Molecular weight estimation using sodium dodecyl sulfate-pore gradient electrophoresis

Pore gradient electrophoresis (PGE) in the presence of sodium dodecyl sulfate (SDS) provides a means for high resolution fractionation of multicomponent protein systems and permits estimation of molecular weights for macromolecules ranging from 10³ to 10⁶. We have evaluated the performance of several methods used to construct calibration curves for estimation of molecular weights using SDS-PGE. A linear relationship between the logarithm of molecular weight, log (M_r), and the logarithm of the relative mobility, log (R_l), can be obtained for a 30-fold range of molecular weights. However, this range of linearity depends on the choice of the concentration gradient, the degree of crosslinking of the gel, and on the nature of the underlying relationship between the retardation coefficient, K_R, and the molecular weight. An empirical relationship, first introduced by Lambin et al. (1976, Anal. Biochem.74, 567) between log (M_r) and the logarithm of the gel concentration at the position reached by the protein, log (%T), provides better linearity over a wider molecular weight range than does the use of log (R_l). We have compared these relatienships by experimental analysis of 10 standard proteins and by a theoretical analysis of an idealized model system. A computer program has been developed which provides appropriate statistical estimation of the molecular weight for an unknown protein, together with its standard error and 95% confidence limits. A new method has also been developed for analysis of nonlinear calibration curves in terms of molecular weight versus distance migrated, based on a theoretically justifiable, physical-chemical model. This model implies that either the relationship between log (M_r) and log (R_l) or the one between log (M_r) and log (%T) will become nonlinear as the range of molecular weight is extended. We suggest that the use of a nonlinear least-squares curve-fitting procedure provides an optimal method for molecular weight estimation when sufficient data are available. Based on these findings, a general strategy is presented for estimation of molecular weights by polyacrylamide gel electrophoresis.     

Trade-off relationships between some reproductive characteristics in plants with special reference to life history stragegy

Several reproductive triats in plants were studied in more than 200 populations of 61 wild species from diverse ecological conditions. As a result, it was found that there occur three distinct types of plants in the energy allocation patterns to reproductive structures (RA) and the propagule output per plant (P_N), i.e. (1) the number of propagules per plant increases in response to the increase in RA (Type I), (2) the number of propagules decreases in response to the increase in RA (Type II), and (3) the RA remains constant despite the great differences in the propagule number per plant. A conspicuous trade-off relationship was also discovered to occur between the RA to a single propagule (R_A) and the propagule output per plant (P_N), such that log R_A=logC−blot P_N, or R_A=C/P_N ^b =CP_N ^−b , where C is a constant. The three different ranges ofb-values were recognized, i.e.b<1.0,b>1.0, andb=1.0, which correspond to Type I, Type II, and Type III, respectively. Related problems to the concept ofr- andK-strategy are also discussed.     

Strategy of nitrogen acquisition and utilization by carnivorous Dionaea muscipula

Plant carnivory represents an exceptional means to acquire N. Snap traps of Dionaea muscipula serve two functions, and provide both N and photosynthate. Using ¹³C/¹⁵N-labelled insect powder, we performed feeding experiments with Dionaea plants that differed in physiological state and N status (spring vs. autumn plants). We measured the effects of ¹⁵N uptake on light-saturated photosynthesis (A _max), dark respiration (R _D) and growth. Depending on N status, insect capture briefly altered the dynamics of R _D/A _max, reflecting high energy demand during insect digestion and nutrient uptake, followed by enhanced photosynthesis and growth. Organic N acquired from insect prey was immediately redistributed, in order to support swift renewal of traps and thereby enhance probability of prey capture. Respiratory costs associated with permanent maintenance of the photosynthetic machinery were thereby minimized. Dionaea’s strategy of N utilization is commensurate with the random capture of large prey, occasionally transferring a high load of organic nutrients to the plant. Our results suggest that physiological adaptations to unpredictable resource availability are essential for Dionaea’s success with regards to a carnivorous life style.     

