Leaf gas exchange, chlorophyll fluorescence and growth responses of Genipa americana seedlings to soil flooding

Effects of soil flooding on photosynthesis and growth of Genipa americana L. seedlings, a neotropical fruit-tree species used in gallery forest restoration programs, were studied under glasshouse conditions. Despite the high survival rate and wide distribution in flood-prone habitats of the neotropics, previous studies demonstrated that growth of G. americana is reduced under soil flooding. Using leaf gas exchange and chlorophyll fluorescence measurements, we tested the hypothesis that stomatal limitation of photosynthesis is the main factor that reduces carbon uptake and growth rates of G. americana seedlings. Throughout a 63-day flooding period, the survival rates were 100%. The maximum values of the net photosynthetic rate (A) and stomatal conductance to water vapor (g_s) of control seedlings were 9.86 μmol CO₂ m⁻² s⁻¹ and 0.525 mol H₂O m⁻² s⁻¹, respectively. The earliest effects of flooding were significant decreases in g_s and A, development of hypertrophied lenticels and decrease in the dry weight of roots. A strong effect of the leaf-to-air vapor pressure deficit (LAVPD) on g_s and A were observed that was enhanced under flooded conditions. Between 14 and 63 days after flooding, significant reductions in g_s (31.7% of control) and A (52.9% of control) were observed followed by significant increments in non-photochemical quenching (q_N) (187.5% of control). During the same period, there were no differences among treatments for the ratio between variable to initial fluorescence (F_v/F₀), the maximum quantum efficiency of the photosystem II (F_v/F_m) and photochemical quenching (q_P), indicating that there was no damage to the photosynthetic apparatus. Based on the results, we conclude that decreases in stomatal opening and stomatal limitation of photosynthesis, followed by decrease in individual leaf area are the main causes of reductions in carbon uptake and whole plant biomass of flooded seedlings.     

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.     

Some physiological and morphological characteristics of citrus plants for drought resistance

Tolerance and avoidance mechanisms to drought stress were studied in 6-month-old plants of Newhall orange (Citrus sinensis (L.) Osbeck) and Ellendale tangor (orange × mandarin hybrid) (Citrus sinensis (L) Osbeck × Citrus reticulata Blanco) during a drought/rewatering cycle under controlled conditions. Drought stress did not promote osmotic adjustment, while elastic adjustment (tissue elasticity increase) was noted in stressed orange and tangor plants. Both citrus plants showed a parallel decrease in leaf conductance (g₁) and leaf water potential (Ψ₁) under water stress. Tangor plants had a more efficient water conservative strategy than orange, based on the characteristics of canopy architecture (lower canopy area and a more closed canopy with leaves nearly vertically oriented) together with a significant decrease in cuticular transpiration rates (TRc) under stress.     

Influence of flood-preconditioning and drought on leaf gas exchange and plant water relations in seedlings of pecan

Four-month old seedlings of pecan [Carya illinoensis (Wangenh) C. Koch] were either not flooded or flooded for 14 days, then transferred to well-drained conditions for 23 days. Water was withheld from one-half of the trees for 6 days, then trees were rewatered, and water was withheld from all trees. Leaf expansion, leaf dry weight, and the number of new leaves that developed were reduced by flooding, but not trunk or root dry weights. Evapotranspiration rates of flooded trees after transfer to well-drained conditions were initially higher than those of unflooded trees, but decreased to rates of control trees after 12 days. Flooding had no effect on photosynthesis after trees had been transferred to well-drained conditions for 23 days. Drought-stressed trees with leaf water potentials as low as − 1.93 MPa had lower leaf photosynthetic CO₂ assimilation rate (A), transpiration (E), and leaf conductance to CO₂ (g_L) as compared to wellwatered trees. Leaf internal CO₂ concentration (c_i) was reduced only by the most severe water-stress treatment. Water use rates and relative water content were lower at the permanent wilting point during a second drought stress when trees had been exposed previously to drought stress.     

Mitochondrial respiratory chain of Tetrahymena pyriformis The properties of submitochondrial particles and the soluble b and c type pigments

Submitochondrial particles isolated from Tetrahymena pyriformis contain essentially the same redox carriers as those present in parental mitochondria: at pH 7.2 and 22 °C there are two b-type pigments with half-reduction potentials of −0.04 and −0.17 V, a c-type cytochrome with a half reduction potential of 0.215 V, and a two-component cytochrome a₂ with E_m7.2 of 0.245 and 0.345 V.

