基于主成分-聚类-逐步回归分析构建番茄苗期耐铝性综合评价体系

铝毒是限制酸性土壤中作物产量的主要因素之一。番茄(Solanum lycopersicum)是适合在酸性土壤中种植的主要经济作物, 不同品种番茄对铝胁迫的响应存在差异, 因此, 筛选苗期耐铝毒种质对番茄生产及研究具有重要意义。以10个番茄品种为材料, 采用室内土培盆栽, 设置1 000 µmol∙L^-1 AlCl₃·6H₂O处理, 测定反映植物铝胁迫下生长状况的16个形态、生理生化及光合指标。通过主成分分析, 将铝胁迫下番茄幼苗的16个指标转化为5个独立的综合指标, 累积贡献率达90.779%。基于耐铝性综合评价值(A)的系统聚类分析, 将供试种质划分为5类, 第I类为高度耐铝品种Qianxi, 第V类为高度不耐铝品种Puluowangsi。经多元线性逐步回归分析得出番茄苗期耐铝评价方程: y=0.046+0.405X₆+0.515X₁₀-0.207X₁₅+0.028X₃ (R²=0.997), 从16个指标中提取出与A值显著相关(P<0.01)的4个指标: 丙二醛含量(X₃)、净光合速率(X₆)、叶面积(X₁₀)和地下部干重(X₁₅)。利用评价方程可判断不同番茄品种苗期的耐铝性, 使番茄耐铝性鉴定工作快速简便。     

Folded conformation of an immunostimulating tetrapeptide rigin: high temperature molecular dynamics simulation study

Employing high temperature quenched molecular dynamics (QMD) simulations the conformational energy space of an immunostimulating tetrapeptide rigin: H-Gly³⁴¹-Gln-Pro-Arg³⁴⁴-OH, is explored. Using distance dependent dielectric (=r_ij) 31 different low energy starting structures with identical sequence were computed for their conformational preferences. According to the hypothesis of O'Connors et al. [J. Med. Chem. 35 (1992), 2870], 83 low-energy conformers resulted from unrestrained molecular dynamics (MD) simulations, could be classified into two energy minimized families: A and B, comprised of 64 (Pro C^γ-endo orientation) and 19 (Pro C^γ-exo orientation) structures, respectively. An examination of these families revealed the existence of a remarkably similar folded backbone conformation: torsion angles being φ_i+1 ≈−65°, ψ_i+1 ≈−65°, φ_i+2 ≈−65°, ψ_i+2 ≈−60°, characterizing a distorted type III β-turn structure across the central Gln-Pro segment. The folded conformation of rigin is devoid of a classical 1 ← 4 intra-molecular hydrogen bond nevertheless, the conformation is stabilized by an effective ‘salt-bridge’, i.e., Gly H₃N⁺… COO⁻ Arg interaction. Surprisingly, in both the families the unusual folded side-chain dispositions of the Gln residue favor the formation of a unique intra-residue ‘main-chain to side-chain’ H-bond, i.e., N–H…N^ε interaction, encompassing a seven-membered ring motif. The conformational attributes may be valuable in de novo construction of structure-based drug candidates having sufficient stimulating activity.     

Optical outer-sphere charge transfer in aqueous ion pairs with sulfidic anions as donors

Various sulfidic anions and the oxidizing cations [Ru(NH₃)₆]³⁺ and N,N′-dimethyl-4,4′-bipyridinium²⁺ (paraquat²⁺) form ion pairs in aqueous solutions which display outer-sphere charge-transfer (CT) absorptions. The CT energies are used to establish a series of sulfidic anions with increasing CT donor strength: SCN⁻2O₃ ²⁻4 ³⁻3S³⁻2 ⁻2S₂ ⁻4 ²⁻.     

