vaCATE: A Platform for Automating Data Output from Compartmental Analysis by Tracer Efflux

Compartmental analysis by tracer efflux (CATE) is fundamental to examinations of membrane transport, allowing study of solute movement among subcellular compartments with high temporal, spatial, and chemical resolution. CATE can provide a wealth of information about fluxes and pool sizes in complex systems, but is a mathematically intensive procedure, and there is a need for software designed to fully, easily, and dynamically analyse results from CATE experiments. Here we present vaCATE (Visualized Automation of Compartmental Analysis by Tracer Efflux), a software package that meets these criteria. A robust suite of test cases using CATE datasets from experiments with intact rice ('Oryza sativa' L.) root systems reveals the high fidelity of vaCATE and the ease with which parameters can be extracted, using a three-compartment model and a curve-stripping procedure to distinguish them on the basis of variable exchange rates. vaCATE was developed using Python 2.7 and can be used in most situations where compartmental analysis is required. Funding Statement: This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Ontario Graduate Scholarship Fund (OGS)

Silver ions disrupt K+ homeostasis and cellular integrity in intact barley (Hordeum vulgare L.) roots

The heavy metals silver, gold, and mercury can strongly inhibit aquaporin-mediated water flow across plant cell membranes, but critical examinations of their side effects are rare. Here, the short-lived radiotracer 42K is used to demonstrate that these metals, especially silver, profoundly change potassium homeostasis in roots of intact barley (Hordeum vulgare L.) plants, by altering unidirectional K+ fluxes. Doses as low as 5 μM AgNO3 rapidly reduced K+ influx to 5% that of controls, and brought about pronounced and immediate increases in K+ efflux, while higher doses of Au3+ and Hg2+ were required to produce similar responses. Reduced influx and enhanced efflux of K+ resulted in a net loss of >40% of root tissue K+ during a 15 min application of 500 μM AgNO3, comprising the entire cytosolic potassium pool and about a third of the vacuolar pool. Silver also brought about major losses of UV-absorbing compounds, total electrolytes, and NH4+. Co-application, with silver, of the channel blockers Cs+, TEA+, or Ca2+, did not affect the enhanced efflux, ruling out the involvement of outwardly rectifying ion channels. Taken together with an examination of propidium iodide staining under confocal microscopy, the results indicate that silver ions affect K+ homeostasis by directly inhibiting K+ influx at lower concentrations, and indirectly inhibiting K+ influx and enhancing K+ efflux, via membrane destruction, at higher concentrations. Ni2+, Cd2+, and Pb2+, three heavy metals not generally known to affect aquaporins, did not enhance K+ efflux or cause propidium iodide incorporation. The study reveals strong and previously unknown effects of major aquaporin inhibitors and recommends caution in their application

Aspectos de la historia del Imperio Romano : Textos de Morstein-Marx, Rosenstein, Mattingly, Ziolkowski, Grey y Drinkwater

Este libro reúne trabajos sobre distintos aspectos de la historia del Imperio Romano desde el surgimiento hasta su crisis terminal en Occidente. La sociedad romana es abordada desde puntos de vista políticos, económicos y sociales, en la medida en que estos pueden ser separados. Se han traducido textos de reconocidos investigadores: Morstein-Marx, Rosenstein, Mattingly, Ziolkowski, Grey y Drinkwater, cuya publicación busca acercar al mundo hispanoparlante estudios actualizados acerca de este período histórico para ser utilizados en la enseñanza de grado de la educación superior y universitaria. Esperamos que impulse la curiosidad de los alumnos sobre esta época, al mostrar su complejidad y lo que podemos aprender de ella para la comprensión de la sociedad en la que vivimos.Facultad de Humanidades y Ciencias de la Educació

Fluxes, compartmentation and metabolism of nitrate and ammonium in spruce roots

Techniques of compartmental analysis and kinetic flux analysis with the radiotracer ¹³N were employed to examine the uptake, compartmentation, and metabolism of NO₃⁻ and NH₄⁺ in roots of white spruce (Picea glauca (Moench) Voss.). Efflux analysis, conducted over 22-min periods, resolved the exchange of inorganic N with three subcellular compartments. These were (I) a root-surface film, (II) an adsorptive component of the cell wall, and (III) the root-cell cytoplasm. The identities of the compartments were tested using various approaches. Half-lives of exchange were (for NH₄⁺) ≈ 2 s, 20 s, and 7 min, respectively, and (for NO₃⁻) 2 s, 30 s, and 14 min, respectively. Under the steady-state conditions assessed by efflux analysis, four to five-fold larger rates of uptake were observed for NH₄⁺ than for NO₃⁻ Steady-state NH₄⁺ influx ranged from 0.3 to 6.5 μmol g⁻¹ (FW) h⁻¹ , while it was 0.08 to 1.2 μmol g⁻¹ h⁻¹ for NO₃⁻, at external concentrations from 0.01 to 1.5 mM of the two N sources. Efflux increased with increasing external concentrations of the N sources and ranged from 10% to 30% of influx for NH₄⁺ and from 1% to 20% for NO₃⁻. Cytoplasmic concentrations were considerably higher for NH₄⁺ than for NO₃⁻; [NH₄⁺][sub cyt] was 2 to 30 mM, whereas [NO₃⁻][sub cyt] was 0.2 to 4 mM under the above conditions. A time-dependent compartmental-analysis study revealed that NO₃⁻ uptake was inducible by external NO₃⁻ and that three days were required for maximal uptake to be achieved at 100 μM [NO₃⁻]₀. The dynamics of NO₃⁻-flux partitioning to different compartments during induction were characterized. Analysis of nitrate reductase activity under identical conditions confirmed the slow inductive time-scale. Kinetic analysis of influx under perturbation conditions revealed distinct uptake systems for both N species. At [NO₃⁻]₀ ≤ 1 mM, NO₃⁻ influx was mediated by a constitutive and saturable high-affinity transport system (CHATS) and by a bisaturable inducible high-affinity transport system (IHATS). Beyond 1 mM, a linear low-affinity system (LATS) was evident. NH₄⁺ influx was not inducible by external NH₄⁺. It was mediated by a constitutive and saturable high-affinity transporter (HATS) at [NH₄⁺]₀ ≤ 1 mM, while a linear low-affinity transporter (LATS) operated beyond 1 mM. K[sub m] values for the initial phase of high-affinity transport were similar for both N species (≈ 20 μM), but V[sub max] was up to 20 times larger for NH₄⁺ than for NO₃⁻ when measured in perturbation. Overall, the study establishes a pronounced physiological limitation in spruce roots in transporting and utilizing NO₃⁻ as compared to NH₄⁺.Science, Faculty ofBotany, Department ofGraduat