EPR spectra of the aerobic submitochondrial particles in the absence of substrate show the presence of low spin ferric hemes with g values at 3.4 and 3.0, a high spin ferric heme with g = 6, and a g = 2.0 signal characteristic of oxidized copper. In the reduced submitochondrial particles signals of various iron-sulfur centers are observed.

Cytochrome c₅₅₃ is lost from mitochondria during preparation of the submitochondrial particles. The partially purified cytochrome c₅₅₃ is a negatively charged protein at neutral pH with an E_m7.2 of 0.25 V which binds to the cytochrome c-depleted Tetrahymena mitochondria in the amount of 0.5 nmol/mg protein with a K_D of 0.8 · 10⁻⁶ M. Reduced cytochrome c₅₅₃ serves as an efficient substrate in the reaction with its own oxidase. The EPR spectrum of the partially purified cytochrome c₅₅₃ shows the presence of a low spin ferric heme with the dominant resonance signal at g = 3.28.

A pigment with an absorption maximum at 560 nm can be solubilized from the Tetrahymena cells with butanol. This pigments has a molecular weight of approx. 18 000, and E_m7.2 of −0.17 V and exhibits a high spin ferric heme signal at g = 6.     

四种常见树木叶片光合模型关键参数对臭氧浓度升高的响应

随着城市化进程的加快, 臭氧(O₃)已经成为中国夏季首要大气污染物。已有研究表明O₃通过气孔进入叶片显著抑制光合作用, 影响陆地生态系统碳水循环过程。但是O₃浓度升高对植物光合和气孔导度模型关键参数影响的研究仍然缺乏。该研究利用开顶式气室, 设置两个O₃处理(CF, 过滤空气; E-O₃, 未过滤空气+ 60 nmol·mol^-1 O₃), 选用4种常见的树木(茶(Camellia sinensis)、复叶槭(Acer negundo)、栾树(Koelreuteria paniculata)和蒙古栎(Quercus mongolica)), 通过测定叶片气体交换参数, 探究O₃浓度升高对植物光合和气孔导度模型关键参数的影响。结果表明: O₃浓度升高显著降低了4种植物的饱和光合速率和光合生化模型参数叶肉导度, 但是O₃对光合生化模型参数最大羧化速率和最大电子传递速率的负效应在不同树种间存在差异。此外, 不同植物气孔导度对O₃的响应也存在差异。通过对最优化气孔导度模型进行参数化, 结果表明O₃显著提高了蒙古栎和复叶槭的斜率参数(g₁), 并显著增加了茶的气孔导度模型截距参数(g₀), 但降低了复叶槭的g₀。在不同O₃处理下4种树木的内源水分利用效率与g₁呈显著线性负相关关系。综上所述, O₃浓度升高显著影响光合生化和气孔导度模型关键参数。     

The use of multi-frequency EPR techniques to identify the radicals produced in irradiated beta-blockers

The identification of radicals trapped in irradiated drugs can be very intricate. A multi-frequency electron paramagnetic resonance (EPR) study is proposed to resolve this problem. The Q-band (ca. 34 GHz) comparison with X-band (ca. 9 GHz) did not show significant differences for the four β-blockers studied (atenolol, esmolol, nadolol and propranolol). The use of a higher frequency (285 GHz) was required. It enabled us to determine the g-tensor values of the radicals present in atenolol and esmolol, respectively, g₁=2.0086, g₂=2.0059 and g₃=2.0021 and g₁=2.0066, g₂=2.0044 and g₃=2.0021. The latter was assigned as a phenoxyl radical, which can not be the case for the former. Therefore, radicals produced in esmolol may result from a more complex mechanism than the abstraction followed by the diffusion of an H atom inside the solid. In addition, two molecules as similar as atenolol and esmolol hydrochloride do not contain the same radicals after irradiation. These two conclusions drawn from the EPR results on β-blockers show clearly the importance of continuing the investigations on radiolytic mechanisms in solid-state drugs.     

