Rate Of Cytoplasmic Streaming Research Articles

Polar auxin transport in relation to long-distance transport of nutrients in the Charales: Table 1.

This paper examines the significance of the recent demonstration of polar auxin transport (PAT) in the green macroalga Chara (Charophyceae: Charales) and, especially, options for explaining some features of PAT in the Charales. The occurrence of PAT in the Charales shows that PAT originated in the algal ancestors of the embryophytes (liverworts, mosses, hornworts, and vascular plants), although it is not yet known if PAT occurs elsewhere in the Charophyceae or in other algae. While in the embryophytes PAT occurs in parenchymatously constructed structures which commonly also have xylem and phloem (or their bryophyte analogues) as long-distance transport processes in parallel to PAT, in Chara corallina PAT shares the pathway for long-distance transport of nutrients though the parenchymatously constructed nodal complexes and the single giant cells of the internode. The speed of auxin movement of PAT is much more rapid than that attributable to diffusion and of the same order as the rate of cytoplasmic streaming in the giant internodal cells, yet complete inhibition of streaming by the inhibitor cytochalasin H does not slow down auxin transport. Explanations for this phenomenon are sought in the operation of other mechanochemical motors, dynein-tubulin and kinesin-tubulin, as alternatives to the myosin-actin system which powers cytoplasmic streaming. Experiments in which microtubules are disrupted, for example by colchicine, could show if one of the tubulin-based motors is involved. If these motors are involved, some mechanism is needed to amplify the speeds known for the motors to explain the order of magnitude higher speeds seen for auxin transport.

Hydrodynamics of cytoplasmic streaming and the cytoskeletal tubulin component in cells of Elodea densa internodes

A spin-echo NMR method was applied to study hydrodynamic parameters of cytoplasmic streaming and to examine translational diffusion of cytoplasmic water in stems of elodea (Elodea densa (Planch.) Casp.) treated with antimitotic drugs. Within the first few hours after colchicine treatment, the dynamics of translational displacement followed the curve with a transient maximum. The action of vinblastine was manifested in a monotonic decrease of the translational diffusion. After 24-h treatments with colchicine and vinblastine, the translational diffusion was slowed down. All these changes induced by antimitotic drugs were observed on the background of unaltered rate of cytoplasmic streaming.

Effect of caffeine on cytosolic Ca2+ level and cytoplasmic streaming inNitella axilliformis

The effect of caffeine on cytosolic Ca2+ level and rate of cytoplasmic streaming was studied inNitella. External application of caffeine induced both a transient rise in cytosolic Ca2+ level and a decline in the rate of cytoplasmic streaming ofNitella. When EGTA-injected cells were bathed in EGTA-containing medium, external application of caffeine inhibited cytoplasmic streaming but induced no transient rise in cytosolic Ca2+ level. These results suggest that the inhibitory effect of caffeine on cytoplasmic streaming is independent of cytosolic Ca2+ level.

Actin in living and fixed characean internodal cells: identification of a cortical array of fine actin strands and chloroplast actin rings

We report on the novel features of the actin cytoskeleton and its development in characean internodal cells. Images obtained by confocal laser scanning microscopy after microinjection of living cells with fluorescent derivatives of F-actin-specific phallotoxins, and by modified immunofluorescence methods using fixed cells, were mutually confirmatory at all stages of internodal cell growth. The microinjection method allowed capture of 3-dimensional images of high quality even though photobleaching and apparent loss of the probes through degradation and uptake into the vacuole made it difficult to record phallotoxin-labelled actin over long periods of time. When injected at appropriate concentrations, phallotoxins affected neither the rate of cytoplasmic streaming nor the long-term viability of cells. Recently formed internodal cells have relatively disorganized actin bundles that become oriented in the subcortical cytoplasm approximately parallel to the newly established long axis and traverse the cell through transvacuolar strands. In older cells with central vacuoles not traversed by cytoplasmic strands, subcortical bundles are organized in parallel groups that associate closely with stationary chloroplasts, now in files. The parallel arrangement and continuity of actin bundles is maintained where they pass round nodal regions of the cell, even in the absence of chloroplast files. This study reports on two novel structural features of the characean internodal actin cytoskeleton: a distinct array of actin strands near the plasma membrane that is oriented transversely during cell growth and rings of actin around the chloroplasts bordering the neutral line, the zone that separates opposing flows of endoplasm.

Mathematical Modeling of Oxygen Diffusion and Respiration in Legume Root Nodules

The O(2) permeability of legume root nodules is under physiological control; decreases in permeability are triggered by various forms of stress. Two linked mathematical models were used to explore several hypotheses concerning the physical nature of the variable diffusion barrier in nodules. Respiration and diffusion of dissolved O(2) and oxygenated leghemoglobin were simulated for the nodule cortex and the nodule interior. Measured nodule permeabilities were shown to be inconsistent with the hypothesis that large numbers of air-filled pores penetrate the diffusion barrier. Changes in the affinity of leghemoglobin for O(2) or in the rate of cytoplasmic streaming in diffusion barrier cells did not result in the large changes in O(2) permeability reported for real nodules. The presence or absence, but not the thickness, of aqueous plugs in radial pores through the cortex was found to have a large effect on permeability. Flooding of intercellular spaces, either between layers of cells in the cortex or in the nodule interior, also caused large changes in simulated permeability. The unsteady-state O(2) method for determining nodule permeability was tested using data generated by the model. The accuracy of the method was confirmed, provided that certain assumptions (full oxygenation of leghemoglobin under pure O(2) and uniform conditions in the nodule interior) are met.

