Morphing structures and signal transduction in Mimosa pudica L. induced by localized thermal stress

Leaf movements in Mimosa pudica, are in response to thermal stress, touch, and light or darkness, appear to be regulated by electrical, hydrodynamical, and chemical signal transduction. The pulvinus of the M. pudica shows elastic properties. We have found that the movements of the petiole, or pinnules, are accompanied by a change of the pulvinus morphing structures. After brief flaming of a pinna, the volume of the lower part of the pulvinus decreases and the volume of the upper part increases due to the redistribution of electrolytes between these parts of the pulvinus; as a result of these changes the petiole falls. During the relaxation of the petiole, the process goes in the opposite direction. Ion and water channel blockers, uncouplers as well as anesthetic agents diethyl ether or chloroform decrease the speed of alert wave propagation along the plant. Brief flaming of a pinna induces bidirectional propagation of electrical signal in pulvini. Transduction of electrical signals along a pulvinus induces generation of an action potential in perpendicular direction between extensor and flexor sides of a pulvinus. Inhibition of signal transduction and mechanical responses in M. pudica by volatile anesthetic agents chloroform or by blockers of voltage gated ion channels shows that the generation and propagation of electrical signals is a primary effect responsible for turgor change and propagation of an excitation. There is an electrical coupling in a pulvinus similar to the electrical synapse in the animal nerves.     

Effects of electrical currents on the absorption of water by eggs of Nereis limbata

Unfertilized eggs of the marine worm Nereis limbata subjected to electrical currents (direct or alternating) undergo remarkable changes. Certain minute granules just inside the surface of the egg absorb water and swell to more than 300 times their original size and thereby produce a mass of jelly which surrounds the egg with a zone about as wide as the original diameter of the egg. The amount of direct current is too small to produce any change of color in eggs stained with neutral red. In direct current the jelly appears first on the side toward the anode and moves toward the anode. In alternating current it appears on opposite sides facing the electrodes. It might be thought that the current changes the chemical character of the granules so that they are able to absorb very large quantities of water but this seems unlikely. If the current is shut off after 1 minute the swelling continues. This might be explained on the ground that each jelly precursor granule is covered with a waterproof film which is removed by the current. It does not seem probable that the effect is due to heat produced by the current since the exposure is so short. It seems possible that the current may strip off micelles from the waterproof covering of the granules and allow water to penetrate. The fact that alternating current is more effective than direct current might be explained on the ground that the egg may be represented as a capacity in parallel with a resistance so constituted that relatively little direct current can enter. The non-aqueous film which covers the surface of the protoplasm appears to be liquid rather than solid.     

Do Flies Have A Red Receptor?

(1) The compound eye of Musca exhibits characteristics which have heretofore frequently been considered evidence for color receptors: (a) The spectral sensitivity curve has several peaks whose relative heights can be altered by selective adaptation to colored lights, and (b) the shape of the retinal action potential varies with wave length. (2) The action spectrum for the red enhancement of on and off responses is compared with the "red receptor" calculated by Mazokhin-Porshnyakov from colorimetric data obtained in rapid color substitutions. Both have maxima at 615 to 620 mµ and appear to be different expressions of the same phenomenon. (3) A red receptor is absent. The evidence which suggests different types of receptors in the region 500 to 700 mµ can be accounted for by variations in the numbers of receptors stimulated. In red light there is a recruitment of additional ommatidia caused by leakage of long wave lengths through the pigment screen, and this spatial summation potentiates the on and off responses. The principal evidence is: (a) a white eye mutant which has no accessory screening pigments also lacks the peak of sensitivity in the red, even when adapted to violet light; (b) white-eyed flies give identical responses with large on and off effects at all wave lengths from 500 to 700 mµ; and (c) reducing the number of excited ommatidia by decreasing the size of the test spot makes the on and off transients smaller relative to the receptor component.     