A submaximal test to assess back muscle capacity: Evaluation of construct validity

A functional endurance test more specific to common occupational tasks is proposed for assessing back muscle capacity. The test involves static intermittent contractions (8-s work-rest cycles) using a predefined absolute load (90 Nm) across subjects. Since the test involved an absolute endurance task, it was hypothesized that performance would be influenced by both the strength and relative endurance of the subjects, thus demonstrating the construct validity of this new test. Fifteen males and 17 females were assessed on three different days to allow familiarization and to measure their Strength as well as their absolute and relative endurance. Absolute and relative endurance were defined as the time to reach exhaustion (Tend_abs and Tend_rel, respectively) during a fatigue protocol including both an absolute (90 Nm) and a relative (40% of individual strength) load (extension moment at the L5/S1 joint). Strength and Tend_rel each explained an almost equivalent portion of Tend_abs (total variance explained: 61.5%), thus confirming the construct validity of the functional endurance test. This new test should better identify the back muscle impairments (weakness, fatigability) often observed in chronic low-back-pain patients.     

石榴园西花蓟马种群动态及其与气象因素的关系

2007-2008年,对云南省建水石榴园西花蓟马种群动态进行了系统调查,并采用回归分析(逐步回归分析、通径分析)、主成分分析及灰色系统分析就气象因子对该虫种群动态的影响进行了系统分析。结果表明,西花蓟马在建水石榴园常年发生,冬季较低,夏季最高,成虫全年种群消长呈单峰型,高峰期为5月份。相关性分析结果表明,西花蓟马种群数量与月相对湿度间呈极显著正相关性(P<0.01),与月均气温和月最低气温间呈显著正相关性(P<0.05),与月最高气温、月均降雨量和月均蒸发量间无相关性(P>0.05)。回归分析结果表明,石榴园西花蓟马种群动态的决定因子中影响最大的气象因素是月最低气温,而月均气温和月相对湿度是影响种群数量变动的主要因素。主成分分析表明,月最低气温是主要成分,其累积方差贡献率达73.03%。灰色系统分析结果表明,影响石榴园6种蓟马种群动态最关键的因子是月相对湿度;年度间影响最大的是年总降雨量;石榴花期各蓟马的种群数量与气象因素间关联度最大的是月最低温;果期各种蓟马的种群数量与气象因素间关联度最大的是月均降雨量。     

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.     

Reconstitution of the R compound allele in maize

The R^r:standard allele in maize, which conditions anthocyanin pigmentation in plant and seed tissues in the presence of appropriate complementary factors, is associated with a tandem duplication. The proximal member of the duplication carries P, the plant pigmenting determiner and the distal member member carries S, the seed pigmenting determiner. Derivatives from R^r that have lost S function are designated r^r. They represent either losses of the distal member of the duplication (P derivatives) or mutations of S to s (P s). Derivatives that have lost P function are designated R^g, and represent either losses of the proximal member of the duplication (S derivatives) or mutations of P to p (p S).—All four possible types of r^r/R^g heterozygotes were tested for their capacity to yield R^r reconstitution by crossing over. No R^r derivatives were obtained from P/S heterozygotes, a result consistent with the view that P and S occupy corresponding positions in homologous chromosome segments. R^r reconstitution was detected in both tandem duplication heterozygotes P s/S and P/p S, and was found to be about ten times more frequent in the latter. The ratio of R^r reconstitution in the two heterozygotes is a function of position of the anthocyanin marker within the duplicated segment. The data from these heterozygotes allow one to measure the distance between P and S, that is to say, the genetic length of the duplicated segment. This distance was found to be 0.16 map units. The highest frequency of R^r reconstitution was obtained from P s/p S heterozygotes, since direct pairing (see PDF) as well as the p//s type of displaced pairing have the potential to produce R^r derivatives. One of the R^g derivatives used in this study, R^g₆, was found to back-mutate in some sublines to R^r. The basis for this instability remains unknown.     

