The redox potentials of the b-type cytochromes of higher plant chloroplasts

1. In fresh chloroplasts, three b-type cytochromes exist. These are b-559_HP (λ_max, 559 nm; E_m at pH 7, +370 mV; pH-independent E_m), b-559_LP (λ_max, 559 nm; E_m at pH 7, +20 mV; pH-independent E_m) and b-563 (λ_max, 563 nm; E_m at pH 7, ?110 mV; pH-independent E_m). b-559_HP may be converted to a lower potential form (λ_max, 559 nm; E_m at pH 7, +110 mV; pH-independent E_m).2. In catalytically active b-f particle preparations, three cytochromes exist. These are cytochrome f (λ_max, 554 nm; E_m at pH 7, +375 mV, pK on oxidised cytochrome at pH 9), b-563 (λ_max, 563 nm; E_m at pH 7, ?90 mV, small pH-dependence of E_m) and a b-559 species (λ_max, 559 nm, E_m at pH 7, +85 mV; pH-independent E_m).3. A positive method of demonstration and estimation of b-559_LP in fresh chloroplasts is described which involves the use of menadiol as a selective reductant of b-559_LP.     

S-allele diversity in Prunus L. Cerasus subgenus from Iran

In this study, S-allele diversity of eight wild and two commercial species of the Cerasus subgenus in Iran was investigated using two primer pairs. A high level of S-allele polymorphism was detected among and within the species evaluated. Furthermore, most of wild species showed 2–4 alleles based on S-allele primers and may be considered as tetraploid. Sweet cherry cultivars, Siah-Mashhad, Siah-Shabestar, Takdaneh-Mashhad, Siah-Daneshkadeh and Protiva showed S₃S₁₂, S₃S₁₂, S₃S₁₂, S₃S₅ and S₃S₄ combinations, respectively, allele S₃ showing the highest frequency. Three Iranian sweet cherry cultivars had the same allelic combination (S₃S₁₂) that the same ancestor in genealogy of these cultivars may explain the loss of diversity observed at the S-locus. Wild cherry (mazzard) accessions showed wide range of alleles such as S₁, S₂, S₇, S₁₄ and S₂₀ and unknown alleles, while sour cherries showed S₆, S₉, S₁₃ and S₂₇ alleles. In conclusion, the conservation of these highly diverse native species of Iranian wild Cerasus germplasm is recommended for future breeding activity.     

Clothing insulation and temperature,layer and mass of clothing under comfortable environmental conditions

This study was designed to investigate the relationship between the microclimate temperature and clothing insulation (I_cl) under comfortable environmental conditions. In total, 20 subjects (13 women, 7 men) took part in this study. Four environmental temperatures were chosen: 14°C (to represent March/April), 25°C (May/June), 29°C (July/August), and 23°C (September/October). Wind speed (0.14ms^-1) and humidity (45%) were held constant. Clothing microclimate temperatures were measured at the chest (T_chest) and on the interscapular region (T_scapular). Clothing temperature of the innermost layer (T_innermost) was measured on this layer 30 mm above the centre of the left breast. Subjects were free to choose the clothing that offered them thermal comfort under each environmental condition. We found the following results. 1) All clothing factors except the number of lower clothing layers (L_lower), showed differences between the different environmental conditions (P<0.05). The ranges of T_chest were 31.6 to 33.5°C and 32.2 to 33.4°C in T_scapular. The range of T_innermost was 28.6 to 32.0°C. The range of the upper clothing layers (L_upper) and total clothing mass (M_total) was 1.1 to 3.2 layers and 473 to 1659 g respectively. The range of I_cl was 0.78 to 2.10 clo. 2) Post hoc analyses showed that analysis of T_innermost produced the same results as for that of I_cl. Likewise, the analysis of L_upper produced the same result as the analysis of the number of total layers (L_total) within an outfit. 3) Air temperature (t_a) had positive relationships with T_chest and T_scapular and with T_innermost but had inverse correlations with I_cl, M_total, L_upper and L_total. T_chest, T_scapular, and T_innermost increased as t_a rose. 4) I_cl had inverse relationships with T_chest and T_innermost, but positive relationships with M_total, L_upper and L_total. I_cl could be estimated by M_total, L_upper, and T_scapular using a multivariate linear regression model. 5) L_upper had positive relationships with I_cl and M_total, but L_lower did not. Subjects hardly changed L_lower under environmental comfort conditions between March and October. This indicates that each of the T_chest, M_total, and L_upper was a factor in predicting I_cl. T_innermost might also be a more influential factor than the clothing microclimate temperature.     

