Phototaxis in a new Allomyces

Summary The zoospores of a new species of Allomyces are highly phototactic. An action spectrum of this phototaxis showed a broad peak in the 470 nm to 525 nm region of the spectrum, and the ultrastructure of the zoospores did not reveal any obvious structural basis for this mechanism. The findings are discussed in relation to phototaxis in Chlamydomonas and the rumposome or fibrous body previously found in several other watermold zoospores.     

Biological aspects of the interaction between Coelomomyces psorophorae zygotes and the larvae of Culiseta inornata: Environmental factors

Zygotes of the obligately parasitic watermold Coelomomyces psorophorae encyst on the cuticular surface of susceptible mosquito larvae as the initial step in the infection process. Zygotes can successfully encyst on Culiseta inornata larvae at temperatures from 12°–30°C, with an optimum of 25°C. Optimum encystment on larvae occurs from pH 6.5–8.5, with activity documented from pH 5.0–9.5. Zygotes are active in water with total salinity of 5.4 ppt down to double glass-distilled water.     

THE RIBONUCLEOPROTEIN NATURE OF LARGE PARTICLES IN THE MEIOSPORANGIA OF ALLOMYCES

Particles averaging 3 to 4 µ in diameter, which are called chromospheres and fill the immature meiosporangia of the watermold Allomyces, were isolated and analyzed. The preparations were obtained by repeated centrifugations or by passage of the homogenate into a column of sand saturated with oleic acid, followed by selective elution of the chromospheres with alternate layers of oleic acid and an aqueous solution. The chromospheres contain approximately 12 per cent RNA, no DNA, and 60 per cent protein. It was concluded that they are pure or nearly pure ribonucleoprotein. Analysis of meiosporangia with chromospheres and after the chromospheres have disappeared showed no significant change in RNA or free amino acids. It was concluded that chromosphere disappearance is a fragmentation into small granules. The relation of chromospheres to postmeiotic chromospheres and nuclear caps is discussed. Speculation as to the function of these bodies is presented.     

Fungal zoospores are induced to encyst by treatments known to degrade cytoplasmic microtubules

Summary Zoospores of the obligately parasitic chytrid Rozella allomycis encyst and germinate after settling on a hypha of the host, the watermold Allomyces arbuscula. Zoospores deprived of a host also encyst after aging, but do not germinate. Hence, means were sought to induce encystment of young zoospores, in order to test whether they would subsequently germinate in the absence of a host.Zoospore suspensions were harvested and exposed to treatments known to degrade cytoplasmic microtubules and to depolymerize fibrillar structures in other organisms: ice temperature, hydrostatic pressure of 2000–10000 psi, cupric ions, and colchicine. These treatments induced rapid encystement—but no germination.The results suggest that the motility, the flagellated state, and the irregular, elongate shape of fungal zoospores depend on the intactness of their fibrillar skeletal structures. The results also support the hypothesis that contact of Rozella with the host surface has two sequential functions: (i) nonspecific (replaceable by other treatments) triggering of encystment, (ii) specific stimulation of germination.     

An aryl β-d-glucosidase of the aquatic fungus Lagenidium giganteum,a parasite of mosquito larvae

Lagenidium giganteum Couch, a watermold parasitic on mosquito larvae possesses an intracellular -d-glucosidase (-d-glucoside glucohydrolase, E. C. 3.2.1.21). The enzyme was purified 132 fold and, with the substrate p-nitrophenyl -d-glucoside, was shown to have the following properties: The pH of optimum enzyme stability and activity lay between 5.5 and 6.0, and the enzyme was inactivated at temperatures above 50°C. The K _m was 4.6×10^-5 M and the Arrhenius activation energy was 8.35 Kcal·mole^-1. Elution from Sephadex G-200 gave an approximate molecular weight of 120000. The enzyme was inhibited by Pb²⁺, Ag²⁺ and Hg²⁺, by glucose and by p-chloromercuribenzoate. The latter inhibition was overcome cy cysteine. Chromatographic studies demonstrated transferase as well as hydrolase properties.This paper represents a portion of a Ph.D. dissertation presented by T. M. McInnis, Jr., to the University of North Carolina at Chapel Hill. The work was supported in part by grants from the American Cancer Society, the University of North Carolina Research Council, the Society of Sigma Xi, and a United States Army Medical Research DevelopmentGrant DADA 17-72-C-2168.     

