Abscisic acid signalling when soil moisture is heterogeneous: decreased photoperiod sap flow from drying roots limits abscisic acid export to the shoots

To investigate the contribution of different parts of the root system to total sap flow and leaf xylem abscisic acid (ABA) concentration ([X-ABA]_leaf), individual sunflower ( Helianthus annuus L.) shoots were grafted onto the root systems of two plants grown in separate pots and sap flow through each hypocotyl measured below the graft union. During deficit irrigation (DI), both pots received the same irrigation volumes, while during partial root zone drying (PRD) one pot ('wet') was watered and another ('dry') was not. During PRD, once soil water content ( θ ) decreased below a threshold, the fraction of sap flow from drying roots declined. As θ declined, root xylem ABA concentration increased in both irrigation treatments, and [X-ABA]_leaf increased in DI plants, but [X-ABA]_leaf of PRD plants actually decreased within a certain θ range. A simple model that weighted ABA contributions of wet and dry root systems to [X-ABA]_leaf according to the sap flow from each, better predicted [X-ABA]_leaf of PRD plants than either [X-ABA]_dry, [X-ABA]_wet or their mean. Model simulations revealed that [X-ABA]_leaf during PRD exceeded that of DI with moderate soil drying, but continued soil drying (such that sap flow from roots in drying soil ceased) resulted in the opposite effect.     

Accounting for sap flow from different parts of the root system improves the prediction of xylem ABA concentration in plants grown with heterogeneous soil moisture

When soil moisture is heterogeneous, sap flow from, and ABA status of, different parts of the root system impact on leaf xylem ABA concentration ([X-ABA]leaf). The robustness of a model for predicting [X-ABA]leaf was assessed. 'Two root-one shoot' grafted sunflower (Helianthus annuus L.) plants received either deficit irrigation (DI, each root system received the same irrigation volumes) or partial rootzone drying (PRD, only one root system was watered and the other dried the soil). Irrespective of whether relative sap flow was assessed using sap flow sensors in vivo or by pressurization of de-topped roots, each root system contributed similarly to total sap flow during DI, while sap flow from roots in drying soil declined linearly with soil water potential (Psisoil) during PRD. Although Psisoil of the irrigated pot determined the threshold Psisoil at which sap flow from roots in drying soil decreased, the slope of this decrease was independent of the wet pot Psisoil. Irrespective of whether sap was collected from the wet or dry root system of PRD plants, or a DI plant, root xylem ABA concentration increased as Psisoil declined. The model, which weighted ABA contributions of each root system according to the sap flow from each, almost perfectly explained [X-ABA] immediately above the graft union. That the model overestimated measured [X-ABA]leaf may result from changes in [X-ABA] along the transport pathway or an artefact of collecting xylem sap from detached leaves. The implications of declining sap flow through partially dry roots during PRD for the control of stomatal behaviour and irrigation scheduling are discussed.     

Long-distance signals regulating stomatal conductance and leaf growth in tomato (Lycopersicon esculentum) plants subjected to partial root-zone drying

Tomato (Lycopersicon esculentum Mill. cv. Ailsa Craig) plants were grown with roots split between two soil columns. After plant establishment, water was applied daily to one (partial root-zone drying-PRD) or both (well-watered control-WW) columns. Water was withheld from the other column in the PRD treatment, to expose some roots to drying soil. Soil and plant water status were monitored daily and throughout diurnal courses. Over 8 d, there were no treatment differences in leaf water potential (psileaf) even though soil moisture content of the upper 6 cm (theta) of the dry column in the PRD treatment decreased by up to 70%. Stomatal conductance (gs) of PRD plants decreased (relative to WW plants) when of the dry column decreased by 45%. Such closure coincided with increased xylem sap pH and did not require increased xylem sap abscisic acid (ABA) concentration ([X-ABA]). Detached leaflet ethylene evolution of PRD plants increased when of the dry column decreased by 55%, concurrent with decreased leaf elongation. The physiological significance of enhanced ethylene evolution of PRD plants was examined using a transgenic tomato (ACO1AS) with low stress-induced ethylene production. In response to PRD, ACO1AS and wild-type plants showed similar xylem sap pH, [X-ABA] and gs, but ACO1AS plants showed neither enhanced ethylene evolution nor significant reductions in leaf elongation. Combined use of genetic technologies to reduce ethylene production and agronomic technologies to sustain water status (such as PRD) may sustain plant growth under conditions where yield would otherwise be significantly reduced.     

