Studies of the pyrolysis of tetraethylammonium tetrahydroborate

Tetraethylammonium tetrahydroborate, Et₄NBH₄, in suspension in refluxing decane-dodecane mixtures has been pyrolysed at temperatures between 175 and 190 °C. Et₃NBH₃, which is produced by partial decomposition of Et₄NBH₄, reacts with Et₄NBH₄ to give the intermediate Et₄NB₃H₈. Et₄NBH₄ and Et₃NBH₃ are also involved in the conversion of Et₄NB₃H_8. to (Et₄N)₂B₉H₉, (Et₄N)₂B₁₀H₁₀, Et₄NB₁₁H₁₄ and (Et₄N)₂B₁₂H₁₂ which are formed in varying proportions during the pyrolysis. A 1:1 Et₄NBH₄Et₃NBH₃ mixture gives the same mixture of final products in the same proportions as Et₄NBH₄ alone, but the reaction time is shorter.Results obtained under various conditions, for instance without solvent at 10⁻² torr (50% yield), are explained by the transfer of BH₃ groups occurring not only through Et₃NBH₃, but also by solid—solid reactions involving Et₄NBH₄. A more complete reaction of Et₃NBH₃ is obtained, giving quantitative yields, only when Et₃N is evacuated from the reaction mixture. Optimum conditions for the formation of each hydroborate are examined.     

Fluorescence excitation spectra of drought resistant and sensitive genotypes of triticale and maize

An influence of soil drought (7 or 14 d) and 7 d recovery on changes of leaf fluorescence excitation spectra at wavelengths of 450, 520, 690, and 740 nm (F₄₅₀, F₅₂₀, F₆₉₀, F₇₄₀) for drought resistant and sensitive genotypes of triticale and maize was compared. In non-stressed plants the differences between maize and triticale were observed for F₄₅₀ and F₅₂₀, but not for F₆₉₀ and F₇₄₀. Drought caused the increase in F₄₅₀, F₅₂₀, and F₆₉₀ and this increase was more distinct for drought sensitive genotypes. After re-hydration, chlorophyll fluorescence mostly recovered to values of control plants. Drought caused significant increase in F₆₉₀/F₇₄₀ but not in F₄₅₀/F₆₉₀ and F₄₅₀/F₅₂₀. For triticale, highest increase in F₆₉₀/F₇₄₀ was observed in the 4^th and 7^th leaves of resistant genotype and contrarily in maize for the sensitive one. After recovery, the F₄₅₀/F₅₂₀, F₄₅₀/F₆₉₀, and F₆₉₀/F₇₄₀ ratios mostly returned to values of control plants.     

Specificity of the interaction of DNA-platinum, amount of platinum, and pH measurement]

Interaction between the sodium salt of a DNA extracted from salmon sperm (41% GC) with [Pt(NH₃)₄]Cl₂, [Pt(NH₂? (CH₂)₂? NH? (CH₂)₂? NH₂Cl]Cl, cis-Pt(NH₂? (CH₂)₂? NH₂)Cl₂, cis-Pt(NH₃)₂Cl₂, trans-Pt(NH₃)₂Cl₂, K[Pt(C₂H₄)Cl₃], and K₂[PtCl₄) indicates at least three types of complexation. A correlation is found between the change of pH and the number of platinum atoms fixed per (AT + GC) unit. The first binding site is located on the G-C pairs (guanine–cytosine), most likely the N-7(G) site, as it was shown in a previous study of the guanosine-platinum salts. The fixation of the second platinum atom by the pair (AT + GC) takes place with liberation of protons. In the case of the complexes cis-Pt(NH₂? (CH₂)₂? NH₂)Cl₂, cis-Pt(NH₃)₂Cl₂, and trans-Pt(NH₃)₂Cl₂ the second interaction seems to involve simultaneously the N-7(A) and the N-1(G) and N-3(C) sites. This latter intercrosslink between guanine and cytosine obviously liberates protons and the decrease of pH is related in this case to the trans effect of the platinum compounds. The first two platinum atoms in the reaction of K₂PtCl₄] or the Zeise salt, K[Pt(C₂H₄)Cl₃] with DNA are fixed on the G-C pairs. A maximum of six platinum atoms per (AT + GC) unit were fixed in this case. Preliminary experiments with a DNA extracted from bacteria Micrococcus lysodeikticus (72% GC) give similar results.     

