Plasmodial Strands Of Physarum Polycephalum Research Articles

Spectral analysis of self-oscillating motility in an isolated plasmodial strand of Physarum polycephalum

In this study the experimental dependencies of the velocity of shuttle endoplasmic motion in the isolated plasmodial strand of Physarum polycephalum obtained by laser Doppler microscopy are presented. The spectral analysis of the time dependencies of the endoplasm allows obtaining two distinct harmonic components. Influence of KCN and SHAM--inhibitors of cellular respiration--leads to a complete cessation of endoplasmic motion in the strand. After removal of the inhibitors the respiratory system becomes normal, gradually restoring the activity of both harmonic oscillation sources. Based on the spectral analysis the simulated time-dependent velocity of the endoplasmic motion is rather good consistent with experimental data.

Asymmetry in the self-sustained oscillation ofPhysarum plasmodial strands

The characteristics of the self-sustained oscillation in the plasmodial strand ofPhysarum polycephalum have been investigated in one steady and two transient conditions. An isolatedPhysarum strand changes its length periodically when it is suspended. In the behaviour of the self-sustained oscillation under the conditions, we provide the first demonstration that the changes in the periods of the oscillation can be ascribed to effects on the shortening phase, while the lengthening periods are almost unaffected. This result means that the asymmetric self-sustained oscillation of thePhysarum strand is composed of an active contracting process, presumably due to actin filaments and myosin-like molecules in the strand, and a passive lengthening process which is merely an extension of the strand under a load.

Bidirectional flow of endoplasm inPhysarum plasmodium under centrifugal acceleration

The behavior of cytoplasmic streaming in plasmodial strand ofPhysarum polycephalum was studied under centrifugal acceleration using a centrifuge microscope of the stroboscopic type. Cytoplasmic streaming in the plasmodium was greatly affected by changes in the acceleration. The endoplasmic flow in the centrifugal direction was accelerated, while that in the centripetal was retarded, by centrifugal acceleration. The centrifugal acceleration required to stop the endoplasmic flow in the centripetal direction did not cause total cessation of streaming but always induced a bidirectional flow of endoplasm in one and the same strand. Each profile of velocity distribution of the bidirectional flow was both parabola with flattened apex. One possible cause of the bidirectional flow is discussed.

Synchronization in a Plasmodial Strand of Physarum Polycephalum as a One-Dimensionally Coupled Oscillator System

Transient behaviors in self-sustained oscillation of a plasmodial strand of Physarum polycephalum have been investigated for various external loads under isotonic conditions. Synchronization between divisions of the strand has been observed in its formation process, which shows that the plasmodial strand can be considered as a one-dimensionally coupled oscillator system. The synchronization has been found to proceed faster with increasing external load applied to the strand. It has furthermore been found that the rate of increase of the amplitude of oscillation increases with the load, whereas the temporal behavior of its period is independent of the load. These results show that the oscillators themselves in the plasmodial strand do not depend on the external load, but the coupling between these oscillators is strongly affected with the external load. The experimental results have also been simulated on the basis of one-dimensionally coupled van der Pol equations.

Information processing for the organization of chemotactic behavior ofPhysarum polycephalum studied by micro-thermography

The spatial and temporal pattern of oscillating temperatures on the cell surface of a plasmodial strand ofPhysarum polycephalum was measured with a sensitive thermal image camera. The longitudinal tension of the strand was studied simultaneously. In the absence of chemical stimulation, the phases of the temperature oscillation observed at various portions of the strand were entrained with almost coincidental phase. The temperature and tension oscillation were synchronized, although the phase difference between them was occasionally changed. With local chemical stimulation, the phase of the temperature oscillation advanced in the portion to which the plasmodium would be induced to migrate. The phases between temperature and tension oscillations then became constant. The mechanism by which the plasmodium processes local information of chemical stimulus to global information for the migration is discussed.

Butyric acid as a supressor of mitochondrial functions in Physarum polycephalum plasmodia

By means of tensionmetric technique, in the presence of butyric acid, a comparison is made between the action of respiratory and glycolytic inhibitors on plasmodial strands of Physarum polycephalum. It is shown that, in presence of this weak acid, glycolysis but not exidative phosphorylation can preserve the contractile ability of the samples. Inhibitory analysis has revealed that the inhibition of mitochondrial functions by butyric acid is non-specific in the sense that the drug influences both KCN-resistant and KCN-sensitive respiration. In all probability the observed responses of plasmodial strands to butyric acid are related to acidification of the cytoplasm.

ATP- and calcium-controlled contraction in a saponin model of Physarum polycephalum.

Saponin models of the plasmodial strand of Physarum polycephalum were constructed to study how Ca2+ and ATP regulate the generation of tension. ATP-induced isometric tension in a saponin model increased with an increase in ATP concentration until maximum tension (0.3-1.7 mg) was reached at about 1 mM. The sensitivity of the model to ATP was heightened three to five times in a basic solution containing an ATP-regenerating system, the maximum tension (0.3-0.6 mg) being reached at 0.2 to 0.3 mM ATP. Contraction of the model also depended on the Ca2+ concentration irrespective of the presence or absence of the ATP-regenerating system. The optimal pCa was 7.0, and tension decreased with a Ca2+ concentration above or below this value. These results indicate that the tension generated in the plasmodial strand of Physarum in vivo may be regulated by ATP and/or Ca2+.

