Noburô Kamiya

The relation of turgor pressure to cell volume inNitella with special reference to mechanical properties of the cell wall

Summary1.A method was developed, by which it was possible to measure the volume of an internodal cell ofNitella flexilis as a function of interior pressure. For this to be done, the cell wall tube, closed at one end with the natural septum, was filled with mercury and pressure was applied to the mercury. The accompanying change in volume of the cell wall tube was measured simultaneously with the applied pressure.2.The time course of volume change of the cell in response to change in interior pressure indicates that cell wall elasticity is composed of at least two components, an instantaneous elastic component, and a retarded elastic component with a retardation time of about 1–5 minutes.3.Both instantaneous and slow processes in volume change vary according to the level of the pressure applied and to the direction of the pressure change.4.The volume of the cell can be kept at different values, under the same interior pressure, according to the direction of the pressure change; in other words, the interior pressure-volume relation shows a hysteresis.5.Taking into consideration the hysteresis character in mechanical properties of the cell wall, the osmotic pressure, turgor pressure and suction force (diffusion pressure deficit) of an internodal cell ofNitella flexilis was illustrated in relation to the cell volume in an osmotic diagram after Höfler. A characteristic of the diagram is that the cell can have different turgor pressures and suction forces within certain limits even though the volume of the cell is the same.6.The length of the living cell was measured under different turgor pressures. The facts that the pressure-cell length relation showed also a distinct hysteresis character and that the wall elasticity of the living cells was in the same order as that of the cells filled with mercury, indicate that the results obtained with cell wall tubes were also true of the living cells.7.The cell wall of the internodal cell ofNitella flexilis extends more in the direction of transverse axis of the cell than in the direction of longitudinal axis under the influence of turgor pressure. When equal tensions in the respective direction are considered, however, the cell wall extends to the same extent in each direction.8.The uniaxial longitudinal tension, caused by loading, elongates the cell about 3–4 times more than does the longitudinal component of the equivalent tension caused by turgor pressure.

Bioelectric phenomena in the myxomycete plasmodium and their relation to protoplasmic flow

Abstract 1. 1. Potential differences between the two loci of the slime mold ( Physarum polycephalum ) connected with a single strand of protoplasm were determined successively and the mode of their variation in relation to time was represented graphically. 2. 2. The electromotive force of the slime mold changes according to a rhythmic pattern, the period of which is the same as that of the cyclic back and forth steaming, and the amplitude of which increases and decreases spontaneously under constant conditions, usually within 10 mv. 3. 3. The rhythmic change in the potential occurs whether the flow along the connecting strand is allowed to take place freely, or if it is made to stop by means of local blocking of the strand, or by application of a balancing pressure. 4. 4. Satisfactory results have been obtained in an attempt to represent graphically the simultaneous variation in potential (electroplasmogram or EPG) and the power to flow (dynamoplasmogram or DPG) from one and the same plasmodium with the aid of a double-chamber method. 5. 5. In addition to the periods of these two curves being the same, a close relationship between them under normal conditions is seen with respect to amplitude, wave form, and polarity. 6. 6. The phases of the two waves do not coincide with each other, that of the EPG always lagging behind that of the DPG usually by 30–100 sec., or 2 5 – 1 7 of their period. 7. 7. The local differences in the bioelectric potential in a plasmodium cannot be regarded as the direct result of the protoplasmic flow or as the streaming potential. Nor is it to be considered as the direct cause responsible for the flow; in other words, the protoplasmic flow is not explained as a phenomenon of electroendosmosis. 8. 8. Besides the slow cyclic variation mentioned above, there is a quick, transient potential variation which is elicited not only spontaneously at times, but also artificially through use of weak mechanical shocks.

Artificial modification of the osmotic pressure of the plant cell

Summary1.When one end of an internodial cell ofNitella is brought in contact with water, and the other end with the solution of sucrose, transcellular osmosis takes place from water side to the sucrose side.2.Accompanying transcellular osmosis, the cell sap on the water side is diluted and that on the sucrose side is concentrated. The magnitude of the polar change in sap concentration is dependent on the difference in osmotic pressure between the two external solutions.3.By tying off an internodial cell ofNitella with strips of silk thread after inducing transcellular osmosis, it is possible to produce cells having arbitrary osmotic pressures within the range of as high as 3 times and as low as 1/4 the normal level.4.The cells thus produced, which are in fact fragments of the mother internodial cell, can survive indefinitely.5.The cell, whose osmotic pressure is abnormally high or low, has a marked tendency to be restored to its normal level.6.The tendency to be restored to the normal osmotic pressure is maintained, if not fully, even when the import or export of solutes to/from the cell is prevented.7.Turgor pressure of the cell plays no essential role in the osmoregulation.

Studies on the velocity distribution of the protoplasmic streaming in the myxomycete plasmodium

SummaryIt was shown that the velocity distribution of the intracapillary streaming of protoplasm in a plasmodium ofPhysarum polycephalum is the same no matter whether the flow is spontaneous or whether it is induced artificially by external local air pressure applied to the plasmodium. Thus we conclude that the protoplasmic flow in the plasmodium is caused by local difference in endoplasm pressure. The view that the seat of the motive force responsible for the flow is located in the streaming protoplasm itself is untenable for this type of streaming.