Modeling aspects of hydrodesulfurization by molybdenum hydride compounds: Desulfurization of thiophene and benzothiophene and C-S bond cleavage of dibenzothiophene

The molybdenum hydride complexes Mo(PMe₃)₅H₂ and Mo(PMe₃)₄H₄ are capable of cleaving the C-S bonds of thiophene, benzothiophene and dibenzothiophene. For example, Mo(PMe₃)₅H₂ reacts with thiophene to give the η⁵-thiophene and butadiene-thiolate complexes, (η⁵-C₄H₄S)Mo(PMe₃)₃ and (η⁵-C₄H₅S)Mo(PMe₃)₂(η²-CH₂PMe₂). These complexes are also obtained from the reaction between Mo(PMe₃)₄H₄ and thiophene under photochemical conditions, whereas at elevated temperatures thiophene is desulfurized to liberate but-1-ene. Similarly, Mo(PMe₃)₄H₄ desulfurizes benzothiophene at elevated temperatures to liberate ethylbenzene, while the arylthiolate complex Mo(PMe₃)₄(SC₆H₄Et)H₃ is obtained photochemically. Furthermore, Mo(PMe₃)₄H₄ cleaves the C-S bond of dibenzothiophene to give [η⁶,κ¹-C₆H₅C₆H₄S]Mo(PMe₃)₂H.     

Organic derivatives of aluminium. Part I. Reactions of alkanolamines with aluminium isopropoxide

Reactions of alkanolamines [R₁R₂NXOH; R₁ = H, CH₃, C₂H₅; R₂ = H, CH₃, C₂H₅ and X = -CH₂CH₂-, -CH₂CH₂CH₂-, -CH₂CHCH₃, -C₆H₄CH₂CH₂-] with aluminium isopropoxide in different molar ratios (1 to 3) yield compounds of the type Al(OPrⁱ)_3?n(OXNR₁R₂)_n, where ‘n’ can be 1, 2 and 3. Most of the derivatives are distillable liquids, soluble in common organic solvents and susceptible to hydrolysis even by atmospheric moisture. The new derivatives are characterized by elemental analysis, IR and ¹H NMR spectra. Molecular weight measurements of Al(OPrⁱ)_3?n(OXNR₁R₂)_n reveal them to be tetrameric in nature.     

Preparation of mono- or di-metal indenyl-iridium edrivatives and of tri-metal iridium-platinum complexes

Treatment of [IrCl(C₂H₄)₄] with K(C₉H₇) (C₉H₇ =indenyl) gives [Ir(C₂H₄)₂(η-C₉H₇)]. This compound is converted quantitatively into [Ir(CO)₂(η-C₉H₇)] by treatment with carbon monoxide. By reacting together these two iridium complexes [Ir₂(μ-CO)(CO)₂(ηC₉H₇)₂] has been obtained. The compound [Ir(CO)₂(η-C₉H₇)] reacts with [Pt(C₂H₄)₂{P(cyclo-C₆H₁₁)₃}] to give the complex [Ir₂Pt(CO)₃{P(cyclo-C₆H₁₁)₃}(η-C₉H₇)₂]. Protonation of the latter affords the salt [Ir₂Pt(μ-H)(CO)₃{P(cyclo-C₆H₁₁)₃}(μ-C₉H₇)₂] [BF₄]. The main features of the molecular structure of these complexes have been established by IR and NMR spectroscopy.     

Preparation of benzophenone imine complexes of transition metals

Benzophenone imine [M(η¹-NHCPh₂)(CO)_nP_5-n]BPh₄ [M = Mn, Re; n = 2, 3; P = P(OEt)₃, PPh(OEt)₂, PPh₂OEt, PPh₃] complexes were prepared by allowing triflate M(κ¹-OTf)(CO)_nP_5-n compounds to react with an excess of the imine. Hydride-imine [MH(η¹-NHCPh₂)P₄]BPh₄ (M = Ru, Os), triflate-imine [Os(κ¹-OTf)(η¹-NHCPh₂)P₄]BPh₄ and bis(imine) [Ru(η¹-NHCPh₂)₂P₄](BPh₄)₂ [P = P(OEt)₃] derivatives were also prepared. The complexes were characterized spectroscopically (IR, ¹H, ³¹P, ¹³C NMR) and a geometry in solution was also established. Hydride-benzophenone imine [IrHCl(η¹-NHCPh₂)L(PPh₃)₂]BPh₄and [IrHCl(η¹-NHCPh₂)L(AsPh₃)₂]BPh₄ [L = P(OEt)₃ and PPh(OEt)₂] complexes were prepared by reacting hydride IrHCl₂L(PPh₃)₂ and IrHCl₂L(AsPh₃)₂ precursors with an excess of imine. Dihydride IrH₂(η¹-NHCPh₂)(PPh₃)₃ complex was also obtained and a geometry in solution was proposed.     