Generation and characterization of cells that can be conditionally depleted of mitochondrial SOD2

Manganese-dependent superoxide dismutase (SOD2) serves as the primary defense against mitochondrial superoxide, and decreased SOD2 activity results in a range of pathologies. To investigate the events occurring soon after depletion of SOD2, we generated SOD2 gene knockout chicken DT40 cells complemented with a human SOD2 (hSOD2) cDNA, whose expression can be switched off by doxycycline (Dox). When SOD2 was depleted by the addition of Dox, the cells grew slightly slower and formed fewer colonies than cells expressing hSOD2. In addition, these cells showed a high sensitivity to paraquat, which produces superoxide, and died through apoptosis. In contrast to results obtained with mouse and DrosophilaSod2 mutants, we found no indication of an increase in DNA lesions due to depletion of SOD2.     

Defensive responses to predatory seastars by two specialist limpets, Notoacmea insessa (Hinds) and Collisella instabilis (Gould), associated with marine algae

The limpets Notoacmea insessa (Hinds) and Collisella instabilis (Gould), which are associated specifically with certain algae, were tested for defensive responses to seastars. Contact with predatory seastars elicited responses by both species of limpets, in contrast to previous work reporting a lack of defensive responses by specialist limpets associated with plants. Non-predatory seastars normally did not elicit defensive responses. The form of the response by Notoacmea insessa differed, depending on whether the limpet was on or off its grazing scar. When the limpet was off its grazing scar, the most common response was movement away from the point of contact. When on the scar, the limpet usually elevated its shell and rocked from side-to-side, but rarely moved from the scar. The responses of Collisella instabilis almost always involved rapid movement away from the point of contact and tended to be more vigorous than those of Notoacmea insessa.     

THE KINETICS OF PENETRATION : XIV. THE PENETRATION OF IODIDE INTO VALONIA

When 0.1 M NaI is added to the sea water surrounding Valonia iodide appears in the sap, presumably entering as NaI, KI, and HI. As the rate of entrance is not affected by changes in the external pH we conclude that the rate of entrance of HI is negligible in comparison with that of NaI, whose concentration is about 10⁷ times that of HI (the entrance of KI may be neglected for reasons stated). This is in marked contrast with the behavior of sulfide which enters chiefly as H₂S. It would seem that permeability to H₂S is enormously greater than to Na₂S. Similar considerations apply to CO₂. In this respect the situation differs greatly from that found with iodide. NaI enters because its activity is greater outside than inside so that no energy need be supplied by the cell. The rate of entrance (i.e. the amount of iodide entering the sap in a given time) is proportional to the external concentration of iodide, or to the external product [N⁺]_o [I^-l_o, after a certain external concentration of iodide has been reached. At lower concentrations the rate is relatively rapid. The reasons for this are discussed. The rate of passage of NaI through protoplasm is about a million times slower than through water. As the protoplasm is mostly water we may suppose that the delay is due chiefly to the non-aqueous protoplasmic surface layers. It would seem that these must be more than one molecule thick to bring this about. There is no great difference between the rate of entrance in the dark and in the light.     

THE PENETRATION OF STRONG ELECTROLYTES

The entrance of strong electrolytes into Valonia is very slow unless the cells are injured. This, together with the very high electrical resistance of the protoplasm, suggests that they may penetrate largely as undissociated molecules formed at the surface of the protoplasm by the collision of ions. Under favorable circumstances KCl may be absorbed to the extent of 3 x 10^–8 mols per hour per sq. cm. of surface together with about 0.17 as much NaCl. Other substances which seem to penetrate to some extent are Li, Rb, Br, BrO₃, I, IO₃, and selenite. Little or no penetration is shown by SCN, ferricyanide, ferrocyanide, formate, salicylate, tungstate, seleniate, NO₂, SO₃, Sb, glycerophosphate, and many heavy metals and the alkaline earths. In sea water whose specific gravity had been increased by CsCl cells of Valonia floated for over a year and there was little or no penetration of Cs except as the result of injury. The penetration of NH₄Cl decreases the specific gravity of the sap and causes the cells to float: under these circumstances they live indefinitely. It is probable that NH₃ or NH₄OH penetrates and is subsequently changed to NH₄Cl. It would seem that if the sea contained a little more ammonia this would be a floating organism.     

