Long–term responses to factorial, NPK fertilizer treatment by Alaskan wet and moist tundra sedge species

At thirteen sites in northern and central Alaska, full factonal and partial factonal NPK fertilizer experiments were completed in wet and moist tundras The effects of the fertilizers on N and P concentrations in leaves, leaf mass per tiller, tilling, and flowering of the dominant sedge species ( Eriophorum vaginatum. E angustifolium, and Carex aquatilis ) were documented for 3–10 yr at each site Almost all sites showed at least some response to the fertilizer treatment, but the specific treatments and elements that caused the responses varied greatly among sites There also was no consistent difference in responses between wet and moist sites There was, however, a consistent temporal pattern to the responses observed, starting with increases in N and P concentration in leaves in the year that fertilizer was added, followed by growth and tilling responses in the second year, and increased flowering in the third year The increases in N concentration generally only appeared in the first year, while increased P concentrations were sustained for 3–4 yr Effects of fertilizer on flowering were still significant after 6 years in some cases Results are discussed in terms of the role of "nutrient limitation" arctic plant communities and detemuning their productivity following disturbance or fertilization     

Febrile Gastroenteritis Due to Salmonella thompson—Report of an Outbreak

Salmonella thompson, a common pathogen of poultry, has received scant attention as a cause of human gastroenteritis. At least 45 persons were infected with S thompson in Sacramento, California, after eating at a chicken restaurant and 38 became symptomatic. Ten required admission to hospital, and all were treated with antibiotics and improved. In 19 cases cultures of stool specimens for S thompson over a 60-day period showed slower but statistically insignificant differences in salmonellal elimination in 7 patients who received antibiotics when compared with 12 who were untreated. We report this outbreak to increase awareness of the virulence and prevalence of gastroenteritis due to S thompson.     

Inhibited light activation of fructose and sedoheptulose bisphosphatase in spinach chloroplasts exposed to osmotic stress

The light activation of fructose-1,6-bisphosphatase (EC 3.1.3.11) and sedoheptulose-1,7-bisphosphatase (EC 3.1.3.37) was inhibited in isolated intact spinach (Spinacia oleracea L.) chloroplasts exposed to reduced osmotic potentials. Decreases in the velocity and magnitude of light activation correlated with the overall reduction in CO₂ fixation rates. Responses of osmotically stressed chloroplasts to both varying pH and exogeous dihydroxyacetone phosphate (DHAP) or 3-phosphoglycerete (PGA) were examined. In the presence of DHAP, the absolute rate of CO₂ fixation was increased and this increase was most pronounced at alkaline pH. Enhanced light activation of these enzymes was also observed under these conditions. However, in the presence of PGA, similar increases in photosynthetic rate and enzyme activation were not evident. Light-dependent stromal alkalization was unaffected by the stress treatments. Inhibition of light activation under hypertonic conditions is discussed in terms of substrate availability, possible alterations of the redox state of ferredoxin and associated electron carriers, and inhibited enzyme-enzyme or enzyme-substrate interactions involved in the light activation process.Abbreviations and symbols DHAP dihydroxyacetone phosphate - PGA 3-phosphoglycerate - _s osmotic potential     

Golgi-mediated vicilin accumulation in pea cotyledon cells is re-directed by monensin and nigericin

Summary A range of drugs was applied to developing pea seed cotyledons in an attempt to perturb the intracellular transport of newly synthesized vicilin through the endoplasmic reticulum and Golgi vesicles to its site of storage, the vacuole. The most pronounced effects, produced by the ionophores monensin and nigericin, were on Golgi-mediated transport. Unlike the situation in most other tissues that have been studied the number of Golgi vesicles did not increase, suggesting that their movement is not slowed or stopped. However, the Golgi-mediated transport of vicilin was redirected from the vacuole tonoplast to the plasmalemma and the newly synthesized vicilin was released from the cotyledon cells to accumulate between the plasmalemma and the cell wall.     

Characterization of a new marine methylotroph

Abstract A methanol-oxidizing bacterium from a marine environment has been isolated and characterized. The bacterium was a Gram-negative rod, capable of growth on methanol and methylamine, but not on multicarbon compounds. It showed a temperature optimum of 30°C, a salt optimum of 0.4% (w/v) and the mol % G + C of its DNA was 46%. Carbon was assimilated via the ribulose monophosphate pathway for formaldehyde fixation during growth on methanol. This bacterium superficially resembled other obligate methylotrophs requiring NaCl reported previously which were designated Methylomonas thalassica . It also appeared similar to many strains of obligate freshwater methylotrophs, except for its NaCl requirement and its lower mol % G + C.     