Comparative thermodynamic elucidation of the structural stability of thermophilic proteins

Differential scanning calorimetry, circular dichroism, and visible absorption spectrophotometry were employed to elucidate the structural stability of thermophilic phycocyanin derived from Cyanidium caldarium, a eucaryotic organism which contains a nucleus, grown in acidic conditions (pH 3.4) at 54°C. The obtained results were compared with those previously reported for thermophilic phycocyanin derived from Synechococcus lividus, a procaryote containing no organized nucleus, grown in alkaline conditions (pH 8.5) at 52°C. The temperature of thermal unfolding (t_d) was found to be comparable between C. caldarium (73°C) and S. lividus (74°C) phycocyanins. The apparent free energy of unfolding (ΔG_[urea]=0) at zero denaturant (urea) concentration was also comparable: 9.1 and 8.7 kcal/mole for unfolding the chromophore part of the protein, and 5.0 and 4.3 kcal/mole for unfolding the apoprotein part of the protein, respectively. These values of t_d and ΔG_[urea]=0 were significantly higher than those previously reported for mesophilic Phormidium luridum phycocyanin (grown at 25°C). These findings revealed that relatively higher values of t_d and ΔG_[urea]=0 were characteristics of thermophilic proteins. In contrast, the enthalpies of completed unfolding (ΔH_d) and the half-completed unfolding (ΔH_d)1/2 for C. caldarium phycocyanin were much lower than those for S. lividus protein (89 versus 180 kcal/mole and 62 versus 115 kcal/mole, respectively). Factors contributing to a lower ΔH_d in C. caldarium protein and the role of charged groups in enhancing the stability of thermophilic proteins were discusse.     

Photosynthetic responses of citrus trees to soil flooding

Continuous soil flooding reduced leaf photosynthetic rate, stomatal conductance to water vapor, chlorophyll concentration and activity of ribulose bisphosphate carboxylase-oxygenase (Rubisco, EC 4.1.1.39) of sweet orange [ Citrus sinensis (L.) Osbeck cv. Hamlin] trees, grafted onto rough lemon (RL; C. jambhiri Lush.) and sour orange (SO; C. aurantium L.) rootstocks. After 24 days of waterlogging, trees showed senescence, wilting and abscission of leaves, and these symptoms were more evident with flooded Hamlin/SO than Hamlin/RL. Reduction of leaf photosynthetic rate at day 24 was ca 94%, of stomatal conductance, 71%, of chlorophyll, 38% and of Rubisco, 62% for flooded Hamlin/SO, compared with 22, 5, 18 and 33%, respectively, for flooded Hamlin/RL. For both Hamlin/RL and Hamlin/SO, leaf photosynthetic rate and stomatal conductance to water vapor were closely correlated (r²= 0.87). Leaf internal CO₂ concentration of flooded trees, however, was not decreased by reduced stomatal conductance. Dark respiration rates of fibrous roots of flooded trees were greatly reduced, but not in leaf tissues. Total nonstructural carbohydrate concentrations were higher in leaves (50 and 80% increases for Hamlin/SO and Hamlin/RL, respectively), but drastically reduced in roots (60 and 45% reductions for Hamlin/SO and Hamlin/RL, respectively), as a result of flooding. The data indicate that Hamlin grafted onto RL rootstocks was more tolerant to soil flooding than Hamlin grafted onto SO rootstocks.     

Inorganic carbon uptake kinetics of the stream macrophyte Callitriche cophocarpa Sendt.

Photosynthetic carbon uptake of Callitriche cophocarpa Sendt. was examined in plants collected from six Danish streams and in plants grown under variable inorganic carbon conditions in the laboratory. Both field and laboratory plants showed a low affinity for inorganic carbon (CO₂ compensation points ranging from 0.7 to 22 μM, and K_0.5(CO₂) from 51 to 121 μM), consistent with C-3 photosynthesis and use of CO₂ alone. Variation in inorganic carbon uptake characteristics was low in both groups of plants. Only in laboratory-grown plants was a coupling found between carbon uptake and the inorganic carbon regime of the medium. The carbon extraction capacity, expressed as a percentage of the initial amount of dissolved inorganic carbon (DIC) assimilated in PH-drift experiments, increased from −1.4 to 11.8% with declining external carbon availability, and the initial slope of the CO₂ response curve increased from 6.4 to 15.3 g⁻¹ h⁻¹ dm³. The plasticity of the inorganic carbon uptake system of C. cophocarpa was very low compared to the plasticity observed for submerged macrophytes with accessory carbon uptake systems (i.e. HCO₃⁻ use or C-4 photosynthesis), suggesting that the plasticity of the C-3 photosynthetic apparatus as such is restricted. The low carbon affinity of C. cophocarpa indicates that this species depends on CO₂ oversaturation for a sufficient supply of CO₂ for photosynthesis and growth.     

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.     

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。     

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.     