Analytical studies of rapidly inactivating and noninactivating sodium currents in differentiated NG108-15 neuronal cells

The rapidly inactivating (I_Naf) and noninactivating Na⁺ currents (I_Na(NI)) were characterized in NG108-15 neuronal cells differentiated with dibutyryl cyclic AMP in this study. Standard activation and inactivation protocols were used to evaluate the steady-state and kinetic properties of the I_Naf present in these cells. The voltage protocols with a slowly depolarizing ramp were implemented to examine the properties of I_Na(NI). Based on experimental data and computer simulations, a window component of the rapidly inactivating sodium current (I_Naf(W)) was also generated in response to the slowly depolarizing ramp. The I_Naf(W) was subtracted from I_Na(NI) to yield the persistent Na⁺ current (I_Na(P)). Our results demonstrate the presence of I_Na(P) in these cells. In addition to modifying the steady-state inactivation of I_Naf, ranolazine or riluzloe could be effective in blocking I_Naf(W) and I_Na(P). The ability of ranolazine and riluzole to suppress I_Na(P) was greater than their ability to inhibit I_Naf(W). In current-clamp recordings, current-induced voltage oscillations were applied to elicit action potentials (APs) through a gradual transition between spontaneous depolarization and upstroke. Ranolazine or riluzole at a concentration of 3 μM then effectively suppressed the AP firing generated by oscillatory changes in membrane current. The data suggest that a small rise in I_Na(NI) facilitates neuronal hyper-excitability due the decreased threshold of AP initiation. The underlying mechanism of the inhibitory actions of ranolazine or riluzole on membrane potential in neurons or neuroendocrine cells in vivo may thus be associated with their blocking of I_Na(NI).     

Dual recognition of S 1 and S 4 pistils by S 4 sm pollen in self-incompatibility of Japanese pear (Pyrus pyrifolia Nakai)

Most cultivars of Japanese pear (Pyrus pyrifolia Nakai) exhibit gametophytic self-incompatibility controlled by a single S-locus with multiple S-haplotypes. A self-compatible (SC) cultivar, ??Osanijisseiki?? (S ₂ S ₄ ^sm ), arising by a bud mutation of ??Nijisseiki?? (S ₂ S ₄ ), has a stylar-part mutant S ₄ ^sm -haplotype, which lacks the pistil S ₄ gene, which is the S ₄ -RNase gene. To efficiently breed SC cultivars, we selected ??Nashi Chuukanbohon Nou 1 Gou?? (??NCN1??) harboring homozygous S ₄ ^sm from a self-progeny of Osanijisseiki and crossed it with ??Okusankichi?? (S ₅ S ₇ ), ??Hakkou?? (S ₄ S ₅ ), or ??Ri-14?? (S ₁ S ₂ ). Fruit set (%) was compared after self-pollination of the trees in the three progenies. All trees derived from the three progenies were predicted to be SC, except for the S ₄ S ₄ ^sm trees in the progeny of NCN1 × Hakkou. However, S ₁ S ₄ ^sm trees in the progeny of NCN1 × Ri-14 proved to be self-incompatible (SI). The pollen from Osanijisseiki was incompatible with ??Doitsu?? (S ₁ S ₂ ), but that from Nijisseiki was compatible, suggesting a possibility that the S ₄ ^sm pollen was rejected by S ₁ -harboring pistils. This possibility was clarified by crossing the pollen from NCN1 (S ₄ ^sm S ₄ ^sm ) to Doitsu, ??Imamuraaki?? (S ₁ S ₆ ), or ??Hougetsu?? (S ₁ S ₇ ), all of which proved incompatible. On the other hand, S ₄ ^sm pollen was accepted by pistils harboring the S ₂ , S ₃ , S ₅ , S ₆ , S ₇ , S ₉ , and S _k haplotypes. The dual recognition of S ₁ and S ₄ pistils by S ₄ ^sm pollen can be attributed to a mutation of the pollen S ₄ gene(s).     