The blue-light reaction in plasmodia of Physarum polycephalum is coupled to respiration

The influence of inhibitors of energy metabolism (2-deoxy-D-glucose, monoiodoacetate, KCN) as well as various substrates for respiration (sodium acetate, glycine, glutamine, α-ketoglutarate, pyruvate) were investigated with respect to the effect of blue light (450 nm) on contractile behaviour of plasmodial strands of Physarum polycephalum. When the energy metabolism is not experimentally modified, blue light induces a prolongation of the period of the contraction-relaxation cycle. This effect appears within 2-3 min and seems to represent the primary reaction of this organism to blue light. Inhibition of respiration by KCN completely abolished this response to blue-light irradiation. In contrast, an impediment of glycolysis enhanced the effect. This indicates that the reaction to blue light is related to respiration, i.e., to the function of mitochondria. Among different substrates for respiration only α-ketoglutarate combined with pyruvate and applied in the presence of inhibitors of glycolysis showed an enhancement of the photoresponse, i.e., a prolongation of the period and an increase of the amplitude of the force oscillations. This indicates that the pyruvate and α-ketoglutarate-dehydrogenase complexes functioning in mitochondrial respiration are involved in the primary blue-light reaction of plasmodia of Physarum polycephalum.

Contractile and structural reactions to impediments of Ca2+-homeostasis in Physarum polycephalum.

A combined application of 5 mM KCN and 19 microM Ca++-ionophore A-23187 leads to pronounced contractures of plasmodial strands of Physarum polycephalum. The appearance of the contractures is independent of the amount of Ca++ in the external medium. Tensiometric registrations of longitudinal contraction activity (isometric regime) reveal an average tension increase of 50 mp compared with the preceding tension level before the addition of KCN and ionophore. This high force output during the contracture coincides with a pronounced increase in the number of cytoplasmic actomyosin fibrils. Their ultrastructure is seen as a high lateral density of strictly parallel arranged F-actin filaments; the state of cytoplasmic actomyosin during this isometric contracture corresponds to the ultrastructure of isometrically contracted fibrils during the normal contraction-relaxation cycle of this organism. A simultaneous impediment of respiration and Ca++ homeostasis strongly favours a shift of the actin equilibrium to the high polymeric side in the form of fibrils and may thus be used as a preparatory step improving the specimens in the context of other investigations, e.g., for immunocytochemical investigations or for the preparation of cell-free models to be reactivated after extraction procedures.

Calcium and ATP regulation of the oscillatory torsional movement in a Triton model of Physarum plasmodial strands

A segment of the plasmodial strand of Physarum polycephalum, when hung vertically, shows oscillatory torsional movements that accompany shortening and elongation, i.e., contraction and relaxation in the vertical direction. Reactivation of such movements was achieved in a fresh, demembranated model system through the use of Triton X-100 and chemically defined physiological solutions. Oscillatory rotations were reactivated in solutions containing 0.5 mM Mg-ATP and 10 −6–10 −4 of free Ca 2+. Lowering the Ca 2+ concentration to 10 −8 M brought about unidirectional rotations with concomitant vertical elongation of the strands, i.e., relaxation. Such unidirectional rotations were also observed either when Mg-ATP concentrations was raised to 5 mM, or when Mg-ATP was replaced with Mg-pyrophosphate. Higher concentrations of free Ca 2+ than 10 −4 M similarly caused unidirectional rotations, but there was no concomitant vertical elongation. These data mean that the oscillatory contraction and relaxation require a factor which is activated at Ca 2+ concentration above 10 −6 M and inactivated at 10 −8 M. The findings that Mg-pyrophosphate or high concentrations of Mg-ATP-induced relaxation suggest that the actomyosin is dissociated in the relaxation phase. In the light of the present study, it is not likely that the periodic movement in the plasmodia is caused by any oscillatory activities in either the ATP-producing system or the plasma membrane.

Lateral apertures as passage-ways between ectoplasm and endoplasm in plasmodial strands of Physarum

Plasmodial strands of Physarum polycephalum are differentiated into an ectoplasmic tube and an endoplasmic core. The border of the ectoplasmic tube represents a circular arranged system of plasmalemma invaginations containing apertures which allow a continuous exchange of endoplasm and ectoplasm during the oscillating contraction-relaxation cycles. The apertures of thick plasmodial strands are described using phase-microscopy of semithin sections. Their physiological importance for signal transmission, endoplasmic mass transport and thereby plasmodial locomotion is discussed.