The effect of transmission route on plant virus epidemic development and disease control

A model for indirect vector transmission and epidemic development of plant viruses is extended to consider direct transmission through vector mating. A basic reproduction number is derived which is the sum of the R₀ values specific for three transmission routes. We analyse the model to determine the effect of direct transmission on plant disease control directed against indirect transmission. Increasing the rate of horizontal sexual transmission means that vector control rate or indirect transmission rate must be increased/decreased substantially to maintain R₀ at a value less than 1. By contrast, proportionately increasing the probability of transovarial transmission has little effect. Expressions are derived for the steady-state values of the viruliferous vector population. There is clear advantage for an insect virus in indirect transmission to plants, especially where the sexual and transovarial transmission rates are low; however information on virulence-transmissibility relationships is required to explain the evolution of a plant virus from an insect virus.     

Assessment strategy and the evolution of fighting behaviour

The view is examined that the adaptive value of conventional aspects of fighting behaviour is for assessment of relative RHP (resource holding power) of the combatants. Outcomes of aggressive disputes should be decided by each individual's fitness budget available for expenditure during a fight (determined by the fitness difference between adoption of alternative strategies, escalation or withdrawal without escalation) and on the rate of expenditure of the fitness budget if escalation occurs (determined by the RHPs of the combatants). Thus response thresholds for alternative strategies (“assessments”) will be determined by natural selection on a basis of which opponent is likely to expend its fitness budget first, should escalation occur. This “loser” should retreat (before escalation) and the winner should stay in possession of the resource. Many aggressive decisions depend on whether one is a resource holder, or an attacker. Assuming the RHP of the combatants to be equal, there are many instances of fitness pay-off imbalances between holder and attacker which should weight the dispute outcome in favour of one or other opponent by allowing it a greater expendable fitness budget. Usually the weighting favours the holder; the attacker therefore needs a correspondingly higher RHP before it may be expected to win. This is not invariably the case, and much observed data fits the predictions of this sort of model. If assessments are perfect and budget expenditure rates exactly predictable, then there would never seem to be any case for escalation. Escalation can be explained in terms of injury inflictions (expenditures) occurring as discrete events; i.e. as “bouts” won or lost during fighting. Assessment can give only a probabilistic prediction of the outcome of a bout. A simple model is developed to investigate escalation situations. Each combatant assesses relative RHP; this correlates with an absolute probability of winning the next bout (c_abs). The stake played for is infliction of loss of RHP and is determined by the fitness budgets of the opponents. (Each individual plays for the withdrawal of its opponent.) This defines a critical probability of winning (c_crit) for each combatant, above which escalation is the favourable strategy (c_abs > c_crit) and below which withdrawal is favourable (c_abs < c_crit). Escalation should occur only where c_abs-c_crit is positive for both combatants. This model gives predictions compatible with the observations, indicating that RHP loss alone can be adequate to explain withdrawal: escalation behaviour. Withdrawal tendency will be increased by low searching costs. Escalations should be restricted to closely matched RHP opponents if RHP disparity is the major imbalance. Outside the “escalation range” of a given individual, the higher RHP individual wins and the lower one loses (i.e. it should withdraw after conventional display). RHP disparity and holder: attacker imbalance should both interact to shape the observed pattern, though their relative importances will depend on species and situation. In some instances selection may favour immediate withdrawal from an occupied territory even without assessment of RHP.     

A graphical analysis of life history evolution in biennial plants

Graphical analysis was done on the lfie history evolution of biennials (or monocarpic perennials). The age of seed production (x), the probability of surviving to agex [l(x)], and the number of seeds produced at agex[b(x)] determine the ultimate rate of population increase (r). The ages whenr=max andr=0 define the optimal and critical age for seed production, respectively, which depend on the shape and combination of thel(x) andb(x) curves. The otpimal age of seed production appears only for the convex function of the natural logarithm of the net reproductive rate [R ₀(x)], while the critical age appears irrespective of the shape of theR ₀(x) curves. The effects of environmental change on the optimal and critical ages are, analyzed, with the conclusion that in an environment imposing higher mortality or lower fecundity, delayed reproduction is favored. Age- and size-dependent productions of seeds have different effects on the variation ofr in a changing environment.     