Electron heat transport through the plasma-electrode boundary in weakly ionized plasma

The average electron thermal energies in the emission flux from the electrode into the plasma, ? ₁, and from the plasma toward the electrode, ? ₂, are determined for the cases of large and small values of the coefficient of kinetic reflection. It is shown that these energies vary within the ranges 0.5k _B T _c < ? ₁ < 2k _B T _c and 0.5k _B T _e < ? ₂ < 2k _B T _e , where T _c and T _e are the temperatures of the cathode and plasma electrons, respectively. The obtained values can be used to formulate the boundary conditions for the hydrodynamic equations at the electrode or a dielectric wall.     

Evolution of enzyme catalytic power. Characteristics of optimal catalysis evaluated for the simplest plausible kinetic model

1. Evolutionary changes in the structure of an enzyme that provide an increase in its K_m value are considered. Provided that K_m increases as a result of increases in the forward rate constants of the catalysis relative to the reverse rate constants, the enzyme catalyses the conversion of a fixed concentration of its substrate more rapidly when its structure provides that K_m>[S] than when K_m<[S]. 2. Catalytic efficiency of enzymes is discussed in terms of the simplest plausible model, the Haldane [(1930) Enzymes, Longmans, London] reversible three-step model: [Formula: see text] The rate equation for the forward reaction of this model (formation of P) may be written in the simple form: [Formula: see text] K_eq. is the equilibrium constant (=[P]_eq./[S]_eq.), and k_cat.=V/[E]_T, where [E]_T is the total enzyme concentration. 3. To assess the effectiveness of an enzyme, it is necessary only to determine the extent to which the constraints of a particular kinetic mechanism permit v₂ (v when K_m»[S]) to approach v_d (the diffusion-limited rate). 4. The value of the optimal rate of catalysis (v_opt., the maximal value of v₂) is dictated by the equilibrium constant for the reaction, K_eq.; v₂=v_d/a, where [Formula: see text] when k₊₁ is assumed equal to k₋₃, and v_opt.=v_d/a_min.. When K_eq.≥1, it is necessary that k₊₂»k₋₁ for a to take its minimum value, a_min.; when K_eq.«1, it is necessary only that k₊₂»K_eq.·k₋₁, i.e. a can equal a_min. even if k₊₂<k₋₁. When K_eq.»1, v_opt.=v_d; when K_eq.=1, v_opt.=v_d/2, and when K_eq.«1, v_opt.=K_eq.·v_d. 5. The analysis, together with predicted effects of evolutionary pressure, suggests that in practice the rates of the fastest enzyme-catalysed freely reversible reactions might be expected to be lower than the value of k₊₁[E]_T[S] by about an order of magnitude, particularly if K_eq.<1. 6. The existing literature suggests that, in general, appropriate values of K_m have evolved for the provision of high rates of catalysis but that many values of k_cat. are not large enough to provide optimal rates of catalysis unless the value of k₊₁ in vivo is lower than its value in free solution.     

