Indications of Hydraulic Lift by Pinus halepensis and Its Effects on the Water Relations of Neighbour Shrubs

We measured the stable deuterium isotopic composition of xylem sap, the shoot predawn and midday water potentials, and the leaf δ¹³C of Mediterranean shrubs Pistacia lentiscus, Globularia alypum and Rosmarinus officinalis in a south-oriented transect from a large (12 m tall) Aleppo pine tree, Pinus halepensis. We aimed to study the possibility of hydraulic lift from the deep roots of this pine tree to the shallow soil layers and its influence on these neighbour shrubs. These same traits were also studied in several individuals of the shrub Pistacia lentiscus growing with different types of neighbours: just shrubs, a small (3 – 4 m) pine tree, and the above mentioned large pine tree. The greater the distance from P. halepensis the plants grew, the higher xylem water δD, the lower the soil water content, and, the lower the predawn and midday water potentials were found. These results suggest the existence of an hydraulic lift from deep roots to shallow soil in this big tree. Further indication of this existence is provided by the improved water status of P. lentiscus (higher water potentials and δD, and lower δ¹³C and, therefore, lower water use efficiencies) when growing close to the big pine in comparison with the same shrub species growing close to small pines or just surrounded by other shrubs. Moreover, all these trends occurred in the dry summer season, but disappeared in the wet spring season. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular characterization of PeSOS1: the putative Na+/H+ antiporter of Populus euphratica

Populus euphratica is a salt-tolerant tree species growing in semi-arid saline areas. A Na⁺/H⁺ antiporter gene was successfully isolated from this species through RACE cloning, and named PeSOS1. The isolated cDNA was 3665 bp long and contained a 3438 bp open reading frame that was predicted to encode a 127-kDa protein with 12 hypothetical transmembrane domains in the N-terminal part and a long hydrophilic cytoplasmic tail in the C-terminal part. The amino acid sequence of this PeSOS1 gene showed 64% identity with the previously isolated SOS1 gene from the glycophyte Arabidopsis thaliana. The level of protein expressed by PeSOS1 in the leaves of P. euphratica was significantly up-regulated in the presence of high (200 mM) concentrations of NaCl, while the mRNA level in the leaves remained relatively constant. Immunoanalysis suggested that the protein encoded by PeSOS1 is localized in the plasma membrane. Expression of PeSOS1 partially suppressed the salt sensitive phenotypes of the EP432 bacterial strain, which lacks the activity of the two Na⁺/H⁺ antiporters EcNhaA and EcNhaB. These results suggest that PeSOS1 may play an essential role in the salt tolerance of P. euphratica and may be useful for improving salt tolerance in other tree species. Yuxia Wu and Nan Ding contributed equally to this work.     

应用多电极记录技术研究海马切片癫痫样放电的起始点和传播方向

弄清癫痫样放电的起始位置和传播方向对研究癫痫机制及其临床治疗有重要意义．为了解决这一问题,应用微电极阵列对低镁人工脑脊液诱导的Sprague-Dawley (SD)大鼠海马切片的癫痫样放电进行记录．分别用癫痫样放电的两种成分：场电位和多单元信号来确定癫痫样放电的起始位置和传播方向．首先计算并比较了海马切片锥体细胞层位置电极记录的癫痫样放电场电位的起始时间,由起始时间的先后关系确定癫痫样放电在锥体细胞层的起始位置和传播方向．然后用整个切片上记录的癫痫样放电的多单元信号动作电位序列进行互相关分析,进一步确定了癫痫样放电在整个海马切片内的起始位置和传播方向．结果显示,CA3区的癫痫样放电具有比CA1区更高的幅度和更长的持续时间,表明CA3区有更高的兴奋性．对于记录到的同步癫痫样放电,CA3b区场电位和多单元信号均比CA3c和CA1区出现更早,起始位置和其随后位置之间的传播延　时与二者之间的距离成正相关．因此,在低镁模型的大鼠海马切片中,癫痫样放电起始于CA3b区并分别向CA3c和CA1区传播．     

