Relation between electrokinetic potentials and growth in callus cultures ofTrigonella foenum-graecum

Callus cultures ofTrigonella foenum-graecum were initiated from radicle or cotyledon portions of seedlings and young leaves and maintained on modified 1-B5 medium. The callus mass was disaggregated by mechanical agitation and the discrete cells thus obtained were used to measure their electrokinetic potential. Studies pertaining to the effects of ageing on electrokinetic potential and growth index revealed a relationship between these two parameters. Thus, the rate of change of electrokinotie potential with age could be employed as a parameter to study the growth kinetics of cells in callus cultures.     

Maternal effects and generation mean analysis of seed-oil content in cotton (Gossypium hirsutum L.)

Summary The nature of gene action and of maternal influence governing cottonseed oil attributes were determined with four lines, two each with high and low seed-oil percentage. For this purpose, P1, P2, F0, F1, F2 and alternative sets of BC1 and BC2 generations were analysed in six cross-combinations and their reciprocals. Marginal extents of heterosis for seed-oil percentage were noticeable in F1, with inbreeding depression in F2. Data from reciprocal backcrosses provided evidence in favour of maternal rather than cytoplasmic effects of seed-oil development. Relatively higher extents of heterosis, sizeable inbreeding depression and reciprocally unequal F2 averages were characteristic of the seed index trait, which often showed a reversal of effects from F1 to F2. Reverse reciprocal backcrosses exhibited some differences, including greater resemblance between the types, (A/B)A and (B/A)A, in addition to variable dose effects in seed index. Thus, the differences between F1 seed index values were not due to cytoplasmic influence. Positive heterotic effects for seed-oil index, especially among the backcrosses, ranged between 16.08% and 47.29% over midparent averages. Genetic component estimates from analysis of similar sets of crosses differing only in reciprocal backcrosses, and also from sets of reciprocal crosses between any two parental combinations, were inconsistent. Scaling tests detected presence of epistasis within and between a majority of cross-combinations. Despite reciprocal differences, additive gene effects for seed-oil percentage were significant in 7 out of 24 crosses, representing high x low, low x high and low x low seed-oil parents. Those were, however, accompanied by significant dominance effects of higher order. In crosses involving low seed-oil percentage parents SA1060 and SA229, all six components were detected significant, with opposite effects of dominance and dominance x dominance epistatic components. Significant additive components were also detected for seed index and seed-oil index in 7 and 5 out of 24 crosses, respectively. In the inheritance of seed index and seed-oil index, dominance effects were more important. Epistatic components of additive x additive, and to a lesser extent, those of dominant x dominant were found significant.     

Periodic electric field as a biopolymer conformation switch: a possible mechanism

A theoretical model is proposed to describe the influence of a periodic electric field (PEF) upon a biopolymer. The biopolymer is treated as a classical mechanical system consisting of subsystems (molecular groups) which interact with each other through potential forces. The PEF is treated as a periodic driving force applied to a molecular group. The energy dissipation is considered using the model of fluid (viscous) friction. Arguments for the non-linear character of the friction-velocity dependence caused by the non-Newtonian rheology of a viscous medium are formulated.A forced molecular-group motion is investigated for the situation of a small driving-force period, with oscillations overdamped and a driving force consisting of more than one harmonic. As a result, it is established that the motion always gets to a terminal stage when only a small-scale vibration about some point, X ^*, takes place. The terminal motion is preceded by a transient characterized by the presence of a directional velocity component and so by a drift along a potential profile. the drift goes on until a barrier is met which has a sufficiently large steepness (the barrier height is not important). As a result, the point X ^* may happen to be remote from the conformation potential local minimum (conformational state). The physical reasons for the drift are described.If we consider the small-scale vibration about X ^* in the framework of the hierarchy of scales for intramolecular mobility, it can be regarded as an equilibrium mobility, whereas the drift can be regarded as a functionally important motion, and X ^* as a new conformational state which is realizable only in the presence of the PEF. It may be concluded, as the result of a consistent treatment and neglecting the small-scale vibration, that the conformational potential is modified by adding a linear term (in the one-dimensional case). In this connection, the set of conformational states can both deform (deviation of the positions of minima and their relative depth) and rearrange qualitatively (some minima can vanish and/or new minima can appear). In particular, the transition from one conformation to another one may happen due to rearrangement.     

A stochastic model for the membrane potential of a stimulated neuron

We present a simple model describing the transition between the prefiring, firing and postfiring phases of a single neuron in a large neural net. Using typical values for the physiological parameters that enter the model, we find average interspike times that are close to those reported in experimental measurements.     

Effect of high-intensity endurance training on isokinetic muscle power

The purpose of this study was to determine the effects of high-intensity endurance training on isokinetic muscle power. Six male students majoring in physical-education participated in high intensity endurance training on a cycle ergometer at 90% of maximal oxygen uptake (VO2max) for 7 weeks. The duration of the daily exercise session was set so that the energy expenditure equalled 42 kJ.kg-1 of lean body mass. Peak knee extension power was measured at six different speeds (30 degrees, 60 degrees, 120 degrees, 180 degrees, 240 degrees, and 300 degrees.s-1) with an isokinetic dynamometer. After training, VO2max increased significantly from mean values of 51.2 ml.kg-1.min-1, SD 6.5 to 56.3 ml.kg-1.min-1, SD 5.3 (P less than 0.05). Isokinetic peak power at the lower test speeds (30 degrees, 60 degrees and 120 degrees.s-1) increased significantly (P less than 0.05). However, no significant differences in muscle peak power were found at the faster velocities of 180 degrees, 240 degrees, and 300 degrees.s-1. The percentage improvement was dependent on the initial muscle peak power of each subject and the training stimulus (intensity of cycle ergometer exercise).     