Influence du pH sur la synthèse de l''oxidase (cytochrome a3) chez Bacillus coagulans, microorganisme thermophile, capable d'' “adaptation respiratoire”

In a new series of experiments on Bacillus coagulans (ATCC 11.369), it was demonstrated that this organism possesses a respiratory system with cytochromes b, c₁, c, (a+a₃) and also cytochrome o. A small decrease in the pH of the growth medium from 6.5 to 5.5 increases the respiratory activity by a factor of 4 and induces a variation of the absorption ratio [₆₀₃ (a+a₃)]/[₅₆₀ (b+c)] resulting in a preponderant increase in the ₆₀₃ absorption. The kinetic studies of the respiratory system synthesis during the phenomenon of “respiratory adaptation” have shown that lowering the pH of the adaption medium has the same effect. Spectral studies of membrane fractions (red dithionite) with or without carbon monoxide showed a preferential synthesis of oxidase a₃.     

体育专业大学生指长比及其波动性不对称的特征

为探讨体育专业大学生指长比及其波动性不对称的特征,进而为体质人类学和优秀运动员身体形态特征的研究积累基础资料,本研究特招募374名18~25岁发育正常的汉族在校大学生为研究对象,按照专业和性别分为男生体育组（n=60）、男生普系组（n=143）、女生体育组（n=61）和女生普系组（n=110）,计算各个指长比及两侧指长比的波动不对称值并进行检验。结果显示男生体育组与男生普系组之间的指长比（R）存在统计学差异（P<0.05）,差异主要表现在R_2/5、R_3/5和R_4/5上,而女生体育组与女生普系组之间的指长比不存在统计学差异（P>0.05）。结果还显示男生体育组与男生普系组之间的偏差(σ)存在统计学差异（P<0.05）,差异主要表现在σ_2/3和σ_2/3上。而女生的指长比偏差在体育组与普系组之间不存在统计学差异（P>0.05）。通过分析讨论提示出大学生指长比及指长比偏差与性别和运动能力有关,R_3/5及σ_3/5可能与早期生长发育过程中的性激素的暴露水平有关,而且有望成为运动员选材的新生物标记。     

Structures and magnetism of rubidium and cesium salts of dimeric oxovanadium(IV) tartrate(4−) complexes

Complexes of type A₄[VO(tart)]₂·nH₂O, where A = Rb or Cs and tart =d,l-tartrate(4−) (n = 2) or d,d-tartrate(4−) (n = 2 for Rb and n = 3 for Cs), were prepared from an aqueous mixture of V₂O₅, AOH and H₄tart. These complexes were studied by single-crystal X-ray diffraction methods: Rb₄[VO(d,l-tart)]₂·2H₂O, space group P1 with a = 8.156(1),b = 8.246(1),c = 8.719(1)Å, = 66.09(1)°, β = 65.07(1)°, γ = 82.40(1)°,Z = 2, 1917 observed reflections, and final R_w = 0.035; Cs₄[VO(d,l-tart)]₂·2H₂O, space group P₂₁/c with a = 9.350(1),b = 13.728(2),c = 8.479(1)Å, β = 106.77(1)°,Z = 4, 2235 observed reflections, and final R_w = 0.054; Rb₄[VO(d,d-tart)]₂·2H₂O, space group P₄₁₂₂ with a = 8.072(1),c = 32.006(3)Å,Z = 8, 1014 observed reflections and final R_w = 0.038; Cs₄[VO(d,d-tart)]₂·3H₂O, space group P₁₂₂ with a = 8.184(1),c = 33.680(5)Å,Z = 8, 1310 observed reflections, and final R_w = 0.063. Bulk magnetic susceptibility data (1.5–300 K) for these compounds and A₄[VOl,l-tart)]₂·nH₂O (A = Rb, Cs) were obtained on polycrystalline samples. These data were analyzed in terms of a Van Vleck exchange coupled S = 1/2 model which was modified to include an interdimer exchange parameters Θ. Analysis of the low-temperature (1.5–20 K) susceptibility data gave 2J = +1.30 cm⁻¹ and Θ = −1.86 K for Rb₄[VO(d,l-tart)]₂·2H₂O, 2J = +1.16 cm⁻¹ and Θ = −1.69 K for Cs₄[VO(d,l-tart)]₂·2H₂O, 2J = +1.90 cm⁻¹ and Θ = −0.82 K for Rb₄[VO(d,d-tart)]₂·2H₂O, 2J = +2.04 cm⁻¹ and Θ = −0.80 K for Rb₄[VO(l,l-tart)]₂·2H₂O, 2J = +1.52 cm⁻¹ and Θ = −0.25 K for Cs₄[VO(d,d-tart)]₂·3H₂O, and 2J = +1.64 cm⁻¹ and Θ = −0.31 K for Cs₄[VO(l,l-tart)]₂·3H₂O. These results suggest the magnitudes of intradimer (ferromagnetic and interdimer (antiferromagnetic) exchange interactions are similar in these complexes, as observed for the analogous Na salts.     

