Quantification of oxygen release by bulrush (Scirpus validus) roots in a constructed treatment wetland

Amount of oxygen released by bulrush (Scirpus validus) roots has been quantified based on the radial oxygen loss (ROL) exhibited by the roots, the number and the length of active lateral roots, and the field plant density. It was found that wetland bulrush contains two types of active lateral roots (showing ROL), viz., laterals of brown and white main roots. The two laterals have distinct oxygen release characteristics. Based on the dissolved oxygen (DO) microprofiles of brown and white laterals, the ROLs were found to be approximately 61 ng O2 cm(-2) root surface min(-1) and approximately 68 ng O2 cm(-2) root surface min(-1), respectively, at bulk 5-day biochemical oxygen demand (BOD5) of 76 mg L(-1). The respective average active root lengths of the brown and the white laterals were approximately 40 and approximately 1676 microm. Based on field and laboratory measurements, the average amount of oxygen released by bulrush was found to be 2.30 mg O2 m(-2) wetland surface d(-1); of this approximately 71% is from the white roots. The results of this study indicate that plants do not release enough oxygen to meet the total oxygen demand of bulk wastewater, and therefore, constructed wetlands should be designed as an anaerobic or an aerobic-anaerobic hybrid system rather than as an aerobic system. However, the results of this study should be viewed in the background of possible errors (including a reactor design flaw), which might have made the measured oxygen release significantly lower than what plant roots actually release. Further studies are needed to quantify wetland plant oxygen release based on micro-scale measurements.     

Activation of AMPA/kainate receptors but not acetylcholine receptors causes Mg2+ influx into Retzius neurones of the leech Hirudo medicinalis

In Retzius neurones of the medicinal leech, Hirudo medicinalis, kainate activates ionotropic glutamate receptors classified as AMPA/kainate receptors. Activation of the AMPA/kainate receptor-coupled cation channels evokes a marked depolarization, intracellular acidification, and increases in the intracellular concentrations of Na+ ([Na+]i) and Ca2+. Qualitatively similar changes are observed upon the application of carbachol, an activator of acetylcholine receptor-coupled cation channels. Using multibarrelled ion-selective microelectrodes it was demonstrated that kainate, but not carbachol, caused additional increases in the intracellular free Mg2+ concentration ([Mg2+]i). Experiments were designed to investigate whether this kainate-induced [Mg2+]i increase was due to a direct Mg2+ influx through the AMPA/kainate receptor-coupled cation channels or a secondary effect due to the depolarization or the ionic changes. It was found that: (a) Similar [Mg2+]i increases were evoked by the application of glutamate or aspartate. (b) All kainate-induced effects were inhibited by the glutamatergic antagonist DNQX. (c) The magnitude of the [Mg2+]i increases depended on the extracellular Mg2+ concentration. (d) A reduction of the extracellular Ca2+ concentration increased kainate-induced [Mg2+]i increases, excluding possible Ca2+ interference at the Mg2+-selective microelectrode or at intracellular buffer sites. (e) Neither depolarizations evoked by the application of 30 mM K+, nor [Na+]i increases induced by the inhibition of the Na+/K+ ATPase caused comparable [Mg2+]i increases. (f) Inhibitors of voltage-dependent Ca2+ channels did not affect the kainate-induced [Mg2+]i increases. Moreover, previous experiments had already shown that intracellular acidification evoked by the application of 20 mM propionate did not cause changes in [Mg2+]i. The results indicate that kainate-induced [Mg2+]i increases in leech Retzius neurones are due to an influx of extracellular Mg2+ through the AMPA/kainate receptor-coupled cation channel. Mg2+ may thus act as an intracellular signal to distinguish between glutamatergic and cholinergic activation of leech Retzius neurones.     

Image‐guided recording system for spatial and temporal mapping of neuronal activities in brain slice

In this study, we introduce the novel image‐guided recording system (IGRS) for efficient interpretation of neuronal activities in the brain slice. IGRS is designed to combine microelectrode array (MEA) and optical coherence tomography at the customized upright microscope. It allows to record multi‐site neuronal signals and image of the volumetric brain anatomy in a single body configuration. For convenient interconnection between a brain image and neuronal signals, we developed the automatic mapping protocol that enables us to project acquired neuronal signals on a brain image. To evaluate the performance of IGRS, hippocampal signals of the brain slice were monitored, and corresponding with two‐dimensional neuronal maps were successfully reconstructed. Our results indicated that IGRS and mapping protocol can provide the intuitive information regarding long‐term and multi‐sites neuronal signals. In particular, the temporal and spatial mapping capability of neuronal signals would be a very promising tool to observe and analyze the massive neuronal activity and connectivity in MEA‐based electrophysiological studies.      

