Morphology of the unusual polyad in Amazonian Parkia legume trees

Key message

An unusual polyad occurs in three Parkia species, named cavitate polyad. It has an internal central space full of lipoprotein substances, contacting all pollen grains, probably aiding pollen germination.

Abstract

This study details the unusual morphology of polyads of three species of Parkia (P. multijuga Benth., P. ulei (Harms) Kuhlm., and P. pendula (Willd.) Benth. ex Walp.) and suggests functions for polyad adaptive traits that are linked to the reproductive success of the species. Polyads within the anthers of the three Parkia species were analysed by surface (scanning electron microscopy) and anatomical (light microscopy) studies. Ultrastructure and development studies were carried out for P. pendula polyads. Polyads are globose and cavitated, i.e., exhibit an internal cavity that varies in size, being more conspicuous in P. ulei and P. pendula. Other differences among species are related to the polyad size, exine ornamentation and the type of substances stored in the pollen grain. The polyad internal cavity is filled with an exudate that may be related to the pollen germination through the internal pores and/or translocation of substances from the anther loculus to the inside or vice versa. This inference is supported by the following observations: the spaces between the pollen grains in a polyad are also filled with the exudate, and the exudate inside the polyad is similar to the anther locular fluid. The morphology and substances stored within the pollen grains of Parkia polyads seem to be more related to polyad functionality and physiology than to the selective pressures exerted by different pollinators on the group.     

Pig reticulocytes. V. Development of Rb+ influx during in vitro maturation

Influx of the K⁺ analogue Rb⁺ was measured through the ouabain-sensitive Na⁺/K⁺ pump and the ouabain-insensitive “leak” pathways in Cl^? or NO in mature red cells from adult pigs and in reticulocytes naturally occurring in 7-day-old piglets. In reticulocytes, Rb⁺ influxes by the two pathways were of about equal magnitude in Cl^? (13 and 10 mmoles/liter cells × hr) and at least 25-fold larger than in mature red cells (0.5 and 0.4 mmoles/liter cells × hr). In Na ⁺ media, a portion of the ouabain-insensitive “leak” flux of Rb⁺ was Cl^? dependent (Rb⁺Cl^? transport) as NO replacement reduced Rb⁺ influx by 90% in reticulocytes and by 40% in mature red cells. The sulfhydryl reagent N-ethylmaleimide (NEM) stimulated Rb⁺Cl^? transport about twofold in reticulocytes and up to 13-fold in mature red cells. When reticulocytes matured to erythrocytes during in vitro incubation, about 90% of both ouabain-sensitive Rb⁺ pump and ouabain-insensitive Rb⁺Cl^? influx were lost. In contrast, the NEM-stimulated Rb⁺Cl^? transport changed much less throughout this period, suggesting an entity operationally but not necessarily structrually distinct from the basal Rb⁺Cl^? transport. Although the experimental variability precluded a full assessment of significant changes in the small Na⁺/K⁺(Rb⁺) pump and Rb⁺Cl^? fluxes in mature pig red cells kept for the same time period in vitro, Rb⁺ flux changes in reticulocytes appear to be maturational in nature, reflecting parallel activity transitions of Na⁺/K⁺ pump and Cl^?-dependent K⁺ fluxes in vivo.     

DFT study of geometrical and vibrational features of a 3′,5′-deoxydisugar-monophosphate (dDSMP) DNA model in the presence of counterions and solvent

