Halophytes are plants which naturally survive in saline environment. They account for ∼1% of the total flora of the world. They include both dicots and monocots and are distributed mainly in arid, semi-arid inlands and saline wet lands along the tropical and sub-tropical coasts. Salinity tolerance in halophytes depends on a set of ecological and physiological characteristics that allow them to grow and flourish in high saline conditions. The ability of halophytes to tolerate high salt is determined by the effective coordination between various physiological processes, metabolic pathways and protein or gene networks responsible for delivering salinity tolerance. The salinity responsive proteins belong to diverse functional classes such as photosynthesis, redox homeostasis; stress/defense, carbohydrate and energy metabolism, protein metabolism, signal transduction and membrane transport. The important metabolites which are involved in salt tolerance of halophytes are proline and proline analog (4-hydroxy-N-methyl proline), glycine betaine, pinitol, myo-inositol, mannitol, sorbitol, O-methylmucoinositol, and polyamines. In halophytes, the synthesis of specific proteins and osmotically active metabolites control ion and water flux and support scavenging of oxygen radicals under salt stress condition. The present review summarizes the salt tolerance mechanisms of halophytes by elucidating the recent studies that have focused on proteomic, metabolomic, and ionomic aspects of various halophytes in response to salinity. By integrating the information from halophytes and its comparison with glycophytes could give an overview of salt tolerance mechanisms in halophytes, thus laying down the pavement for development of salt tolerant crop plants through genetic modification and effective breeding strategies.

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Metal homoenolates are characterized by the juxtaposition of an organometallic species b to a carbonyl group. These bifunctional reagents require a delicate balance between stability and reactivity for applications in C À C bond formations. A particularly useful class of homoenolates is zinc homoenolates. It is not surprising that known zinc and related metal homoenolates are limited primarily to those bearing weakly electrophilic esters, amides, and nitriles. [1,2] In contrast, little is known about zinc homoenolates of ketones and aldehydes because of the known proclivity of metal homoenolates to cyclize into the corresponding cyclopropoxides. [3] An attractive synthesis of cyclopropanols by treatment of a,bepoxy ketones with CH 2 (ZnI) 2 indeed corroborates facile cyclization of zinc keto homoenolates to the corresponding cyclopropoxides.[4] Nonetheless, we hypothesized that subsequent transmetalation with a suitable metal could shift the otherwise unfavorable equilibrium to generate b-keto homoenolates for subsequent elaboration [Eq. (1); M = metal]. As part of research programs on synthetic applications of the Kulinkovich cyclopropanation, [5,6] we report herein the preparation and in situ S N 2' alkylation of mixed zinc/copper keto homoenolates.Treatment of cyclopropanol with diethylzinc should result in formation of the zinc alkoxide A and ethane (Scheme 1). A could be in equilibrium with the homoenolate B, where the former is expected to be strongly favored. In situ trapping of B by transmetalation could afford D for subsequent reactions.

A convenient method for preparing attractively functionalized 1,4-diketones has been devised by palladium-catalyzed cross-coupling of cyclopropanols and acyl chlorides. The utility of this method has been demonstrated in an enantioselective synthesis of (+)-myrmicarin 217.

Prolonged benzodiazepine treatment leads to tolerance and increases the risk of dependence. Flurazepam (FZP) withdrawal is associated with increased anxiety correlated with increased AMPAR-mediated synaptic function and AMPAR binding in CA1 pyramidal neurons. Enhanced AMPAR synaptic strength is also associated with a shift toward inward rectification of synaptic currents and increased expression of GluR1, but not GluR2 subunits, suggesting augmented membrane incorporation of GluR1-containing, GluR2-lacking AMPARs. To test this hypothesis, the postsynaptic incorporation of GluR1 and GluR2 subunits in CA1 neurons after FZP withdrawal was examined using postembedding immunogold quantitative electron microscopy. The percentage of GluR1 positively-labeled stratum radiatum (SR) synapses was significantly increased in FZP-withdrawn rats (88.2 ± 2.2%) compared to controls (74.4 ± 1.9%). In addition, GluR1 immunogold density was significantly increased by 30% in SR synapses in CA1 neurons from FZP-withdrawn rats compared to control rats (FZP: 14.1 ± 0.3 gold particles/μm; CON: 10.8 ± 0.4 gold particles/μm). In contrast, GluR2 immunogold density was not significantly different between groups. Taken together with recent functional data from our laboratory, the current study suggests that the enhanced glutamatergic strength at CA1 neuron synapses during benzodiazepine withdrawal is mediated by increased incorporation of GluR1-containing AMPARs. Mechanisms underlying synaptic plasticity in this model of drug dependence are therefore fundamentally similar to those that operate during activity-dependent plasticity.

Lu S, Das P, Fadool DA, Kaczmarek LK. The Slack sodium-activated potassium channel provides a major outward current in olfactory neurons of Kv1.3Ϫ/Ϫ super-smeller mice.