Effects of calcium input/output on the stability of a system for calcium-regulated viscoelastic strain fields

The Goodwin and Trainor model of pattern generation in calcium-regulated strain fields is studied in the case where calcium input and calcium output processes are involved. It is shown that the properties of the original model may still remain provided that the input-output processes are not unstable. In this last case, despite the eventual stabilizing effect of the calcium exchange term, perturbations of the generalized system can grow and lead to inhomogeneous solutions. Applications to cell differentiation and cell growth are discussed.     

The singularly perturbed Hodgkin-Huxley equations as a tool for the analysis of repetitive nerve activity

A qualitative analysis of the Hodgkin-Huxley model (Hodgkin and Huxley 1952), which closely mimics the ionic processes at a real nerve membrane, is performed by means of a singular perturbation theory. This was achieved by introducing a perturbation parameter that, if decreased, speeds up the fast variables of the Hodgkin-Huxley equations (membrane potential and sodium activation), whereas it does not affect the slow variables (sodium inactivation and potassium activation). In the most extreme case, if the perturbation parameter is set to zero, the original four-dimensional system degenerates to a system with only two differential equations. This degenerate system is easier to analyze and much more intuitive than the original Hodgkin-Huxley equations. It shows, like the original model, an infinite train of action potentials if stimulated by an input current in a suitable range. Additionally, explanations for the increased sensitivity to depolarizing current steps that precedes an action potential can be found by analysis of the degenerate system. Using the theory of Mishchenko and Rozov (1980) it is shown that the degenerate system does not only represent a simplification of the original Hodgkin-Huxley equations but also gives a valid approximation of the original model at least for stimulating currents that are constant within a suitable range.     

Rhodobacter capsulatus strain BK5 possesses a membrane bound respiratory nitrate reductase rather than the periplasmic enzyme found in other strains

Rhodobacter capsulatus strain BK5 possesses a membrane bound respiratory nitrate reductase rather than the periplasmic enzyme found in other strains. The enzyme in strain BK5 is shown to be both functionally and structurally related to the nitrate reductase of Paracoccus denitrificans and Escherichia coli.Abbreviation TMAO trimethylamine-N-oxide     

Tissue water relations in elfin cloud forest tree species of Serrania de Macuira,Guajira, Colombia

Summary Diurnal courses of stomatal conductance, leaf water potential, and the components of tissue water potential were measured in six canopy species in an elfin cloud forest. High values of stomatal conductance were measured on cloudy days and during early morning and late afternoon of sunny days. Decreases in stomatal conductance with increases in vapour pressure deficit may have been a response to avoid further water deficits and suggested a stomatal response to changes in relative humidity. Daily transpiration varied between 470 and 1014 g m^-2 day^-1 during cloudy days and between 532 and 944 g m^-2 day^-1 during clear days. Stomatal conductance may have also responded to changes in leaf water potential, which was minimum at noon. The minimum tissue water potential measured in the field was -1.8 MPa in Myrcianthes fragrans, and the minimum turgor pressure was 0.49 MPa also in M. fragrans. There was a correlation between the osmotic potential and the minimum tissue water potential, suggesting that osmotic potential plays a major role in the maintenance of turgor in these species, in spite of the great variability in the elastic properties of leaf tissues. Turgor pressure decreased during the day following the course of water potential but never approached the turgor loss point, as it has been measured in some lowland rain forest trees. This is a strong indication that elfin cloud forest trees do not suffer severe water deficits, and that small tree stature is not directly related to water shortage.     

Cell age-related differences in the interaction of a potential-sensitive fluorescent dye with nuclear envelopes of Acetabularia mediterranea

Abstract. To study whether an electrical potential difference exists across the nuclear envelope or inner nuclear membrane of plant cells, the authors have used an optical probe of membrane potential, the cationic fluorescent dye, DiOC₆(3) (MW = 572.5). This dye was microinjected into the nucleoplasm of isolated Acetabularia nuclei (which are still surrounded by a thin layer of cytoplasm) and its subnuclear localization visualized by fluorescence microscopy. Striking differences, which seemed to be correlated with the developmental stage of the isolated nucleus, were observed. In nuclei isolated from cells at the stage of early cap stage formation, the dye was restricted to the nuclear envelope. In nuclei isolated from cells with intermediate or fully developed caps, there was increased nucleoplasmic staining, and the staining of the envelope was frequently diminished or abolished. In all nuclei, the dye remained within the nucleus after injection. Cytoplasmic staining was only observed when nuclei isolated from cells at the stage of early cap formation were incubated in a hyper- or hypo-tonic medium. Various ionophores, injected before the dye into the nucleoplasm, had no effect on the subsequent nuclear localization of DiOC₆(3), although they did rapidly induce nucleolar condensation in nuclei isolated from cells at the stage of early cap formation. The results suggested that the electrical properties of Acetabularia nuclear envelopes or inner nuclear membranes change during cell maturation. Furthermore, the retention of the dye in the nucleoplasm under isotonic conditions indicated that the nuclear pores were not open channels for molecules of this size.