Receptor of the serpentine-type and heterotrimeric G protein as targets of action of polylysine dendrimers

Molecular processes of the action of polycationic peptides that represent polylysine homo- and heterodendrimers on the functional activity of the biogenic amine- and peptide hormone-sensitive adenylyl cyclase signaling system (AC system) in rat myocardium and brains were studied. An intended use of these peptides is that of highly effective polymer carriers for biologically active substances. The polylysine homodendrimers of the third [(NH₂)₁₆(Lys)₈(Lys)₄(Lys)₂Lys-Ala-NH₂] (I), fourth [(NH₂)₃₂(Lys)₁₆(Lys)₈(Lys)₄(Lys)₂Lys-Ala-NH₂] (II), and fifth [(NH₂)₆₄(Lys)₃₂(Lys)₁₆(Lys)₈(Lys)₄(Lys)₂Lys-Ala-NH₂] (III) generations, as well as polylysine heterodendrimers of the fifth generation, [(NH₂)₆₄(Lys-Glu)₃₂(Lys-Glu)₁₆(Lys-Glu)₈(Lys-Glu)₄(Lys-Glu)₂Lys-Ala-Ala-Lys(ClAc)-Ala-NH₂] (IV), [(NH₂)₆₄(Lys-Ala)₃₂(Lys-Ala)₁₆(Lys-Ala)₈(Lys-Ala)₄(Lys-Ala)₂Lys-Ala-Lys(ClAc)-Ala-Ala-NH₂] (V) and [(NH₂)₆₄(Lys-Gly-Gly)₃₂(Lys-Gly-Gly)₁₆(Lys-Gly-Gly)₈(Lys-Gly-Gly)₄(Lys-Gly-Gly)₂Lys-Gly-Gly-Lys(ClAc)-Ala-Ala-NH₂] (VI), interact with the C-terminal regions of α subunits of the heterotrimeric G proteins, preferably of the inhibitor type, and stimulate its activity in respector-independent manner. The most effective G-protein activators were homodendrimers II and III and heterodendrimer V. The polylysine dendrimers disturbed the functional coupling of receptors of biogenic amines and peptide hormones with G_i proteins and, to a lesser extent, G_s proteins. This was manifested as a decrease in the regulatory effects of the hormones on AC activity and the GTP binding of the G protein, as well as by a decrease in the affinity of receptors to agonists in the presence of polylysine dendrimers, which is a consequence of the dissociation of the receptor-G protein complex. It has also been shown that, based on their molecular mechanisms and selectivity of action on G proteins, polylysine dendrimers are similar to mastoparan and melittin, which are natural toxins of insect venom.     

Characterization of ribonucleoprotein subparticles from 50 S ribosomal subunits of Escherichia coli.