Previously, we reported that the GABA A receptor antagonist picrotoxin also antagonizes serotonin (5-HT) 3 receptors and that its effects are subunit-dependent. Here, we sought to identify amino acids involved in picrotoxin inhibition of 5-HT 3 receptors. Mutation of serine to alanine at the transmembrane domain 2 (TM2) 2Ј position did not affect picrotoxin (PTX) sensitivity in murine 5-HT 3A receptors. However, mutation of the 6Ј TM2 threonine to phenylalanine dramatically reduced PTX sensitivity. Mutation of 6Ј asparagine to threonine in the 5-HT 3B subunit enhanced PTX sensitivity in heteromeric 5-HT 3A/3B receptors. Introduction of serine (native to the human 3B subunit) at the 6Ј position also increased PTX sensitivity, suggesting a species-specific effect. Mutation of the 7Ј leucine to threonine in 5-HT 3A receptors increased PTX sensitivity roughly 10-fold, comparable with that observed in GABA A receptors, and also conferred distinct gating kinetics. The equivalent mutation in the 3B subunit (i.e., 7Ј valine to threonine) had no impact on PTX sensitivity in 5-HT 3A/3B receptors. Interestingly,, a high-affinity ligand to the convulsant site in GABA A receptors, did not exhibit specific binding in 5-HT 3A receptors. The structurally related compound, tert-butylbicyclophosphorothionate (TBPS), which potently inhibits GABA A receptors, did not inhibit 5-HT 3 currents. Our results indicate that the TM2 6Ј residue is a common determinant of PTX inhibition of both 5-HT 3 and GABA A receptors and demonstrate a role of the 7Ј residue in PTX inhibition. However, lack of effects of EBOB and TBPS in 5-HT 3A receptors suggests that the functional domains in the two receptors are not equivalent and underscores the complexity of PTX modulation of LGICs.The 5-hydroxytryptamine type 3 (5-HT 3 ) receptor is a member of the cys-loop superfamily of ligand-gated ion channels (LGICs) that includes nicotinic acetylcholine receptors, GABA A , GABA c , glycine receptors, and invertebrate glutamate-gated chloride channels (Reeves et al., 2001;Karlin, 2002). 5-HT 3 receptor antagonists are useful as antiemetics in chemotherapy-induced emesis and in irritable bowel syndrome. They also may have utility in treatment of neuropsychiatric diseases such as anxiety and drug dependence and in management of pain (Costall and Naylor, 2004).The 5-HT 3A subunit was identified initially and shown to form functional homomeric receptors (Maricq et al., 1991). A second subunit (5-HT 3B ) was subsequently cloned and characterized (Davies et al., 1999). The 5-HT 3B subunit is incapable of forming functional homomeric cell surface receptors because it is retained in the endoplasmic reticulum in the absence of the 3A subunit (Boyd et al., 2003). However, coexpression of 5-HT 3B with the 5-HT 3A subunit results in a heteromeric receptor with distinct biophysical properties (Davies et al., 1999). Recently, three additional putative 5-HT 3 subunits, 5-HT 3C , 3D , and 3E have been cloned (Niesler et al., 2003). The pharmacological and functional ...

The central nervous system convulsant picrotoxin (PTX) inhibits GABA A and glutamate-gated Cl ؊ channels in a use-facilitated fashion, whereas PTX inhibition of glycine and GABA C receptors displays little or no use-facilitated block. We have identified a residue in the extracellular aspect of the second transmembrane domain that converted picrotoxin inhibition of glycine ␣1 receptors from non-use-facilitated to usefacilitated. In wild type ␣1 receptors, PTX inhibited glycine-gated Cl ؊ current in a competitive manner and had equivalent effects on peak and steady-state currents, confirming a lack of use-facilitated block. Mutation of the second transmembrane domain 15-serine to glutamine (␣1(S15Q) receptors) converted the mechanism of PTX blockade from competitive to non-competitive. However, more notable was the fact that in ␣1(S15Q) receptors, PTX had insignificant effects on peak current amplitude and dramatically enhanced current decay kinetics. Similar results were found in ␣1(S15N) receptors. The reciprocal mutation in the ␤2 subunit of ␣1␤2 GABA A receptors (␣1␤2(N15S) receptors) decreased the magnitude of use-facilitated PTX inhibition. Our results implicate a specific amino acid at the extracellular aspect of the ion channel in determining use-facilitated characteristics of picrotoxin blockade. Moreover, the data are consistent with the suggestion that picrotoxin may interact with two domains in ligand-gated anion channels.Glycine receptors belong to a superfamily of ligand-gated chloride channels that include GABA A 1 receptors, GABA C receptors, and glutamate-gated chloride channels (1). In native tissue, glycine receptors exist as either ␣ homomers or ␣␤ heteromers (1). They comprise five subunits (usually three ␣ subunits and two ␤ subunits) arranged asymmetrically around the ion pore. Each subunit is made up of a large extracellular N-terminal region, four transmembrane domains (TM), and a large cytoplasmic domain; TMII forms the channel lumen (2). Glycine receptors are targets of therapeutics such as anesthetics as well as toxins like the central nervous system convulsant picrotoxin (1).Picrotoxin inhibits all known anionic ligand-gated Cl Ϫ channels (3-5). The mechanism of action and the exact location of picrotoxin binding are still unknown (6 -12). However, several studies have indicated that TMII is the probable site for picrotoxin action (6, 13-22) (Fig. 1). For example, the TMII of the glycine ␤ subunit was found to be responsible for conferring resistance to picrotoxin in heteromeric glycine ␣ n ␤ receptors (n ϭ 1-3) (6). Subsequent work has defined the existence of a phenylalanine residue at the 6Ј position of the TMII glycine ␤ subunit in conferring insensitivity to picrotoxin (16). In addition, other TMII residues (2Ј and 19Ј) have also been implicated directly or indirectly in the mechanism by which picrotoxin inhibits these channels (13, 15,16). The mutations at positions 2Ј and 19Ј have been shown to affect the type of the inhibition (competitive versus non-competitive) by picrotoxin ...