Reduced oxygen concentration improves the developmental competence of mouse oocytes following in vitro maturation

Reduced atmospheric oxygen concentration is beneficial to embryo development; however, optimal oxygen concentration for oocyte maturation remains undetermined. Likewise, there is no consensus of appropriate medium supplementation during maturation. The objective of this study was to determine whether oxygen tension (20% or 5% O2) and epidermal growth factor (EGF) affect oocyte metabolism and subsequent embryo development. Cumulus-oocyte complexes (COCs) were collected from 28-day-old equine chorionic gonadotropin (eCG) primed or unprimed F1 (C57BL/6xCBA) mice. COCs were matured in defined medium in one of four groups: 20% O2, 20% O2 + EGF, 5% O2, 5% O2 + EGF. In vivo matured COCs were also collected for analysis. COCs from unprimed mice, matured in 5% O2 +/- EGF or 20% O2 + EGF had higher metabolic rates than COCs matured in 20% O2 (P < 0.05). COCs from primed mice had higher metabolic rates when matured in the presence of EGF, regardless of oxygen tension (P < 0.01). Oxygen uptake and mitochondrial membrane potential were higher for in vivo matured oocytes and oocytes matured under 5% O2 compared to oocytes matured under 20% O2 (P < 0.05). Blastocyst formation was not different between maturation groups (primed or unprimed); however, embryo cell numbers were 20-45% significantly higher when COCs were matured at 5% O2 (P < 0.05). Results suggest that oocytes matured in physiological concentrations of oxygen have improved development and metabolic activity, more closely resembling in vivo maturation. These findings have implications for oocyte maturation in both clinical and research laboratories.     

Effects of nutrient solution zinc activity on net uptake,translocation, and root export of cadmium and zinc by separated sections of intact durum wheat (Triticum turgidum L. var durum) seedling roots

Cd accumulation in durum wheat presents a potential health risk to consumers. In an effort to understand the physiological mechanisms involved with Cd accumulation, this study examined the effects of Zn on Cd root uptake and phloem translocation in a split– root system. Durum wheat seedlings were grown in chelate-buffered nutrient solution with intact root systems divided into two sections. Each root section grew in a separate 1 l pot, one of which contained 0.2 μM CdSO₄. In addition, each two-pot system contained ZnSO₄ in the following combinations (in μm) (for -cd root system: +cd root system): 1:1, 1:10, 10:1,10:10, 1:19, and 19:1. Harvested plant material was analyzed for Cd and Zn. In addition, rates of Cd and Zn net uptake, translocation to the shoot, and root export (translocation from one root segment to the other) between days 8 and 22 were calculated. Results show that Zn was not translocated from one root section to its connected root section. Uptake rates of Cd increased as solution Zn concentrations increased. Cd translocation from one root section to the other decreased significantly when the Zn concentration in either pot was greater than 1 μM. These results show the potential of Zn to inhibit movement of Cd via the phloem, and suggests that providing adequate Zn levels may limit phloem loading of Cd into wheat grain. Increasing the rhizosphere activity of Zn²⁺ in Cd-containing soils may therefore result in reduced Cd accumulation in grain even while net Cd uptake is slightly enhanced. This revised version was published online in June 2006 with corrections to the Cover Date.     

Mechanisms of inorganic carbon acquisition in Gracilaria gaditana nom. prov. (Rhodophyta)

The mechanisms for acquisition of dissolved inorganic carbon (DIC) in the red macroalga Gracilaria gaditana nom. prov. have been investigated. The capacity for HCO₃ ⁻ use by an extracellular carbonic anhydrase (CA; EC 4.2.1.1), and by an anion exchanger with similar properties to that of red blood cells (AE1), has been quantified. It was illustrated by comparing O₂ evolution rates with those theoretically supported by CO₂, as well as by photosynthesis-pH curves. Both external and internal CA, and a direct uptake were involved in HCO₃ ⁻ use, since photosynthesis and pH evolution were affected by acetazolamide, 6-ethoxyzolamide (inhibitors of external and total CA, respectively) and 4,4′-diisothiocyanatostilbene-2,2′-disulfonate, (DIDS; an inhibitor of HCO₃ ⁻ exchanger protein). The activity of the external CA was detected by a potentiometric method and by an alternative method based on the study of O₂ evolution after addition of CO₂ and acetazolamide. The latter method showed a residual photosynthetic rate due to direct HCO₃ ⁻ use. Inhibitors caused a reduction in the pH compensation points in pH-drift experiments. The CO₂ compensation points for photosynthesis increased when the inhibitors were applied, indicating a suppresion of the pathways involved in the carbon-concentrating mechanism. The net photosynthesis rates as a function of DIC concentration displayed a biphasic pattern that could be supported by the occurrence of the two mechanisms of HCO₃ ⁻ use. The potential contribution to HCO₃ ⁻ acquisition by the DIDS-sensitive mechanism was higher after culturing at a high pH. Our results suggest that the HCO₃ ⁻ use by Gracilaria gaditana is carried out by the two DIC uptake mechanisms. These operate simultaneously with different affinities for DIC, the indirect HCO₃ ⁻ use by an external CA activity being the main pathway. The presence of a carbon-concentrating mechanism confers eco-physiological advantages in a fluctuating ecosystem subjected daily to high pHs and low DIC concentrations. Received: 3 July 1998 / Accepted: 30 November 1998     