Growth, mortality and stock assessment of kelee shad, Hilsa kelee (Fam: Clupeidae) in the coastal waters of Pakistan

Growth of kelee shad, Hilsa kelee, in the coastal waters of Pakistan was estimated from the lengthfrequency samples. The von Bertalanffy growth equation was L _t = 23.10 (1 ? exp (?0.94(t + 0.18))). Estimated parameters of total mortality (Z), natural mortality (M) and fishing mortality (F) were 2.08 year^?1, 1.78 year^?1, and 0.30 year^?1 respectively. The length-at-first capture was Lc = 10.88 cm. Biomass per recruitment (B/R) and yield per recruitment (Y′/R) were 0.87 and 0.031 respectively. The annual exploitation rate was U = 0.12. The exploitation ratio for maximum yield per recruit E _max = 0.73 and fishing mortality for maximum yield per recruit F _max = 1.52; biological reference point F _opt = 0.89 year^?1 and F _limit = 1.18 year^?1. Present estimations showed that the natural mortality was higher than fishing mortality in Hilsa kelee, indicating that the state of the stock is sustainable and the fishery of kelee shad should not be increased beyond current levels in the coastal waters of Pakistan.     

Insect-Flower Interaction Network Structure Is Resilient to a Temporary Pulse of Floral Resources from Invasive Rhododendron ponticum

Invasive alien plants can compete with native plants for resources, and may ultimately decrease native plant diversity and/or abundance in invaded sites. This could have consequences for native mutualistic interactions, such as pollination. Although invasive plants often become highly connected in plant-pollinator interaction networks, in temperate climates they usually only flower for part of the season. Unless sufficient alternative plants flower outside this period, whole-season floral resources may be reduced by invasion. We hypothesized that the cessation of flowering of a dominant invasive plant would lead to dramatic, seasonal compositional changes in plant-pollinator communities, and subsequent changes in network structure. We investigated variation in floral resources, flower-visiting insect communities, and interaction networks during and after the flowering of invasive Rhododendron ponticum in four invaded Irish woodland sites. Floral resources decreased significantly after R. ponticum flowering, but the magnitude of the decrease varied among sites. Neither insect abundance nor richness varied between the two periods (during and after R. ponticum flowering), yet insect community composition was distinct, mostly due to a significant reduction in Bombus abundance after flowering. During flowering R. ponticum was frequently visited by Bombus; after flowering, these highly mobile pollinators presumably left to find alternative floral resources. Despite compositional changes, however, network structural properties remained stable after R. ponticum flowering ceased: generality increased, but quantitative connectance, interaction evenness, vulnerability, H’₂ and network size did not change. This is likely because after R. ponticum flowering, two to three alternative plant species became prominent in networks and insects increased their diet breadth, as indicated by the increase in network-level generality. We conclude that network structure is robust to seasonal changes in floral abundance at sites invaded by alien, mass-flowering plant species, as long as alternative floral resources remain throughout the season to support the flower-visiting community.     

On the Origin and the Signal-Shaping Mechanism of the Fast Photosignal in the Vertebrate Retina