Pigmentation and autofluorescence of Cryptococcus species after growth on tryptophan and anthranilic acid media

Cryptococcus neoformans and Candida albicans produced a pink pigment from media containing tryptophan. Approximately 30% of the C. neoformans strains produced large amounts of the pink (purple after 6 days) pigment in the absence of light whereas 70% of the Cryptococcus neoformans strains, as well as C. laurentii, C. albidus, C. diffluens, and C. albicans also produced the pink pigment with light being required for significant early production (2–6 days). Significant production did occur for Cryptococcus but not Candida species in the dark after extended incubation (10–25 days). C. terreus produced brown pigments from tryptophan and C. luteolus produced a trace of a buff pigment. Most Candida species produced either pink or brown pigments but not both. In contrast, many Cryptococcus species producing the pink pigment simultaneously produced brown pigments. C. terreus, C. albidus, and C. diffluens produced brown pigments from anthranilic acid whereas C. neoformans, C. laurentii, C. luteolus, and the medically important Candida species did not produce significant amounts of pigments from anthranilic acid. Cryptococcus and Candida species were autofluorescent when tryptophan was a major nitrogen source whereas yeast cell autofluorescence was not observed when anthranilic acid was used. Pigmentation of some Cryptococcus species also the substrate.Operated for the U.S. Department of Energy under contract number EY-76-C-05-0033This article is based on work supported by the Division of Biomedical and Environmental Research.     

The kinetic mechanism of action of an uncoupler of oxidative phosphorylation

Summary The chemiosmotic hypothesis predicts that the mechanism by which weak acids uncouple oxidative phosphorylation in mitochondria is identical to the mechanism by which they transport hydrogen ions across artificial bilayer membranes. We report here the results of a kinetic study of uncoupler-mediated hydrogen ion transport across bilayer membranes. We made electrical relaxation measurements on black lipid membranes exposed to the substituted benzimidazole 5,6-dichloro-2-trifluoromethylbenzimidazole. The simplest model consistent with our experimental data allowed us to deduce values for adsorption coefficients and rate constants. Our major conclusions are that the back diffusion of the neutral species is the rate limiting step for the steady state transport of hydrogen ions, that both the neutral and charged forms of the uncoupler adsorb strongly to the interfaces, and that the reactions at the membrane-solution interfaces occur sufficiently rapidly for equilibrium to be maintained. Independent measurements of the adsorption coefficients of both the neutral and anionic forms of the weak acid and also of the permeability of the membrane to the neutral form agreed well with the values deduced from the kinetic study.     

Mild phosphorus stress in barley and a related low-phosphorus-adapted barleygrass: Phosphorus fractions and phosphate absorption in relation to growth

Barleygrass ( Hordeum leporinum ) from Australian low-P (phosphorus) soils and commercial barley ( H. vulgare ) with high fertilizer requirements were grown in solution culture at 3 levels of P supply. The high-P-adapted barley produced more biomass at all levels of P supply and was more responsive to added P in terms of rate of tillering, rate of leaf production, final leaf size, and therefore total shoot weight compared to barleygrass. In both species root: shoot ratio decreased in response to improved tissue P status, even at P levels where total biomass did not respond to P supply. Removal of endosperm reserves of barley reduced total biomass to a greater extent than it altered phosphate absorption rate, thus increasing tissue P status and making plants less responsive to added P. Similarly, barleygrass had a slower growth rate but a comparable P absorption rate to that of barley. Thus barleygrass also accumulated tissue P and was unresponsive to added P. All phosphorus chemical fractions increased in response to improved tissue P status, but to differing extents (inorganic-P > nucleic acid-P > lipid-P > ester-P), suggesting that all P fractions (particularly inorganic P) serve, in part, a storage function. Both barleygrass and barley without endosperm had higher concentrations of all P fractions (particularly inorganic P) than did unaltered barley, but this was due entirely to their higher P status (due to slow growth) rather than to any major difference in P metabolism between species. We conclude that slow growth is more important than interspecific differences in P metabolism, P absorption, or efficiency of P utilization in explaining the success of barleygrass and other low-P-adapted species on infertile soils.     

Proton transport through membranes induced by weak acids: A study of two substituted benzimidazoles

Summary We report here a kinetic study of the mechanism by which the weak acid TTFB (4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazole) transports protons across phospholipid bilayer membranes. A previous kinetic study of the homologous dichloro compound, DTFB, revealed that the rate limiting step for proton translocation was the back diffusion of the neutral, HA, form of the weak acid; we conclude here that this is also the rate limiting step for proton translocation with TTFB. At high concentrations of either DTFB or TTFB the charged permeant species is an HA ₂ ^– complex. The kinetic analysis and independent measurements reveal that the permeability of the membrane to HA and adsorption coefficients of A^– and HA are an order of magnitude higher for TTFB than for DTFB. When either DTFB or TTFB was present in a solution where the pH was less than the pK of the weak acid, an unusual relaxation in the current was noted on application of a voltage step. The amplitude of the relaxation decreased as the voltage was increased. This relaxation is possibly due to a reorientation of the benzimidazole molecules at the membrane-solution interface. We also report experiments performed with DTFB on mitochondria. It was possible to reconcile these results with the bilayer data and, therefore, with the chemiosmotic hypothesis by postulating that the dielectric constant of the mitochondrial membrane is greater than that of a bilayer formed with decane as a solvent. To demonstrate the effect of dielectric constant on permeability, we replaced decane by 1-chlorodecane. This increased the capacitance of the artificial bilayer by a factor of two and the permeability of the bilayer to the A^– form of DTFB by two orders of magnitude.