Purification of characterization of a minor form of hepatic microsomal cytochrome P-450 from rats treated with polychlorinated biphenyls

A minor form of hepatic microsomal cytochrome P-450 has been purified to apparent homogeneity from rats treated with the polychlorinated biphenyl mixture, Aroclor 1254. This newly isolated hemoprotein, cytochrome P-450_e, is inducible in rat liver by Aroclor 1254 and phenobarbital, but not by 3-methylcholanthrene. Two other hemoproteins, cytochromes P-450_b and P-450_c, have also been highly purified during the isolation of cytochrome P-450_e based on chromatographic differences among these proteins. By Ouchterlony double-diffusion analysis with antibody to cytochrome P-450_b, highly purified cytochrome P-450_e is immunochemically identical to cytochrome P-450_b but does not cross-react with antibodies prepared against other rat liver cytochromes P-450 (P-450_a, P-450_c, P-450_d) or epoxide hydrolase. Purified cytochrome P-450_e is a single protein-staining band in sodium dodecyl sulfate-polyacrylamide gels with a minimum molecular weight (52,500) slightly greater than cytochromes P-450_b or P-450_d (52,000) but clearly distinct from cytochromes P-450_a (48,000) and P-450_c (56,000). The carbon monoxide-reduced difference spectral peak of cytochrome P-450_e is at 450.6 nm, whereas the peak of cytochrome P-450_b is at 450 nm. Ethyl isocyanide binds to ferrous cytochromes P-450_e and P-450_b to yield two spectral maxima at 455 and 430 nm. At pH 7.4, the 455:430 ratio is 0.7 and 1.4 for cytochromes P-450_b and P-450_e, respectively. Metyrapone binds to reduced cytochromes P-450_e and P-450_b (absorption maximum at 445–446 nm) but not cytochromes P-450_a, P-450_c, or P-450_d. Metabolism of several substrates catalyzed by cytochrome P-450_e or P-450_b reconstituted with NADPH-cytochrome c reductase and dilauroylphosphatidylcholine was compared. The substrate specificity of cytochrome P-450_e usually paralleled that of cytochrome P-450_b except that the rate of metabolism of benzphetamine, benzo[a]pyrene, 7-ethoxycoumarin, hexobarbital, and testosterone at the 16α-position catalyzed by cytochrome P-450_e was only 15–25% that of cytochrome P-450_b. In contrast, cytochrome P-450_e catalyzed the 2-hydroxylation of estradiol-17β more efficiently (threefold) than cytochrome P-450_b. Cytochrome P-450_d, however, catalyzed the metabolism of estradiol-17β at the greatest rate compared to cytochromes P-450_a, P-450_b, P-450_c, or P-450_e. The peptide fragments of cytochromes P-450_e and P-450_b, generated by either proteolytic or chemical digestion of the hemoproteins, were very similar but not identical, indicating that these two proteins show minor structural differences.     

Identification of S-genotypes in Chinese cherry cultivars (Prunus pseudocerasus Lindl.)

Self-incompatibility has been studied extensively at the molecular level in Solanaceae, Rosaceae, and Scrophulariaceae, all of which exhibit gametophytic self-incompatibility. In the present study, we successfully isolated nine S-RNase alleles from cultivars of Chinese cherry by PCR amplification from genomic DNA and stylar cDNA combining with cleaved amplified polymorphic sequence marker. Analysis of amino acid sequences revealed five novel S-alleles, S ₂ , S ₄ , S ₆ , S ₈ , and S ₉ , with respective accession numbers in the NCBI database of EF541168, EF541173, EF541172, FJ628598, and FJ628599. Results showed that “Dongtang” and “Yinzhu” contained six S-alleles (S ₁ , S ₃ , S ₅ , S ₇ , S ₈ , and S ₉ ); “Taishanganying” contained four S-alleles (S ₁ , S ₂ , S ₄ , and S ₆ ); “Daiba”, “Dayingzui”, and “Xiaomizi” contained four S-alleles (S ₁ , S ₂ , S ₅ , and S ₈ ); “Laiyangduanzhi”, “Shuangquanchangba”, and “Daqingye” contained three S-alleles (S ₁ , S ₂ , and S ₈ ). It is interesting that different cultivars collected from the same place hold the same S-genotypes. Moreover, pollination tests and pollen tube growth assays showed that nine cultivars were self-compatible. Chinese cherry presented in this article are naturally polyploidy, which is a very useful material for the study of self-compatibility, and much of this information will be valuable for further work on self-(in)compatibility of fruit tree in Rosaceae.     