The B3LYP/6–31++G* theoretical level was used to study the influence of various hexahydrated monovalent (Li⁺, Na⁺, K⁺) and divalent (Mg²⁺) metal counterions in interaction with the charged PO₂^? group, on the geometrical and vibrational characteristics of the DNA fragments of 3′,5′-dDSMP, represented by four conformers (g⁺g⁺, g⁺t, g^?g^? and g^?t). All complexes were optimized through two solvation models [the explicit model (6H₂O) and the hybrid model (6H₂O/Continuum)]. The results obtained established that, in the hybrid model, counterions (Li⁺, Na⁺, K⁺, Mg²⁺) always remain in the bisector plane of the O1–P–O2 angle. When these counterions are explicitly hydrated, the smallest counterions (Li⁺, Na⁺) deviate from the bisector plane, while the largest counterions (K⁺ and Mg²⁺) always remain in the same plane. On the other hand, the present calculations reveal that the g⁺g⁺ conformer is the most stable in the presence of monovalent counterions, while conformers g⁺t and g^?t are the most stable in the presence of the divalent counterion Mg²⁺. Finally, the hybrid solvation model seems to be in better agreement with the available crystallographic and spectroscopic (Raman) experiments than the explicit model. Indeed, the six conformational torsions of the C4′-C3′-O3′-PO^?₂-O5′-C5′-C4′ segment of all complexes of the g^?g^? conformer in 6H₂O/Continuum remain similar to the available experimental data of A- and B-DNA forms. The calculated wavenumbers of the g⁺g⁺ conformer in the presence of the monovalent counterion and of g^?t conformer in presence of the divalent counterion in the hybrid model are in good agreement with the Raman experimental data of A- and B-DNA forms. In addition, the maximum deviation between the calculated wavenumbers in the 6H₂O/Continuum for the g⁺g⁺ conformer and experimental value measured in an aqueous solution of the DMP-Na⁺ complex, is <1.07% for the PO₂^? (asymmetric and symmetric) stretching modes and <2.03% for the O5′-C5′ and O3′-C3′ stretching modes.

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Graphical abstract dDSMP-(OO)^? Mg²⁺/6W/Continuum

     

Inorganic polyphosphates and heavy metal resistance in microorganisms

The mechanisms of heavy metal resistance in microbial cells involve multiple pathways. They include the formation of complexes with specific proteins and other compounds, the excretion from the cells via plasma membrane transporters in case of procaryotes, and the compartmentalization of toxic ions in vacuoles, cell wall and other organelles in case of eukaryotes. The relationship between heavy metal tolerance and inorganic polyphosphate metabolism was demonstrated both in prokaryotic and eukaryotic microorganisms. Polyphosphates, being polyanions, are involved in detoxification of heavy metals through complex formation and compartmentalization. The bacteria and fungi cultivated in the presence of some heavy metal cations contain the enhanced levels of polyphosphate. In bacteria, polyphosphate sequesters heavy metals; some of metal cations stimulate an exopolyphosphatase activity, which releases phosphate from polyphosphates, and MeHPO₄^? ions are then transported out of the cells. In fungi, the overcoming of heavy metal stresses is associated with the accumulation of polyphosphates in cytoplasmic inclusions, vacuoles and cell wall and the formation of cation/polyphosphate complexes. The effects of knockout mutations and overexpression of the genes encoding polyphosphate-metabolizing enzymes on heavy metal resistance are discussed.

Graphical abstract

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An insight into hydration structure of sodium glycinate from <Emphasis Type="Italic">ab initio</Emphasis> quantum chemical study

The hydration structure of sodium glycinate (Na⁺GL^?) is probed by the Monte-Carlo multiple minimum (MCMM) method combined with quantum mechanical (QM) calculations at the MP2/6-311++G(d,p) level. In the gas phase, the energy of [Na⁺GL^?]_β is more than 30 kJ mol^?1 higher than [Na⁺GL^?]_α. With higher degrees of hydration, our results indicate that the most stable conformers of [Na⁺GL^?]?(H₂O)₈ were derived from [Na⁺GL^?]_β instead of [Na⁺GL^?]_α. The stable conformers determined by the conductor-like polarizable continuum model (CPCM) also show that [Na⁺GL^?]_β is more stable than [Na⁺GL^?]_α in the liquid phase. By analyzing the hydration process, water…water hydrogen bonding interaction will be more preferable than ion…water interaction as the number of water molecules increases. According to the electronic density at the bond critical point on the Na-X bonds (X?=?O1, O2, N) in the low-energy conformers, Na⁺GL^? will be dissociated as Na⁺ and GL^? in the bulk water, which is not predicted by the CPCM model. The structure features and the charge redistribution of Na⁺GL^? will provide a physical explanation for the weakening Na-O1 interaction.

