The results indicate that under photorespiratory conditions the relationship between % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaOqaaiabeA8aMnaaBa% aaleaacaWGdbGaam4tamaaBaaameaacaaIYaaaleqaaaqabaaaaa!3BD3!\[\phi _{CO_2 } \] and both _I and _II is non-linear and variable. The relationship between _I and _II under these circumstances remains predominantly linear. Under non-photorespiratory conditions, leaves with a low rate of photosynthesis due to sink limitation exhibit a non-linear relationship between _I and _II, though the relationship between _I and _II remains linear suggesting a close relationship between linear electron flow and CO₂ fixation. Leaves irradiated at the CO₂ compensation point also exhibit a non-linear relationship between _I and _II. These results suggest that for leaves in air linear electron flow is the predominant source of energy for metabolism. The role of cyclic electron transport is considered when the requirement for the products of linear electron transport is depressed.Abbreviations q_p the coefficient for photochemical quenching of chlorophyll fluorescence - _exe the quantum efficiency of excitation energy capture by open PS II traps - _II the quantum efficiency for electron transport by PS II - _I the quantum efficiency (for electron transport) by PS I - % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaOqaaiabeA8aMnaaBa% aaleaacaWGdbGaam4tamaaBaaameaacaaIYaaaleqaaaqabaaaaa!3BD3!\[\phi _{CO_2 } \] the quantum yield for CO₂ fixation (obtained as the gross rate of CO₂ fixation divided by the irradiance) - % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaOqaaiabgs5aenaaBa% aaleaacqaH8oqBdaWgaaadbaGaamisamaaCaaabeqaaiabgUcaRaaa% aeqaaaWcbeaaaaa!3CB0!\[\Delta _{\mu _{H^ + } } \] trans-thylakoid proton potential difference - PAQF photosynthetically active quantum flux     

Isolation of phages infecting<Emphasis Type="Italic"> Actinoplanes</Emphasis> SN223 and characterization of two of these viruses

Phages infecting the industrially important Actinoplanes strain SN223 were isolated from soil samples collected at the shores of inland waters in Germany. The genome sizes range from 53 kb to 58 kb. Preliminary analyses revealed G+C contents comparable with the G/C bias of the host. Electron microscopy of three selected viruses displayed no obvious morphological differences, the phage heads being icosahedral and their tails non-contractible. Two of the phages (Asp2, Asp3.1) characterized in more detail are capable of provoking putative pseudolysogenic growth of the host bacterium. The carrier state for Asp2, in which cells are tightly packed with viruses, was demonstrated by electron microscopy. The latter phage is apparently widely distributed, as it was isolated from regions which are distantly located, i.e. more than 600 km apart from each other.     

Photon yield of O2 evolution and chlorophyll fluorescence characteristics at 77 K among vascular plants of diverse origins

Photon yields of oxygen evolution at saturating CO₂ were determined for 44 species of vascular plants, representing widely diverse taxa, habitats, life forms and growth conditions. The photonyield values on the basis of absorbed light ( ^a) were remarkably constant among plants possessing the same pathway of photosynthetic CO₂ fixation, provided the plants had not been subjected to environmental stress. The mean ^a value ±SE for 37 C₃ species was 0.106±0.001 O₂·photon^-1. The five C₄ species exhibited lower photon yields and greater variation than the C₃ species ( ^a=0.0692±0.004). The ^a values for the two Crassulaceanacid-metabolism species were similar to those of C₃ species. Leaf chlorophyll content had little influence on ^a over the range found in normal, healthy leaves. Chlorophyll fluorescence characteristics at 77 K were determined for the same leaves as used for the photon-yield measurements. Considerable variation in fluorescence emission both at 692 nm and at 734 nm, was found 1) among the different species; 2) between the upper and lower surfaces of the same leaves; and 3) between sun and shade leaves of the same species. By contrast, the ratio of variable to maximum fluorescence emission at 692 nm (F_v/F_M, 692) remained remarkably constant (The mean value for the C₃ species was 0.832±0.004). High-light treatments of shade leaves resulted in a reduction in both ^a and the F_v/F_M, 692 ratio. The extent of the reductions increased with time of exposure to bright light. A linear relationship was obtained when ^a was plotted against F_v/F_M, 692. The results show that determinations of the photon yield of O₂ evolution and the F_v/F_M, 692 ratio can serve as excellent quantitative measures of photoinhibition of overall photosynthetic energy-conversion system and of photochemistry of photosystem II, respectively. This is especially valuable in field work where it is often impossible to obtain appropriate controls.Abbreviations and symbols CAM Crassulacean acid metabolism - PFD photon flux density (photon fluence rate) - PSI, PSII photosystem I, II - F_o, F_M, F_v instantaneous, maximum, variable fluorescence emission - absorptance - ^a photon yield (absorbed light) - ⁱ photon yield (incident light) C.I.W.-D.P.B. Publication No. 923     

