Effect of Cuticle Treatments on Infection of Phaseolus vulgaris by Rhizoctonia solani

Rhizoctonia solani, the causal agent of stem canker of beans, does not commonly infect beans more than two weeks old. Treatment of the cuticular layer by abrasion or chloroform rinsing results in decreased cuticular autofluorescence and the ability of stains to penetrate the hypocotyl surface. Infection cushions preferentially formed near these treated areas on both young and old plants. The morphology of infection cushions on older plants is simpler than those found on young, susceptible plants, but they are fully competent to form lesions.     

Adaptive variation in sex determination in a crustacean, Gammarus duebeni

In some animals sex is determined after conception by environmental factors (environmental sex determination. ESD). In the amphipod Gammarus duebeni sex is reportedly determined by photoperiod: there is a higher proportion of males in broods reared under long-day than under short-day photoperiods. It has been proposed that this is an adaptive response to seasonal population dynamics. A test of the hypothesis would be to demonstrate changes in the degree to which sex is determined by the environment in populations from different latitudes with different dynamics. This study reports such a test. Environmental response is significantly less strong in a southern population with a long breeding season than in a northern one in which breeding is seasonally restricted. Moreover, the threshold of the ESD cue for male or female determination is not defined when the breeding season is weakly seasonal. There is a broad correlation between latitude (and hence breeding seasonality) and the strength of ESD response across a series of population studies. Similarities between the Gammarus system of sex determination and that of the Atlantic silverside Menidia menidia, a fish with thermal ESD, are discussed.     

Creatine kinase activity of urinary bladder and skeletal muscle from control and streptozotocin-diabetic rats

The urinary bladder depends on intracellular ATP for the support of a number of essential intracellular processes including contraction. The concentration of ATP is maintained constant primarily via the rapid transfer of a phosphate from creatine phosphate (CP) to ADP catalyzed by the enzyme creatine kinase (CK). Since muscular pathologies associated with diabetes are in part related to intracellular alterations in metabolism, we have characterized the CK activity in both skeletal muscle and urinary bladder from control and streptozotocin-diabetic rats.The following is a summary of the results: 1) Bladder tissue from control rats showed linear kinetics with a V_max = 390 nmoles/mg protein/min, and a K_m = 275 µM. 2) Urinary bladder tissue isolated from diabetic rats displayed biphasic kinetics with V_max = 65 and 324 nmoles/mg protein/min, and K_m's = 10 µM and 190 µM respectively. 3) Skeletal muscle isolated from control rats showed linear kinetics with an approximate V_max of 800 nmoles/mg protein/min and a K_m of 280 µM CP. 4) Homogenates of skeletal muscle from diabetic rats showed complex kinetics not separable into distict component forms. 5) The K_m for ADP for both skeletal muscle and bladder was approximately 10 µM.These studies demonstrate that whereas bladders isolated from both control and diabetic rats possess a low-affinity isomer(s) of CK with similar maximum enzymatic activity, there is a high affinity isomer present within the urinary bladder muscle of diabetic rats that is not present in bladder tissue isolated from control rats. Skeletal muscle isolated from both diabetic and control rats exhibited a maximal activity 2 to 3 times higher than that of the bladder.     

Carbohydrate ingestion and muscle glycogen depletion during marathon and ultramarathon racing

Two studies were undertaken to characterize the effects of carbohydrate ingestion on fuel/hormone response to exercise and muscle glycogen utilization during prolonged competitive exercise. In study 1, eighteen subjects were divided into three groups, matched for maximum oxygen consumption (VO2max) and blood lactate turnpoint. All subjects underwent a 3-day carbohydrate (CHO) depletion phase, followed by 3 days of CHO loading (500-600 g.day-1). During the race, the groups drank either 2% glucose (G), 8% glucose polymer (GP), or 8% fructose (F). Muscle biopsies were performed before and after the race and venous blood was sampled before and at regular intervals during the race. In study 2, eighteen subjects divided into 2 matched groups ingested either a 4% G or 10% GP solution during a 56 km race. Despite significantly greater CHO ingestion by GP and F in study 1 and by GP in study 2, blood glucose, free fatty acids and insulin concentrations, muscle glycogen utilization and running performance were not different between groups. These studies show (i) that hypoglycaemia is uncommon in athletes competing in races of up to 56 km provided they CHO-load before and ingest a minimum of 10 g CHO.h-1 during competition; (ii) that neither the amount (10 g vs 40 g.h-1) nor the type of carbohydrate (G vs GP vs F) has any effect on the extent of muscle glycogen depletion or running performance in matched subjects racing over distances up to 56 km.     

Mechanism of A23187-induced airway obstruction in the guinea pig

Exposure of conscious guinea pigs to A23187 aerosol produced a concentration-related increase of excised lung gas volume (ELGV), . ., postmortem pulmonary gas trapping. Measurements of ELGV were highly correlated with measurements of dynamic compliance (C_dyn) and total pulmonary resistance (R_L) and were used as an indication of airway obstruction. We pretreated guinea pigs intravenously with the following drugs: atropine; LY163443, a selective LTD₄/E₄ antagonist; indomethacin; propranolol; and pyrilamine. The guinea pigs were exposed for 8 minutes to the A23187 aerosol, and ELGV measurements were then made. Atropine or pyrilamine prevented the A23187-induced gas trapping. Indomethacin or propranolol tended to potentiate the response and when combined, they potentiated the gas trapping by 80%. LY163443 had no effect alone, but when combined with indomethacin, propranolol, and pyrilamine, inhibited A23187-induced gas trapping by 67%. We conclude that cholinergic and histaminergic mechanisms play major roles in the ionophore-induced pulmonary gas trapping of the guinea pig. With appropriate pretreatment, sulfidopeptide leukotrienes may produce a substantial effect.     