Recognition of a pathogen and a nonpathogen by barley coleoptile cells (I). Cytoplasmic responses to the nonpathogen, Erysiphe pisi, prior to its penetration

Cytoplasmic responses of barley coleoptile cells to Erysiphe pisi, a nonpathogen for barley, were examined during the prepenetration stages of fungal infection using a time-lapse video system and oil droplets microinjected into cells. Conspicuous cytoplasmic strands were seen underneath and extending away from appressoria of the fungus. These strands became visible when a circular structure appeared in one of the appressorial lobes, a feature which was used to define appressorial maturity. Thereafter, active cytoplasmic streaming occurred near the appressoria. These cytoplasmic responses were evident 4–5 h prior to the actual penetration of the host cell by the fungus. To monitor the cytoplasmic activity of coleoptile cells, a droplet of silicon oil was injected into individual coleoptile cells before the fungus was inoculated, and the movement of the oil droplet was monitored with a video system. The droplet moved at 2–3 μm min −1 soon after injection but its velocity increased to 4–5 μm min −1 after a germling of the fungus was transferred onto the individual coleoptile cell. When the appressoria matured on the cells, the velocity increased dramatically to 73 μm min −1. High velocities were then maintained, except for intermittent periods of slowing, until cytoplasmic aggregates were initiated beneath appressoria, when the velocity was reduced to 4–5 μm min −1 and the oil droplet remained near the appressorium. Although movement of the oil droplet did not correlate closely with rate of cytoplasmic streaming, the changes in droplet movement clearly indicated that cell cytoplasm responded to the presence of the fungus. These results suggest that appressoria of the fungus release a signal(s) upon maturation, 4–5 h prior to penetration, which induces physiological changes in the cytoplasm of the coleoptile cell.

Effect of calcium ion on cytoplasmic streaming during turgor regulation in a brackish water charophyte Lamprothamnium

Abstract The brackish water charophyte Lamprothamnium succinctum regulates its turgor pressure against changes in the external osmotic pressure. Upon hypotonic treatment, the rate of cytoplasmic streaming in the internodal cells fell to almost zero, and then recovered to the original value within 20 min. The decrease could be inhibited by lowering the external Ca2+ concentration in the hypotonic medium. Also, cytoplasmic streaming in tonoplast‐free cells of L. succintum was sensitive to Ca2+ like freshwater charophyte. Thus, the concentration of free Ca2+ in the cytoplasm seems to increase transiently upon hypotonic treatment.

Cytoplasmic streaming and ionic regulation inNitella flexilis having artificial cell saps of low ionic strength

The cell sap of the internode ofNitella flexilis was replaced with the isotonic artificial pond water of high Ca2+-concentration (0.1 mM KCl, 0.1 mM NaCl, 10 mM CaCl2 and 275 mM mannitol) and changes in osmotic value and concentrations of K+, Na+ and Cl− of the cells were followed. When the operated cells were incubated in the artificial pond water containing 0.1 mM each of KCl, NaCl, CaCl2, they survived for only a short period of time (<10 hr). The cells did not absorb ions from the artificial pond water and showed a conspicuous decrease in the rate of cytoplasmic streaming. In such cell the concentration of K+ in the protoplasm decreased significantly. In order to reverse normal concentration gradients of K+ and Na+ across the protoplasmic layer, the cells of low vacuolar ionic concentrations were incubated in the artificial cell sap (90 mM KCl, 40 mM NaCl, 15 mM CaCl2, 10 mM MgCl2). It was found that the cells rapidly absorbed much K+, Na+ and Cl− and survived for a longer period (1–2 days). During this period the rate of cytoplasmic streaming was nearly normal. Furthermore, the cell lost much mannitol, indicating an enormous increase in permeability to it. Since both absorption of ions and leakage of mannitol at 1 C occurred at nearly the same rates as at 22 C, the processes are assumed to be passive.

Protoplasmic streaming, cytochalasin B, and growth of the pollen tube

Pollen tubes were grown in nutrient medium with increasing concentrations of cytochalasin B that inhibited cytoplasmic streaming to different degrees. The streaming of cytoplasmic particles and the growth rate of pollen tubes were measured by cinc photography and frame by frame analysis of the film. A direct correlation has been found between the concentration of cytochalasin B in the medium, the rate of cytoplasmic streaming, and the rate of growth of the pollen babe. The functioning of microfilaments is thus implicated in the control of pollen tube growth.

X-RAY TOLERANCE OF LIVING CELLS AS MEASURED BY CYTOPLASMIC STREAMING

An investigation was undertaken to determine the immediate effects of X radiation on living, nondividing cells using the rate of cytoplasmic streaming as a measure of cell vitality. The observations were carried out on stamen hairs and pollen tubes of Tradescantia paludosa (diploid) and Tradescantia virginiana (tetraploid). No significant variation in the rate of streaming of cytoplasm in either stamen hairs or pollen tubes was noted with low doses of X rays. In both diploid and tetraploid stamen hairs, 700,000 r. was required to stop all streaming. In the pollen tubes of diploid and tetraploid plants, all streaming was stopped by 250,000 r. and 200,000 r. respectively, a difference that was statistically significant. Greater sensitivity, as shown by resulting cell death, was found with an increased initial dosage of continuous irradiation.