Large ribonucleoprotein subparticles were recovered upon ribonuclease digestion of the 50 S ribosomal subunits of Escherichia coli, partially deproteinized by LiCl. Both their RNA and their protein compositions were analysed. The subunits, treated with LiCl at a concentration of 5.5 m, released an homogeneous subparticle containing proteins L₃, L₄, L₁₃, L₁₇, L₂₂ and L₂₉, about 70% of the 13 S fragment of 23 S RNA and about 50% of the 18 S one. Slightly larger species of subparticles were obtained from 50 S subunits treated with LiCl at concentrations between 3 m and 5 m; they contained in addition proteins L₂₀, L₂₁ and L₂₃ or L₂, L₁₄, L₂₀, L₂₁ and L₂₃ and a few small 23 S RNA fragments. No large subparticle was recovered from the 6 m-LiCl-treated 50 S subunits which contain only proteins L₃, L₁₃ and L₁₇. These LiCl subparticles were compared with those obtained from intact, unfolded and sodium doecyl sulphatetreated 50 S subunits.These studies reveal that in the presence of 0.10 m-magnesium acetate there is a very compact area within 50 S subunits consisting of proteins L₃, L₄, L₁₃, L₁₇, L₂₂ and L₂₉ and of about 60% of 23 S RNA; this area probably has an essential structural role. The results also show that 23 S RNA has a more folded conformation when within the 50 S subunit than when isolated, this conformation being stabilized by some of the 50 S proteins, in particular proteins L₄, L₂₂, L₂₀ and L₂₁. Finally these data permit a more definite localization of the primary and/or secondary binding sites of proteins L₂, L₃, L₄, L₁₄, L₁₇, L₂₀, L₂₁ and L₂₂ on 23 S RNA.     

Reduction of structural dimensionality through incorporation of auxiliary ligands in lanthanide tetracyanoplatinates

The synthesis of a series of lanthanide tetracyanoplatinates containing the auxiliary ligands 1,10′-phenanthroline (phen) or 2,2′-bipyridine (bpy) have been carried out by reaction of Ln³⁺ nitrate salts with phen or bpy and potassium tetracyanoplatinate in solvent systems containing dimethylsulfoxide and dimethylformamide. The use of these solvents has lead to the isolation of [{Ln(DMSO)₂(C₁₂H₈N₂)(H₂O)₃}₂Pt(CN)₄](Pt(CN)₄)₂·2C₁₂H₈N₂·4H₂O (Ln = Eu (Eu-1), Tb (Tb-1), Yb(Yb-1)), [Ln(DMF)₃(C₁₂H₈N₂)(H₂O)₂NO₃]Pt(CN)₄ (Ln = La (La-2), Eu (Eu-2), Tb (Tb-2)), and [Ln(DMF)₃(C₁₀H₈N₂)(H₂O)₂NO₃]Pt(CN)₄ (Ln = La (La-3), Sm (Sm-3), Eu (Eu-3), Tb (Tb-3)) in the form of single crystals. Single-crystal X-ray diffraction has been used to investigate their structural features. The use of DMSO versus DMF as the solvent results in markedly different structural features. Eu-1 contains [{Eu(DMSO)₂(C₁₂H₈N₂)(H₂O)₃}₂Pt(CN)₄]²⁺ complex cations where the two Eu³⁺ centers are linked by a trans-bridging Pt(CN)₄²⁻ anion to form a dimeric lanthanide complex cation. An additional uncoordinated Pt(CN)₄²⁻ anion balances charge. Eu-2 and Eu-3 consist of zero-dimensional salts with [Eu(DMF)₃(C₁₂H₈N₂)(H₂O)₂(NO₃)]²⁺ or [Eu(DMF)₃(C₁₀H₈N₂)(H₂O)₂(NO₃)]²⁺ complex cations, respectively, and only non-coordinated Pt(CN)₄²⁻ anions. Photoluminescence measurements illustrate that the Eu³⁺ and Tb³⁺ compounds for all three structure types display enhanced emission due to intramolecular energy transfer from the coordinated cyclic amines.     

Gibberellins in Embryo-Suspensor of Phaseolus coccineus Seeds at the Heart Stage of Embryo Development

Gibberellins (GAs) in suspensors and embryos of Phaseolus coccineus seeds at the heart stage of embryo development were analyzed by combined gas chromatography-mass spectrometry (GC-MS). From the suspensor four C₁₉-GAs, GA₁, GA₄, GA₅, GA₆, and one C₂₀ GA, GA₄₄, were identified. From the embryo, five C₁₉-GAs GA₁, GA₄, GA₅, GA₆, GA₆₀ and two C₂₀ GAs, GA₁₉ and GA₄₄ were identified. The data, in relation to previous results, suggest a dependence of the embryo on the suspensor during early stages of development.     