Fast photosignals (FPS) with R₁ and R₂ components were measured in retinas of cattle, rat, and frog within a temperature range of 0° to 60°C. Except for temperatures near 0°C the signal rise of the R₁ component was determined by the duration of the exciting flash. The kinetics of the R₂ component and the meta transition of rhodopsin in the cattle and rat retina were compared. For the analysis of the FPS it is presupposed that the signal is produced by light-induced charges on the outer segment envelope membrane that spread onto the whole plasma membrane of the photoreceptor cell. To a good approximation, this mechanism can be described by a model circuit with two distinct capacitors. In this model, the charging capacitance of the pigmented outer segment envelope membrane and the capacitance of the receptor's nonpigmented plasma membrane are connected via the extra- and intracellular electrolyte resistances. The active charging is explained by two independent processes, both with exponential rise (R₁ and R₂), that are due to charge displacements within the pigmented envelope membrane. The time constant τ₂ of the R₂ membrane charging process shows a strong temperature dependence that of the charge redistribution, τ_r, a weak one. In frog and cattle retinas the active charging is much slower within a large temperature range than the passive charge redistribution. From the two-capacitor model it follows for τ_r « τ₂ that the rise of the R₂ component is determined by τ_r, whereas the decay is given by τ₂. For the rat retina, however, τ₂ approaches τ_r at physiological temperatures and becomes <τ_r above 45°C. In this temperature range where τ₂ ≈ τ_r, both processes affect rise and decay of the photosignal. The absolute values of τ_r are in good accordance with the known electric parameters of the photoreceptors. At least in the cattle retina, the time constant τ₂ is identical with that of the slow component of the meta II formation. The strong temperature dependence of the meta transition time gives rise to the marked decrease of the R₂ amplitude with falling temperature. As the R₁ rise could not be fully time resolved the signal analysis does not yield the time constant τ₁ of the R₁ generating process. It could be established, however, within the whole temperature range that the decay of the R₁ component is determined by τ_r. Using an extended model that allows for membrane leakage, we show that in normal ringer solution the membrane time constant does not influence the signal time-course and amplitude.     

Insect-plant interactions on a planet of weeds

Two conflicting views confront ecologists and evolutionary biologists on the degree of symmetry in interactions between plants and phytophagous insects. The symmetrical view holds that insects and plants have strong effects on one another's evolutionary and ecological dynamics. Thus, herbivores are regarded as a major influence on plant distribution and abundance in contemporary ecosystems, and coevolution is commonly invoked to explain adaptive radiation in plants and insects, host specialization in insects, as well as much of the morphological and chemical variety observed in plants. The asymmetrical view acknowledges that plants have major effects on insects, but claims that insects seldom impose significant effects on plants. Proponents of the asymmetric view tend to ignore or discount insect-plant interactions in communities and ecosystems altered by human impacts. If we recognize the scope and scale of human impacts, and ways in which these impacts change insect-plant interactions, then our views about symmetry or asymmetry in insect-plant interactions will change. To understand, predict, and manage insect herbivory we need to study it in all its manifestations. In particular, the study of interactions involving alien species is both an urgent priority for environmental management and potentially a source of ecological insights on the role of herbivores in plant population and community dynamics. A complete theory of insect/host plant interactions must explain and predict interactions both within and beyond the native range. Such a theory might guide efforts to deal with environmental problems stemming from rapid rates of extinction and homogenization of the world's biota.     

Accumulation and excretion of pesticides used as insecticides or fungicides in agricultural products by the willow shiner Gnathopogon caerulescens

The average bioconcentration factors (BCF) in the whole body of willow shiner (Gnathopogon caerulescens) after 24–336 hr exposure were 810 for chlorpyriphosmethyl, 802 for vamidothion, 110 for edifenphos, 25 for ethoprophos, 83 for bendocarb, 39 for pirimicarb and 114 for methyl parathion. The correlations between a logarithm of 48 hr-Lc₅₀ to carp (log Lc₅₀ and the parameters (a logarithm of n-octanol-water partition coefficiens (log P_ow) and log BCF in willow shiner) were investigated for the pesticides studied here and already reported. The correlation factor (r) was −0.136 (N = 21) for log Lc₅₀ vs log P_ow and 0.039 (N = 24) for log Lc ₅₀ vs log BCF. The excretion rate constants (k) from the whole body of the fish were 0.01 hr⁻¹ for chlorpyriphosmethyl, 0.03 hr⁻¹ for vamidothion, 0.11 hr⁻¹ for edifenphos, 0.27 hr⁻¹ for ethoprophos, 0.18 hr⁻¹ for bendiocarb, 0.01 hr⁻¹ for pirimicarb and 0.08 hr⁻¹ for methyl parathion. The correlation between log k and log BCF was investigated for 22 pesticides already reported and studied here. The r value was not so high (−0.537, N = 22) but higher (−0.672, N = 2) in the case of excluding simetryne.     