Analysis of the Ca2+ domain in the Arabidopsis H+/Ca2+ antiporters CAX1 and CAX3

Ca²⁺ levels in plants are controlled in part by H⁺/Ca²⁺ exchangers. Structure/function analysis of the Arabidopsis H⁺/cation exchanger, CAX1, revealed that a nine amino acid region (87–95) is involved in CAX1-mediated Ca²⁺ specificity. CAX3 is 77% identical (93% similar) to CAX1, and when expressed in yeast, localizes to the vacuole but does not suppress yeast mutants defective in vacuolar Ca²⁺ transport. Transgenic tobacco plants expressing CAX3 containing the 9 amino acid Ca²⁺ domain (Cad) from CAX1 (CAX3-9) displayed altered stress sensitivities similar to CAX1-expressing plants, whereas CAX3-9-expressing plants did not have any altered stress sensitivities. A single leucine-to-isoleucine change at position 87 (CAX3-I) within the Cad of CAX3 allows this protein to weakly transport Ca²⁺ in yeast (less than 10% of CAX1). Site-directed mutagenesis of the leucine in the CAX3 Cad demonstrated that no amino acid change tested could confer more activity than CAX3-I. Transport studies in yeast demonstrated that the first three amino acids of the CAX1 Cad could confer twice the Ca²⁺ transport capability compared to CAX3-I. The entire Cad of CAX3 (87–95) inserted into CAX1 abolishes CAX1-mediated Ca²⁺ transport. However, single, double, or triple amino acid replacements within the native CAX1 Cad did not block CAX1 mediated Ca²⁺ transport. Together these findings suggest that other domains within CAX1 and CAX3 influence Ca²⁺ transport. This study has implications for the ability to engineer CAX-mediated transport in plants by manipulating Cad residues.     

On the integration of subthreshold inputs from Perforant Path and Schaffer Collaterals in hippocampal CA1 pyramidal neurons

Using a realistic model of a CA1 hippocampal pyramidal neuron, we make experimentally testable predictions on the roles of the non-specific cation current, I _h , and the A-type Potassium current, I _A , in modulating the temporal window for the integration of the two main excitatory afferent pathways of a CA1 neuron, the Schaffer Collaterals and the Perforant Path. The model shows that the experimentally observed increase in the dendritic density of I _h and I _A could have a major role in constraining the temporal integration window for these inputs, in such a way that a somatic action potential (AP) is elicited only when they are activated with a relative latency consistent with the anatomical arrangement of the hippocampal circuitry.     

Membrane Potential Dependent Duration of Action Potentials in Cultured Rat Hippocampal Neurons

(1) Fluctuations of the membrane potential states are essential for the brain functions from the response of individual neurons to the cognitive function of the brain. It has been reported in slice preparations that the action potential duration is dependent on the membrane potential states. (2) In order to examine whether dependence of action potential duration on the membrane potential could happen in isolated individual neurons that have no network connections, we studied the membrane potential dependence of the action potential duration by artificially setting the membrane potentials to different states in individual cultured rat hippocampal neurons using patch-clamp technique. (3) We showed that the action potential of individual neurons generated from depolarized membrane potentials had broader durations than those generated from hyperpolarized membrane potentials. (4) Furthermore, the membrane potential dependence of the action potential duration was significantly reduced in the presence of voltage-gated K⁺ channel blockers, TEA, and 4-AP, suggesting involvement of both delayed rectifier I _K and transient I _A current in the membrane potential dependence of the action potential duration. (5) These results indicated that the dependence of action potential duration on the membrane potential states could be an intrinsic property of individual neurons. Bo Gong and Mingna Liu contributed equally to this work.     