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Graphical Abstract Hydration structure of sodium glycinate from ab initio quantum chemical study

     

Relative contribution of AtHAK5 and AtAKT1 to K+ uptake in the high‐affinity range of concentrations

The relative contribution of the high‐affinity K⁺ transporter AtHAK5 and the inward rectifier K⁺ channel AtAKT1 to K⁺ uptake in the high‐affinity range of concentrations was studied in Arabidopsis thaliana ecotype Columbia (Col‐0). The results obtained with wild‐type lines, with T‐DNA insertion in both genes and specific uptake inhibitors, show that AtHAK5 and AtAKT1 mediate the ‐sensitive and the Ba²⁺‐sensitive components of uptake, respectively, and that they are the two major contributors to uptake in the high‐affinity range of Rb⁺ concentrations. Using Rb⁺ as a K⁺ analogue, it was shown that AtHAK5 mediates absorption at lower Rb⁺ concentrations than AtAKT1 and depletes external Rb⁺ to values around 1 μM. Factors such as the presence of K⁺ or during plant growth determine the relative contribution of each system. The presence of in the growth solution inhibits the induction of AtHAK5 by K⁺ starvation. In K⁺‐starved plants grown without , both systems are operative, but when is present in the growth solution, AtAKT1 is probably the only system mediating Rb⁺ absorption, and the capacity of the roots to deplete Rb⁺ is reduced.     

Combined cryo- and thin sectioning (TEM) in the elucidation of mimosoid tetrad/polyad ultrastructure

Cryosections (freeze-sections) of tetrads/polyads and their subsequent examination in the SEM complement traditional methods (LM, SEM, and TEM) by providing both a dynamic three-dimensional overview of polyad morphology and clarifying aperture morphology, internal wall characters and tetrad/polyad cohesion mechanisms. Cryosections of Dinizia tetrads reveal that cohesion is maintained through adhesion/fusion of the apices of clavate elements in localized regions of the subproximal and proximal walls — a feature not discernible using traditional SEM preparations. Cryosections of the globose 20-grained polyads of Parkia species reveal small central grains and triradiate-shaped proximal apertures — features unobservable or misinterpreted using traditional LM, SEM and TEM methods. In Anadenathera polyads, cryosections have clarified the nature and distribution of small gaps present in the lateral and proximal walls of individual grains.     

Glycoprotein effect on the osmotic permeability of liposomes

• 1.1. Proteoliposomes with incorporated α₁-acid glycoprotein were found to be osmotically sensitive to alkali metal salts.
• 2.2. The apparent permeabilities of monovalent metal cations were determined. They were compared with those of pure liposomes in the presence of amphoterecin B.
• 3.3. It was found that proteoliposomes showed a selective permeability to K⁺ in spite of the fact that pure liposomes in the presence of amphotericin B are more permeable to Rb⁺.
• 4.4. It was assumed that this difference arises apparently from the modification of lecithin bilayer in the presence of glycoprotein molecule.

     

The protonated 2-halogenated imidazolium cation as the noncovalent interaction donor: the σ-hole and π-hole interactions

The σ-hole and π-hole of the protonated 2-halogenated imidazolium cation (XC₃H₄N₂ ⁺; X = F, Cl, Br, I) were investigated and analyzed. The monomers of (CH₃)₃SiY(Y=F, Cl, Br, I), considered as the Lewis base, were combined with the σ-hole and π-hole of XC₃H₄N₂ ⁺ to form the σ-hole and π-hole interactions in the bimolecular complexes (CH₃)₃SiY?·?·?·?XC₃H₄N₂ ⁺ and (CH₃)₃SiY?·?·?·?C₃(X)H₄N₂ ⁺(X/Y=F, Cl, Br, I), respectively. For both the σ-hole and π-hole interactions, the equilibrium geometries of complexes show regular changes according to the sequence of heavy sequence of the noncovalent interaction acceptors and donors. The electrostatic energy is the main contribution in the formation of both kinds of interactions, it has linear relations with the V _S,max values of σ-hole and the V′ _S,max values of π-hole. Both the σ-hole and π-hole interactions belong to the closed-shell and noncovalent interactions. The π-hole interactions are stronger than the σ-hole interactions. For the π-hole interactions, the contribution percents of the dispersion energies are somewhat greater than those of the σ-hole interactions, while it is contrary for the polarization energy.