交替灌溉对山黧豆叶片气体交换和土壤水分以及产量指标的影响

改变土壤根系的分布以汲取深层土壤水分的能力是植物避免干旱的主要策略。山黧豆是一种抗逆性强的豆类作物,该研究通过起垄条播控制性沟灌的方式,设置传统灌溉(FI)、交替灌溉(PRD,灌水量减少50%)和不灌溉(NI)3种处理模式,探索不同灌溉模式对播种后不同时期山黧豆土壤水分、根系分布、叶片气体交换、水分利用效率和籽粒产量的影响。结果表明：(1)在FI、PRD和NI处理下,山黧豆的根系分别有89.8%、86.9%和84.9%生长在0~20 cm的表层土壤中;干旱胁迫使PRD和NI处理下深层土壤中根系的比例提高至13.05%和15.07%。(2)在整个生育期内,土壤干旱显著降低了山黧豆叶片的净光合速率、蒸腾速率和气孔导度;在种植后60 d时,PRD和NI处理下叶片的瞬时水分利用效率分别较FI处理显著提高了21.4%和14.9%。(3)干旱胁迫显著降低了山黧豆植株高度、第一豆荚高、平均结荚数和豆粒数以及地上部和根系的干重,但显著增加了根冠比;PRD处理对豆荚长度、豆荚重和每荚豆粒重没有显著影响;PRD和NI处理下山黧豆平均籽粒产量分别比FI处理显著降低了53%和63%。研究发现,在干旱胁迫条件下,山黧豆能够通过提高深层土壤中根系的比例、更多吸收深层土壤水分、显著增加根冠比以及显著提高生殖生长期叶片的瞬时水分利用效率,减轻干旱胁迫对自身生长的影响。该研究结果可为山黧豆在旱区推广种植提供理论依据。     

Ferrocenyl-derived face-capping ligands: syntheses and molecular structures of [(FcTt)Cu]4 and [FcTt]2M (M = Fe, Co, Ni; FcTt = ferrocenyltris((methylthio)methyl)borate)

The synthesis and characterization of a ferrocenyl-derived tridentate ligand, ferrocenyltris((methylthio)methyl)borate (FcTtP⁻), and its representative metal complexes, [(FcTt)Cu]₄ and [FcTt]₂M (M = Fe, Co and Ni), are reported. The M = Fe complex exhibits spin-crossover behavior with a μ_eff = 1.19 μ_B at 25°C. The low-spin Co(II) derivative (1.88 μ_B) exhibits a characteristic axial electron paramagnetic resonance (EPR) spectrum, g_av = 2.13, A = 53 G and A_¦ = 43 G. The [FcTt]₂M complexes display reversible two-electron redox processes assigned to ligand-centered events about 200 mV negative of the ferrocene-ferrocenium couple. [(FcTt)Cu]₄ and [FcTt]₂Ni have been characterized by X-ray diffraction. X-ray data for [(FcTt)Cu]₄: monoclinic space group C2/c, with a = 24.3747(3) Å, b = 20.0857(2) Å, c = 17.2747(4) Å, β = 95.843(1)°, V = 8413.5(3) ų, and Z = 4; [FcTt]₂Ni: monoclinic space group C2/c, with a = 12.6220(3) Å, b = 11.6002(3) Å, c = 25.0125(7) Å, β = 94.067(1)°, V = 3653.1(2) ų, and Z = 4.     

