Kiyoko Kuroda

Cytoplasmic streaming in plant cells.

Publisher Summary This chapter discusses the cytoplasmic streaming in plant cells with special reference to the internodal cells of Characeae . These cells are large cylindrical coenocytes, about 500 pm in diameter and several centimeters in length. On the inside of the cell wall and the plasmalemma, the endoplasm flows along the chloroplast files anchored in cell cortex in a slightly spiral belt separated into two half-cylinders by two indifferent lines. The endoplasmic rotation is continuous and steady. The streaming velocity is very high and extremely constant under an external condition. Characean cells are excellent material for the study of cytoplasmic streaming and also many physiological phenomena, such as osmosis, ion relations, excitability, and electrophysiological phenomena. In most plant cells, various patterns of cytoplasmic streaming are observed at the characteristic velocity of each cell. There are five main types of cytoplasmic streaming in plant cells: agitation, circulation, rotation, fountain streaming, and multistriate streaming. These patterns of streaming can interchange over short or long periods of time.

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.

Propulsive force of Paramecium as revealed by the video centrifuge microscope

Using the video centrifuge microscope we constructed, we observed the behavior of Paramecium cells in a solution of graded densities under centrifugal acceleration. Beyond 300g, they not only gather in the zone where the density is closest to theirs, but also orient themselves with their longitudinal axis parallel to the direction of centrifugation turning their anterior ends toward either centripetal or centrifugal direction. Since all of them retain still active swimming capacity, it is possible to calculate their propulsive force from the difference in density between theirs (1.04 g cm-3) and that of the upper or lower layer which they can reach. The propulsive force of single Paramecium cells thus obtained was calculated to be about 7 x 10(-4) dyn.

A polarized light and electron microscopic study of the birefringent fibrils inPhysarum plasmodia

SummaryThe birefringent fibrils in thin-spread plasmodium ofPhysarum polycephalum have been investigated with both polarizing and electron microscopes. The birefringent fibrils were classified into three groups by polarized light microscopy. The first type of fibril is observed in the advancing frontal region as a mutual orthogonal array. The birefringence changes rhythmically in accordance with the shuttle streaming. The second type of birefringent fibril is located in the strand region and runs parallel or somewhat oblique to the strand axis. The third type is observed in the strand region always perpendicular to the streaming axis. Electron microscopy confirmed that all these fibrils are composed of microfilaments, which range in densities in the cross view of the fibril from 1.2 to 1.7 × 103/μm2 (1.5 × 103/(xm2 on the average).

Identification of a birefringent structure which appears and disappears in accordance with the shuttle streaming inPhysarum plasmodia

SummaryR-HMM (rhodamine-heavy meromyosin) stained the birefringent fibrous structure which appears and disappears cyclically in parallel with the periodic shuttle streaming in the plasmodium ofPhysarum polycephalum. In addition, 0.6 M KI readily made the birefringent fibrils fade away. These results clearly show that the birefringent fibrils are composed of actin filaments and prove the possibility of actin filaments to alter in the aggregation state during the cyclic production of the motive force responsible for the cytoplasmic streaming.

Actin cytoskeleton of resting bovine platelets

Actin filaments in resting discoid bovine platelets were examined by fluorescence and electron microscopy. Rhodamine-phalloidin staining patterns showed a characteristic wheel-like structure which consisted of a central small circle connected by several radial spokes to a large peripheral circle. This wheel-like structure was composed of actin filaments forming a characteristic arrowhead structure with heavy meromyosin from muscle. Actin filaments were densely arrayed in parallel with a marginal microtubule band and radiated out from the center to the periphery. Platelets treated with colchicine lost their marginal microtubule band but retained their wheel-like structure and normal discoid form. Cytochalasin B disrupted the wheel-like structure but not the marginal microtubule band or the normal discoid form. After simultaneous treatment with both cytochalasin B and colchicine, platelets lost their discoid shape. These results suggest that actin filaments and microtubules both play important roles in the maintenance of the discoid shape of resting bovine platelets.

Reactivation of a glycerinated model of Amoeba

SummaryMotile models ofAmoeba proteus prepared by extraction at −20 °C with a 50% buffered glycerol solution showed remarkable contraction on addition of Mg-ATP with retainment of Ca++ sensitivity. The initial contraction around the nucleus occurred on addition of Mg-ATP independently of the Ca++ concentration, and was followed by contractions of three different patterns. In 10−8M Ca++, the granuloplasm contracted as a whole and separated from the membrane leaving no detectable particles in the anterior region. In 10−6M Ca++, the granuloplasm contracted leaving some granules which showed active and vigorous two-directional streaming similar to that in the living cell. Sometimes a part of the plasma membrane twitched. The streaming lasted up to 20 minutes. In 10−4M Ca++, after the initial contraction around the nucleus, no significant movement was observed. All these movements in the models were inhibited by cytochalasin B or N-ethylmaleimide. The relationship between the Mg-ATP and the Ca++ concentrations was examined.

Temporal and spatial localization of Ca2+ in movingAmoeba proteus visualized with aequorin

The intracellular regulation of cytoplasmic structure and cell motility are generally considered to be related to the modulation of the actomyosin system under different cytoplasmic free calcium concentration. The role of Ca 2 + in regulating amoeboid movement has been studied by methods using purified amoeba actin (SoNOBE etal. 1986), a glycerinated model (KuRODA and SONOBE 1981, SONOBE and KURODA 1986), a demembranated model (TAYLOR et al. 1973) and microinjected aequorin (CoBBOLD 1980, TAYLOR etal. 1980), but its role is not yet completely understood. Measuring total luminescence of microinjected aequorin, COBBOLD (1980) reported that the locomotion of Chaos carolinense was not under the control of changes in the free calcium concentration. However, TAYLOR etaL (1980) stated that during amoeboid movement, the free calcium ion concentration fluctuated within the range of 1.0 x 107 M to 3.6 x 10-6M. The discrepancy between these observations remains to be investigated. Also required studies are the spatial distribution and temporal sequence of free calcium ion in amoeba in relation to the locomotion.