CD studies of double-stranded polydeoxynucleotides composed of repeating units of contiguous homopurine residues

Double-stranded synthetic polydeoxynucleotides of the general form poly[d(G_nC_n)] · poly[d(G_nC_n)], poly[d(G_nC)] · poly[d(GC_n)], and poly[d(A_nT_n)] · poly[d(A_nT_n)] have been synthesized. When n = 4 or larger, the CD spectra of polymers of the form poly[d(G_nC_n)] · poly[d(G_nC_n)] or poly[d(G_nC)] · poly[d(GC_n)] closely resemble the spectrum of poly[dG] · poly[dC], suggesting that a string of four continguous guanosine residues is sufficient to induce a conformation resembling that of the polypurine · polypyrimidine. With polymers of the form poly[d(A_nT_n)] · poly[d(A_nT_n)], however, the CD spectrum only gradually approaches that of poly[dA] · poly[dT].     

Slow relaxation of the magnetization in high-nuclearity Ln-complexes

By the surface modification strategy, a novel high-nuclearity lanthanide complex with a discrete structure, Er₂₆I(μ₃-OH)₂₀(μ₃-O)₆(NO₃)₉(IN)₃₃(OH)₃(H₂O)₃₃ (noted Er₂₆, HIN = isonicotinic acid), has been prepared under hydrothermal conditions. The magnetic properties of Er₂₆ and two analogue dysprosium assemblies Dy₃₀I(μ₃-OH)₂₄(μ₃-O)₆(NO₃)₉(IN)₄₁(OH)₃(H₂O)₃₈ (noted Dy₂₆-I) and Dy₂₆I(μ₃-OH)₂₀(μ₃-O)₆(NO₃)₉(IN)_31.25(OH)_4.75(H₂O)_41.75 (noted Dy₂₆-II) have been studied. The results show that the slow relaxation of the magnetization is newly found in Dy₂₆-I constructed from {Dy₂₆} and {Dy₄} cluster units. The {Dy₄} units in Dy₂₆-I, the relative orientation of the complex or the inter-molecular interactions between {Dy₂₆} cores might play an important role in the origin of this magnetic behavior.     

Spectroscopical identification of residues of subunit G of the yeast V-ATPase in its connection with subunit E

A critical point in the V₁ sector and entire V₁V_O complex is the interaction of stalk subunits G (Vma10p) and E (Vma4p). Previous work, using precipitation assays, has shown that both subunits form a complex. In this work, we have analysed the N-terminal segment of subunit G (G_1–59) of the V₁V_O ATPase from Saccharomyces cerevisiae by using nuclear magnetic resonance (NMR) spectroscopy. Analyses of ¹H-¹⁵N heteronuclear single quantum coherence (HSQC) spectra of G_1–59 in the absence and presence of the N-terminal peptides E_1–18 and E_18–38 as well as the produced and purified C-terminal segment (E_39–233) shows specific interactions only with the peptide fragment E_18–38. The binding of this peptide occurs via the residues M₁, V₂, S₃, and K₅ as well for V₂₂, S₂₃, K₂₄, A₂₅ and R₂₆ of G_1–59. The specific E_18–38/G_1–59 binding has been confirmed by fluorescence correlation spectroscopy data. The E_18–38 peptide has been studied by CD spectroscopy and NMR. The 3D structure of this peptide adopts a stable helix-hinge-helix formation in solution. A model structure of the E_18–38/G_1–59 complex reveals the orientation of E_18–38 relative to G_1–59 via salt-bridges of the polar residues and van der Waals forces at the very N-terminus of both segments.     

Torque Generation of Enterococcus hirae V-ATPase

V-ATPase (V_oV₁) converts the chemical free energy of ATP into an ion-motive force across the cell membrane via mechanical rotation. This energy conversion requires proper interactions between the rotor and stator in V_oV₁ for tight coupling among chemical reaction, torque generation, and ion transport. We developed an Escherichia coli expression system for Enterococcus hirae V_oV₁ (EhV_oV₁) and established a single-molecule rotation assay to measure the torque generated. Recombinant and native EhV_oV₁ exhibited almost identical dependence of ATP hydrolysis activity on sodium ion and ATP concentrations, indicating their functional equivalence. In a single-molecule rotation assay with a low load probe at high ATP concentration, EhV_oV₁ only showed the “clear” state without apparent backward steps, whereas EhV₁ showed two states, “clear” and “unclear.” Furthermore, EhV_oV₁ showed slower rotation than EhV₁ without the three distinct pauses separated by 120° that were observed in EhV₁. When using a large probe, EhV_oV₁ showed faster rotation than EhV₁, and the torque of EhV_oV₁ estimated from the continuous rotation was nearly double that of EhV₁. On the other hand, stepping torque of EhV₁ in the clear state was comparable with that of EhV_oV₁. These results indicate that rotor-stator interactions of the V_o moiety and/or sodium ion transport limit the rotation driven by the V₁ moiety, and the rotor-stator interactions in EhV_oV₁ are stabilized by two peripheral stalks to generate a larger torque than that of isolated EhV₁. However, the torque value was substantially lower than that of other rotary ATPases, implying the low energy conversion efficiency of EhV_oV₁.     