Hydrophobic hydration processes: General thermodynamic model by thermal equivalent dilution determinations

The “hydrophobic hydration processes” can be satisfactorily interpreted on the basis of a common molecular model for water, consisting of two types of clusters, namely W_I and W_II accompanied by free molecules W_III. The principle of thermal equivalent dilution (TED) is the potent tool (Ergodic Hypothesis) employed to monitor the water equilibrium and to determine the number ξ_w of water molecules W_III involved in each process. The hydrophobic hydration processes can be subdivided into two Classes: Class A includes those processes for which the transformation A(−ξ_wW_I → ξ_wW_II + ξ_wW_III + cavity) takes place with the formation of a cavity, by expulsion of ξ_w water molecules W_III whereas Class B includes those processes for which the opposite transformation B(−ξ_wW_II − ξ_wW_III → ξ_wW_I − cavity) takes place with reduction of the cavity, by condensation of ξ_w water molecules W_III. The number ξ_w depends on the size of the reactants and measures the extent of the change in volume of the cavity. Disaggregating the thermodynamic functions ΔH_app and ΔS_app as the functions of T (or lnT) and ξ_w has enabled the separation of the thermodynamic functions into work and thermal components. The work functions ΔG_Work, ΔH_Work and ΔS_Work only refer specifically to the hydrophobic effects of cavity formation or cavity reduction, respectively. The constant self-consistent unitary (ξ_w = 1) work functions obtained from both large and small molecules indicate that the same unitary reaction is taking place, independent from the reactant size. The thermal functions ΔH_Th and ΔS_Th refer exclusively to the passage of state of water W_III.Essential mathematical algorithms are presented in the appendices.     

Energetics of Active Transport Processes

Discussions of active transport usually assume stoichiometry between the rate of transport J₊ and the metabolic rate J_r. However, the observation of a linear relationship between J₊ and J_r does not imply a stoichiometric relationship, i.e., complete coupling. Since coupling may possibly be incomplete, we examine systems of an arbitrary degree of coupling q, regarding stoichiometry as a limiting case. We consider a sodium pump, with J₊ and J_r linear functions of the electrochemical potential difference, -X₊, and the chemical affinity of the metabolic driving reaction, A. The affinity is well defined even for various complex reaction pathways. Incorporation of a series barrier and a parallel leak does not affect the linearity of the composite observable system. The affinity of some region of the metabolic chain may be maintained constant, either by large pools of reactants or by regulation. If so, this affinity can be evaluated by two independent methods. Sodium transport is conveniently characterized by the open-circuit potential (Δψ)_I=0 and the natural limits, level flow (J₊)_X+=0, and static head X⁰₊ = (X₊)_J+=0. With high degrees of coupling -X⁰₊/F approaches the electromotive force E_Na (Ussing); -X⁰₊/F cannot be identified with ((RT/F) ln f)_X+=0, where f is the flux ratio. The efficiency η = -J₊X₊/J_rA is of significance only when appreciable energy is being converted from one form to another. When either J₊ or -X₊ is small η is low; the significant parameters are then the efficacies ε_J+ = J₊/J_rA and ε_X+ = -X₊/J_rA, respectively maximal at level flow and static head. Leak increases both J₊ and ε_J+ for isotonic saline reabsorption, but diminishes -X⁰₊ and ε_X♀. Electrical resistance reflects both passive parameters and metabolism. Various fundamental relations are preserved despite coupling of passive ion and water flows.     