Measurement of the motive force of the protoplasmic rotation inNitella

SummaryThe present work is a first attempt at calculating the absolute amount of the motive force responsible for the rotational protoplasmic streaming. The calculation was made on the basis of the conclusion we arrived at previously through the analysis of intracellular velocity distribution, namely, that the active driving mechanism responsible for the rotational streaming is located at the interface between the cortical gel and the outer edge of the endoplasmic layer. The motive force, which is the shifting force generated at this interface, was determined in the internodal cell ofNitella flexilis to be within the range of 1–2 dynes/cm2 at room temperature.

Physiology of the motive force of protoplasmic streaming

Summary1.The motive force responsible for the protoplasmic streaming in the myxomycete plasmodium,Physarum polycephalum, was measured by means of the double-chamber method under the influence of various chemical agents.2.The motive force rather increases than decreases under anaerobic state as well as under the effect of KCN. The process is reversible.3.Monoiodoacetic acid and sodium fluoride, both fermentation poisons, decrease the strength of the force back of the protoplasmic streaming.4.2,4-dinitrophenol inhibits the motive force production both under aerobic and anaerobic conditions.5.ATP admitted from without markedly increases the motive force of the protoplasmic streaming. The effect is manifested several minutes after the reagent is applied and continues several ten minutes after the reagent is removed.6.As the fermentation poisons depresses the generation of the motive force while conditions inhibiting respiration do not depress it, it was concluded that the direct energy source of the protoplasmic streaming is ATP synthesized by fermentation process.

The Rate of the Protoplasmic Flow in the Myxomycete Plasmodium. II

Two special methods have made it possible to represent in an undulating curve the relation between the rate of flow and time. The maximum velocity of the streaming changes in each rhythm, sometimes exceeding 1 mm/sec at optimum temperature. In one of the instances mentioned in the present report, the maximum speed reached 1.35 mm/sec, which is the greatest velocity of protoplasmic flow ever recorded. The patterns of the curves representing the rise and fall of the streaming rate in relation to time are all different according not only to the material used but also to the time of measurement in one and the same material. The general characteristics of these velocity curves show close parallelism with those of the motive force or dynamoplasmograms, though the former involve more complex factors than the latter. The pronounced changes in the wave form and amplitude are most satisfactorily understood from the standpoint of intraplasmic interfference advanced by the author on the basis of the analysis of the motive force curve.

Studies on contraction rhythm of the plasmodial strand I. Synchronization of local rhythms

SummaryA strand segment excised from a network ofPhysarum plasmodium showed no significant rhythmic activities at first, but started rhythmic contraction locally after 10–20 minutes. To express the development of local rhythms and their synchronizing process in the strand under isotonic conditions, the isolated strand was divided into several subsegments of nearly equal length with small resin particles attached as index markers. Changes in the length of each subsegment were then registered photographically every 10 seconds to obtain an overall view of local contractions. Thus we were able to find the time coordinates of individual sub-segments reaching their maximal length within the span of each corresponding wave representing contraction of the whole strand. Their standard deviation decreased with time becoming as small as 3–5 seconds or 3% of the period of the main waves after 30 minutes. Under isometric conditions, the method using index markers was useful, but we also could demonstrate the synchrony by the fact that the amplitude, period and phase of the tension waves became independent of the length of the strand. Once the contraction-relaxation cycle of each segment in the strand is synchronized, it is maintained under isotonic as well as isometric conditions.

Studies on contraction rhythm of the plasmodial strand III. Role of endoplasmic streaming in synchronization of local rhythms

SummaryTwo separate segments of plasmodial strands (Physarum polycephalum) generally contract and relax with different periods, but if the two are bridged with another small strand segment to make into a single system, the contraction cycles of the two previously separate segments become gradually unified under isometric as well as isotonic conditions. To clarify the possible role of the streaming endoplasm as the information carrier for synchronization, we stopped the streaming between two halves of a single strand either by cutting it or by using the double-chamber method without cutting it. When the endoplasm is prevented from flowing between the two halves of the same continuous system, which had been in good synchrony, their contraction-relaxation rhythms become out of phase with each other. After the endoplasm in the strand is allowed to stream freely again, the synchrony of their cyclic contraction is reestablished. It was concluded that endoplasm flowing back and forth in a plasmodial strand must carry a factor(s) which coordinates the period and phase of the contraction-relaxation cycle but does not control the amplitude of the cycle.

The protoplasmic flow in the myxomycete plasmodium as revealed by a volumetric analysis

SummaryThe manner of the locomotion of the slime mold,Physarum polycephalum, was shown graphically using a double-chamber volumeter developed by the author. It enabled him to represent in undulating curves every detail of the way in which the slime mold moves on little by little by availing itself of the difference in transport-volume of the endoplasm produced at each repetition of the back and forth streaming.The curve showing the locomotion of the organism pointed out that more than 4 mm3 of protoplasm is sometimes shifted in a direction in one streaming duration. No close relationship is found between the streaming duration and the transport-volume of protoplasm. The intensity of the flow, which may be defined as the volume of protoplasm transported per unit time, can be obtained from the transport-volume curve through its graphical differentiation.