Characterisation of neuropeptides of the AKH/RPCH-family from corpora cardiaca of Coleoptera

Summary Extracts of corpora cardiaca from two members of the family Tenebrionidae,Zophobas rugipes andTenebrio molitor, from one member of the Chrysomelidae,Leptinotarsa decemlineata, and from three members of the Scarabaeidae,Pachnoda marginata, P. sinuata andMelolontha hippocastani, were assayed for adipokinetic and hypertrehalosaemic activity in acceptor locusts (Locusta migratoria) and cockroaches (Periplaneta americana), respectively. All corpus cardiacum material tested, except that from the cockchafer,M. hippocastani, gave positive bioassay results. Biological activities of corpus cardiacum extracts from all species investigated can be resolved on reversed-phase high performance liquid chromatography (RP-HPLC). Gland extracts from the two tenebrionid species each show a single peak of biological activity associated with a single peak of UV absorbance having an identical retention time in both species. The two biologically active fractions from the corpora cardiaca of the potato beetle,L. decemlineata, coelute with exogenous (synthetic) hypertrehalosaemic hormones I and II of the American cockroach. The two species of the genusPachnoda contain two active compounds in their glands; compound I of each species is more abundant and elutes just ahead of the (synthetic) hypertrehalosaemic hormone of the cockroachBlaberus discoidalis. The gland material ofM. hippocastani exhibits and absorbance peak with the same retention time as the major peak from thePachnoda-species; however, this peak material does not elicit biological activity in the assays used here. After fractionation by RP-HPLC the main biologically active compounds were subjected to amino acid analyses. All factors are peptidic and contain 8 amino acid residues. The peptides from the tenebrionid species have the amino acid residues Asx₍₂₎, Glx₍₁₎, Ser₍₁₎, Pro₍₁₎, Leu₍₁₎, Phe₍₁₎ and Trp_(i), whereas the main peptide from corpora cardiaca ofP. marginata contains the residues Asx₍₂₎, Glx₍₁₎, Ser₍₁₎, Pro₍₁₎, Tyr₍₁₎, Leu₍₁₎ and Trp₍₁₎. Amino acid composition analyses of the two active fractions fromL. decemlineata reveal the residues Asx₍₂₎, Glx₍₁₎, Ser₍₁₎, Pro₍₁₎, Val₍₁₎, Phe₍₁₎ and Trp₍₁₎ for compound I and Asx₍₁₎, Glx₍₁₎, Thr₍₂₎, Pro₍₁₎, Leu₍₁₎, Phe₍₁₎ and Trp₍₁₎ for compound II.     

Enhancement of BKCa channel activity induced by hydrogen peroxide: Involvement of lipid phosphatase activity of PTEN

Large-conductance calcium and voltage-dependent potassium (BK_Ca) channel is an important determinant of vascular tone. It is activated by hydrogen peroxide (H₂O₂) which occurs in various physiological and pathological processes. However, the regulation mechanism is not fully understood. In the present study, the mSlo in the presence or absence of hβ1 were cotransfected with the PTEN_wt, PTEN_C124S, PTEN_G129E in HEK 293 cells. Typical BK_Ca channel currents could be recorded in cell-attached configurations. We found that PTEN_wt reduced the H₂O₂-induced BK_Ca channel activation during the initial 10 min treatment. In contrast, coexpression with catalytically inactive PTEN_C124S/PTEN_G129E mutants that lack lipid phosphatase activity produced no regulation on the H₂O₂-induced BK_Ca channel activation. These results demonstrated that PTEN regulated the H₂O₂-induced BK_Ca channel activation through phosphatidylinositol 3-phosphatse. However, the inhibitory effect of PTEN on the H₂O₂-induced BK_Ca channel activation was attenuated when cells were treated with H₂O₂ at concentrations higher than 100 μM or at 100 μM for long-term treatment. In addition, the p-AKT expression level in PTEN_wt overexpressing cells was lower than that in control cells, and the increase of cytoplasmic free calcium concentration ([Ca²⁺]_i) induced by H₂O₂ was also inhibited. These findings may elucidate a new mechanism for H₂O₂-induced BK_Ca channel activation and provide some evidences for the role of PTEN on vasodilation induced by H₂O₂.     