How are neuronal thermosensitivity and lack of thermoreception related in the duck's hypothalamus? A tentative answer

1. 1.|In 15 conscious Pekin ducks, 40 “warm sensitive” hypothalamic neurons were identified according to their discharge rates at 40°C T_hy (F₄₀), local temperature coefficients (Δ/ΔT) and Q₁₀.

2. 2.|Q₁₀ and either F₄₀ or ΔF/ΔT were little or not related.

3. 3.|A positive correlation between F₄₀ and ΔF/ΔT was observed which was particularly close (r = 0.94 and 0.96) when the neurons were classified according to their Q₁₀ of <2 and >2.

4. 4.|The results suggest that neurons with positive temperature coefficients in the duck's hypothalamus mostly exhibit linear to exponential temperature-discharge relationships.

5. 5.|This is an contrast to observations on mammalian hypothalamic thermosensitive neurons and may relate to the absence of the thermosensory function in the duck's rostral brainstem.

Hetero-polynuclear complexes containing bridging diphenylphosphino-alkenes and -alkynes. The crystal structure of an Rh2{μ−ν:ν−P(Ph2) (CH2)3C≡CR}Co2 complex

The phosphinoalkenes Ph₂P(CH₂)_nCH=CH₂ (n= 1, 2, 3) and phosphinoalkynes Ph₂P(CH₂)_n C≡CR (R = H, N = 2, 3; R = CH₃, N = 1) have been prepared and reacted with the dirhodium complex (η−C₅H₅)₂Rh₂(μ−CO) (μ−η²−CF₃C₂CF₃). Six new complexes of the type (ν−C₅H₅)₂(Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃)L, where L is a P-coordinated phosphinoalkene, or phosphinoalkyne have been isolated and fully characterized; the carbonyl and phosphine ligands are predominantly trans on the Rh---Rh bond, but there is spectroscopic evidence that a small amount of the cis-isomer is formed also. Treatment of the dirhodium-phosphinoalkene complexes with (η−CH₃C₅H₄)Mn(CO)₂thf resulted in coordination of the manganese to the alkene function. The Rh₂---Mn complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂P(CH₂)₃CH=CH₂} (η−CH₃C₅H₄)Mn(CO)₂] was fully characterized. Simi treatment of the dirhodium-phosphinoalkyne complexes with Co₂(CO)₈ resulted in the coordination of Co₂(CO)₆ to the alkyne function. The Rh₂---Co₂ complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂PCH₂C≡CCH₃}Co₂(CO)₂], C₃₇H₂₅Co₂F₆O₇PRh₂, was fully characteriz spectroscopically, and the molecular structure of this complex was determined by a single crystal X-ray diffraction study. It is triclinic, space group (C_i¹, No. 2) with a = 18.454(6), B = 11.418(3), C = 10.124(3) Å, = 112.16(2), β = 102.34(3), γ = 91.62(3)°, Z = 2. Conventional R on |F| was 0.052 fo observed (I > 3σ(I)) reflections. The Rh₂ and Co₂ parts of the molecule are distinct, the carbonyl and phosphine are mutually trans on the Rh---Rh bond, and the orientations of the alkynes are parallel for Rh₂ and perpendicular for Co₂. Attempts to induce Rh₂Co₂ cluster formation were unsuccessful.     