The Influences of I h on Temporal Summation in Hippocampal CA1 Pyramidal Neurons: A Modeling Study

Recent experimental and theoretical studies have found that active dendritic ionic currents can compensate for the effects of electrotonic attenuation. In particular, temporal summation, the percentage increase in peak somatic voltage responses invoked by a synaptic input train, is independent of location of the synaptic input in hippocampal CA1 pyramidal neurons under normal conditions. This independence, known as normalization of temporal summation, is destroyed when the hyperpolarization-activated current, I _h, is blocked [Magee JC (1999a), Nature Neurosci. 2: 508–514]. Using a compartmental model derived from morphological recordings of hippocampal CA1 pyramidal neurons, we examined the hypothesis that I _h was primarily responsible for normalization of temporal summation. We concluded that this hypothesis was incomplete. With a model that included I _h, the persistent Na⁺ current (I _NaP), and the transient A-type K⁺ current (I _A), however, we observed normalization of temporal summation across a wide range of synaptic input frequencies, in keeping with experimental observations.     

The role of various calcium and potassium channels in the regulation of somatodendritic serotonin release

We prepared slices from midbrain containing the raphe nuclei and from hippocampus of rats. The brain slices were loaded with [³H]serotonin and superfused in order to measure the release of radioactivity at rest and in response to electrical stimulation. No difference was observed in the resting and stimulated fractional release of tritium in the somatodendritic and axon terminal parts of serotonergic neurons. The selective 5-HT_1A receptor agonist 8-OH-DPAT decreased the electrically induced tritium effux from raphe nuclei slices preloaded with [³H]serotonin, and this inhibition was reversed by 5-HT_1A receptor antagonist (+)WAY-100135. The 5-HT_1B receptor agonist CGS-12066B but not 8-OH-DPAT, inhibited the stimulation-evoked tritium efflux from hippocampal slices after labeling with [³H]serotonin. The electrical stimulation-evoked tritium efflux in raphe nuclei slices incubate with [³H]serotonin was completely external Ca²⁺-dependent, and omega-conotoxin GVIA and Cd²⁺, but not diltiazem, inhibited the tritium overflow. In raphe nuclei slices 4-aminopyridine enhanced the electrical stimulation-induced trititum release in a concentration-dependent manner. The inhibition of tritium efflux by 8-OH-DPAT was abolished with 4-aminopyridine. Glibenclamide or tolbutamide proved to be ineffective. These data indicate that (1) different 5-HT receptor subtypes (5-HT_1A and 5-HT_1B) regulate dendritic and axon terminal 5-HT release; (2) serotonin release from the dendrites may be regulated by the voltage-sensitive N-type Ca²⁺ channels; (3) the 5-HT_1A receptor-mediated inhibition of serotonin release may be due to opening of voltage-sensitive K⁺ channels.     

Net nitrogen mineralization in soils under six indigenous tree species,an abandoned pasture and a secondary forest in the atlantic lowlands of costa rica

Nitrogen mineralization, nitrification potentials, pH, total N, C, extractable P and cations were measured in soils under 4-year-old, mono-specific stands of six fast-growing, native tree species, an abandoned pasture, and a 20-year-old secondary forest, as part of a study on the use of indigenous tree species for rehabilitation of soil fertility on degraded pastures at the La Selva Biological Station in the Atlantic humid lowlands of Costa Rica. Soil net nitrification potential rates were higher under two N-fixing, leguminous species,Stryphnodendron microstachyum Poepp. et Endl. (1.1–1.9 mg kg^–1 day^–1) andDalbergia tucurensis Donn. Smith (0.7–1.5 mg kg^–1 day^–1), than under the non-N-fixing trees in the plantation,Vochysia guatemalesis Don. Sm.,Vochysia ferruginea Mart,Dipteryx panamensis (Pittier) Record and Mell andHyeronima alchorneoides Fr. Allemao (0.2–0.8 mg kg^–1 day^–1). Values under the N-fixing trees were comparable to those found in secondary forest. There were no statistically significant differences in soil total N or in other nurtients between the species. Results of pH measurements done before and after incubation did not show any clear evidence of a pH drop attributable to nitrification.     