The propensity of alkoxide and aryloxide derivatives of tungsten carbonyls to aggregate in solution. Synthesis and X-ray structures of dinuclear, trinuclear and tetranuclear complexes derived from the MeOW(CO)5 anion

The complex [Et₄N][W(CO)₅OMe] (1) has been prepared from the reaction of the photochemically generated W(CO)₅THF adduct and [Et₄N][OH] in methanol. Complex 1 was shown to undergo rapid CO dissociation in THF to quantitatively provide the dimeric dianion, [W(CO)₄OMe]₂²⁻. The resulting THF insoluble salt [Et₄N]₂[W(CO)₄OMe]₂ (2) has been structurally characterized by X-ray crystallography, with the doubly bridging methoxide ligands being in an anti configuration. Complex 2 was found to subsequently react with excess methoxide ligand in a THF slurry to afford the face-sharing octahedron complex [Et₄N]₃[W₂(CO)₆(OMe)₃] (3) which contains three doubly bridging methoxide groups. In the absence of excess methoxide ligand complex 2 cleanly yields the tetrameric complex [Et₄N]₄[W(CO)₃OMe]₄ (4) which has been structurally characterized as a cubane-like arrangement with triply bridging μ³-methoxide groups and W(CO)₃ units. Although complex 3 was not characterized in the solid state, the closely related glycolate derivative [Et₄N]₃[W₂(CO)₆(OCH₂CH₂OH)₃] (5) was synthesized and its structure determined by X-ray crystallography. The trianions of complex 5 are linked in the crystal lattice by strong intermolecular hydrogen bonds. Crystal data for 2: space group P2₁/n, a = 7.696(2), b = 22.019(4), c = 9.714(2) Å, β = 92.22(3)°, Z = 4, R = 6.43%. Crystal data for 4: space group Fddd, a = 12.433(9), b = 24.01(2), c = 39.29(3) Å, Z = 8, R = 8.13%. Crystal data for 5: space group P2₁2₁2₁, a = 11.43(2), b = 12.91(1), c = 29.85(6) Å, Z = 8, R = 8.29%. Finally, the rate of CO ligand dissociation in the closely related aryloxide derivatives [Et₄N][W(CO)₅OR] (R = C₆H₅ and 3,5-F₂C₆H₃) were measured to be 2.15 × 10⁻² and 1.31 × 10⁻³ s⁻¹, respectively, in THF solution at 5°C. Hence, the value of the rate constant of 2.15 × 10⁻² s⁻¹ establishes a lower limit for the first-order rate constant for CO loss in the W(CO)₅OMe⁻ anion, since the methoxide ligand is a better π-donating group than phenoxide.     

An unexpected ‘4+2’ [N3S]/[NS] rhenium(IV) complex formed upon cleavage of a Re(V) imido bond

The reaction of [Re(NMe)Cl₃(PPh₃)₂] with the pentadentate [N₃S₂] ligand pyN₂H₂S₂---H₂ [2,6-bis(2-mercaptophenylamino)dimethylpyridine] (1) in the presence of triethylamine did not yield the anticipated six-coordinate complex [Re(NMe)(η⁵-pyN₂HS₂)] (2), but rather resulted in cleavage of the Re(V)=NMe bond. A novel six-coordinate Re(IV) [N₃S]/[NS] complex [Re(η⁴-SC₆H₄---2-NCH₂---C₅H₃N---C=NC₆H₄---2-S)(η²-NHC₆H₄---2-S)] (4) was thus obtained with the simultaneous coordination of 2-aminothiophenol, a dianionic bidentate [NS] donor resulting from the decomposition of the parent ligand and ligand 3, a dianionic tetradentate [N₃S] donor formed by partial self-condensation and subsequent oxidation of the parent ligand 1. Crystal data for 4: C₂₅H₁₈N₄S₃Re·CH₂Cl₂, monoclinic, space group P2₁/n, a=9.255(2) Å, b=11.181(2) Å, c=25.316(4) Å, β=97.434(3)°, V=2587.8(7) Å³ and Z=4.     