Activation of peritoneal macrophages in patients with gynecological malignancies by sizofiran and recombinant interferon-γ

We investigated the influence of the combined use of sizofiran, a-1,3-glucan and a recombinant interferon- (rIFN-) upon biological activities of peritoneal macrophages (M). The number of peritoneal M and the production of cytokines (interleukin-1, interferon- and tumor necrosis factor) was increased by the combined treatment. Fully activated peritoneal M based on the increased number of elongated pseudopods were observed by electromicroscope. Sizofiran seems to assure a sufficient supply of M to kill tumor cells in the peritoneal cavity and co-administered rIFN- seems to directly stimulate the accumulated M in addition to its direct cytotoxicity against tumor cells. This combination therapy may be a step to the prevention of the recurrence of gynecological malignancies including ovarian cancer, after a negative second-look laparotomy.Abbreviations rIFN- recombinant interferon- - IL-1 interleukin-1 - TNF tumor necrosis factor - SLL second look laparotomy     

Reproduction of tracking movements and target positioning of the forearm in humans in the absence of visual control

In 17 healthy volunteers, we studied movements of the forearm, which included episodes of positioning on the target level. The trajectory of the non-ballistic (relatively slow) movement looked like a double trapezium (flexion of the elbow joint from the state of full extension, 0 deg, positioning on the 50 deg level, further flexion to the limit angle of 100 deg, and a similar reverse sequence). The command trajectory and the trajectory of the realized movement were visualized with movements of cursors on a monitor in time/joint angle coordinates. We compared parameters of the tracking movements (in the presence of visual feedback) and their blindfold reproduction (with the complete absence of visual control). It was found that blindfold reproduction movements differ from sample tracking movements and their reproduction with partial limitation of visual control [16] in higher peak velocities and shorter durations, i.e., a trend toward conversion of such movements into ballistic ones was observed. Under conditions of elimination of visual control, movements that led to positioning were mostly hypermetric, i.e., positioning was usually accompanied by positive systematic errors (whose sign coincided with the direction of the preceding movement phase). The mean intragroup value of the systematic error of the first positioning (after flexion to the target level) was +6.73 ± 1.15 deg, while the respective mean for the second positioning (after extension to the same level) was +4.00 ± 1.31 deg. The nonlinear properties of stretch receptors of muscles whose activity provides the formation of a proprioceptive estimate of the joint angle are considered the crucial reason for systematic errors of blindfold positioning.Neirofiziologiya/Neurophysiology, Vol. 36, Nos. 5/6, pp. 393–404, September–December, 2004.This revised version was published online in April 2005 with a corrected cover date and copyright year.     

Average phase difference theory and 1∶1 phase entrainment in interlimb coordination

The dynamics of coupled biological oscillators can be modeled by averaging the effects of coupling over each oscillatory cycle so that the coupling depends on the phase difference between the two oscillators and not on their specific states. Average phase difference theory claims that mode locking phenomena can be predicted by the average effects of the coupling influences. As a starting point for both empirical and theoretical investigations, Rand et al. (1988) have proposed d/dt= — K sin ), with phase-locked solutions =arcsin( /K), where is the difference between the uncoupled frequencies and K is the coupling strength. Phase-locking was evaluated in three experiments using an interlimb coordination paradigm in which a person oscillates hand-held pendulums. was controlled through length differences in the left and right pendulums. The coupled frequency _c was varied by a metronome, and scaled to the eigenfrequency _v of the coupled system K was assumed to vary inversely with _c. The results indicate that: (1) and K contribute multiplicatively to (2) =0 or = regardless of K when =0; (3) 0 or regardless of when K is large (relative to ); (4) results (1) to (3) hold identically for both in phase and antiphase coordination. The results also indicate that the relevant frequency is _c/_v rather than _c. Discussion high-lighted the significance of confirming =arcsin(/K) for more general treatments of phase-locking, such as circle map dynamics, and for the 11 phase-entrainment which characterizes biological movement systems.     