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Graphical Abstract The protonated 2-halogenated imidazolium cation as the noncovalent interaction donor: the σ-hole and π-hole interactions?

     

Nigericin forms highly stable complexes with lithium and cesium

Nigericin is a monocarboxylic polyether molecule described as a mobile K⁺ ionophore unable to transport Li⁺ and Cs⁺ across natural or artificial membranes. This paper shows that the ion carrier molecule forms complexes of equivalent energy demands with Li⁺, Cs⁺, Na⁺, Rb⁺, and K⁺. This is in accordance with the similar values of the complex stability constants obtained from nigericin with the five alkali metal cations assayed. On the other hand, nigericinalkali metal cation binding isotherms show faster rates for Li⁺ and Cs⁺ than for Na⁺, K⁺, and Rb⁺, in conditions where the carboxylic proton does not dissociate. Furthermore, proton NMR spectra of nigericin-Li⁺ and nigericin-Cs⁺ complexes show wide broadenings, suggesting strong cation interaction with the ionophore; in contrast, the complexes with Na⁺, K⁺, and Rb⁺ show only clear-cut chemical shifts. These latter results support the view that nigericin forms highly stable complexes with Li⁺ and Cs⁺ and contribute to the explanation for the inability of this ionophore to transport the former cations in conditions where it catalyzes a fast transport of K⁺>Rb⁺>Na⁺.Part of the results of this paper were presented at the 14th International Congress of Biochemistry in Prague, Czechoslovakia.     

Can the positive aromatic ring be as ��-electron donor in ��-halogen bond? A MP2 theoretical investigation on the unusual ��-halogen bond interaction between three-membered ring \left( {\hbox{BNN}} \right)_3^{+} and X1X2 (X1, X2?=?F, Cl, Br)

The unusual ??-halogen bond interactions are investigated between $ \left( {\hbox{BNN}} \right)_3^{+} $ and X1X2 (X1, X2?=?F, Cl, Br) employing MP2 at 6-311?+?G(2d) and aug-cc-pVDZ levels according to the ??CP (counterpoise) corrected potential energy surface (PES)?? method. The order of the ??-halogen bond interactions and stabilities of the complexes are obtained to be $ \left( {\hbox{BNN}} \right)_3^{+} \ldots {{\hbox{F}}_2} < \left( {\hbox{BNN}} \right)_3^{+} \ldots {\hbox{ClF < }}\left( {\hbox{BNN}} \right)_3^{+} \ldots {\hbox{C}}{{\hbox{l}}_2} < \left( {\hbox{BNN}} \right)_3^{+} \ldots {\hbox{BrCl}}\quad { < }\quad \left( {\hbox{BNN}} \right)_3^{+} \ldots {\hbox{B}}{{\hbox{r}}_2}\quad { < }\quad \left( {\hbox{BNN}} \right)_3^{+} \ldots {\hbox{BrF}}{.} $ at MP2/aug-cc-pVDZ level. The analyses of the Mulliken charge transfer, natural bond orbital (NBO), atoms in molecules (AIM) theory and electron density shifts reveal that the nature of the ??-halogen bond interaction in the complexes of ClF, BrF and BrCl might partly be charge transfer from the delocalized ??-HOMO orbital of $ \left( {\hbox{BNN}} \right)_3^{+} $ to X1X2. This result suggests that the positive aromatic ring $ \left( {\hbox{BNN}} \right)_3^{+} $ might act as a ??-electron donor to form the ??-halogen bond.

The hydrolysis of α-amino-acid esters in mixed ligand complexes with copper(II)-iminodiacetate

α-Amino-acid esters (EH⁺) interact with [Cu(IMDA)]° to give mixed ligand complexes according to the equilibrium,

where EH⁺ represents the protonated ester ⁺NH₃CH(R)CO₂R′ and IMDA^2? is HN(CH₂CO_2^?)₂. The mixed ligand complexes are only formed over a rather narrow pH range (ca. pH 5.8–6.5). At higher pH there is kinetic evidence for the competing equilibrium,

Rate constants k_OH have been obtained by pH-stat for the hydrolyses [where A^? = NH₂CH(R)CO_2^?]