Hypoxic preconditioning induces neuroprotection against transient global ischemia in adult rats via preserving the activity of Na(+)/K(+)-ATPase

We demonstrated previously that 30 min of hypoxic preconditioning (HPC) applied 1 day before 10 min of transient global cerebral ischemia (tGCI) reduced neuronal loss in the hippocampal CA1 subregion in adult rats. The aim of the present study was to investigate the role of Na⁺/K⁺-ATPase and protein kinase Mζ (PKMζ) in the protective effect of HPC against tGCI in adult rats. We found that the activity of Na⁺/K⁺-ATPase decreased in the hippocampal CA1 subregion after 10 min of tGCI. This effect was not seen after 30 min of HPC in adult rats. Corresponding to the changes in Na⁺/K⁺-ATPase activity, the surface expression of Na⁺/K⁺-ATPase α1 subunit increased after HPC. Furthermore, HPC dramatically reduced the number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells in the hippocampal CA1 subregion after tGCI. However, neither PKMζ nor phosphorylation of PKMζ was changed after tGCI or HPC. The results of the present study are consistent with the hypothesis that both enhanced recovery of Na⁺/K⁺-ATPase activity due to preserved the protein levels of Na⁺/K⁺-ATPase α1 subunit and reduced DNA fragmentation after tGCI contribute to the protection afforded by HPC. However, PKMζ activation does not appear to play a role in this neuroprotection.     

Non-Decaying postsynaptics potentials and delayed spikes in hippocampal pyramidal neurons generated by a zero slope conductance created by the persistent Na+ current

The negative slope conductance created by the persistent sodium current (I_NaP) prolongs the decay phase of excitatory postsynaptic potentials (EPSPs). In a recent study, we demonstrated that this effect was due to an increase of the membrane time constant. When the negative slope conductance opposes completely the positive slope conductances of the other currents it creates a zero slope conductance region. In this region the membrane time constant is infinite and the decay phase of the EPSPs is virtually absent. Here we show that non-decaying EPSPs are present in CA1 hippocampal pyramidal cells in the zero slope conductance region, in the suprathreshold range of membrane potential. Na⁺ channel block with tetrodotoxin abolishes the non-decaying EPSPs. Interestingly, the non-decaying EPSPs are observed only in response to artificial excitatory postsynaptic currents (aEPSCs) of small amplitude, and not in response to aEPSCs of big amplitude. We also observed concomitantly delayed spikes with long latencies and high variability only in response to small amplitude aEPSCs. Our results showed that in CA1 pyramidal neurons I_NaP creates non-decaying EPSPs and delayed spikes in the subthreshold range of membrane potentials, which could potentiate synaptic integration of synaptic potentials coming from distal regions of the dendritic tree.     

Hippocampal glucocorticoid receptor expression in the tree shrew: Regulation by psychosocial conflict

Summary 1. This study was conducted to determine whether chronic psychosocial conflict alters the expression of glucocorticoid receptor (GR) mRNA in the hippocampus of male tree shrews (Tupaia belangeri).2. To generate probes for thein situ hybridization, the tree shrew GR gene was partly cloned. There was a 90% homology between the deduced amino acid sequence of the cloned tree shrew GR and that of the corresponding human GR sequence.³⁵S-Labeled riboprobes which had been transcribed from the tree shrew GR clone hybridized to pyramidal neurons in all subregions of the tree shrew hippocampal formation and to granule neurons in the dentate gyrus.3. Afterin situ hybridization, the expression of GR mRNA was semiquantitatively determined by counting silver grains over single neurons of the hippocampal formation of psychosocially stressed tree shrews and control animals. After 12 days of social conflict, the number of silver grains in the CA1 and CA3 pyramidal neurons of stressed animals was significantly lower than in controls. No statistically significant differences in mRNA expression were observed in the pyramidal neurons of the subiculum and in the granule neurons of the dentate gyrus.4. The present results suggest that psychosocial stress leads to a site-specific down-regulation of hippocampal GR via modification of mRNA expression.     