Distribution of endogenous gibberellins in vegetative and reproductive organs of Brassica

Recognizing the physiological diversity of different plant organs, studies were conducted to investigate the distribution of endogenous gibberellins (GAs) in Brassica (canola or oilseed rape). GA₁ and its biosynthetic precursors, GA₂₀ and GA₁₉, were extracted, chromatographically purified, and quantified by gas-chromatography-selected ion monitoring (GC-SIM), using [²H₂]GAs as internal standards. In young (vegetative) B. napus cv. Westar plants, GA concentrations were lowest in the roots, increased acropetally along the shoot axis, and were highest in the shoot tips. GA concentrations were high but variable in leaves. GA₁ concentrations also increased acropetally along the plant axis in reproductive plants. During early silique filling, GA₁ concentrations were highest in siliques and progressively lower in flowers, inflorescence stalks (peduncles plus pedicels), stem, leaves, and roots. Concentrations of GA₁₉ and GA₂₀ showed similar patterns of distribution except in leaves, in which concentrations were higher, but variable. Immature siliques were qualitatively rich in endogenous GAs and GA₁, GA₃, GA₄, GA₈, GA₉, GA₁₇, GA₁₉, GA₂₀, GA₂₄, GA₂₉, GA₃₄, GA₅₁, and GA₅₃ were identified by GC-SIM. In whole siliques, GA₁₉, GA₂₀, GA₁, and GA₈ concentrations declined during maturation due to declining levels in the maturing seeds; their concentrations in the silique coats remained relatively constant and low. These studies demonstrate that GAs are differentially distributed in _Brassica with a general pattern of acropetally increasing concentration in shoots and high concentration in actively growing and developing organs.     

桂西南岩溶区八种适生植物光合性状的变异与关联

为探究岩溶植物的光合生理适应机制，采用Li-6400XT便携式光合作用测量系统，对广西平果市岩溶区8种适生植物的叶片净光合速率(P_n)、气孔导度(G_s)、胞间CO₂浓度(C_i)、蒸腾速率(T_r)、水分利用效率(WUE)和气孔限制值(L_s)等光合特征参数进行了测定分析。结果表明：(1)6个光合特征参数在种内和种间均存在不同程度的变异，并且种内变异均大于种间变异。(2)G_s和T_r的变化主要来源于种间变异(46.72%～49.76%),而P_n、C_i、WUE和L_s变化主要来源于种内变异(48.66%～64.50%)。在生活型水平上，P_n、G_s和T_r的种内变异表现为常绿植物小于落叶植物，而C_i、WUE和L_s则相反。(3)各参数的种间变异均表现为落叶植...     

Improvement of antagonistic capability of Trichoderma harzianum by UV-Irradiation for management of Macrophomina phaseolina

Antagonistic capability of Trichoderma harzianum was improved through UV-irradiation. Four different type of mutants, T. harzianum - M_a (Th-M_a), T. harzianum - M_b(Th-M_b), T. harzianum - M_c (Th-M_c), T. harzianum - M_d (Th-M_d) of T. harzianum and the parent strain (Th-P) were selected for further studies. Th-M_a and Th-M_b showed more antagonistic capability against Macrophomina phaseolina than its parent strain Th-P in dual culture. Biochemical analysis of these four mutants and the parent strain showed that Th-M_a releases higher level of two lytic enzymes i.e. chitinases and cellulases and Th-M_b produces more β-1,3-glucanase activity than the parent strain. Culture filtrate of Th-M_a also showed antifungal properties. Study of the competitive saprophytic ability (CSA) of these four mutants and the parent strain were also made. Th-M_a exhibited higher CSA than the parental isolate while Th-M_d had less CSA than all other mutants and the parent strain of T. harzianum.