Genetic specifics of the breeding of cotton varieties with cleistogamous flowers

As a prerequisite to studying the genetics and breeding of chasmogamous and cleistogamous flowers, a preliminary experiment was performed to estimate the extent of cross-pollination in cotton varieties and hybrids. Vicinism estimates varied from 0.53 to 15.36%, i.e., the proportion of cross-pollination was relatively high, leading to a biological contamination. As a result of such contamination, genetic collection lines and varieties lose genetic homogeneity and become heterozygous and genetically heterogeneous. The genetic control of the flower type was studied in the Gossipium hirsutum L. × G. barbadense L. interspecific hybrids, and phenotypic segregation of the 3: 1 and 15: 1 types with monogenic (3: 1) and digenic (15: 1) differences of noncumulative polymerization was observed. The corresponding types of genotypic segregation were 1: 2: 1 (1Cg ₁ Cg ₁ cg ₂ cg ₂ : 2Cg ₁ cg ₁ cg ₂ cg ₂ : 1cg ₁ cg ₁ cg ₂ cg ₂ ) and 1: 2: 2: 4: 1: 2: 1: 2: 1 (1) Cg ₁ Cg ₁ Cg ₂ Cg ₂ -1; (2) Cg ₁ Cg ₁ cg ₂ cg ₂ -2; (3) Cg ₁ cg ₁ Cg ₂ Cg ₂ -2; (4) Cg ₁ cg ₁ Cg ₂ cg ₂-4; (5) Cg ₁ Cg ₁ cg ₂ cg ₂ -1; (6) Cg ₁ cg ₁ cg ₂ cg ₂ -2; (7) cg ₁ cg ₁ Cg ₂ Cg ₂-1; (8) cg ₁ cg ₁ Cg ₂ cg ₂ -2; (9) cg ₁ cg ₁ cg ₂ cg ₂ -1. Genotypes (1)–(8) had chasmogamous flowers, while double-recessive genotype (9) had cleistogamous flowers. Based on this, genotypes with individual phenotypic expression were identified in F2, and their correlation with the most important morphological, biological, and agricultural features was studied. Special attention was paid to the productivity of hybrid plants intended for use in breeding to obtain intensive varieties. The study made it possible to isolate forms, families, genetic collection lines, and varieties with isogenic or nonisogenic determination of these characters and chasmogamous and cleistogamous flowers of G. hirsutum L. and G. barbadense L. prototypes by using original methods to examine the two types of flowers; the methods do not have analogs in cotton breeding worldwide.     

Mesophyll conductance variations in response to diurnal environmental factors in Myrcia paivae and Minquartia guianensis in Central Amazonia

Mesophyll conductance (g _m) is essential to determine accurate physiological parameters used to model photosynthesis in forest ecosystems. This study aimed to determine the effects of time of day on photosynthetic parameters, and to assess the effect of using either intercellular CO₂ concentration (C _i) or chloroplast CO₂ concentration (C _c), on maximum carboxylation velocity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), V _cmax. We used Amazonian saplings of Myrcia paivae and Minquartia guianensis. Photosynthetic parameters were measured using an infrared gas analyzer (IRGA); g _m was determined using both gas exchange and chlorophyll (Chl) a fluorescence and gas-exchange data alone. Leaf thickness (L _T) and specific leaf area (SLA) were also measured. Air temperature, relative humidity or understory light did not correlate with g _m and on average daily IRGA-fluorometer-determined g _m was 0.04 mol(CO₂) m^?2 s^?1 for M. paivae and 0.05 mol(CO₂) m^?2 s^?1 for M. guianensis. Stomatal conductance (g _s), g _m, electron transport rate (J _F), and light-saturated net photosynthetic rate (P _Nmax) were lower in the afternoon than in the morning. However, no effect of time of day was observed on V _cmax. L _T and SLA did not affect any of the examined parameters. IRGA-determined g _m was almost the double of the value obtained using the IRGA-fluorescence method. V _cmax values determined using C _c were about 25% higher than those obtained using C _i, which highlighted the importance of using C _c in V _cmax calculation. Decline in P _Nmax at the end of the afternoon reflected variations in g _s and g _m rather than changes in V _cmax. Diurnal variation in g _m appeared to be associated more with endogenous than with atmospheric factors.     