Replacement of endoplasm with artificial media in plasmodial strands of Physarum polycephalum: Effects on contractility and morphology

The endoplasm in a plasmodial strand of Physarum polycephalum was translocated with pressure and replaced with artificial media by pushing the endoplasm into other regions of the vein. Effects of injected chemicals were studied by measuring the oscillating tension force of the strands as well as their morphological response to this experimental procedure. The results can be summarized as follows. 1. 1. Cross sections of the strands show that nearly all of the endoplasm was replaced with injected media. 2. 2. The oscillatory contraction of the strand continued after replacing the endoplasm with oil or air. However, the amplitude of the tension force became smaller for about 5–10 min after the injection. 3. 3. An internal application of an aqueous solution (30 mM KCl, 3 mM MgCl 2, 1 mM CaCl 2, 10 mM Tris-HCl, pH 7.1) arrested the oscillatory contraction and also caused a decrease of the tension force level. An addition of ATP to this solution induced oscillatory contraction, the optimal ATP concentration being 0.2 mM. Injection of a high ATP concentration led to a collapse of the ectoplasmic tube. 4. 4. The minimal requirement of injected Ca 2+ for contraction activity as well as for protoplasmic streaming was determined to be 2 × 10 −7 M, when the free Ca 2+ level was maintained by CaEGTA buffer. Effects of ATP and Ca 2+ on the contractility can be compared with those of ATPase activity of extracted actomyosin from Physarum polycephalum. Our results indicate that the ectoplasmic tube of a plasmodial strand is responsible for the contraction activity and that the chemicals injected as aqueous solutions have access more directly to the contractile system than those applied from outside the vein.

Cyclic production of tension force in the plasmodial strand of Physarum polycephalum and its relation to microfilament morphology.

Cyclic contraction and relaxation of plasmodial strands of Physarum polycephalum were measured under both isotonic and isometric conditions, and their relation to changes in microfilament (MF) morphology was investigated. The contraction-relaxation rhythm of a strand segment was insignificant and irregular immediately after isolation from the mother plasmodium. It became regular half an hour later when local minute rhythms were synchronized spontaneously. If a strand kept under isotonic conditions was loaded with a heavier weight or a strand kept under isometric conditions was stretched a few times, the amplitude of each contraction wave was enhanced. After a strand had been thus conditioned, it was fixed at a selected phase of the contraction-relaxation cycle under both isotonic and isometric conditions. The state of MFs changed strikingly according to the phase of the contraction cycle. In the shortening phase of the strand under isotonic contractions, MFs with a diameter of 6--7 nm were arranged parallel to each other to form large compact bundles in which adjacent filaments were bridged with cross linkages. Among these MFs, thicker filaments were sporadically scattered. At about the phase of minimal strand length, most of the MFs became kinky and formed networks. In the elongating phase, new loose bundles of MFs developed from the network. These loose bundles became compact again when the strand reached its maximal elongation phase. In the isometric contraction, MFs in the increasing tension phase were nearly the same as those in the shortening phase in isotonic contraction. Around the maximal tension phase, dense areas of MFs appeared along the bundles in place of the network formed in the isotonic contraction phase. These areas were closely packed, with MFs arranged parallel to each other. In the decreasing and minimal tension phases in isometric contraction, MFs were arranged similarly to those in the elongating and maximally elongated phases, respectively, in isotonic contraction. Alternation between the straight bundle and fine network configuration of the MFs observed in isotonic contraction was inconspicuous in isometric contraction. This was probably due to spatial restriction of shortening under isometric contraction. The results are interpreted in terms of cyclic changes of the aggregation pattern of the MFs in the form of F-actin, as opposed to the possibility that the contraction-relaxation cycles depend on cyclic G-F transformation of actin.

Ca-Histochemistry in slime mold plasmodia

Calcium is supposed to play an important role in the control of protoplasmic streaming in slime mold plasmodia. The motive force for protoplasmic streaming is generated by the interaction of actin and myosin. This contraction is supposed to be controlled by intracellular Ca-fluxes similar to the triggering system in skeleton muscle. The histochemical localisation of calcium however is problematic because of the possible diffusion artifacts especially in aquous media.To evaluate this problem calcium localisation was studied in small pieces of shock frozen (liquid propane at -189°C) plasmodial strands of Physarum polycephalum, which were further processed with 3 different methods: 1) freeze substitution in ethanol at -75°C, staining in 100% ethanol with 1% uranyl acetate, and embedding in styrene-methacrylate. For comparison the staining procedure was omitted in some preparations. 2)Freeze drying at about -95°C, followed by immersion with 100% ethanol containing 1% uranyl acetate, and embedding. 3) Freeze fracture, carbon coating and SEM investigation at temperatures below -100° C.

Synchrony in the rhythm of the contraction-relaxation cycle in two plasmodial strands of Physarum polycephalum.

Rhythmicity of contraction of plasmodial strands of Physarum polycephalum was studied, by measuring the isometric tension exerted by isolated segments of the strands. When 2 strands were connected by way of a plasmodial mass, the contraction-relaxation cycle of the 2 strands synchronized. Such cycle activity of the strand was found to be well coordinated with shuttle streaming in the plasmodial mass which had been in connection with the strand. The presence of a control system which induces synchrony of periodic activity over the entire body of a plasmodium is discussed.