Development of water stress in kale leaves of different insertion levels

The mutual relationship between the water potential (γ _w ), its components, namely the osmotic potential (γ _s ) and the pressure potential (γ _p ), and the water saturation deficit (ΔW _sat ) were determined in the leaves of different insertion levels. During the water stress development in kale plants induced by decreasing soil moisture theγ _w decreased, parallely in all the leaves but the same decrease ofγ _q was accompanied by the highest decrease of theγ _p , probably due to the accumulation of osmotically active solutes, and the lowest decrease ofγ _p in the upper leaves and with the lowest decrease ofγ _s and the highest decrease ofγ _p in the lower leaves. Also the corresponding values of the ΔW _sat were always lower in the upper than in the middle and lower leaves. Thus the upper leaves wilted at more negative values ofγ _w than the other leaves. On the contrary, during the wilting of the cut off leaves the relationship betweenγ _w and ΔW _sat in the upper, middle and lower leaves was practically the same. The very slightly higher decrease ofγ _s in the upper leaves in comparison with the other leaves was compensated by a lower deerease of theirγ _p . These changes in the ratios ofγ _w ,γ _s ,γ _p and ΔW _sat with the leaf insertion levels enabled the preference of the upper leaves in retaining the necessary water supply during the wilting of plantsin situ.     

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.     

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.     

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.     

Inheritance and interactions of incompatibility alleles in the tetraploid sour cherry

Three progenies of sour cherry (Prunus cerasus) were analysed to correlate self-(in)compatibility status with S-RNase phenotype in this allotetraploid hybrid of sweet and ground cherry. Self-(in)compatibility was assessed in the field and by monitoring pollen tube growth after selfing. The S-RNase phenotypes were determined by isoelectric focusing of stylar proteins and staining for RNase activity and, for the parents, confirmed by PCR. Seedling phenotypes were generally consistent with disomic segregation of S-RNase alleles. The genetic arrangements of the parents were deduced to be ‘Köröser’ (self-incompatible) S ₁ S ₄ .S _B S _D , ‘Schattenmorelle’ (self-compatible) S ₆ S ₁₃ .S _B S _B , and clone 43.87 (self-compatible) S ₄ S ₁₃ .S _B S _B , where “.” separates the two homoeologous genomes. The presence of S ₄ and S ₆ alleles at the same locus led to self-incompatibility, whereas S ₁₃ and S _B at homoeologous loci led to self-compatibility. The failure of certain heteroallelic genotypes in the three crosses or in the self-incompatible seedlings indicates that S ₄ and S ₆ are dominant to S _B . However, the success of S ₁₃ S _B pollen on styles expressing corresponding S-RNases indicates competitive interaction or lack of pollen-S components. In general, the universal compatibility of S ₁₃ S _B pollen may explain the frequent occurrence of S ₁₃ and S _B together in sour cherry cultivars. Alleles S _B and S _D , that are presumed to derive from ground cherry, and S ₁₃ , presumably from sweet cherry, were sequenced. Our findings contribute to an understanding of inheritance of self-(in)compatibility, facilitate screening of progenies for self-compatibility and provide a basis for studying molecular interactions in heteroallelic pollen.     

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.     

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.     

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.     

Two-Electron Reactions S2QB → S0QB and S3QB → S1QB are Involved in Deactivation of Higher S States of the Oxygen-Evolving Complex of Photosystem II

The oxygen-evolving complex of Photosystem II cycles through five oxidation states (S₀-S₄), and dark incubation leads to 25% S₀ and 75% S₁. This distribution cannot be reached with charge recombination reactions between the higher S states and the electron acceptor Q_B⁻. We measured flash-induced oxygen evolution to understand how S₃ and S₂ are converted to lower S states when the electron required to reduce the manganese cluster does not come from Q_B⁻. Thylakoid samples preconditioned to make the concentration of the S₁ state 100% and to oxidize tyrosine Y_D were illuminated by one or two laser preflashes, and flash-induced oxygen evolution sequences were recorded at various time intervals after the preflashes. The distribution of the S states was calculated from the flash-induced oxygen evolution pattern using an extended Kok model. The results suggest that S₂ and S₃ are converted to lower S states via recombination from S₂Q_B⁻ and S₃Q_B⁻ and by a slow change of the state of oxygen-evolving complex from S₃ and S₂ to S₁ and S₀ in reactions with unspecified electron donors. The slow pathway appears to contain two-electron routes, S₂Q_B → S₀Q_B, and S₃Q_B → S₁Q_B. The two-electron reactions dominate in intact thylakoid preparations in the absence of chemical additives. The two-electron reaction was replaced by a one-electron-per-step pathway, S₃Q_B → S₂Q_B → S₁Q_B in PS II-enriched membrane fragments and in thylakoids measured in the presence of artificial electron acceptors. A catalase effect suggested that H₂O₂ acts as an electron donor for the reaction S₂Q_B → S₀Q_B but added H₂O₂ did not enhance this reaction.     