Modification of yttrium alkoxides: β-Ketoesterate-substituted yttrium alkoxo/hydroxo/oxo clusters

Reaction of Y₅O(OiPr)₁₃ (“yttrium iso-propoxide”) with one molar equivalent of isopropyl acetoacetate (iprac) per Y resulted in the formation of Y₉O(OH)₉(OiPr)₈(iprac)₈, a rare example of an yttrium alkoxo/hydroxo/oxo cluster. Reaction in a 1:3 molar ratio gave Y₄(OH)₂(iprac)₁₀ and Y₆(OH)₆(iprac)₁₂ instead. A fourth cluster, Y₉O(OH)₉(iprac)₁₆, structurally closely related to Y₉O(OH)₉(OiPr)₈(iprac)₈, was obtained upon recrystallization of Y₄(OH)₂(iprac)₁₀ from CDCl₃.     

Conformation-specific precipitation of human α2-macroglobulin by divalent zinc or calf thymus histone H3

Highly purified native α₂-macroglobulin (α₂M), α₂M-trypsin, and α₂M-methylamine were compared in experiments designed to study protein precipitation. Significant turbidity developed within 30 min in solutions containing histone H3 and either α₂M-methylamine or α₂M-trypsin, as determined by absorbance at λ = 550 nm. No turbidity was detected in solutions that contained histone H3 and native α₂M or histone H3 alone. Experiments with radioiodinated histone H3 or radioiodinated proteinase inhibitor confirmed that both the H3 and the α₂M “fast” forms (α₂M-methylamine, α₂M-trypsin) were present in the precipitates generated. As much as 70% of the ¹²⁵I-α₂M-methylamine was recovered in the precipitate after incubation with a 120-fold molar excess of H3 (concentration of α₂M-methylamine, 0.28 μm). The ratio of histone to proteinase inhibitor by weight in the precipitate was approximately two. Under comparable conditions, somewhat less α₂M-trypsin precipitated from solutions containing H3 than did α₂M-methylamine; however, inactivation of the α₂M-trypsin with phenylmethylsulfonyl fluoride prior to incubation increased the level of precipitation significantly. Solutions containing poly-l-lysine (M_r ~ 13,000) instead of histone did not form precipitates with any of the forms of α₂M studied. In a second set of experiments, radioiodinated native α₂M, α₂M-trypsin, and α₂M-methylamine were incubated in solutions containing ZnCl₂, BaCl₂, CdCl₂, CuSO₄, MgCl₂, or NiCl₂ (concentration of divalent cation between 5 μm and 1.0 mm). Native α₂M was soluble in all of these salts. By contrast, α₂M-methylamine and α₂M-trypsin precipitated extensively from solutions containing greater than 100 μm ZnCl₂. Precipitation was greater than 90% complete at 1 mm ZnCl₂. A similar effect was not observed with any of the other divalent cations.     

The effect of leaf-level spatial variability in photosynthetic capacity on biochemical parameter estimates using the Farquhar model: a theoretical analysis