Leaf hydraulic traits and their trade-offs for nine Chinese temperate tree species with different wood properties

Aims Trees with different wood properties display variations in xylem anatomy and leaf vein structure, which may influence tree water transport efficiency and water-use strategy, and consequently constrain tree survival, growth and distribution. However, the effects of wood properties on leaf hydraulic conductance and vulnerability and their potential trade-offs at leaf level are not well understood. Our aims were to examine variations in leaf hydraulic traits of trees with different wood properties and explore potential trade-offs between leaf hydraulic efficiency and safety.
Methods Nine tree species with different wood properties were selected for measuring the leaf hydraulic traits, including three diffuse-porous species (Populus davidiana, Tilia amurensis, Betula platyphylla), three ring-porous species (Quercus mongolica, Fraxinus mandshurica, Juglans mandshurica), and three non-porous species (Picea koraiensis, Pinus sylvestris var. mongolica, Pinus koraiensis). Four dominant and healthy trees per species were randomly selected. The hydraulic traits measured included leaf hydraulic conductance on leaf area (K_area) and dry mass (K_mass) basis, leaf hydraulic vulnerability (P₅₀), and leaf water potential at turgor loss point (TLP), while the leaf structural traits were leaf dry mass content (LDMC), leaf density (LD) and leaf mass per unit area (LMA).
Important findings The K_area, K_mass, and P₅₀ differed significantly among the tree species with different woody properties (p < 0.05). Both K_area and K_mass were the lowest for the non-porous trees, and did not differ significantly between the diffuse-porous and ring-porous trees. The ring-porous trees had the highest P₅₀ values, while the diffuse-porous and non-porous trees showed no significant differences in P₅₀. Both K_area and K_mass were negatively correlated with P₅₀ (p < 0.05) for all the trees, and the relationships for the diffuse-porous, ring-porous, and non-porous trees were fitted into linear, power, exponential functions, respectively. This indicates that significant trade-offs exist between leaf hydraulic efficiency and safety. The K_mass was correlated (p < 0.01) with TLP in a negative linear function for the diffuse- and ring-porous trees and in a negative exponential function for the non-porous trees. The P₅₀ increased with increasing TLP. These results suggest that apoplastic and symplastic drought resistance are strictly coordinated in order to protect living cells from approaching their critical water status under water stresses. The K_mass was negatively correlated (p < 0.01) with LDMC, LD, or LMA, while the P₅₀ was positively correlated with LDMC and LD; this suggests that variations in K_mass and P₅₀ are driven by similar changes in structural traits regardless of wood traits. We conclude that the tree tolerance to hydraulic dysfunction increases with increasing carbon investment in the leaf hydraulic system.     

九种不同材性的温带树种叶水力性状及其权衡关系

不同材性树种的解剖、叶脉分布等结构性状差异会影响树木的水分运输效率和水分利用策略, 进而限制树木的生存、生长和分布。然而, 材性对叶导水率、水力脆弱性及其潜在的权衡关系的影响尚不清楚。该研究选择东北温带森林中不同材性的9种树种(散孔材: 山杨(Populus davidiana)、紫椴(Tilia amurensis)、白桦(Betula platyphylla); 环孔材: 蒙古栎(Quercus mongolica)、水曲柳(Fraxinus mandshurica)、胡桃楸(Juglans mandshurica); 无孔材: 红皮云杉(Picea koraiensis)、樟子松(Pinus sylvestris var. mongolica)、红松(Pinus koraiensis), 测量其基于叶面积和叶质量的叶导水率(K_area和K_mass)、水力脆弱性(P₅₀)、膨压丧失点水势(TLP)及叶结构性状, 以比较不同材性树种叶水力性状的差异, 并探索叶水力效率与安全的权衡关系。结果表明: 3种材性树种的K_area、K_mass和P₅₀均差异显著(p < 0.05)。无孔材树种的K_area和K_mass最低, 而散孔材和环孔材树种差异不显著; 环孔材树种P₅₀最高, 而散孔材和无孔材树种差异不显著。K_area和K_mass均与P₅₀显著负相关(p < 0.05), 但散孔材、环孔材和无孔材树种的相关关系分别呈线性、幂函数和指数函数关系。这表明叶水力效率与安全之间存在一定的权衡关系, 但该关系受树木材性的影响。K_mass与TLP显著负相关(p < 0.01), 其中散孔材和环孔材树种呈线性负相关, 无孔材树种呈负指数函数关系; P₅₀随TLP的增加而增加, 这表明树木在面临水分胁迫时, 其质外体和共质体抗旱阻力共同协调保护叶片活细胞, 防止其水分状况到达临界阈值。K_mass与叶干物质含量、叶密度、比叶重均显著负相关, 而P₅₀与之显著正相关(p < 0.01, P₅₀与比叶重的关系除外), 表明树木叶水力特性的变化受相同叶结构特性驱动, 树木增加对水力失调的容忍需要在叶水力系统构建上增加碳投资。     