长白山阔叶红松林生态系统光能利用率的动态变化及其主控因子

生态系统光能利用率(LUE)反映了植被通过光合作用利用光能吸收和固定大气中CO₂的能力, 是表征生态系统生产力的重要指标。选取长白山温带阔叶红松(Pinus koraiensis)林生态系统为研究对象, 利用涡度相关通量观测数据, 采用直角双曲线方程获取了生态系统光合作用的表观量子效率(ε); 基于总生态系统初级生产力(GEP)与下垫面入射光合有效辐射(Q)的比值得到生态光能利用率(LUE_eco)。研究表明: 在季节尺度上, ε与LUE_eco均表现出显著的单峰变化特征, 并主要受到土壤温度和归一化植被指数(NDVI)的调控, 同时, ε和LUE_eco都受到GEP的显著影响, 而与Q的相关性较弱或无显著相关关系, 但散射辐射的增加在一定程度上有助于提高生态系统的LUE。ε与LUE_eco存在显著的线性正相关关系, 但ε明显高于LUE_eco。2003-2005年, ε与LUE_eco每年最大值的平均值分别为(0.087 ± 0.003)和(0.040 ± 0.002) μmol CO₂·μmol photon^-1, 年际间变异度分别为4.17%和4.25%, 而不同年份之间最大差异均达到8%或8%以上, 从而对模型模拟结果产生明显影响。因此, 在基于光能利用率模型的模拟研究中, 最大LUE的年际变异需要在参数反演和优化中给予重要考虑。     

Dynamics and regulations of ecosystem light use efficiency in a broad-leaved Korean pine mixed forest,Changbai Mountain

Aims Ecosystem light use efficiency (LUE) reflects the ability of CO₂ uptake and light utilization via photosynthesis, which is a key parameter in ecosystem models to evaluate ecosystem productivity. The objectives of this study were to: (1) compare the differences of LUE derived from different methods; (2) elucidate the seasonal dynamics of LUE and its regulatory factors; and (3) evaluate the maximum LUE (LUE_max) and its variability based on eddy-covariance (EC) flux.Methods Using the flux data from an EC tower during 2003-2005 at a broad-leaved Korean pine (Pinus koraiensis) mixed forest, Changbai Mountain, two types of LUE indicators were generated from: 1) the apparent quantum yield (ε) estimated with rectangular hyperbolic curve, and 2) the ecological light use efficiency (LUE_eco) calculated as the ratio between gross ecosystem productivity (GEP) and photosynthetically-active radiation (Q).Important findings The seasonal variation of ε and LUE_eco appeared a unimodal pattern within a year, with the variations significantly dominated by soil surface temperature and Normalized Difference Vegetation Index (NDVI). A positive correlation between GEP and LUE was found for both ε and LUE_eco, with the effect of Q on LUE relatively weak. The increase in diffusion radiation appeared favorable for enhanced LUE. Generally, there was a significant positive relationship between ε and LUE_eco, while ε was higher than LUE_eco, especially during the mid-season. The annual maximum value of ε and LUE_eco was (0.087 ± 0.003) and (0.040 ± 0.002) μmol CO₂·μmol photon^-1 over the three years, respectively. The interannual variability of LUE_max for ε and LUE_eco was 4.17% and 4.25%, respectively, with a maximum difference of >8%, likely resulted from considerable uncertainty in model simulations. Our results indicated that the inversion and optimization of maximum LUE should be taken seriously in the application of LUE models.     

Ergosterol peroxides as phospholipase A2 inhibitors from the fungus Lactarius hatsudake

Four ergosterol derivatives (1–4) have been isolated for the first time from the fruiting bodies of a basidiomycete fungus, Lactarius hatsudake, through activity-guided fractionation. Their structures were determined, using spectroscopic analysis, as: (22E,24R)-ergosta-5,7,22-dien-3β-ol (ergosterol, 1); 5,8-epidioxy-(22E,24R)-ergosta-6,22-dien-3β-ol (ergosterol peroxide, 2); 5,8-epidioxy-(24S)-ergosta-6-en-3β-ol (3); and (22E,24R)-ergosta-7,22-dien-3β,5,6β-triol (cerevisterol, 4). Compounds 2 and 3 showed selective inhibitory activity against Crotalus adamenteus venom phospholipase A₂ (PLA₂) enzyme, but not against Apis mellifcra bee venom PLA₂. The antiphospholipase A₂ activity of compounds 2 and 3 are reported here for the first time.     