The complexed α-amino-acid esters undergo base hydrolysis ca. 10⁴ times faster than the free esters E. Values of k_OH show little dependence on the nature of the alkyl substituent R but the normal leaving group effect of methyl esters hydrolyzing at ca. twice the rate of ethyl esters is observed. Activation parameters have been determined for base hydrolysis of [Cu(IMDA)(glyOMe)]°, and possible mechanisms for the reaction are considered.     

Kinetic mechanism of Na+, K+, Cl−-cotransport as studied by Rb+ influx into HeLa cells: Effects of extracellular monovalent ions

Summary Ouabain-insensitive, furosemide-sensitive Rb⁺ influx (J _Rb) into HeLa cells was examined as functions of the extracellular Rb⁺, Na⁺ and Cl^– concentrations. Rate equations and kinetic parameters, including the apparent maximumJ _Rb, the apparent values ofK _m for the three ions and the apparentK _i for K⁺, were derived. Results suggested that one unit molecule of this transport system has one Na⁺, one K⁺ and two Cl^– sites with different affinities, one of the Cl^– sites related with binding of Na⁺, and the other with binding of K⁺(Rb⁺). A 11 stoichiometry was demonstrated between ouabain-insensitive, furosemidesensitive influxes of²²Na⁺ and Rb⁺, and a 12 stoichiometry between those of Rb⁺ and³⁶Cl^–. The influx of either one of these ions was inhibited in the absence of any one of the other two ions. Monovalent anions such as nitrate, acetate, thiocyanate and lactate as substitutes for Cl^– inhibited ouabain-insensitive Rb⁺ influx, whereas sulfamate and probably also gluconate did not inhibitJ _Rb. From the present results, a general model and a specialized cotransport model were proposed: 1) In HeLa cells, one Na⁺ and one Cl^– bind concurrently to their sites and then one K⁺ (Rb⁺) and another Cl^– bind concurrently. 2) After completion of ion bindings Na⁺, K⁺(Rb^–) and Cl^– in a ratio of 112 show synchronous transmembrane movements.     

The comparative transport of K+ and Rb+ in normal and malignant rat tissuesin vivo and in liver slices,diaphragm, and tumor slicesin vitro

Summary The selectivity in the steady state uptakes of Rb⁺ and K⁺ has been studied in a number of normal and malignant rat tissues. The selectivity is minimal in erythrocytes and the two fastest-growing of four transplantable tumors, in which there is little discrimination between the two ions, and ranges upwards to a maximum Rb⁺ uptake in liver. In each tissue, the selectivity is independent of Rb⁺ concentration or of K⁺ deficiency (except in skeletal muscle). In liver slicesin vitro, reduction of energy metabolism by lowering the temperature or by the addition of metabolic inhibitors reduces the Rb⁺K⁺ discrimination proportionately much more than K⁺ transport. Diaphragm and slices of a transplantable tumor give similar results. With temperature reduction, there is a logarithmic relation between the Rb⁺K⁺ discrimination ratio and the respiration rate of liver slices. The results are quantitatively accounted for by simultaneous diffusion and metabolically coupled transport across a homogeneous membrane in which Rb⁺ transport is more closely coupled than that of K⁺ to a metabolic flux across the membrane. There is evidence that the tissue differences in Rb⁺K⁺ selectivity originate in the different levels of the coupling metabolic flux in different cell types and thus of the energy expenditure on ion transport. In contrast to the differences in steady state selectivity between Rb⁺ and K⁺, the initial ratio of uptakes of trace⁴³K and⁸⁶Rb, in otherwise steady state conditions, is close to unity in both liver and tumor slices, in agreement with theoretical calculations.     