Photon- and carbon-use efficiency in<Emphasis Type="Italic"> Ulva rigida</Emphasis> at different CO<Subscript>2</Subscript> and N levels

The seaweed Ulva rigida C. Agardh (Chlorophyta) was cultured under two CO₂ conditions supplied through the air bubbling system: non-manipulated air and 1% CO₂-enriched aeration. These were also combined with N sufficiency and N limitation, using nitrate as the only N source. High CO₂ in U. rigida led to higher growth rates without increasing the C fixed through photosynthesis under N sufficiency. Quantum yields for charge separation at photosystem II (PSII) reaction centres (_PSII) and for oxygen evolution (_O2) decreased at high CO₂ even in N-sufficient thalli. Cyclic electron flow around PSII as part of a photoprotection strategy accompanied by decreased antennae size was suspected. The new re-arrangement of the photosynthetic energy at high CO₂ included reduced investment in processes other than C fixation, as well as in carbon diverted to respiration. As a result, quantum yield for new biomass-C production (^growth) increased. The calculation of the individual quantum yields for the different processes involved allowed the completion of the energy flow scheme through the cell from incident light to biomass production for each of the CO₂ and N-supply conditions studied.Abbreviations A total thallus absorptance - A_pig absorptance due to pigments - A_str Absorptance due to non-pigmented structures - a* spectrally averaged in vivo absorption cross-section of chlorophyll a - CCM carbon-concentrating mechanism - Chl chlorophyll - DOC dissolved organic carbon - ETR electron transport rate - F_v/F_m optimum quantum yield for PSII charge separation - GP gross O₂ evolution rate - k_pig specific light absorption coefficient for pigments - k_str specific light absorption coefficient for non-pigmented structures - OP optimum O₂ evolution rate - PFR photon fluence rate - POC particulate organic carbon - PS photosystem - q_N non-photochemical quenching - q_P photochemical quenching - ^growth quantum yield for new biomass-C production - _O2 quantum yield for gross O₂ evolution - _PSII quantum yield for PSII charge separation     

Global asymptotic stability of the size distribution in probabilistic models of the cell cycle

Probabilistic models of the cell cycle maintain that cell generation time is a random variable given by some distribution function, and that the probability of cell division per unit time is a function only of cell age (and not, for instance, of cell size). Given the probability density, f(t), for time spent in the random compartment of the cell cycle, we derive a recursion relation for _n(x), the probability density for cell size at birth in a sample of cells in generation n. For the case of exponential growth of cells, the recursion relation has no steady-state solution. For the case of linear cell growth, we show that there exists a unique, globally asymptotically stable, steady-state birth size distribution, _*(x). For the special case of the transition probability model, we display _*(x) explicitly.This work was supported by the National Science Foundation under grants MCS8301104 (to J.J.T.) and MCS8300559 (to K.B.H.), and by the National Institutes of Health under grant GM27629 (to J.J.T.).     

Carotenoid composition and photon-use efficiency of photosynthesis inGossypium hirsutum L. grown under conditions of slightly suboptimum leaf temperatures and high levels of irradiance

Summary Cotton (Gossypium hirsutum L. var. DP 61) was grown at different temperatures during 12-h light periods, with either 1800–2000 mol photons m^–2 s^–1 (high photon flux density, PFD) or 1000–1100 mol m^–2 s^–1 (medium PFD) incident on the plants. Night temperature was 25°C in all experiments. Growth was less when leaf temperatures were below 30°C during illumination, the effect being greater in plants grown with high PFD (Winter and Königer 1991). Leaf pigment composition and the photon-use efficiency of photosynthesis were analysed to assess whether plants grown with high PFD and suboptimal temperatures experienced a higher degree of high irradiance stress during development than those grown with medium PFD. The chlorophyll content per unit area was 3–4 times less, and the content of total carotenoids about 2 times less, with the proportion of the three xanthophylls zeaxanthin + antheraxanthin + violaxanthin being greater in leaves grown at 20–21°C than in leaves grown at 33–34°C. In leaves from plants grown at 21°C and 1800–2000 mol photons m^–2 s^–1, zeaxanthin accounted for as much as 34% of total carotenoids in the middle of the photoperiod, the highest level recorded in this study. This finding is consistent with a protective role of zeaxanthin under conditions of excess light. At the lower temperatures, the photochemical efficiency of photosystem II, measured as the ratio of variable to maximum fluorescence yield (F _V/F _M) after 12-h dark adaptation, was 0.76 in medium PFD plants and 0.75 in high PFD plants compared with 0.83 and 0.79, respectively, at the higher temperatures. The photon-use efficiency of O₂ evolution () based on absorbed light between 630 and 700nm, decreased with decrease in temperature from 0.102 to 0.07 under conditions of high PFD, but remained above 0.1 at medium PFD. Owing to compensatory reactions in these long-term growth experiments, sustained differences inF _V/F _M and were much less pronounced than the differences in chlorophyll content and dry matter, particularly in plants which had developed at high PFD and low temperature. In fact, in these plants, which exhibited pronounced photobleaching, a largely functional photosynthetic apparatus was still maintained in cells adjacent to the lower leaf surfaces. This was indicated by measurements of photon use efficiencies of photosynthetic O₂ evolution with leaves illuminated first at the upper, and then at the lower surface.Abbreviations F _O yield of dark level fluorescence - F _M maximum yield of fluorescence, induced in a pulse of saturating light - F _V yield of variable fluorescence (=F _M-F _o) - PFD photon flux density - _iw photon use efficiency of O₂ evolution based on white (400–700 nm) incident light - _ir photon use efficiency based on red (630–700 nm) incident light - _aw photon use efficiency based on white absorbed light - _ar photon use efficiency based on red absorbed light     

What kind of movement detector is triggering the landing response of the housefly?