Application of the widely used Farquhar model of photosynthesis in interpretation of gas exchange data assumes that photosynthetic properties are homogeneous throughout the leaf. Previous studies showed that heterogeneity in stomatal conductance (g_s) across a leaf could affect the shape of the measured leaf photosynthetic CO₂ uptake rate (A) versus intercellular CO₂ concentration (C_i) response curve and, in turn, estimation of the critical biochemical parameters of this model. These are the maximum rates of carboxylation (V_c,max), whole-chain electron transport (J_max), and triose-P utilization (V_TPU). The effects of spatial variation in V_c,max, J_max, and V_TPU on estimation of leaf averages of these parameters from A-C_i curves measured on a whole leaf have not been investigated. A mathematical model incorporating defined degrees of spatial variability in V_c,max and J_max was constructed. One hundred and ten theoretical leaves were simulated, each with the same average V_c,max and J_max, but different coefficients of variation of the mean (CV_VJ) and varying correlation between V_c,max and J_max (Ω). Additionally, the interaction of variation in V_c,max and J_max with heterogeneity in V_TPU, g_s, and light gradients within the leaf was also investigated. Transition from V_c,max- to J_max-limited photosynthesis in the A-C_i curve was smooth in the most heterogeneous leaves, in contrast to a distinct inflection in the absence of heterogeneity. Spatial variability had little effect on the accuracy of estimation of V_c,max and J_max from A-C_i curves when the two varied in concert (Ω = 1.0), but resulted in underestimation of both parameters when they varied independently (up to 12.5% in V_c,max and 17.7% in J_max at CV_VJ = 50%; Ω = 0.3). Heterogeneity in V_TPU also significantly affected parameter estimates, but effects of heterogeneity in g_s or light gradients were comparatively small. If V_c,max and J_max derived from such heterogeneous leaves are used in models to project leaf photosynthesis, actual A is overestimated by up to 12% at the transition between V_c,max- and J_max-limited photosynthesis. This could have implications for both crop production and Earth system models, including projections of the effects of atmospheric change.     

The supersilylated tetrasulfane tBu3Si-S4-SitBu3: Synthesis, structure, and its reaction behavior towards [Fe(CO)5]

The tetrasulfane tBu₃Si-S₄-SitBu₃ was formed in high yield when S₂Cl₂ was treated with two equivalents of Na(thf)₂SSitBu₃ in thf. X-ray quality crystals of the tetrasulfane tBu₃Si-S₄-SitBu₃ (monoclinic space group P2₁/c) were grown from a benzene solution at ambient temperature. UV-induced degradation of [Fe(CO)₅] in the presence of the tetrasulfane tBu₃Si-S₄-SitBu₃ led to the formation of the carbonyliron complex [Fe₄(μ₄−S)₂(CO)₁₁].     

小麦和玉米叶片光合-蒸腾日变化耦合机理

植物叶片光合-蒸腾耦合是陆地生态系统碳-水耦合的基础.已有研究将叶片光合-蒸腾耦合笼统归因于气孔的共同控制作用,缺乏对其耦合机理的全面分析.选择华北地区大田作物冬小麦(C3)和夏玉米(C4)为研究对象,分别在小麦开花期和玉米拔节期选择典型晴天进行叶片光合蒸腾日变化观测(8:00-18:00).结果发现:1)光合速率(An)、蒸腾速率(Tr)以及光合有效辐射(PAR)、叶片表面温度(T)和气孔导度(gs)均表现出单峰日变化特征,峰值出现在正午前后;2)An-Tr具有极显著线性正相关关系(小麦和玉米的相关系数分别为0.75**和0.92**,回归直线斜率分别为1.99和3.62);3)PAR、T和gs与An和Tr有线性正相关关系;4)PAR-An与PAR-Tr、T-An与T-Tr、gs-An与gs-Tr的回归直线形态非常相似.分析认为:1)在光合-蒸腾耦合特征方面,C3作物小麦和C4作物玉米叶片光合-蒸腾都有明显的线性耦合关系,但两者的耦合关系特征存在明显差异,玉米的An-Tr线性回归斜率要明显大于小麦;2)在光合-蒸腾耦合机理方面,日变化中PAR、T和gs同时受太阳辐射调控与An、Tr发生趋向相同、形态相似且近似同步的变化,因此PAR-An与PAR-Tr、T-An与T-Tr、gs-An与gs-Tr具有形态相似的线性关系,这保证了在PAR、T和gs等调控因子发生较大变化的日变化过程中光合-蒸腾保持良好的线性耦合关系.