PROTOPLASMIC ASYMMETRY IN NITELLA AS SHOWN BY BIOELECTRIC MEASUREMENTS

Using multinucleate cells of Nitella 2 or 3 inches in length it is possible to kill one end with chloroform without producing at the other any immediate alteration which can be detected by our present methods. When a spot in external contact with sap is killed its potential difference falls approximately to zero and it is therefore possible to measure the potential difference across the protoplasm at any desired point merely by leading off from that point to the one where the protoplasm has been killed. The results indicate that the inner and outer protoplasmic surfaces differ, for when both surfaces are in contact with the same solution (cell sap) there is an electromotive force of about 15.9 millivolts, the inner surface being positive to the outer (i.e. the positive current tends to flow from the inner surface through the electrometer to the outer surface). The situation resembles that in Valonia where the corresponding value (with Valonia sap applied to the outside) has been reported as about 14.5 millivolt (the inner surface being positive to the outer). It would seem appropriate to designate this as radial polarity.     

Clonal interference, multiple mutations and adaptation in large asexual populations

Two important problems affect the ability of asexual populations to accumulate beneficial mutations and hence to adapt. First, clonal interference causes some beneficial mutations to be outcompeted by more-fit mutations that occur in the same genetic background. Second, multiple mutations occur in some individuals, so even mutations of large effect can be outcompeted unless they occur in a good genetic background that contains other beneficial mutations. In this article, we use a Monte Carlo simulation to study how these two factors influence the adaptation of asexual populations. We find that the results depend qualitatively on the shape of the distribution of the fitness effects of possible beneficial mutations. When this distribution falls off slower than exponentially, clonal interference alone reasonably describes which mutations dominate the adaptation, although it gives a misleading picture of the evolutionary dynamics. When the distribution falls off faster than exponentially, an analysis based on multiple mutations is more appropriate. Using our simulations, we are able to explore the limits of validity of both of these approaches, and we explore the complex dynamics in the regimes where neither one is fully applicable.     

Cone Photoreceptor Sensitivities and Unique Hue Chromatic Responses: Correlation and Causation Imply the Physiological Basis of Unique Hues

This paper relates major functions at the start and end of the color vision process. The process starts with three cone photoreceptors transducing light into electrical responses. Cone sensitivities were once expected to be Red Green Blue color matching functions (to mix colors) but microspectrometry proved otherwise: they instead peak in yellowish, greenish, and blueish hues. These physiological functions are an enigma, unmatched with any set of psychophysical (behavioral) functions. The end-result of the visual process is color sensation, whose essential percepts are unique (or pure) hues red, yellow, green, blue. Unique hues cannot be described by other hues, but can describe all other hues, e.g., that hue is reddish-blue. They are carried by four opponent chromatic response curves but the literature does not specify whether each curve represents a range of hues or only one hue (a unique) over its wavelength range. Here the latter is demonstrated, confirming that opponent chromatic responses define, and may be termed, unique hue chromatic responses. These psychophysical functions also are an enigma, unmatched with any physiological functions or basis. Here both enigmas are solved by demonstrating the three cone sensitivity curves and the three spectral chromatic response curves are almost identical sets (Pearson correlation coefficients r from 0.95–1.0) in peak wavelengths, curve shapes, math functions, and curve crossover wavelengths, though previously unrecognized due to presentation of curves in different formats, e.g., log, linear. (Red chromatic response curve is largely nonspectral and thus derives from two cones.) Close correlation combined with deterministic causation implies cones are the physiological basis of unique hues. This match of three physiological and three psychophysical functions is unique in color vision.     