巴郎山糙皮桦叶片光合氮利用效率的海拔响应

为深入认识植物对环境变化的响应和适应,以分布在川西巴郎山的糙皮桦为研究对象,选择海拔2200、2500、3100和3400 m 4个分布点,测定计算了各分布点叶片光合氮利用效率(PNUE)、CO₂扩散导度(叶肉细胞导度g_m与气孔导度g_s)和氮分配比例(Rubisco氮分配比例P_R、生物力能学组分氮分配比例P_B、捕光组分氮分配比例P_L与细胞壁氮分配比例P_CW)等参数,分析了其沿海拔的变化趋势以及叶片PNUE与其他参数的相关关系.结果表明: 糙皮桦叶片PNUE、P_R和P_B在海拔2500和3100 m相对较高;叶片g_s和g_m则随海拔升高而增加,P_L随海拔升高而降低.糙皮桦叶片P_R和P_B与PNUE呈显著正相关关系,说明P_R和P_B是PNUE随海拔变异的重要内部因素.糙皮桦叶片光合系统氮分配比例P_P在海拔2500和3100 m相对较高,叶片P_CW随海拔升高而降低,叶片其他组分氮分配比例P_other随海拔升高而增加,说明随海拔的升高,糙皮桦叶片趋向将更大比例的氮分配于除光合系统和细胞壁外的其他组分中.     

水蚀风蚀交错区不同土地利用方式的土壤水气传输特性

研究水蚀风蚀交错区土地利用方式转变对土壤水气传输的影响,可为黄土高原生态恢复过程中有限水土资源的高效利用提供参考.为了分析不同土地利用方式下的土壤水气传输特性,探究饱和导水率(K_s)、导气率(K_a)和相对气体扩散率(D_P/D₀)间的关系,对柠条地、撂荒地、苜蓿地、农地和裸地样地0~5 cm深度土层原状土,采用定水头法测定K_s,气室法测定D_P/D₀,土壤导气率测定仪测定田间持水量(FC)下的K_a.结果表明: 土壤0~5 cm容重(ρ_b)的大小顺序为苜蓿地>裸地>撂荒地>柠条地>农地,撂荒地、裸地和苜蓿地ρ_b与农地差异显著.土壤总孔隙度(Φ)的大小顺序为农地>柠条地>撂荒地>裸地>苜蓿地,相比农地,苜蓿地、裸地和撂荒地土壤Φ分别低7.5%、4.7%和3.1%.充气孔隙度(ε₁₀₀)的大小顺序为农地>撂荒地>柠条地>裸地>苜蓿地,苜蓿地、裸地、柠条地和撂荒地ε₁₀₀分别较农地低38.3%、33.6%、12.8%和10.1%.土壤K_s的大小顺序为撂荒地>柠条地>苜蓿地>裸地>农地,其中,撂荒地K_s显著高于其他4种土地利用方式;土壤K_a的大小顺序为撂荒地>苜蓿地>柠条地>裸地>农地,撂荒地与农地之间差异显著;土壤D_P/D₀的大小顺序为撂荒地>柠条地>苜蓿地>农地>裸地,其中,柠条地和撂荒地土壤D_P/D₀显著大于农地,分别较农地高36.8%和61.6%.土壤K_s和FC条件下的K_a、D_P/D₀之间呈显著相关.土地利用方式转变显著改变了土壤的通透性,耕地撂荒或者种植柠条及苜蓿改善了表层土壤导水和导气性能,农地和裸地土壤水气传输能力较差.     

Selection and preliminary characterization of β-glycosidases producer Patagonian wild yeasts

Four pre-selected indigenous yeast strains belonging to Candida guilliermondii (V₂ and V₅), Candida pulcherrima (V₆) and Kloeckera apiculata (V₉), were used as β-glucosidase (βGL) and β-xylosidase (βXL) sources. The optimization of yeast culture conditions was carried out and the effects of oenological parameters on β-glycosidase activities were evaluated. C. guilliermondii V₂ and C. pulcherrima V₆ strains were selected. These strains showed intracellular (C. pulcherrima V₆) and parietal (C. guilliermondii V₂) constitutive βGL and βXL. The enzymatic activities were active at pH, glucose, ethanol and SO₂ concentrations usually found in winemaking and they were able to release monoterpenols and alcohols from grape juice glycoside extracts. Additionally, these yeast strains were not able to produce volatile acidity and off flavour. Regional ecological relevance of these species was also discussed. Our results evidence that the selected C. guilliermondii V₂ and C. pulcherrima V₆ strains have interesting oenological characteristics and allow us to think in their potential application in winemaking.     