Movement and dissolution of the nucleus (germinal vesicle) during Rana oocyte meiosis: Effect of demecolcine (Colcemid) and centrifugation

Demecolcine (Colcemid; DE), a colchicine derivative, augmented meiosis reinitiation by progesterone in the follicle-enclosed oocyte of the frog, Rana pipiens. Whereas DE treatment alone had a minor stimulatory effect on germinal vesicle dissolution (GVD), this treatment elicited significant germinal vesicle movement (GVM) as evidenced by translocation of the GV to the oocyte surface. The effects of DE on GVM and progesterone-induced GVD were also elicited in oocytes lacking follicle cells or other follicle wall components (type IV follicles), indicating that DE has a direct action on the oocyte itself. DE alone did not alter oocyte membrane voltage (V_m), resistance (R_m), or current (I_m) and did not interfere with the changes in these parameters usually elicited by progesterone. After 5 hr incubation of follicle-enclosed oocytes with either DE or progesterone, or combinations of both, the GV could be moved to the animal pole surface with less centrifugal force compared to control follicles. This result suggests that a decrease in ooplasmic viscoelasticity is induced by progesterone, which is mimicked by DE before GVM or GVD normally begins. The results presented here support the idea that DE-sensitive oocyte components such as microtubules are involved in the process of steroid-induced meiosis. These findings provide a physiological basis for future studies of cytoskeletal involvement in the events of meiosis.     

Acetylcholine-Induced Na+ influx in the mouse lacrimal gland acinar cells: Demonstration of multiple Na+ transport mechanisms by intracellular Na+ activity measurements

Summary In the isolated, superfused mouse lacrimal gland, intracellular Na⁺ activities (aNa _i ) of the acinar cells were directly measured with double-barreled Na⁺-selective microelectrodes. In the nonstimulated conditionaNa _i was 6.5±0.5 mM and membrane potential (V _m ) was –38.9±0.4 mV. Addition of 1 mM ouabain or superfusion with a K⁺-free solution slightly depolarized the membrane and caused a gradual increase inaNa _i . Stimulation with acetylcholine (ACh, 1 M) caused a membrane hyperpolarization by about 20 mV and an increase inaNa _i by about 9 mM in 5 min. The presence of amiloride (0.1 mM) reduced the ACh-induced increase inaNa _i by approximately 50%, without affectingV _m and input resistance in both nonstimulated and ACh-stimulated conditions. Acid loading the acinar cells by an addition/withdrawal of 20 mM NH₄Cl or by replacement of Tris⁺-buffer saline solution with HCO ₃ ^– /CO₂-buffered solution increasedaNa _i by a few mM. Superfusion with a Cl^–-free NO ₃ ^– solution or 1 mM furosemide or 0.5 mM bumetanide-containing solution had little effect on the restingaNa _i levels, however, it reduced the ACh-induced increase inaNa _i by about 30%. Elimination of metabolite anions (glutamate, fumarate and pyruvate) from the superfusate reduced both the restingaNa _i and the ACh-induced increase inaNa _i .The present results suggest the presence of multiple Na⁺ entry mechanisms activated by ACh, namely, Na⁺/H⁺ exchange, Na-K-Cl cotransport and organic substrate-coupled Na⁺ transport mechanisms.     

Electrophysiological properties ofDictyostelium derived from membrane potential measurements with microelectrodes

Summary Electrical membrane properties of the cellular slime moldDictyostelium discoideum were investigated with the use of intracellular microelectrodes. The rapid potential transients (1 msec) upon microelectrode penetration of normal cells had a negative-going peak-shaped time course. This indicates that penetration of a cell with a microelectrode causes a rapid depolarization, which can just be recorded by the microelectrode itself. Therefore, the initial (negative) peak potential transient valueE _p (–19 mV) should be used as an indicator of the resting membrane potentialE _m ofD. discoideum before impalement, rather than the subsequent semistationary depolarized valueE _n (–5 mV). Using enlarged cells such as giant mutant cells (E _p=–39 mV) and electrofused normal cells (E _p=–30 mV) improved the reliability ofE _p as an indicator ofE _m. From the data we concluded thatE _m ofD. discoideum cells bathed in (mm) 40 NaCl, 5 KCl and 1 CaCl₂ is at least –50 mV. This potential was shown to be dependent on extracellular potassium. The average input resistanceR _i of the impaled cells was 56 M for normalD. discoideum. However, our analysis indicates that the membrane resistance of these cells before impalement is >1 G. Specific membrane capacitance was 1–3 pF/cm². Long-term recording of the membrane potential showed the existence of a transient hyperpolarization following the rapid impalement transient. This hyperpolarization was associated with an increase inR _i of the impaled cell. It was followed by a depolarization, which was associated with a decrease inR _i. The depolarization time was dependent on the filling of the microelectrode. The present characterization of the electrical membrane properties ofDictyostelium cells is a first step in a membrane electrophysiological analysis of signal transduction in cellular slime molds.     