Role of the cocoon ofAcrolepiopsis assectella (Lep., Hyponomeutoidae) in host recognition by the parasitoidDiadromus pulchellus (Hym., Ichneumonidae)

The study of various behavioural criteria of femaleDiadromus pulchellus parasitoids in the presence of theirAcrolepiopsis assectella hosts has shown the essentially chemical nature of the stimulant determining host recognition. The physical stimuli of the cocoon seem not to be implicated. Thus cocoons whose original texture has been completely altered, either mechanically or chemically, as well as the silk excreted by the host caterpillars significantly stimulates the female parasitoids. The cocoon contact kairomones are detected in testing the aqueous extracts ofA. assectella which provoke a positive behavioural response from the females in a threshold concentration of 1 cocoon-equivalent. The comparison of aqueous extracts ofA. assectella host cocoons, and of non-host species:Bombyx mori, Ephestia kuehniella andCacoecimorpha pronubana demonstrate the kairomone specificity of the silk, the extracts of non-host cocoons being ignored by the parasitoid, as were the silk threads left byE. kuehniella caterpillars. Finally the contact kairomones linked to the silk seem to be independent of the host plant and of the nutrient diet of the host caterpillars. The cocoons spun by the caterpillars reared on leeks or on artificial diets with or without powdered leek provoke similar responses in the parasitoids.     

Rapid acclimatization to low temperature in the Queensland fruit fly, Dacus tryoni

Dacus tryoni, which overwinters in conditions of wide diurnal fluctuations in temperature, is capable of rapid acclimatization with respect to thresholds for torpor and flight but ability for metabolic compensation is apparently lacking. The rate of reacclimatization on abrupt transfer to lower temperatures is quicker the less the temperature drops and extrapolation of this relationship suggests a time of the order of 1 min for a drop as small as 1°C. This explains why continuous reacclimatization appears to take place during gradual cooling, even when this is as fast as 1°C/min. The insect can rapidly produce its maximum response to extensive drops of temperature as long as the latter falls gradually at a rate no faster than 1°C/min. Acclimatization in nature is therefore ‘immediate’. Reacclimatization to higher temperatures (deacclimatization to cold) depends upon the temperature that the insects are raised to and thus is slower the smaller the rise and understandably is not accomplished more rapidly by a gradual transition.     

Congruent responses to weather variability in high arctic herbivores

Assessing the role of weather in the dynamics of wildlife populations is a pressing task in the face of rapid environmental change. Rodents and ruminants are abundant herbivore species in most Arctic ecosystems, many of which are experiencing particularly rapid climate change. Their different life-history characteristics, with the exception of their trophic position, suggest that they should show different responses to environmental variation. Here we show that the only mammalian herbivores on the Arctic islands of Svalbard, reindeer (Rangifer tarandus) and sibling voles (Microtus levis), exhibit strong synchrony in population parameters. This synchrony is due to rain-on-snow events that cause ground ice and demonstrates that climate impacts can be similarly integrated and expressed in species with highly contrasting life histories. The finding suggests that responses of wildlife populations to climate variability and change might be more consistent in Polar regions than elsewhere owing to the strength of the climate impact and the simplicity of the ecosystem.     

Mean field model of acetylcholine mediated dynamics in the cerebral cortex

A recent continuum model of the large scale electrical activity of the cerebral cortex is generalized to include cholinergic modulation. In this model, dynamic modulation of synaptic strength acts over the time scales of nicotinic and muscarinic receptor action. The cortical model is analyzed to determine the effect of acetylcholine (ACh) on its steady states, linear stability, spectrum, and temporal responses to changes in subcortical input. ACh increases the firing rate in steady states of the system. Changing ACh concentration does not introduce oscillatory behavior into the system, but increases the overall spectral power. Model responses to pulses in subcortical input are affected by the tonic level of ACh concentration, with higher levels of ACh increasing the magnitude firing rate response of excitatory cortical neurons to pulses of subcortical input. Numerical simulations are used to explore the temporal dynamics of the model in response to changes in ACh concentration. Evidence is seen of a transition from a state in which intracortical inputs are emphasized to a state where thalamic afferents have enhanced influence. Perturbations in ACh concentration cause changes in the firing rate of cortical neurons, with rapid responses due to fast acting facilitatory effects of nicotinic receptors on subcortical afferents, and slower responses due to muscarinic suppression of intracortical connections. Together, these numerical simulations demonstrate that the actions of ACh could be a significant factor modulating early components of evoked response potentials.     