Physiological responses of potato (Solanum tuberosum L.) to partial root-zone drying: ABA signalling, leaf gas exchange, and water use efficiency

The physiological responses of potato (Solanum tuberosum L. cv. Folva) to partial root-zone drying (PRD) were investigated in potted plants in a greenhouse (GH) and in plants grown in the field under an automatic rain-out-shelter. In the GH, irrigation was applied daily to the whole root system (FI), or to one-half of the root system while the other half was dried, for 9 d. In the field, the plants were drip irrigated either to the whole root system near field capacity (FI) or using 70% water of FI to one side of the roots, and shifted to the other side every 5-10 d (PRD). PRD plants had a similar midday leaf water potential to that of FI, whereas in the GH their root water potential (Psi(r)) was significantly lowered after 5 d. Stomatal conductance (g(s)) was more sensitive to PRD than photosynthesis (A) particularly in the field, leading to greater intrinsic water use efficiency (WUE) (i.e. A/g(s)) in PRD than in FI plants on several days. In PRD, the xylem sap abscisic acid concentration ([ABA](xylem)) increased exponentially with decreasing Psi(r); and the relative [ABA](xylem) (PRD/FI) increased exponentially as the fraction of transpirable soil water (FTSW) in the drying side decreased. In the field, the leaf area index was slightly less in PRD than in FI treatment, while tuber biomass was similar for the two treatments. Compared with FI, PRD treatment saved 30% water and increased crop water use efficiency (WUE) by 59%. Restrictions on leaf area expansion and g(s) by PRD-induced ABA signals might have contributed to reduced water use and increased WUE.     

黑沙蒿光合能量分配组分在生长季的相对变化与调控机制

为了探明典型荒漠灌木优势物种黑沙蒿(俗名油蒿, Artemisia ordosica)光合过程能量中分配对环境波动的相对变化及其长期调节机制, 该研究于2018年4-10月在宁夏盐池毛乌素沙地, 同时使用MONITORING-PAM多通道荧光监测仪和LI-6400XT便携式光合测量仪对黑沙蒿叶片的最小荧光产量(F_o)、最大荧光产量(F_m)、稳态荧光产量(F_s)、光下最大荧光产量(F_m′)、净光合速率(P_n)、暗呼吸速率(R_d)、蒸腾速率(E)和叶片气孔导度(g_s)进行现场测定, 在实验室内计算比叶面积(SLA)、单位面积氮含量(N_area)、叶绿素含量(C_Chl)和叶绿素a/b (Chl a/b), 分析黑沙蒿光合过程能量分配中固碳耗能占比(Φ_A)、光呼吸耗能占比(Φ_PR)、调节性热耗散耗能占比(Φ_NPQ)和非调节性热耗散耗能占比(Φ_NO)与环境参数和叶性状参数之间的关系以及能量分配各组分之间的相对变化。结果表明, 光化学反应组分(Φ_A、Φ_PR)和热耗散组分(Φ_NPQ、Φ_NO)之间呈负相关竞争关系, 两组分内部呈正相关协同关系, E和Φ_A、Φ_PR正相关, 和Φ_NPQ、Φ_NO负相关。在低土壤含水量(SWC)和高饱和水汽压差(VPD)环境条件下, 黑沙蒿Φ_A、Φ_PR和SLA显著降低, Φ_NPQ和Φ_NO显著增加。研究认为, 在长期干旱或高蒸散条件下, 黑沙蒿通过降低SLA等途径避免水分的过度流失, 同时将部分过剩光能由光呼吸代谢途径转移到热耗散组分进行耗散。波动环境下黑沙蒿形态性状的变异和光合过程能量分配的长期调节机制, 反映了其利用形态与生理的协同可塑性对逆境的适应。     