Role of coarse woody debris in the carbon cycle of Takayama forest,central Japan

Coarse woody debris (CWD) is an important component of the forest carbon cycle, acting as a carbon pool and a source of CO₂ in temperate forest ecosystems. We used a soda-lime closed-chamber method to measure CO₂ efflux from downed CWD (diameter ≥5 cm) and to examine CWD respiration (R _CWD) under field conditions over 1 year in a temperate secondary pioneer forest in Takayama forest. We also investigated tree mortality (input to the CWD pool) from the data obtained from the annual tree census, which commenced in 2000. We developed an exponential function of temperature to predict R _CWD in each decay class (R ² = 0.81–0.97). The sensitivity of R _CWD to changing temperature, expressed as Q ₁₀, ranged from 2.12 to 2.92 and was relatively high in decay class III. Annual C flux from CWD (F _CWD) was extrapolated using continuous air temperature measurements and CWD necromass pools in the three decay classes. F _CWD was 3.0 (class I), 17.8 (class II), and 13.7 g C m^?2 year^?1 (class III) and totaled 34 g C m^?2 year^?1 in 2009. Annual input to CWD averaged 77 g C m^?2 year^?1 from 2000 to 2009. The budget of the CWD pool in the Takayama forest, including tree mortality inputs and respiratory outputs, was 0.43 Mg C ha^?1 year^?1 (net C sink) owing to high tree mortality in the mature pioneer forest. The potential CWD sink is important for the carbon cycle in temperate successional forests.     

Clustering of spin-labeled cholesterol analog diluted in bilayers of saturated and unsaturated phospholipids

Clustering of spin-labeled cholesterol analog, 3β-doxyl-5α-cholestane (DChl), diluted in bilayers comprised of either saturated dipalmitoyl-glycero-phosphocholine (DPPC) or unsaturated dioleoyl-glycero-phosphocholine (DOPC) phospholipids was studied. DChl molar fraction X varied between 0.005 and 0.04. EPR spectroscopy applied at low temperatures (200 K) enabled exploring magnetic dipole-dipole (d-d) interaction between spin labels. For DOPC bilayers, EPR spectra were found to broaden remarkably with X increase. The broadening was simulated for the models of 2-dimentional (2-D) clusters with enhanced local concentration, X_loc, which was several times larger than X, and for 1-dimensional (1-D) DChl clusters. The distance of closest approach in these simulations attained the intermolecular lateral distance in the membrane (~0.7 nm). For DPPC bilayers, EPR spectra showed only small broadening, which in these simulations could not be reproduced even if X_loc was taken as small as X. However strong concentration dependence was found for electron spin echo (ESE) decays. Both the EPR and ESE data for DPPC bilayers were explained within the model assuming encapsulation of DChl molecules in lipid shells so preventing them to approach each other closer than a certain distance, R_min. The R_min value was found to vary between ~2.5 nm and 5 nm, for X varying between 0.04 and 0.005; X_loc in these simulations was several times larger than X. So the DChl clustering in DOPC bilayers is driven by attractive lipid-mediated forces, while in DPPC bilayers long-range nanoscale lipid-mediated repulsive/attractive forces take place for distances smaller and larger R_min, correspondingly.     