The distance between cytochromes a and a3 in the azide compound of bovine-heart cytochrome oxidase

The electron-spin relaxation rates of the two species of cytochrome a³⁺₃-azide found in the azide compound of bovine-heart cytochrome oxidase were measured by progressive microwave saturation at T = 10 K. It has been shown previously that Cyt a⁺³₃-azide gives rise to two distinct EPR resonances, depending upon the oxidation state of Cyt a. When Cyt a is ferrous, Cyt a³⁺₃-azide has g = 2.88, 2.19 and 1.64; upon oxidation of Cyt a, the a³⁺₃-azide g-values become g = 2.77, 2.18, and 1.74 (Goodman, G. (1984) J. Biol. Chem. 259, 15094–15099). The relaxation effect of Cyt a on Cyt a₃ could be measured as the difference in microwave field saturation parameter H_1/2 between the g = 2.77 and g = 2.88 species. For each signal the spin-lattice relaxation time T₁ was determined from H_1/2 using the transverse relaxation time T₂. The value of T₂ at 10 K was extrapolated from a plot of line-width vs. temperature at higher temperature. The dipolar contribution to T₁ was related to the Cyt a-Cyt a₃ spin-spin distance utilizing available information on the relative orientation of Cyt a₃-azide and Cyt a (Erecinska, M., Wilson, D.F. and Blasie, J.K. (1979) Biochim. Biophys. Acta 545, 352–364). By taking into account the relaxation parameters for both g_x and g_z components of the Cyt a₃-azide g-tensor, the angle between the g_z components of the Cyt a and Cyt a₃g-tensors was determined to be between 0 and 18°, and the Cyt a-Cyt a₃ spin-spin distance was found to be 19 ± 8 Å.     

Dihydroxamic acid complexes of iron (III): ligand pKa and coordinated water hydrolysis constants

A series of dihydroxamic acid ligands of the formula [RN(OH)C(O)]₂(CH₂)_n, (n = 2, 4, 6, 7, 8; R = CH₃, H) has been studied in 2.0 M aqueous sodium perchlorate at 25.0 °C. These ligands may be considered as synthetic analogs to the siderophore rhodotorulic acid. Acid dissociation constants (pK_a) have been determined for the ligands and for N-methylacetohydroxamic acid (NMHA). The pK_a1 and pK_a2 values are: n = 2, R = CH₃ (8.72, 9.37); N = 4, R = CH₃ (8.79, 9.37); N = 6, R = CH₃; N = 7, R = CH₃ (8.95, 9.47); N = 8, R = CH₃ (8.93, 9.45); N = 8, R = H (9.05, 9.58). Equilibrium constants for the hydrolysis of coordinated water (log K) have been estimated for the 1:1 feeric complexes of the ligands n = 2, 4, 8; R = CH₃. The N = 8 ligand forms a monomeric complex with Fe(III) while the n = 2 and 4 ligands form dimeric complexes. For hydrolysis of the n = 8 monomeric complex, log K₁ = −6.36 and log K₂ = −9.84. Analysis of the spectrophotometric data for the dimeric complexes indicates deprotonation of all four coordinated waters. The successive hydrolysis constants, log K_1–4, for the dimeric complexes are as follows: n = 2 (−6.37, −5.77, −10.73, −11.8); n = 4 (−5.54, −5.07, −11.57, −10.17). The log K₂ values for the dimers are unexpectedly high, higher in fact than log K₁, inconsistent with the formation of simple ternary hydroxo complexes. A scheme is proposed for the hydrolysis of the ferric dihydroxamate dimers, which includes the possible formation of μ-hydroxo and μ-oxo bridges.     