Water relations of Fino lemon plants on two rootstocks under flooded conditions

Potted two-year-old Fino lemon plants (Citrus limon (L.) Burm. fil.) grafted on two different rootstocks: sour orange (C. aurantium) (SO), and C. macrophylla (CM) were submitted to two different treatments: non-flooded (control) and flooded for 8 days, under field conditions. Lemon/CM plants had lower plant plus soil resistance to water flow (R_(p+s)) values for both treatments. The decrease in leaf water potential (Ψ_l) and leaf turgor potential (Ψ_p) values, observed in the last part of the flooding period, in both flooded scion/rootstock combinations, can be related to the increase in the resistance to water flow. The maintenance in Ψ_l and Ψ_p values in flooded plants at values similar to those of the control plants, at the beginning of the flooding period and during the recovery period, can be ascribed to the stomatal control observed (decrease in leaf conductance (g₁) values). The later g₁ recovery in lemon/CM than in lemon/SO flooded plants, could explain the lower vegetative growth of lemon/CM plants by flooding effect. The observed g₁ response to soil flooding suggested that porometry is a reliable indicator of the altered behaviour caused by flooding in lemon plant.     

Mechanistic details for metathetical exchange between XCO (X = O and RN) and the tin(II) dimer, {Sn[N(SiMe3)2] (μ-OBu)}2

Metathetical exchange between carbon dioxide and the tin(II) dimer, {Sn[N(SiMe₃)₂](μ-OBu¹)}₂ (3) has been observed to cleanly produce the two new heteroleptic tin(II) dimers, Sn[N(SiMe₃)₂](μ-OBu^t)₂Sn(OSiMe₃) (6) and [Sn(OSiMe₃)](μ-OBu^t)]₂ (7]). In addition, reaction of 3 with I equiv, of tert-butylisocyanate (8), at 25°C, quantitatively provides 6, and with 2 equiv., quantitatively provides 7. Likewise 6 reacts with 1 equiv, of 8 to quantitatively provide 7. The mechanism for these latter processes has been investigated by low temperature ¹H NMR spectroscopy which reveals that metathetical exchange does not involve the tri-coordinate tin(II) centers of the dimeric structures, but rather, it occurs, in each case, via the transient monomeric tin(II) species, Sn[N(SiMe₃)₂](μ-OBu^t) (4), that undergoes metathesis to produce, initially the open dimer intermediate, Sn(OCNBu^t)(OSiMe₃)(μ-OBu^t)Sn(OBu^t) (OSiMe₃) (12), that is observed at −10°C. Subsequent redistribution reactions then generate the final products that are observed. Together, these mechanistic details provide additional support for the ‘monomeric tin(II)’ hypothesis proposed earlier for metathetical exchange between XCO and Sn[N (SiMe₃)₂]₂ (1).     

Synthesis of one dimensional tin selenides in supercritical amines

Three new crystalline tin selenide salts have been prepared from the reactions of [PPh₄]₂[Sn(Se₄₃] in supercritical solvents. The starting material pyrolyzes in supercritical acetonitrile to form [PPh₄]₄[Sn₆Se₂₁] (I), and it also reacts with SnSe in supercritical ammonia leading to a mixture of [PPh₄]₄[Sn₃Se₁₁]₂ (II). and [PPh₄]₂[Sn(Se₄)(Se₆)₂] (III). All three compounds have been characterized by single crystal X-ray diffraction. Crystallographic data: for I, C₉₆H₉₀P₄Se₂₁Sn₆, space group triclinic, P-1, A = 18.763(3), B = 24.600(4), C = 13.137(1) Å, = 102.63(1), β = 93.66(1), γ = 108.72(1)°, V = 5544(1) ų, Z = 2, R = 0.0350, R_W = 0.0317: for II, C₉₆H₈₀P₄Se₂₂Sn₆, space group monoclinic P2₁/c, A = 31.500(4), B = 16.572(3), C = 22.352(3) Å, β = 103.53(1)°, V = 11344(3) ų, Z = 4, R = 0.0771, R_W = 0.0664: for III, C₄₈H₄₀P₂Se₁₆Sn, space group monoclinic, C2/c, A = 25.381(2), B = 13.934(4), C = 19.465(3) Å, β = 121.587(8)°, V = 5867(2) ų, Z = 4, R = 0.0807, R_W = 0.0650. One of the compounds, [PPh₄]₂[Sn(Se₄(Se₆₂], is a molecular cluster while the other two complexes [PPh₄]₄[Sn₃Se₁₁]₂ and [PPh₄]₄[Sn₆Se₂₁], are one dimensional tin selenide chains. The structures of the two chains are related and consits of tetrahedral and distorted trigonal bipyramidal tin(IV) centers bridged by Se²⁻, Se₂²⁻ and Se₃²⁻ chains.     