Limited transfer of nitrogen between wood decomposing and ectomycorrhizal mycelia when studied in the field

Transfer of ¹⁵N between interacting mycelia of a wood-decomposing fungus (Hypholoma fasciculare) and an ectomycorrhizal fungus (Tomentellopsis submollis) was studied in a mature beech (Fagus sylvatica) forest. The amount of ¹⁵N transferred from the wood decomposer to the ectomycorrhizal fungus was compared to the amount of ¹⁵N released from the wood-decomposing mycelia into the soil solution as ¹⁵N-NH₄. The study was performed in peat-filled plastic containers placed in forest soil in the field. The wood-decomposing mycelium was growing from an inoculated wood piece and the ectomycorrhizal mycelium from an introduced root from a mature tree. The containers were harvested after 41 weeks when physical contact between the two foraging mycelia was established. At harvest, ¹⁵N content was analyzed in the peat (total N and ¹⁵NH₄ ⁺) and in the mycorrhizal roots. A limited amount of ¹⁵N was transferred to the ectomycorrhizal fungus and this transfer could be explained by ¹⁵NH₄ ⁺ released from the wood-decomposing fungus without involving any antagonistic interactions between the two mycelia. Using our approach, it was possible to study nutritional interactions between basidiomycete mycelia under field conditions and this and earlier studies suggest that the outcomes of such interactions are highly species-specific and depend on environmental conditions such as resource availability.     

Involvement of photosynthesis in the action of temperature on plasmalemma transport inNitella

Summary At membrane potentials different fromE _K, the temperature effect on membrane potential ofNitella consists of two components. One of them changes its sign atE _K, the other one does not. This leads to the assignment of these components to changes in the K⁺ channel and in the H⁺ pump, respectively. It is shown that the fast time constant (3 to 30 sec) of the temperature effect on the H⁺ pump measured as a change in membrane potential and that of the temperature effect on the K⁺ channel measured as a change in resistance (having about twice the value of that of the pump) are sensitive to light intensity. Both time constants measured inNitella become smaller if light intensity increases from 0 to 15 Wm^–2. This supports the suggestion of Fisahn and Hansen (J. Exp. Bot. 37:440–460, 1986) that temperature acts on plasmalemma transport via photosynthesis via the same mechanism as light does.     

Expression of a Novel Antiporter Gene from Brassica napus Resulted in Enhanced Salt Tolerance in Transgenic Tobacco Plants

Tobacco leaf discs were transformed with a plasmid pBIBnNHX1, containing the selectable marker neomycin phosphotransferase gene (nptII) and Na⁺/H⁺ vacuolar antiporter gene from Brassica napus (BnNHX1), via Agrobacterium tumefaciens-mediated transformation. Thirty-two independent transgenic plants were regenerated. Polymerase chain reaction (PCR) and Southern blot analyses confirmed that the BnNHX1 gene had integrated into plant genome and Northern blot analysis revealed the transgene expression at various levels in transgenic plants. Transgenic plants expressing BnNHX1 had enhanced salt tolerance and could grow and produce seeds normally in the presence of 200 mM NaCl. Analysis for the T₁ progenies derived from seven independent transgenic primary transformants expressing BnNHX1 showed that the transgenes in most tested independent T₁ lines were inherited at Mendelian 3:1 segregation ratios. Transgenic T₁ progenies could express _BnNHX1 and had salt tolerance at levels comparable to their T₀ parental lines. This study implicates that the BnNHX1 gene represents a promising candidate in the development of crops for enhanced salt tolerance by genetic engineering.     