As shown before, the latency of the housefly's landing response depends on the conditions of the visual stimulus (Borst 1986). Accordingly, the latency can be used to characterize the movement detection system which is triggering the landing response.The stimulus was a sinusoidal periodic pattern of vertical stripes presented bilaterally in the frontolateral eye region of the fly. It started to move, simultaneously on either side, from front to back at a given time. The latency of the response was measured by means of an infrared light-beam that was interrupted whenever the fly lifted its forelegs to assume a preprogrammed landing posture (Fig. 1). The latency was found to vary in a range from 60 ms up to several seconds depending on the pattern's spatial wavelength , contrast frequency cf and contrast C.For sufficiently high pattern contrast the optimum of the reaction (minimum latency) is found at spatial wavelengths of 30–40° and contrast frequencies of 8–17 periods/s (Fig. 3a). This is about 2–10 times more than is anticipated from the optomotor response under similar conditions. Evaluation of the optimum contrast frequency cf _OPT at different wavelengths shows that cf _OPT is not independent of (Fig. 3b, solid line). The same is true for the contrast dependence of the reaction: reduction of the contrast leads not only to a general decrease in the response amplitudes (prolongation of the latency) (Fig. 4a), but also to a shift of cf _OPT towards lower contrast frequencies (Fig. 4b, solid line).In the theory of the correlation-type movement detector (Reichardt 1961) which underlies the optomotor response of flies the dependence of cf _OPT on pattern wavelength and/or pattern contrast is not expected under stationary conditions. However, as shown by computer simulation all experimental results can be explained by a homogeneous retinotopic array of correlation movement detectors (Fig. 2) if their response under non-stationary conditions is taken into account. We simply assume that the spatially and temporally integrated output of the movement detectors is evaluated by a threshold device (Fig.5). The correlation-type movement detection in combination with a temporal integrator system predicts the rather complex dependence of the optimum contrast frequency on pattern wavelength and pattern contrast (dashed lines in Fig. 3b and 4b) and provides the missing explanation of the variable latencies of the landing response.Comparing the parameters of the correlation-type movement detector derived in the present study with those of the optomotor response, the landing response seems to use the same type of movement detection system. To account for the high wavelength optimum, however, the input elements of the movement detection system of the landing response might have an increased visual field (e.g. by pooling neighbouring visual elements) and, accordingly, a reduced visual acuity as compared with the input elements of the optomotor system.Abbreviations (°) spatial pattern wavelength - w(°/s) angular velocity of the pattern - cf (Hz) contrast frequency=w/ - cf _OPT(Hz) cf leading to the shortest latency - (Hz) angular frequency=2cf - I mean luminance of the pattern - I modulation amplitude of the pattern - C pattern contrast=I/ - (ms) time constant of a filter - (°) angle between the optical axis of neighbouring visual elements - (°) acceptance angle of visual elements     

Nonlinearly coupled double chain systems

We report here on numerical studies of a pair of linearly coupled mass chains with nonlinear ⁴ coupling between the two chains. General implications for double chain systems known to exist in nature such as DNA and RNA are discussed.     

Lytic activity localized to membrane-spanning region of ?X174 E protein

Summary Lytic activity of the X174E (lysis) protein had previously been localized to the amino terminal 51 amino acids (a.a.) of the molecule (Blasi and Lubitz 1985). This E gene lytic activity has here been further localized to the amino terminal 29 a.a., a region of the protein which is thought to just span the cell membrane (Young and Young 1982). X174 E gene fusions to both the lacZ gene and the chloramphenicol acetyl transferase (CAT) gene resulted in fusion proteins with lytic activity. Fusion to a third protein, trpE, did not result in lytic activity. These results support a model of oligomerization of the X174 E protein for lytic activity since both -galactosidase and CAT exist as tetramers in their native state. A difference in the composition of the charged amino acids at the cytoplasmic boundary between the various fusion proteins could also account for these results, since these amino acids may play a role in proper anchoring of the E protein in the cell membrane. In a spontaneous E gene mutant, which introduces a proline residue at position 9 of the E protein, lytic activity of the E protein was decreased, but not abolished. The presence of the helix-breaking proline at this position may interfere with insertion of the lysis protein into the cell membrane, leading to the decreased functional activity of the protein.