Interactions between thiamine and large anions. Crystal structures of (H-thiamine)[Pt(SCN)4] · 3H2O and (H-thiamine)[Pt(SCN)6] · H2O

The reaction of thiamine with K₂Pt^IICl₄ and with Pt^IVCl₄ in the presence of excess NaSCN in aqueous solution gave thiamine salts, (H-thiamine)[Pt(SCN)₄] · 3H₂O (1) and (H-thiamine)[Pt(SCN)₆] · H₂O (2), respectively, structures of which have been determined by X-ray diffraction. The thiamine molecule adopts the usual F conformation in each salt. In 1, [Pt(SCN)₄]²⁻ ions act as large planar spacers in the crystal lattice and interact scarcely with thiamine, except for a hydrogen bonding with the terminal hydroxy O(5γ). Instead, water molecules form two types of host–guest-like interactions with the pyrimidine and the thiazolium moieties of a thiamine molecule, one being a C(2)–Hwaterpyrimidine bridge and the other being an N(4′)–Hwaterthiazolium bridge. In 2, despite the much larger ion size, octahedral [Pt(SCN)₆]²⁻ ions form a C(2)–Hanionpyrimidine bridge and an N(4′)–Hanionthiazolium bridge. An additional hydrogen bonding between the anion and the terminal O(5γ) of thiamine creates a hydrogen-bonded macrocyclic ring {thiaminium–[Pt(SCN)₆]²⁻}₂, a supramolecule.     

Pustulan and branched β-galactofuranan from the phytopathogenic fungus Guignardia citricarpa, excreted from media containing glucose and sucrose

Guignardia citricarpa is a phytopathogenic fungus and the causal agent of citrus black spot. Incubation in a semi-defined media resulted in formation of exopolysaccharides [EPS(s)]. A medium containing glucose gave rise to a (1→6)-linked β-glucan (200 kD), pustulan, which was characterized by NMR and methylation analysis. A sucrose-containing medium provided a homogalactan (376 kD) and methylation analysis showed nonreducing end- (20%), 6-O- (53%) and 5,6-di-O-substituted Galf units (27%). An HMQC spectrum of the homogalactan showed C-1/H-1 signals at δ 108.2/4.820, 108.3/4.820 and 107.1/5.079, corresponding to three types of β- -Galf units. A DEPT analysis showed inverted signals (CH₂) at δ 67.8 and 67.2, corresponding to 6-O-substituted β- -Galf units, whereas a C-5 signal at δ 77.0 suggests 5-O-substitution, confirming a novel structure for a β-galactofuranan.     

Evidence for modulation of cell-to-cell electrical coupling by cAMP in mouse islets of Langerhans

The effects of forskolin on electrical coupling among pancreatic β-cells were studied. Two microelectrodes were used to measure membrane potentials simultaneously in pairs of islet β-cells. Intracellular injection of a current pulse (ΔI) elicited a membrane response ΔV₁ in the injected cell and also a response ΔV₂ in a nearby β-cell confirming the existence of cell-to-cell electrical coupling among islet β-cells. In the presence of glucose (7 mM), application of forskolin evoked a transient depolarization of the membrane and electrical activity suggesting that the drug induced a partial inhibition of the β-cell membrane K⁺ conductance. Concomitant with this depolarization of the membrane there was a marked decrease in β-cell input resistance (ΔV₂/ΔI) suggesting that exposure to forskolin enhanced intercellular coupling. Direct measurements of the coupling ratio ΔV₂/ΔV₁ provided further support to the idea that forskolin enhances electrical coupling among islet cells. Indeed, application of forskolin reversibly increased the coupling ratio. These results suggest that cAMP might be involved in the modulation of electrical coupling among islet β-cells.     