Enhanced Dendritic Action Potential Backpropagation in Parvalbumin-positive Basket Cells During Sharp Wave Activity

In this study two-photon imaging and single cell electrophysiological measurements were carried out in PV+ hippocampal interneurons to compare the dendritic calcium dynamics of somatically evoked backpropagating action potentials (BAPs) and in vitro sharp wave oscillation (SPW) activated BAPs at different distances from the soma. In the case of 300 μm thick, non-oscillating slices, the BAP-evoked Ca²⁺ (BAP-Ca²⁺) influx propagated along the dendritic tree in a non-uniform manner and its amplitude gradually reduced when measured at more distal regions. In contrast to the evoked BAP-Ca²⁺s, the spontaneous SPW-induced Ca²⁺ influx had only a small distance-dependent decrement. Our results suggest that similarly to nicotinic acetylcholine receptor activation, synaptic activity during hippocampal SPWs increases AP backpropagation into distant dendritic segments. Bath application of Nimodipine, a specific Ca²⁺ channel blocker and tetrodotoxine decreased the amplitude of the somatically evoked Ca²⁺ influx, which suggests that L-type Ca²⁺ channels play an important role both during somatically evoked and SPW-induced BAPs.     

Do deep tree roots provide nutrients to the tropical rainforest?

The contribution of deep tree roots to the nutrition of a tropicalrainforest were studied along an edaphic transect in French Guyana. Soil typeswere mapped in relation to the texture of the upper horizons and the depth ofoccurrence of the loamy saprolite. The position of mature individuals of fourcommon species, differing by they rooting depth, was identified and tree leaveswere analysed for major nutrients and strontium (Sr) isotopic ratios.On average, the range of leaf isotopic ratio (⁸⁷Sr/⁸⁶Sr= 0.714–0.716) was narrow compared to that of bulk soils(⁸⁷Sr/⁸⁶Sr = 0.72–0.77). Steep gradients ofincreasing ⁸⁷Sr/⁸⁶Sr in roots with soil depth were foundin all investigated profiles, which indicated that the flux of Sr deposited inrain and leached from the litter layer was tightly retained in the upper soillayers. Over the whole of the site, as well as within each soil unit, tree⁸⁷Sr/⁸⁶Sr ratios were very similar whatever the species,and close to litter and near-surface roots ⁸⁷Sr/⁸⁶Srratios, suggesting no or very little Sr contribution from deep tree roots.Variations of Ca and Sr concentrations in leaves were strongly correlated butnot with leaf ⁸⁷Sr/⁸⁶Sr ratios. These results support thetheory that Sr and Ca uptake and cycling are mostly superficial in tropicalrainforests.     

Functional validation of a novel isoform of Na+/H+ antiporter from Pennisetum glaucum for enhancing salinity tolerance in rice

Salt stress is an environmental factor that severely impairs plant growth and productivity. We have cloned a novel isoform of a vacuolar Na⁺/H⁺ antiporter from Pennisetum glaucum (PgNHX1) that contains 5 transmembrane domains in contrast to AtNHX1 and OsNHX1 which have 9 transmembrane domains. Recently we have shown that PgNHX1 could confer high level of salinity tolerance when overexpressed in Brassica juncea. Here, we report the functional validation of this antiporter in crop plant rice. Overexpression of PgNHX1 conferred high level of salinity tolerance in rice. Transgenic rice plants overexpressing PgNHX1 developed more extensive root system and completed their life cycle by setting flowers and seeds in the presence of 150 mM NaCl. Our data demonstrate the potential of PgNHX1 for imparting enhanced salt tolerance capabilities to salt-sensitive crop plants for growing in high saline areas.     

Increased calcium in carrots by expression of an Arabidopsis H+/Ca2+ transporter

We demonstrate that carrots expressing the Arabidopsis H⁺/Ca²⁺ transporter CAX1 (Cation Exchanger 1) contained up to 50% more calcium (Ca) than plants transformed with control vectors. The CAX1-expressing carrots were fertile, and robust plant growth was seen in the majority of the transgenic plants. CAX1-expressing carrots were crossed to a commercial carrot variety to confirm that the increased Ca accumulation was mediated by CAX1-expression, and the increased Ca content was clearly correlated with the transgene. This study suggests that modulation of ion transporters could be an important means of increasing the Ca content of agriculturally important crops. To our knowledge, this study represents the first attempts to use biotechnology to increase the Ca content of an agriculturally important crop.