Glycine-Glomus-Rhizobium Symbiosis: II. Antagonistic Effects between Mycorrhizal Colonization and Nodulation

Soybean (Glycine max [L.] Merr.) plants grown in pot cultures were inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe and Rhizobium japonicum strain 61A118 at planting (G₁R₁) or at 20 days (G₂₀R₂₀), or with one of the endophytes after the other has colonized the host root (G₁R₂₀, G₂₀R₁). Nodulated (PR₁) and VAM (G₁N) dipartite associations, or nonsymbiotic plants (PN) using nutrient solutions with N, P, or N + P concentrations providing endophyte-equivalent nutrient inputs were used as controls. The delayed tripartite associations received the appropriate N, P, or N + P amendment while one or both endophytes were absent during the first 20 days of growth. Prior inoculation with one endophyte significantly inhibited development of the other. Root hexose sugar concentrations were negatively correlated with VAM colonization (r = −0.89), nodule activity (r = −0.91), and root P content (r = −0.93). Nodule (r = 0.97) and root (r = 0.96) P content correlated positively with VAM colonization. Nodule weight or VAM-fungal biomass were significantly greater in associations grown with only one endophyte. Dry weights of the PN, G₁N, PR₁, and G₂₀R₂₀ plants were significantly greater than those of tripartite plants inoculated at planting with either or both endophytes. Interendophyte inhibition is attributed to competition for root carbohydrates, and this effect apparently also affects overall plant productivity. The objective of the study was to determine if the timing of endophyte introduction and establishment affected the development of the other symbiotic partners.     

Growth, in vivo extensibility, and tissue tension in developing pea internodes

The relationship between growth, in vivo extensibility, and tissue tension in the first 3 internodes of 5, 6, and 7 day-old pea plants (Pisum sativum L. cv Alaska), grown under continuous red light was investigated. The upper 15 millimeters of each internode was marked with ink and its elongation growth measured over the next subsequent 8 hours. In vivo extensibility was measured by stretching living tissue at constant force (creep test) in a custom-built extensiometer. Tissue tension was determined by (a) measuring the rate of expansion of the isolated cortical cylinder after adding water and the amount of contraction of the epidermis after peeling, and (b) by use of the `split section test.' A good correlation between rate of elongation growth, in vivo extensibility, and tissue tension was established. The epidermis peeled from the growing third internode of 7 day-old plants and measured immediately showed a plastic extensibility (E<sub>pl</sub> twice that of peels from nongrowing excised sections. This high E<sub>pl</sub>-value was lost on incubation of the sections in distilled water, and was subsequently restored by incubating the sections in auxin (indole-3-acetic acid). We conclude that the in situ growth of the internodes is a function of tissue-tension, which provides the driving force of organ growth, and the extensibility (E<sub>pl</sub> of the outer epidermal wall, which is in the growing plant in a `loosened' state. We furthermore suggest that in the intact plant auxin is causally involved in the wall loosening process in the epidermis.     

Nonlinear Dependences of Optical Properties of Spherical Core–Shell Silver–Gold and Gold–Silver Nanoparticles on Their Parameters

Modeling of nonlinear optical properties of spherical core–shell gold–silver and silver–gold nanoparticles (NPs) placed in water was carried out on the base of extended Mie theory. Efficiency cross sections of absorption σ _abs, scattering σ _sca, and extinction σ _ext of radiation with wavelengths λ?=?400 and 532 nm for core–shell NPs with constant core radii r ₀₀?=?5, 10, 20, and 40 nm and in the range of relative radii r ₁/r ₀₀?=?1–8 were calculated (r ₁ is the radius of shell). Dependences of optical properties of gold–silver and silver–gold NPs on increasing of core radius r ₀ in the range 0???r ₁ under condition r ₁?=?const and increasing of r ₀ under r ₁???r ₀?=?const were investigated. Results show the nonlinear behavior of optical properties of core–shell gold–silver and silver–gold NPs on radiation wavelengths (optical indexes of metals), different core and shell radii, and their correlation, on relative NP radii r ₁/r ₀₀. An increase and decrease of absorption, scattering, and extinction efficiency cross sections of core–shell NPs with changing of wavelengths, core and shell radii, and relative NP radii r ₁/r ₀₀ are established. These dependences can be used for experimental investigation of the interesting first stages of shell formation on core and optical determination of core–shell NP parameters.