光化学反射指数在比较葡萄叶片耐霜冻能力中的应用

以12个葡萄(Vitis vinifera)品种为试材,在秋季采集叶片,进行霜冻处理,测定了霜冻过程中叶片光化学反射指数(PRI)的变化。提取有效参数,采用隶属函数法比较了不同叶片的耐霜冻能力。结果表明,随着温度的降低,叶片光化学反射指数呈下降趋势。在–8–0°C范围内,PRI及其相对值Rt与温度都存在显著的线性关系;叶片PRI在0°C、–8°C时的相对值R0、R–8,以及–8–0°C范围中,Rt与温度的回归直线斜率SLP都具有品种特异性,可以反映不同品种的耐霜冻能力。隶属函数法结合聚类分析结果显示,在12个候选品种中,抗霜冻能力最好的是Cabernet Sauvignon,其R0、R–8和SLP分别为72.3%、50.19%和2.78。     

Activation by reduction of the resting form of cytochrome c oxidase: Tests of different models and evidence for the involvement of CuB

(1) The reaction of the resting form of oxidised cytochrome c oxidase from ox heart with dithionite has been studied in the presence and absence of cyanide. In both cases, cytochrome a reduction in 0.1 M phosphate (pH 7) occurs at a rate of 8.2 · 10⁴ M⁻¹ · s⁻¹. In the absence of cyanide, ferrocytochrome a₃ appears at a rate (k_obs) of 0.016 s⁻¹. Ferricytochrome a₃ maintains its 418 nm Soret maximum until reduced. The rate of a₃ reduction is independent of dithionite concentration over a range 0.9 mM–131 mM. In the presence or cyanide, visible and EPR spectral changes indicate the formation of a ferric a₃/cyanide complex occurs at the same rate as a₃ reduction in the absence of cyanide. A g = 3.6 signal appears at the same time as the decay of a g = 6 signal. No EPR signals which could be attributed to copper in any significant amounts could be detected after dithionite addition, either in the presence or absence of cyanide. (2) Addition of dithionite to cytochrome oxidase at various times following induction of turnover with ascorbate/TMPD, results in a biphasic reduction of cytochrome a₃ with an increasing proportion of the fast phase of reduction occurring after longer turnover times. At the same time, the predominant steady state species of ferri-cytochrome a₃ shifts from high to low spin and the steady-state level of reduction of cytochrome a drops indicating a shift in population of the enzyme molecules to a species with fast turnover. In the final activated form, oxygen is not required for fast internal electron transfer to cytochrome a₃. In addition, oxygen does not induce further electron uptake in samples of resting cytochrome oxidase reduced under anaerobic conditions in the presence of cyanide. Both findings are contrary to predictions of certain O-loop types of mechanism for proton translocation. (3) A measurement of electron entry into the resting form of cytochrome oxidase in the presence of cyanide, using TMPD or cytochrome c under anaerobic conditions, shows that three electrons per oxidase enter below a redox potential of around +200 mV. An initial fast entry of two electrons is followed by a slow (k_obs ≈ 0.02 s) entry of a third electron. Above +200 mV, the number of electrons taken up in the initial fast phase drops as a redox center (presumably Cu_A) titrates with an apparent mid-point potential of +240 mV. The slow phase of reduction remains at the more positive redox values. (4) The results are interpreted in terms of an initial fast reduction of cytochrome a (and Cu_A at redox values more negative than +240 mV) followed by a slow reduction of Cu_B. Cu_B reduction is proposed to spin-uncouple cytochrome a₃ to form a cyanide sensitive center, and trigger a conformational change to an activated form of the enzyme with faster intramolecular electron transfer.     

Assignment of the g = 4.1 ERP signal to manganese in the S2 state of the photosynthetic oxygen-evolving complex: An X-ray absorption edge spectroscopy study

X-ray absorption spectroscopy at the Mn K-edge has been utilized to study the origin of the g = 4.1 EPR signal associated with the Mn-containing photosynthetic O₂-evolving complex. Formation of the g = 4.1 signal by illumination of Photosystem II preparations at 140 K is associated with a shift of the Mn edge inflection point to higher energy. This shift is similar to that observed upon formation of the S₂ multiline EPR signal by 190 K illumination. The g = 4.1 signal is assigned to the Mn complex in the S₂ state.     

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.