ELECTRICAL RESPONSES FROM THE LATERAL-LINE NERVES OF FISHES : IV. THE REPETITIVE DISCHARGE

The spontaneous discharge of impulses from the lateral-line nerves of trout and catfish has been examined. 1. Broken endings of nerve fibers supplying receptors of the lateral-lines of trout and catfish may be the source of a repetitive discharge of nerve impulses. 2. This injury discharge occurs more frequently in trout and may mask the spontaneous discharge from the receptor cells. Experiments indicate that the latter discharge is not the result of injury. 3. The injury discharge ceases in from 10 to 15 minutes. The spontaneous receptor discharge in trout may continue for an hour if the circulation remains intact. The receptor response also fails in from 10 to 15 minutes after failure of the circulation. 4. The receptor discharge, the injury discharge, or the summed discharges frequently become synchronized. The excitability of the fibers of the nerve trunk appears to vary synchronously, so that nerve impulses initiated in fibers from tactile receptors not contributing to the spontaneous discharge can be conducted only during the part of the cycle occupied by the spontaneous discharge.     

The rotifer trap of Zoophagus

The predacious watermold Zoophagus insidians traps loricate rotifers on short, lateral branches of the main, hyphal axis. These branches or traps are packed at their distal ends with a number of vesicles filled with an electron-dense matrix. Electron micrographs of the mycelium disclose a two-layered wall; the outer layer is electron dense and the inner, electron transparent. The outer dense layer on the tip of the trap is organized into a number of fine ridges and occasional discontinuities. Thin sections through recently trapped rotifers indicate that the cilia of the animals are stuck to the trap by a glue. This adhesive is derived from secretion of the matrix of the vesicles aggregated in the tip of the trap. The secretion mechanism is triggered by the animal and is accompanied by: 1. The separation of the two layers of the wall, 2. fusion of the vesicles with the cell membrane and 3. extrusion of the glue through pits in the tip of the inner wall of the trap. After snaring a rotifer, the previously arrested branch grows as a haustorium into the body cavity of the animal. The host tissues disintegrate within a few hours and appear to be the main nutrient source of the fungus.     

Specific features of a single-pulse sliding discharge in neon near the threshold for spark breakdown

Experimental data on the spatial structure of a single-pulse sliding discharge in neon at voltages below, equal to, and above the threshold for spark breakdown are discussed. The experiments were carried at gas pressures of 30 and 100 kPa and different polarities of the discharge voltage. Photographs of the plasma structure in two discharge chambers with different dimensions of the discharge zone and different thicknesses of an alumina dielectric plate on the surface of which the discharge develops are inspected. Common features of the prebreakdown discharge and its specific features depending on the voltage polarity and gas pressure are analyzed. It is shown that, at voltages below the threshold for spark breakdown, a low-current glow discharge with cathode and anode spots develops in the electrode gap. Above the breakdown threshold, regardless of the voltage polarity, spark channels directed from the cathode to the anode develop against the background of a low-current discharge.     

Stroke rehabilitation: a model predicting return home.

We undertook this study to describe the changes in functional status for patients in a rehabilitation program for acute stroke and to identify the variables that best predict discharge home. Of 282 patients, 75% were discharged home. Increases in functional status were found for all 18 activities of the Functional Independence Measure from admission to discharge. Significant predictors of discharge disposition in a logistic regression model were the admission and discharge functional status scores, length of stay, and living arrangement before the stroke. The functional status at discharge was the most important predictor. Knowledge of these predictors can contribute to more appropriate treatment and discharge planning.     

Experimental Study of a Vacuum Spark Discharge over a Dielectric Surface

A decrease in the amplitude of the current of a vacuum spark discharge over a dielectric surface with increasing discharge gap length is established. It is shown that, in the presence of a longitudinal magnetic field, the leading edge of the discharge voltage pulse is extended, whereas the clearly pronounced current pulse transforms into a train of alternating current oscillations. The discharge is found to decelerate when the spark is preceded by a low-current discharge.     