Photobiomodulation Therapy Improves Acute Inflammatory Response in Mice: the Role of Cannabinoid Receptors/ATP-Sensitive K<Superscript>+</Superscript> Channel/p38-MAPK Signalling Pathway

Although photobiomodulation therapy (PBM) has been applied clinically for the treatment of pain and inflammation, wound healing, sports and soft tissue injuries, as well as to repair injured spinal cords and peripheral nerves, it remains unclear which molecular substrates (receptor) are implicated in the cellular mechanisms of PBM. Here, we reported that PBM (660 nm, 30 mW, 0.06 cm², 50 J/cm², plantar irradiation) significantly inhibited carrageenan-induced paw oedema, but not noxious thermal response, through positive modulation to both CB1 and CB2 cannabinoid receptors. The use of CB1 antagonist AM281 or CB2 antagonist AM630 significantly reversed the anti-inflammatory effect of PBM. Analysis of signalling pathway downstream of cannabinoid receptors activation reveals that anti-inflammatory effects of PBM depend, in great extent, on its ability to activate ATP-dependent K⁺ channels and p38 mitogen-activated protein kinase. Moreover, PBM therapy significantly reduced the levels of pro-inflammatory cytokine IL-6 in both paw and spinal cord, and restored the reduction of the level of anti-inflammatory cytokine IL-10 in spinal cord after carrageenan injection. Unlike the potent cannabinoid receptor agonist (WIN 55212-2), PBM did not exert any CNS-mediated effects in the tetrad assay. Finally, PBM does not reduce inflammation and noxious thermal response induced by LPS and zymosan, a TLR4 and TLR2/dectin-1 ligand, respectively. Thus, cannabinoid receptors and, possibly, the endocannabinoid system, represent an important site of action of PBM that opens the possibility of complementary and nonpsychotropic therapeutic interventions in clinical practice.

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Graphical Abstract ?

     

Synthesis of a series of first-row tris-imidazolylphosphine sandwich complexes and their potential for formation of polymetallic species

A series of tris-[2-(1-methylimidazolyl)phosphine] sandwich complexes with Co²⁺ (1), Ni²⁺ (2), Cu²⁺ (3) and Zn²⁺ (4) have been synthesized and characterized with the intent of using these complexes as templates for building polymetallic species. X-ray analysis reveals that each metal is six-coordinate with octahedral geometry. Compound 3 exhibits a tetragonal distortion resulting from a Jahn-Teller distortion of a Cu²⁺ (d⁹) complex. Electrochemistry of 1-4 displayed peaks assigned to both ligand-based oxidation at 1.45-1.56 V and a perchlorate-based reduction at −2.36 to −2.78 V versus FcH⁺/FcH. Metal-based reduction was also observed for 2, with a reversible Ni^2+/3+ oxidation at 0.89 V, consistent with the relatively poor donor ability of the imidazolyl nitrogen bases; and 3, with a irreversible Cu^2+/1+ reduction at −1.29 V versus FcH⁺/FcH, consistent with the decomposition of the complex upon reduction. X-ray structures indicate large steric crowding around the phosphorus atom resulting from the orientation of the methyl substituent on the imidazoles. This crowding may prohibit the formation of polymetallic species through phosphorus-metal bonding.     

Interaction of Cyclic Cytosine-, Guanine-, Thymine-, Uracil- and Mixed Guanine-Cytosine Base Tetrads with K+, Na+ and Li+ Ions—A Density Functional Study

Abstract

We have carried out B3LYP hybrid density functional studies of complexes formed by cyclic cytosine-, guanine-, thymine-, uracil- and mixed guanine cytosine-tetrads with Li⁺, Na⁺ and K⁺ ions to determine their structures and interaction energies. The conformations studied have been restricted to a hydrogen bond pattern closely related to the tetrads observed in experimental nucleic acid structures. A comparison of the alkali metal ion/tetrad complexes with the tetrads without cations indicates that alkali metal ions modulate the tetrad structures significantly and that even the hydrogen bond pattern may change. Guanine-tetrad cation complexes show the strongest interaction energy compared to other tetrads that occur less frequently in experimental structures. The most stable G-tetrad/metal ion structure adopts a nearly planar geometry that is especially suitable for tetraplex formation, which requires approximately parallel tetrad planes. In the cytosine-tetrad there is a very large central cavity suitable for cation recognition, but the complexes adopt a non-planar structure unsuitable for stacking, except possibly for ions with very large radii. Uracil and thymine tetrads show a significant different characteristics which may contribute to the differences between DNA and RNA.