土壤水分对黄土区苹果园土壤-植物-大气连续体(SPAC)中水势梯度的影响

开展土壤-植物-大气连续体(SPAC)中水势变化的联动分析对于揭示植物水分状况对环境变化的响应机制有重要意义。在黄土高原苹果园对果树生长季大气水势(Ψ_air)、木质部水势(Ψ_stem)、土壤水势(Ψ_soil)进行连续监测与分析。结果表明: 苹果树在生长季的日平均Ψ_stem为-0.57 MPa,在-0.24～-2.0 MPa间变化。苹果树SPAC连续体中水势梯度(Ψ_soilΨ_stemΨ_air)平均为1∶9.8∶1155,其中植-土界面的水势梯度(Ψ_stemΨ_soil)与土壤体积含水率(VWC)间呈极显著的线性正相关关系,Ψ_stem与Ψ_soil间呈良好的线性关系,且相关性强于Ψ_stem与Ψ_air间的相关性。当Ψ_soil<-0.08 MPa(VWC=17%,约为田间持水量的0.56倍)时,Ψ_stem对Ψ_soil变化响应的敏感性明显降低,气-植界面的水势梯度(Ψ_airΨ_stem)与Ψ_soil间由无明显关系转变为紧密的线性相关关系(R²=0.93)。Ψ_air对Ψ_stem的驱动存在阈值效应,在Ψ_air降到-69 MPa前,Ψ_stem日变化幅度随Ψ_air增加而增加,之后呈下降趋势。土壤含水率降低引起苹果树水势、SPAC各界面上的水势梯度明显下降,且在土壤含水率降至约17%时存在阈值效应。研究结果为理解树木水分状况对土壤、大气干旱的响应机制提供了重要依据。     

Characterization of functional VIP/PACAP receptors in the human erythroleukemic HEL cell line

R. LEMA-KISOKA, N. HAYEZ, I. LANGER, P. ROBBERECHT, E. SARIBAN AND C. DELPORTE. Characterization of functional VIP/PACAP receptors in the human erythroleukemic HEL cell line. PEPTIDES. The presence of VIP/PACAP receptors was investigated on the human erythroleukemic cell line HEL. Specific binding of [¹²⁵I]-PACAP or [¹²⁵I]-VIP on HEL cells or membranes was very low and did not allow to perform competition curves. At 37°C PACAP transiently increased cAMP levels in the presence of the non-specific phosphodiesterase inhibitor IBMX, suggesting rapid desensitization. Kinetic studies revealed that optimal conditions to measure the EC₅₀ of PACAP(1–27) were 10 min at 20°C. Under those conditions, PACAP-related peptides increased cAMP levels with EC₅₀ in agreement with the pharmacological profile of the VPAC₁ receptor subtype: PACAP = VIP > [K¹⁵, R^16, L²⁷]VIP(1–7)/GRF(8–27) = [R¹⁶]ChSn (two VPAC₁ agonists) HELODERMIN = secretin. RO 25–1553, a selective activator of VPAC₂ receptor was inactive at 1 μM. Dose-response curves of VPAC₁ agonist molecules (PACAP, VIP, [K¹⁵, R¹⁶, L²⁷]VIP(1–7)/GRF(8–27), [R¹⁶]ChSn) were shifted to the right by the VPAC₁ receptor antagonist [AcHis¹, D-Phe², Lys¹⁵, Leu¹⁷]VIP(3–7)/GRF(8–27), with a K_i of 3 ± 1 nM (n = 3). The presence of VPAC₁ receptor mRNA was confirmed by RT-PCR. Preincubation with PACAP or PMA showed that VPAC₁ receptors underwent homologous and heterologous desensitization.

This study provides the first evidence for the expression of functional VPAC₁ receptors undergoing rapid desensitization in HEL cells.