Structure and physicochemical properties of barley non-starch polysaccharides—II. Alkaliextractable β-glucans and arabinoxylans

Three fractions containing hemicellulosic material were obtained by sequential extraction of barley residue (left after removal of water-extractable polysaccharides) with saturated barium hydroxide [Ba(OH)₂ fraction], distilled water [Ba(OH)₂/H₂O fraction], and 1 m sodium hydroxide [NaOH fraction]. The yields of the fractions were 1.6, 1.7, and 2.6% (w/w), respectively, of the dry barley grist. The Ba(OH)₂ fraction contained mainly arabinose and xylose, 35.8% and 60.9%, respectively. The Ba(OH)₂/H₂O fraction in addition to 26.7% Ara and 36.6% Xyl contained also 34.8% Glc. The NaOH fraction was composed of 14.2% Ara, 44.0% Xyl, and 40.9% Glc. The Ba(OH)₂/H₂O and NaOH extracts were further fractionated by stepwise (NH₄)₂SO₄ precipitation into several subfractions with varying amounts of β-glucans and arabinoxylans. β-Glucans in Ba(OH)₂/H₂O and NaOH fractions were characterized by high ratios of β-(1→4)/β-(1→3) linkages, large amounts of contiguously linked β-(1→4) segments, and high ratios of cellotriosyl/cellotetraosyl units. The alkali-extractable arabinoxylans, especially those NaOH-extractable, were characterized by a very low degree of substitution, high xylose/arabinose ratio, and a small content of doubly substituted xylose residues. Some populations of arabinoxylans displayed structural features that would enable them to self-associate or to interact with β-glucans.     

C60-fullerenides of ytterbium and lutetium

Cp^#₂Yb (Cp^#=C₅H₄(CH₂)₂NMe₂) has been obtained by reaction of YbI₂(THF)₂ with 2 equiv. of C₅H₄(CH₂CH₂NMe₂)K in THF. The X-ray structure analysis shows a bent structure with intramolecular coordination of both nitrogen atoms to ytterbium. The reaction of C₆₀-fullerene with Cp^#₂Yb leads to the formation of the fullerenide derivative [Cp^#₂Yb]₂C₆₀, which shows an ESR signal in the solid state and in THF solution at room temperature (solid: ΔH = 50 G, G = 1.9992; solution: ΔH = 10 G, G = 2.0001) and a magnetic moment of 3.6 BM. The lutetium fullerenides CpLu(C₆₀)(DME) (3) and Cp^*Lu(C₆₀)(DME)(C₆H₅CH₃) (4), (Cp = η⁵−C₅H₅, Cp^* = η⁵−C₅Me₅), were obtained by reaction of C₆₀ with CpLu(C₁₀H₈) (DME) and Cp^*Lu(C₁₀H₈) (DME) in toluene. Both complexes are paramagnetic (μ_eff = 1.4 and 0.9 BM) and exhibit temperature-dependent ESR signals (293 K: g = 1.992 and 2.0002 respectively).     

Biochemical and biophysical studies on cytochrome aa3 VIII. Effect of cyanide on the catalytic activity

1. 1. Cyanide inhibits the catalytic activity of cytochrome aa₃ in both polarographic and spectrophotometric assay systems with an apparent velocity constant of 4·10³ M⁻¹·s⁻¹ and a K_i that varies from 0.1 to 1.0 μM at 22 °C, pH 7·3.

2. 2. When cyanide is added to the ascorbate-cytochrome c-cytochromeaa₃−O₂ system a biphasic reduction of cytochrome c occurs corresponding to an initial K_i of 0.8 μM and a final K_i of about 0.1 μM for the cytochrome aa₃−cyanide reaction.

3. 3. The inhibited species (a²+a₃³⁺HCN) is formed when a²⁺a₃³⁺ reacts with HCN, when a²⁺a₃²⁺HCN reacts with oxygen, or when a³⁺a₃³⁺HCN (cyano-cytochrome aa₃) is reduced. Cyanide dissociates from a²⁺a₃³⁺HCN at a rate of 2·10⁻³ s⁻¹ at 22 °C, pH 7.3.