玻璃绝缘的钨丝微电极尖端的修整方法

用微电极拉制器直接拉制成钨丝微电极的玻璃绝缘层在大多数情况下,裸露的尖端容易弯曲和过长。在显微镜下,可以用一种简单的方法把尖端弯曲和过长部分修整成任何需要的长度和形状。     

The bioelectronic nose and tongue using olfactory and taste receptors: Analytical tools for food quality and safety assessment

Food intake is the primary method for obtaining energy and component materials in the human being. Humans evaluate the quality of food by combining various facets of information, such as an item of food's appearance, smell, taste, and texture in the mouth. Recently, bioelectronic noses and tongues have been reported that use human olfactory and taste receptors as primary recognition elements, and nanoelectronics as secondary signal transducers. Bioelectronic sensors that mimic human olfaction and gustation have sensitively and selectively detected odor and taste molecules from various food samples, and have been applied to food quality assessment. The portable and multiplexed bioelectronic nose and tongue are expected to be used as next-generation analytical tools for rapid on-site monitoring of food quality. In this review, we summarize recent progress in the bioelectronic nose and tongue using olfactory and taste receptors, and discuss the potential applications and future perspectives in the food industry.     

Generation of DNA double-strand breaks and inhibition of somatic embryogenesis by tungsten microparticles in wheat

Particles of metallic tungsten, known also as tungsten microprojectiles, are routinely used to deliver foreign DNA into target cells and tissues. Some side effects of biolistic transformation have been observed but never studied in detail. Here we present evidence that intact tungsten particles can promote a breakage of phosphodiester bonds in native DNA, at a limited number of sites. A single, double-strand break appeared within almost each of the circular pUC119 molecules after a short incubation of plasmid DNA with a suspension of tungsten particles. No further DNA cutting could be induced even if the reaction rate was accelerated by increasing the concentration of tungsten in the incubation mixture. Indirect evidence indicates that similar lesions may be generated in cellular DNA of bombarded tissues. These lesions are rapidly repaired, as evidenced by increasing incorporation of labelled DNA precursors in bombarded wheat embryos. The rate of repair is, however, not high enough to restore all the genome functions. Neither germination of mature embryos nor initiation of callus tissues from immature embryos was inhibited by biolistic bombardment. Nevertheless, the frequency of formation of somatic embryos in calli derived from bombarded embryos was markedly lower than in calli derived from control embryos. Both immediate (generation of a limited number of double-strand breaks) and remote (selective inhibition of somatic embryogenesis) side effects of the biolistic process strongly suggest that biological activity of tungsten deserves special attention. This revised version was published online in June 2006 with corrections to the Cover Date.     

Screening plants for salt tolerance by measuring K+ flux: a case study for barley

Development of salt-tolerant genotypes is central both to remediation of salinity-affected land and to meet increasing global food demand, which has been driving expansion of cropping into marginal areas. The bottleneck of any breeding programme is the lack of a reliable screening technique. This study tested the hypothesis that the ability of plants to retain K⁺ under saline conditions is central to their salt tolerance. Using seven barley cultivars contrasting in salt tolerance (CM72, Numar, ZUG293, ZUG95, Franklin, Gairdner, ZUG403), a comprehensive study was undertaken of whole-plant (growth rate, biomass, net CO₂ assimilation, chlorophyll fluorescence, root and leaf elemental and water content) and cellular (net fluxes of H⁺, K⁺, Na⁺ and Ca²⁺) responses to various concentrations of NaCl (20–320 m m ). Na⁺ selective microelectrodes were found to be unsuitable for screening purposes because of non-ideal selectivity of the commercially available Na⁺ LIX. At the same time, our results show very strong negative correlation between the magnitude of K⁺ efflux from the root and salt tolerance of a particular cultivar. K⁺ efflux from the mature root zone of intact 3-day-old seedlings following 40 min pretreatment with 80 m m NaCl was found to be a reliable screening indicator for salinity tolerance in barley. As a faster and more cost-effective alternative to microelectrode measurements, a procedure was developed enabling rapid screening of large numbers of seedlings, based on amount of K⁺ leaked from plant roots after exposure to NaCl.