Mucosal Immunization with Integrase-Defective Lentiviral Vectors Protects against Influenza Virus Challenge in Mice

Recent reports highlight the potential for integrase-defective lentiviral vectors (IDLV) to be developed as vaccines due to their ability to elicit cell-mediated and humoral immune responses after intramuscular administration. Differently from their integrase-competent counterpart, whose utility for vaccine development is limited by the potential for insertional mutagenesis, IDLV possess a mutation in their integrase gene that prevents genomic integration. Instead, they are maintained as episomal DNA circles that retain the ability to stably express functional proteins. Despite their favorable profile, it is unknown whether IDLV elicit immune responses after intranasal administration, a route that could be advantageous in the case of infection with a respiratory agent. Using influenza as a model, we constructed IDLV expressing the influenza virus nucleoprotein (IDLV-NP), and tested their ability to generate NP-specific immune responses and protect from challenge in vivo. We found that administration of IDLV-NP elicited NP-specific T cell and antibody responses in BALB/c mice. Importantly, IDLV-NP was protective against homologous and heterosubtypic influenza virus challenge only when given by the intranasal route. This is the first report demonstrating that IDLV can induce protective immunity after intranasal administration, and suggests that IDLV may represent a promising vaccine platform against infectious agents.     

INCREASE IN OSMIOPHILIA OF AXONAL MEMBRANES OF CRAYFISH AS A RESULT OF ELECTRICAL STIMULATION, ASPHYXIA, OR TREATMENT WITH REDUCING AGENTS

Certain axonal membranes of crayfish abdominal nerve cord display ultrastructural changes if the axons are fixed, during electrical stimulation, by aldehydes followed by osmium. Such changes are characterized by an increase in electron opacity and thickness of the unit membranes' dense strata in the axon surface, endoplasmic reticulum, and outer mitochondrial membranes. The electron opacity completely disappears if the sections are treated with hydrogen peroxide solutions. This suggests that the changes represent an increase in the membranes' reactivity for osmium. An unmasking of SH groups could explain such increased osmiophilia, since SH groups are very reactive with osmium, while disulfide bonds are considerably less reactive. This hypothesis was tested by treating control, glutaraldehydefixed nerve cords with disulfide reducing agents. In these preparations an increase in electron opacity and thickness was observed to be localized in the same axonal membranes which reacted as a result of electrical stimulation. The phenomenon did not appear if the SH groups were blocked by maleimide or N-ethylmaleimide before treatment with osmium. These findings seem to suggest that certain axonal membranes of crayfish contain proteins rich in sulfur whose SH groups are unmasked as a result of electrical stimulation. In preliminary experiments an increase in osmiophilia localized in the same membranes with the same characteristics and distribution was observed also in axons from nerve cords asphyxiated either in vitro or in the living animal.     

Mechanical and electrical anisotropy in Mimosa pudica pulvini

Thigmonastic or seismonastic movements in Mimosa pudica, such as the response to touch, appear to be regulated by electrical, hydrodynamical and chemical signal transduction. The pulvinus of Mimosa pudica shows elastic properties, and we found that electrically or mechanically induced movements of the petiole were accompanied by a change of the pulvinus shape. As the petiole falls, the volume of the lower part of the pulvinus decreases and the volume of the upper part increases due to the redistribution of water between the upper and lower parts of the pulvinus. This hydroelastic process is reversible. During the relaxation of the petiole, the volume of the lower part of the pulvinus increases and the volume of the upper part decreases. Redistribution of ions between the upper and lower parts of a pulvinus causes fast transport of water through aquaporins and causes a fast change in the volume of the motor cells. Here, the biologically closed electrochemical circuits in electrically and mechanically anisotropic pulvini of Mimosa pudica are analyzed using the charged capacitor method for electrostimulation at different voltages. Changing the polarity of electrodes leads to a strong rectification effect in a pulvinus and to different kinetics of a capacitor discharge if the applied initial voltage is 0.5 V or higher. The electrical properties of Mimosa pudica''s pulvini were investigated and the equivalent electrical circuit within the pulvinus was proposed to explain the experimental data. The detailed mechanism of seismonastic movements in Mimosa pudica is discussed.Key words: electrophysiology, plant electrostimulation, pulvinus, Mimosa pudica, charged capacitor method, electrical circuits, ion channels     