Diffusional conductances to CO2 as a target for increasing photosynthesis and photosynthetic water-use efficiency

A key objective for sustainable agriculture and forestry is to breed plants with both high carbon gain and water-use efficiency (WUE). At the level of leaf physiology, this implies increasing net photosynthesis (A _N) relative to stomatal conductance (g _s). Here, we review evidence for CO₂ diffusional constraints on photosynthesis and WUE. Analyzing past observations for an extensive pool of crop and wild plant species that vary widely in mesophyll conductance to CO₂ (g _m), g _s, and foliage A _N, it was shown that both g _s and g _m limit A _N, although the relative importance of each of the two conductances depends on species and conditions. Based on Fick’s law of diffusion, intrinsic WUE (the ratio A _N/g _s) should correlate on the ratio g _m/g _s, and not g _m itself. Such a correlation is indeed often observed in the data. However, since besides diffusion A _N also depends on photosynthetic capacity (i.e., V _c,max), this relationship is not always sustained. It was shown that only in a very few cases, genotype selection has resulted in simultaneous increases of both A _N and WUE. In fact, such a response has never been observed in genetically modified plants specifically engineered for either reduced g _s or enhanced g _m. Although increasing g _m alone would result in increasing photosynthesis, and potentially increasing WUE, in practice, higher WUE seems to be only achieved when there are no parallel changes in g _s. We conclude that for simultaneous improvement of A _N and WUE, genetic manipulation of g _m should avoid parallel changes in g _s, and we suggest that the appropriate trait for selection for enhanced WUE is increased g _m/g _s.     

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].     

Analysis of changes of insect-plant ratio-improvement of key-factor analysis for evaluating bottom-up effects in insect population dynamics

A revised key-factor analysis was presented for analyzing the temporal changes in the ratio of insect absolute number to plant resource. Ten data sets for 5 insect species were then analyzed. In this key-factor analysis, the key factor is defined as the factor contributing highly to between-year variation inR _r , the log rate of the inter-year change of the insect-plant ratio. The yearly change of plant resource was handled as a separate factor, expressed byr _pl , log ratio of plant resource in yearn to plant resource in yearn+1. The following was revealed: 1) In 7 of the 10 data sets examined,r _pl influenced variations ofR _r ; in particular in 3 casesr _pl was the main key factor. 2) Generation-to-generation fluctuations of absolute insect densities showed density dependence in 4 cases, while those of insect-plant ratios, in 8 cases. 3) The Royama model or a linear model, explained well the relationship between log insect-plant ratio (X _r ) andR _r and the relationship betweenX _r and log yearly change rate of absolute insect density (R _abs ). However, in the 7 cases in whichr _pl was a critical factor for variations ofR _r , with, increase ofX _r ,R _r showed a steeper, decrease around the equilibrium point (the point for whichR _r is 0) thanR _abs . This occurred becauser _pl tended to be negatively correlated withX _r . Consequently, in two casesX _r fluctuated cyclicly or chaotically although without the changes in plant resource, fluctuations ofX _r would be damped oscillations approaching equilibrium.     

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.     

Immunochemical and spectroscopic evidence for protein conformational changes in phytochrome transformations

Phytochrome was examined by immunochemical and spectroscopic techniques to detect differences between the protein moieties of red- and far red-absorbing phytochrome (P_r and P_fr). No differences in the reaction of P_r and P_fr with phytochrome antibody were discernible on Ouchterlony double diffusion plates. However, the microcomplement fixation assay showed a greater degree of antibody reaction with P_fr than with P_r, indicating some difference in the surface characteristics of the two forms. Circular dichroism spectroscopy between 300 and 200 nanometers revealed differences between P_r and P_fr which may reflect differences in the protein conformation. The circular dichroism spectrum of P_r showed a negative band at 285 nanometers which was not present in the spectrum of P_fr, and the large negative circular dichroism band at 222 nanometers with P_fr, associated with the α-helical content, was shifted 2 nanometers to shorter wave length with P_r although there was no change of magnitude of this band. The absorbancy of P_r and P_fr is very nearly the same in the 280 nanometer spectral region, but sensitive difference spectra between P_r and P_fr did reveal spectra which were similar to solvent perturbation spectra obtained by others with different proteins. In total, the experiments indicate that there are conformational differences between the protein moieties of P_r and P_fr but that these differences are rather slight from a standpoint of gross structure.     

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.     

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).     

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.     

Limitation factors for photosynthesis in ‘Bluecrop’ highbush blueberry (Vaccinium corymbosum) leaves in response to moderate water stress

The levels of stomatal, mesophyll and biochemical limitations in CO₂ assimilation of ‘Bluecrop’ highbush blueberry leaves were compared at two different levels of leaf water potential. The leaf water potentials were ?1.49 and ?1.94 MPa in daily-irrigated (DI) and non-irrigated (NI) shrubs, respectively. The NI shrubs represented plants under moderate water stress. Mesophyll conductance (g _m) and chloroplastic CO₂ concentration (C _c) were estimated by combined measurements of gas exchange and chlorophyll fluorescence under various intercellular CO₂ concentrations (C _i). Net CO₂ assimilation rates (A _n) as a function of C _c were used for calculating maximum carboxylation efficiency (α _cmax) at the real sites of CO₂ assimilation. Maximum A _n (A _nmax) from the light response curves at 400 μmol mol^?1 air of ambient CO₂ concentration (C _a) were lower in the leaves of NI shrubs than in those of DI ones. However, electron transport rates were higher in the leaves of NI shrubs than in those of DI ones. The decrease in CO₂ assimilation following water stress may be caused by a decrease in g _m rather than a decrease in stomatal conductance (g _s) according to limitation analysis. Limitation rates by g _s, calculated at 400 μmol mol^?1 air of C _a in A _n-C _i curves, were not significantly different between the leaves of DI and NI shrubs. However, limitation rates by g _m from A _n-C _c curves were significantly higher in the leaves of NI shrubs than in those of DI ones. Maximum carboxylation efficiency (α _cmax) values calculated from the A _n-C _c curve, contrary to those calculated from the A _n-C _i curve, were higher in the leaves of NI shrubs than in those of DI ones. Consequently, mesophyll limitation than stomatal and biochemical limitations mainly down-regulated the photosynthesis in the leaves of ‘Bluecrop’ blueberry shrubs during moderate water stress.