Potassium Translocation into the Root Xylem

Abstract: Potassium is the most abundant cation in cells of higher plants and plays vital roles in plant growth and develop ment. Since the soil is the only source of potassium, plant roots are well adapted to exploit the soil for potassium and supply it to the leaves. Transport across the root can be divided into three stages: uptake into the root symplast, transport across the symplast and release into the xylem. Uptake kinetics of potassium have been studied extensively in the past and sug gested the presence of high and low affinity systems. Molecular and electrophysiological techniques have now confirmed the existence of discrete transporters encoded by a number of genes. Surprisingly, detailed characterisation of the transpor ters using reverse genetics and heterologous expression shows that a number of the transporters (AKT and AtKUP family) func tion both in the low (μM) and high (mM) K⁺ range. Electrophy siological studies indicate that K⁺ uptake by roots is coupled to H⁺, to drive uptake from micromolar K⁺. However, thus far only Na⁺ coupled K⁺ transport has been demonstrated (HKT1). Ion channels play a major role in the exchange of potassium be tween the symplast and the xylem. An outward rectifying chan nel (KORC) mediates potassium release. Cloning of the gene en coding this channel (SKOR) shows that it belongs to the Shaker super-family. Both electrophysiological and genetic studies demonstrate that K⁺ release through this channel is controlled by the stress hormone abscisic acid. Interestingly, xylem par enchyma cells of young barley roots also contain a number of in ward rectifying K⁺ channels that are controlled by G-proteins. The involvement of G-proteins emphasises once more that po tassium transport at the symplast/xylem boundary is under hor monal control. The role of the electrical potential difference across the symplastxylem boundary in controlling potassium release is discussed.     

Phosphopeptides with improved cellular uptake properties as ligands for the polo-box domain of polo-like kinase 1

Human polo-like kinase 1 (Plk1) is involved in cell proliferation and overexpressed in a broad variety of different cancer types. Due to its crucial role in cancerogenesis Plk1 is a potential target for diagnostic and therapeutic applications. Peptidic ligands can specifically interact with the polo-box domain (PBD) of Plk1, a C-terminal located phosphoepitope binding motif. Recently, phosphopeptide MQSpTPL has been identified as ligand with high binding affinity. However, a radiolabeled version of this peptide showed only insufficient cellular uptake. The present study investigated peptide dimers consisting of PBD-targeting phosphopeptide MQSpTPL and a cell-penetrating peptide (CPP) moiety. The new constructs demonstrate superior uptake in different cancer cell-lines compared to the phosphopeptide alone. Furthermore, we could demonstrate binding of phosphopeptide-CPP dimers to PBD of Plk1 making the compounds interesting leads for the development of molecular probes for imaging Plk1 in cancer.     

燕麦-绿豆间作效应及氮素转移特性

为探究燕麦(Avena sativa)-绿豆(Phaseolus radiatus)间作效应及氮素转移特性, 在不施氮肥的大田试验条件下, 设置3种种植模式(燕麦单作、绿豆单作和燕麦-绿豆间作), 采用传统挖根法和¹⁵N同位素标记法进行研究。结果表明, 间作系统中燕麦侵袭力强于绿豆, 绿豆生长受到抑制。整个生育期, 间作燕麦地上部干物质积累量比单作增加14.9%-33.1%, 2年成熟期间作燕麦的氮素积累量比单作分别提高53.1%和44.8%; 间作减少了开花结荚期绿豆氮素积累量和根瘤重量, 降低了绿豆的固氮效率, 绿豆的固氮效率2年平均降低23.7%, 生物固氮量平均减少11.66%。间作绿豆向燕麦的氮素转移率2年平均值达31.7%, 氮素转移量为212.16 kg∙hm^-2。燕麦-绿豆间作降低了开花结荚期绿豆的根瘤固氮酶活性和固氮效率, 但绿豆体内氮素转移增加了燕麦对氮素的吸收利用, 实现了地上部与地下部生长的相互调节和促进, 优化了农田生态系统的氮素管理。     