Evidence for cotransport of nitrate and protons in maize roots : I. Effects of nitrate on the membrane potential

The electrical response of nitrate-grown maize (Zea mays L.) roots to 0.1 millimolar nitrate was comprised of two sequential parts: a rapid and transient depolarization of the membrane potential, followed by a slower, net hyperpolarization to a value more negative than the original resting potential. The magnitude of the response was smaller in roots of seedlings grown in the absence of nitrate, but, within 3 hours of initial exposure to 0.1 millimolar nitrate, increased to that of nitrate-grown roots. Chloride elicited a separate electrical response with a pattern similar to that of the nitrate response. However, the results presented in this study strongly indicate that the electrical response to nitrate reflects the activity of a nitrate-inducible membrane transport system for nitrate which is distinct from that for chloride. Inhibitors of the plasmalemma H⁺-ATPase (vanadate, diethylstilbestrol) completely inhibited both parts of the electrical response to nitrate, as did alkaline external pH. The magnitude of the initial nitrate-dependent, membrane potential depolarization was independent of nitrate concentration, but the subsequent nitrate-dependent hyperpolarization showed saturable dependence with an apparent K_m of 0.05 millimolar. These results support a model for nitrate uptake in maize roots which includes a depolarizing NO₃⁻/H⁺ symport. The model proposes that the nitrate-dependent membrane potential hyperpolarization is due to the plasma membrane proton pump, which is secondarily stimulated by the operation of the NO₃⁻/H⁺ symport.     

The I-D fluorescence transient. An indicator of rapid energy distribution changes in photosynthesis

The I-D transient in the chlorophyll fluorescence induction curve (Kautsky effect) is investigated in the view of recently discovered rapid changes in energy distribution between the two photosystems (Schreiber, U. and Vidaver, W., FEBS Lett., in the press). Fluorescence induction curves differ appreciably depending on whether measured at λ < 690 nm, originating in pigment system II, or at λ > 715 nm, which is in part from pigment system I. The differences occur as well in the rapid part of the induction curve (O-I-D-P) as in the slower P-S decay. Most significant changes in energy distribution are indicated in the region of the I-D dip, being induced by appropriate preillumination. The effect is studied by (a) comparing the individual fluorescence time courses at λ < 690 nm and λ > 715, (b) plotting F < 690 vs. F > 715 and (c) recording time courses of $\text{F < 690}\text{F > 715}$ ratios. In (a) the I and D characteristics are delayed at F > 715 relative to F < 690, which is accompanied by periods close to I and D, where the two emissions follow inverse courses. In (b) the I-D dip corresponds to a loop. And in (c) it is shown that a rapid ratio decay, reflecting increasing excitation of System I pigments, is initiated before the I-D dip. These data indicate that the I-D transient is caused by a rapid switch of energy distribution in favor of System I and the resulting stimulation of Q reoxidation via the electron transport chain. It is suggested that as with the slow fluorescence transients the rapid also can be understood as a composite of two different changes, (1) direct changes resulting from a switch in energy distribution, which are inverse for F < 690 and F > 715, and (2) indirect changes due to stimulated Q reduction or Q oxidation, which are parallel for both emissions. The rapid ratio decay, correlated to I-D, persists and is even stimulated in the presence of electron transport inhibitors. This and the speed of the phenomenon make it improbable that the rapid energy distribution changes are affected by an ion flux-induced mechanism. It is proposed that the electrical field across the thylakoid membrane is involved in the energy switch mechanism.