Making sense of the combined effect of interleukin-2 and interleukin-4 on lymphocytes using a mathematical model

The cytokines are the information superhighway of the immune system. They are an important component of the integrated behavior of the system. In order to be able to have a good understanding of the immune system, we must be able to model the effect of cytokines and their combined effect. This work is a step in that direction. We study the combined effect of two cytokines: interleukin-2 (IL-2) and interleukin-4 (IL-4) on some cells of the immune system. Interleukin-2 and interleukin-4 are important growth and differentiation factors for B and T cells. Interleukin-4 antagonizes the effect of interleukin-2 on B cells and some T cells while it synergizes with interleukin-2 on other T cells. We build a mathematical model of the interaction of both cytokines on T and B cells as a building block toward a model of the Th1/Th2 cross-regulation. The response of a given cell to the combination of interleukin-2 and interleukin-4 is shown to involve competing dynamical effects which can lead to either antagnostic or synergistic combined effect. Author to whom correspondence should be addressed at Department of Engineering and Public Policy. Work supported by NIH grant nv: Ai31427.     

The Microaerophile SPirillum volutans: Cultivation on Complex Liquid and Solid Media

Spirillum volutans grows only under microaerobic conditions in a peptone-succinate-salts broth, but can grow aerobically when the peptone is replaced by vitamin-free acid-hydrolyzed casein broth. The addition of potassium metabisulfite, norepinephrine, catalase or superoxide dismutase (SOD) permitted aerobic growth in peptone-succinate-salts broth. A combination of catalase and SOD had a synergistic effect. S. volutans lacked catalase and had only a low level of peroxidase activity, but did possess SOD activity (12 to 14 U/mg of protein). The organism was found to be extraordinarily sensitive to exogenous hydrogen peroxide. Illumination of peptone-succinate-salts broth generated hydrogen peroxide and rendered the medium inhibitory to growth. A combination of catalase and SOD prevented this inhibition. Growth of S. volutans on solid media, not previously possible, was accomplished by the use of vitamin-free acid-hydrolyzed casein and peptone-succinate-salts agar media; maximum growth responses were dependent on the following combination of factors: addition of bisulfite, catalase, or SOD, protection of the media from illumination, incubation in a highly humid atmosphere, and incubation under atmospheres of 12% oxygen or less. The results indicate that the microaerophilic nature of S. volutans is attributable largely to the high sensitivity of the organism to exogenous hydrogen peroxide and, to a lesser extent, superoxide radicals occurring in the culture medium.     

Temperature,hydrochemistry and plankton in Wicken Brickpits, 1930–1931

Temperature, selected chemical constituents and plankton were analysed from three depths, fortnightly, by day and occasionally by night, in two flooded brickpits, between May 1930 and August 1931.Br was 3.3 m deep, with clear water and little weed; III was only 1.8 m deep, with thick submerged weed, more sheltered than Br and becoming eutrophic. Neither had direct inflow nor outlet. Both conformed to the second order for dimictic lakes, with summer and winter stratification, leading, for varying periods, to stagnation marked by pH between 6.6 and 7.2 and O₂ much depleted or absent at the bottom.During stagnation, release of SiO₂, soluble inorganic phosphate-P, ammonium ions and bases from the bottom was shown by sampling water close to the mud. This finding preceded the definition of redox potential by others.Thermistor temperature measurements, used for the first time, showed comparable summer gradients in both ponds: on windy days these were usually sigmoid, with discontinuity at various depths, or else nearly isothermal; on calm days, they were exponential, when transmission of heat, from surface to bottom, was apparently due to radiation alone, without water circulation. Stability was then high.Diatoms were abundant in both ponds; but planktonic Rotifera and Crustacea differed in the two, apart fromDiaptomus gracilis, which was dominant in both.     

Physiological Adaptations in Response to Environmental Stress During an N2-Fixing Anabaena Bloom

Anabaena spiroides has the ability to maintain intense biomass production for extensive periods in the epilimnion of a small eutrophic lake characterized by conditions shown to cause photooxidative death in a number of other phytoplankton. By the enhancement of carotenoid synthesis chlorophyll a was protected from photooxidation and prevented from catalyzing other photooxidative reactions within the cells. By temporally separating CO₂ and N₂ fixation, maximum utilization of photosynthetically active radiation was achieved. Because CO₂ fixation was more sensitive than N₂ fixation to a high oxygen concentration, the former was maximized during morning hours, before the afternoon buildup of dissolved oxygen. The diurnal partitioning of carbon and N₂ fixation has two additional advantages; possible competition for reductant-generating compounds is minimized, and adequate endogenous pools of carbon skeletons are assured to accept newly fixed ammonia. Hence, Anabaena, far from undergoing photooxidative death, appears to utilize a physiological strategy which allows optimization of radiant energy use for reductive processes and dominance of surface waters and shading of deeper phytoplankton during summer blooms.