Cholinergic innervation of the retrosplenial cortex via the fornix pathway as determined by high affinity choline uptake,choline acetyltransferase activity,and muscarinic receptor binding in the rat

The cholinergic projections from basal forebrain nuclei to the retrosplenial cortex (RSC) have previously been studied using a variety of histological approaches. Studies using acetylcholinesterase (AChE) histochemistry and choline acetyltransferase (ChAT) immunocytochemistry have demonstrated that this projection travels via the cingulum on route to the RSC. Preliminary studies from our laboratory, however, have shown that the fornix may also be involved in this projection. The present study uses the combination of pathway lesions, and the analysis of cholinergic neurochemical markers in the RSC to determine the role of the fornix in the cholinergic projection to the RSC. High affinity choline uptake (HACU) and ChAT activity were measured in the RSC of control rats, animals with cingulate lesions, and animals with fornix plus cingulate lesions. Fornix plus cingulate lesions resulted in significant deceases in HACU and ChAT activity in comparison to cingulate lesions alone. Muscarinic receptor binding was also evaluated in combination with the various lesions, and a significant increase in retrosplenial receptor binding was noted following fornix lesions. Together, these results support the concept of a fornix-mediated cholinergic pathway to the RSC.     

Lead as an inductor of some morphological and functional changes in synaptosomes from rat brain

Summary 1. The effect of lead (in vivo) on the uptake of GABA, dopamine, and histidine as a precursor of histamine in synaptosomes obtained from chronically lead-treated rats was studied.2. Lead decreased the uptake of GABA, increased the uptake of dopamine, and did not change the uptake of histidine. These effects were independent of calcium concentration.3. Lead administration to the rat changed the morphology of the synaptosomes, as manifested in the decreased number of synaptic vesicles and disturbed mitochondrial structure.4. The results suggest the existence of several mechanisms of lead toxicity on uptake, related to individual neurotransmitters, which are not necessarily connected with a Pb²⁺/Ca²⁺ interaction.     

Retention of NO_3^ - in an upland streamenvironment: A mass balance approach

Models of the effects of atmosphericN deposition in forested watersheds have notadequately accounted for the effects of aquatic andnear-stream processes on the concentrations and loadsof NO in surface waters. This studycompared the relative effects of aquatic andnear-stream processes with those from the terrestrialecosystem on the retention and transport ofNO in two contrasting stream reaches ofthe Neversink River, a forested watershed in theCatskill Mountains of New York that receives among thehighest load of atmospheric N deposition in thenortheastern United States. Stream water samples werecollected every two hours and ground-water andtributary samples were collected daily at base flowconditions during four 48-hour periods from April toOctober 1992, and NO mass balances werecalculated for each site. Results indicated diurnalvariations in stream NO concentrations inboth reaches during all four sampling periods; this isconsistent with uptake of NO byphotoautotrophs during daylight hours. Mass-balanceresults revealed significant stream reach losses ofNO at both sites during all samplingperiods. The diurnal variations in NO concentrations and the retention of NO relative to terrestrial contributions to the streamreaches were greater downstream than upstream becausephysical factors such as the head gradients ofinflowing ground water and the organic matter contentof sediment are more favorable to uptake anddenitrification downstream. The mass retention ofNO increased as the mean 48-hr streamdischarge increased at each site, indicating that theresponsible processes are dependent onNO supply. Low stream temperatures duringthe April sampling period, however, probably reducedthe rate of retention processes, resulting in smallerlosses of NO than predicted from streamdischarge alone. Water samples collected from thestream, the hyporheic zone, and the alluvial groundwater at sites in both reaches indicated that the neteffect of hyporheic processes on downstreamNO transport ranged from conservativemixing to complete removal by denitrification. Therelative effects of biological uptake anddenitrification as retention mechanisms could not bequantified, but the results indicate that bothprocesses are significant. These results generallyconfirm that aquatic and near-stream processes causesignificant losses of NO in the NeversinkRiver, and that the losses by these processes atdownstream locations can exceed the NO contributions to the stream from the terrestrialenvironment during summer and fall base-flowconditions. Failure to consider these aquatic andnear-stream processes in models of watershed responseto atmospheric N deposition could result inunderestimates of the amount of NO leaching from forested ecosystems and to an inabilityto unequivocally relate geographic differences inNO concentrations of stream waters tocorresponding differences in terrestrial processes.