4. 4. The results are interpreted in terms of a scheme in which one mole of cyanide binds more tightly and more rapidly to a²⁺a₃³⁺ than to a³⁺a₃³⁺.

Piezoelectric properties of poly-β-hydroxybutyrate and copolymers of β-hydroxybutyrate and β-hydroxyvalerate

The shear piezoelectricity was observed in oriented films of poly-β-hydroxybutyrate (PHB) and copolymers of β-hydroxybutyrate (HB) and β-hydroxyvalerate (HV). The piezoelectric stress constant 3₁₄ = e′₁₄ − ie″₁₄ (polarization/strain), the piezoelectric strain constant d₁₄ = d′₁₄ − id″₁₄ (polarization/stress), the elastic constant c = c′ + ic″ and the dielectric constant = ′ − i″ were determined at a frequency of 10 Hz over a temperature range from −150° to +150°C. Piezoelectric relaxations as well as elastic and dielectric relaxations were clearly observed at the glass transition temperature of about 15°C. In order to evaluate the piezoelectric constants (e₂ and d₂) for the piezoelectric phase which consists of the crystalline region and the oriented non-crystalline region, a spherical dispersion two phase model was utilized. Assuming the appropriate fixed values for the elastic and dielectric constants in the piezoelectric phase, d₂ and d₂ were calculated as a function of temperature. For a PHB and a copolymer (17 HV/83 HB), e₂ and d₂ showed relaxations, leading to a conclusion that the instantaneous piezoelectric constant in the crystalline phase is constant independent of temperature but the piezoelectric constant in the oriented non-crystalline phase is relaxational and has the opposite sign. For a copolymer (25 HV/75 HB) and a chloroform treated copolymer (17 HV/83 HB), e₂ and d₂ were constant independent of temperature, indicating that the oriented non-crystalline phase has disappeared owing to the increased molecular flexibility due to copolymerization or annealing in chloroform vapour.     

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.     

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.     

The physiological ecology of haemocyanin in some selected crabs. II. The characteristics of haemocyanin in relation to terrestrialness

The haemocyanins of five crabs ranging in habit from aquatic to terrestrial have been investigated.

The mean P₅₀ values of the respiratory pigments were determined at 0 mm Hg CO₂ and 28 °C (the average environmental temperature of all the species). Comparison of these data adjusted to the individual mean physiological pH indicate an increase in P₅₀ with terrestrialization, perhaps related to the greater abundance of oxygen in the aerial than in some the aquatic habits, and the progressive elaboration of lung breathing with terrestrialization.

The Bohr shifts (Δ log P₅₀/ΔpH) were determined (using different P_CO2 values to vary pH) and were found to decrease with terrestrialization, perhaps in adaptation to an associated rise in internal P_CO2 (6–8-fold between the aquatic Callinectes sapidus Rathbun and the terrestrial Cardisoma guanhumi Latreille and probably resulting from progressive gill reduction.

The temperature shifts (ΔH cal/mol) of the haemoeyanins were found and it is suggested that they diminish with increasing evironmental temperature and temperature fluctuation accompanying terrestrialization.     

A solid state NMR study of locust bean gum galactomannan and Konjac glucomannan gels

This paper describes a ¹³C solid state NMR study of hydrated powders and gels of locust bean gum galactomannan-LBG and Konjac glucomannan-KGM. Changes in relative spectral intensities, cross-polarization dynamics (T_CH, T_1ρH) and relaxation times (T_1C, T_1H, T_2H) show that hydration (0–90%) of LBG powders increases the 10⁸ Hz frequency molecular motions, probably reflecting the enhanced motion of non-aggregating segments and chain ends. Slower motions (10⁴–10⁵ Hz) are enhanced only slightly at 90% hydration. LBG gel shows higher spatial distinction between aggregated and non-aggregated segments than the hydrated powder and relaxation times indicate higher mobility for galactose-ramified segments, compared to linear mannose segments. While the dynamics of KGM hydration is similar to that of LBG, i.e. mainly affecting fast 10⁸ Hz motions, the gel is significantly more rigid. Both spectra and relaxation times show that glucose residues in KGM gel are particularly hindered, probably due to their preferential involvement in chain aggregation.