Evidence for the involvement of serine protease in the conidial discharge of Conidiobolus coronatus

The involvement of serine protease(s) in the conidial discharge of Conidiobolus coronatus was investigated using the parent strain and a variant strain with reduced conidial discharge. Time course profiles of protease levels and conidial discharge showed that maximum protease levels coincided with maximum conidial discharge in both the parent and variant strains. Inhibition of serine protease(s) by phenyl methyl sulfonyl fluoride showed that low protease levels resulted in inhibition of the conidial discharge and a minimum activity of 1.0 U/mg protein is essential for triggering the conidial discharge. Using casein to induce proteases, it was further observed that early gain in the protease level (1.0 U/mg protein) leads to early onset of conidial discharge. The above evidence suggests the involvement of protease(s) in the conidial discharge of C. coronatus.     

Effects of Airspeed and Humidity Changes on Spore Discharge in Sordaria fimicola

An improved experimental system is described for studying therate of spore discharge in Sordaria fimicola subjected to anair-stream of controlled rate and relative humidity. Under nearlysaturated conditions the rate of air-flow does not seem to affectthe rate of discharge. Reduction of the R.H. from 95 per centto 70 per cent or 35 per cent leads to an immediate but temporaryincrease in discharge rate. 70 per cent R.H. seems only to affectactual discharge, but prolonged exposure to 35 per cent R.H.interferes as well with earlier stages in spore development.It is suggested that the immediate effect on discharge is physicalrather than biochemical. There is evidence that the perithecialwall plays some part in the control of spore discharge.     

Discharge of myeloperoxidase from neutrophils during bacterial sorption]

A study was made of conditions and dynamics of discharge of myeloperoxidase (MPO) from rabbit neutrophils in case of encounter with staphylococci. The discharge began not later than 9--12 minutes after the administration of Staph. aureus into the neutrophil suspension, i. e. as early as the stage of bacterial sorption, and reached the maximum by the 30th minute. The contact of neutrophils with individual bacteria was an adequate signal for the beginning of the discharge. The greatest discharge was with the ratio of 5 bacteria per one neutrophil. The discharge was retarded when this ratio reached 80: 1. A hypothesis on the "avalanche" switchingon of the system of MPO discharge: a single bacteria injection mu/ml a discharge from an individual neutrophil of MPO and cation proteins; the latter switch on discharge from several other neutrophils, without any participation of bacteria. Cation proteins intensified the MPO discharge in the concentration of the 10--20 switch on. Biolgical significance of the phenomenon of early discharge of antibacterial factors no directed to the provision of phagocytosis is discussed.     

Simulations of a surface glow discharge in a supersonic gas flow in the presence of external ionization

Results of two-dimensional hydrodynamic simulations of a surface glow discharge operating at pressures of 0.2–0.5 Torr in a nitrogen flow propagating with a velocity of 1000 m/s in the presence of external ionization are presented. The effect of the external ionization rate on discharge operation is analyzed. The current-voltage characteristics of the discharge are calculated for different intensities of external ionization in both the presence and absence of secondary electron emission from the cathode. The discharge structure and plasma parameters in the vicinity of the loaded electrode are considered. It is shown that, when the discharge operates at the expense of secondary emission from the cathode, the discharge current and cathode sheath configuration are insensitive to external ionization. It is also demonstrated that, even at a high rate of external ionization, the discharge operates due to secondary emission from the cathode.     

Effect of the Air Flow Velocity on the Characteristics of a Pulsating Discharge Produced by a DC Power Source

Results are presented from experimental studies of a pulsating discharge produced by a dc power source in subsonic and supersonic cold (T = 150–300 K) air flows at static air pressures in the flow of 40–760 Torr. Two modes of pulsating discharge were implemented experimentally: without and with (from one to five) intermediate breakdowns. The discharge pulsation frequency, the maximum attainable voltage across the discharge gap, the length of the plasma channel, and the electric field in the discharge plasma were studied as functions of the air flow velocity and discharge current.     

Alternating nonsteady gas-discharge modes in an atmospheric-pressure air flow blown through a point-plane gap

The electric and spectral characteristics of a nonsteady discharge in an atmospheric air flow blown through a point-plane interelectrode gap were investigated experimentally. The discharge was produced by applying a constant positive voltage to the point electrode, the amplitude of the applied voltage being much higher than the corona ignition voltage. The nonsteady character of the discharge is due to the spontaneously repeating streamer-spark breakdown, followed by the formation of either a diffuse ultracorona or a filamentary glow discharge. In the latter case, the length of the plasma column increases progressively, being blown off by the gas flow from the discharge gap. The extinction of a filamentary discharge is unrelated to the break of the current channel: the discharge decays abruptly when the filament length reaches its critical value. The distribution of active particles (O, OH, and N*₂) carried out from the discharge gap is determined from the data of spectral measurements.     

基于城镇排污视角的水功能区纳污能力模型及其应用

水功能区纳污能力是区域水功能区限制纳污和责任考核管理的重要依据.为了适应目前以县为主体的水功能区水环境管理方式,本研究从水功能区城镇污染物允许排放量的视角研究水功能区纳污能力,建立水功能区城镇排污模型,并应用于泾河入渭段主要城镇礼泉县和泾阳县.结果表明: 礼泉县和泾阳县月允许排污量与河道流量密切相关,丰水期允许排污量高于枯水期.泾河礼泉段当年11月至来年3月水体COD浓度劣于该水功能区水质目标,应削减该时间段礼泉县排污口排污量.排污口排污流量的取值会影响河道水功能区纳污能力的计算结果,城镇排污模型利用相对稳定的排污口排污浓度计算排污口允许排污流量,得到的水功能区纳污能力更为合理.研究结果可为严格的水资源管理提供科学依据.     

A theoretical basis for conditional probability analyses of neural discharge activity

A theory has been developed which allows the estimation of the probability density of a discharge, given that an arbitrary condition is fulfilled. It is shown that the common methods for the evaluation of a post-stimulus time (PST) histogram and a hazard function can be considered as special applications of this theory. Whereas the usual hazard function shows how the probability of a discharge depends on the time elapsed since the last discharge, generalized hazard functions proposed in the present paper allow to reveal also the influence of the last but one discharge, the last but two discharge, and so on. In contrast to the usual method for the estimation of a hazard function, the applicability of the procedures proposed here is not restricted to stationary discharge activity. Some elementary applications are illustrated by analysing simulated discharge activity mimicing the response of a single auditory-nerve fiber to a high-intensity tone burst.     

Abnormal and subnormal regimes of a spherical glow discharge in the drift-diffusion approximation

A spherical glow discharge with a pointlike anode is considered in a self-consistent drift-diffusion approximation. The model includes the time-dependent continuity equations for ions and electrons in the drift-diffusion approximation and Poisson’s equation for the radial electric field. In finding steady-state distributions, Ohm’s law is used to relate the discharge voltage and discharge current. Steady-state distributions of the plasma parameters across the discharge gap, current-voltage characteristics, and cathode characteristics for an abnormal spherical discharge in molecular nitrogen are obtained. In a subnormal glow-discharge regime, oscillations in the conduction current, potential, and other discharge parameters are revealed. Similar regimes are also observed in conventional discharges in tubes.     

Discharge properties of human motor units during sustained contraction at low level force.

The characteristic of discharge behaviors of motor units (MUs) during low level contraction was investigated. The discharge of MUs in the m. vastus medialis was observed during the sustained contraction at 4 different levels below 10% MVC (2, 4, 8 and 10% MVC) for 15 min. The spike interval of all observed MUs gradually elongated during an initial several minutes of the contraction and the characteristic discharge patterns following the elongation were observed. i.e. continuous discharge throughout the contraction (CONT), decruitment (D-N), and re-recruitment following decruitment (D-REC).The relationship between recruitment threshold force (F(th)) and discharge pattern was not significant at 2% MVC but, at 10% MVC, there were significant differences in F(th) between D-N and CONT, and between D-REC and CONT MU populations.In pooled data, the MUs with the shorter mean spike interval at the beginning of the contraction (MSI(0), below 90 ms) tend to discharge continuously, but the MUs with longer MSI(0) showed various discharge patterns.In conclusion, during low level contraction MUs discharge characteristically, and the MU with high excitation levels tend to discharge continuously, but individual MU represents an intrinsic discharge pattern at not a high excitation level.