Turgid Cells Research Articles

Force and compliance: rethinking morphogenesis in walled cells

In the turgid cells of plants, protists, fungi, and bacteria, walls resist swelling; they also confer shape on the cell. These two functions are not unrelated: cell physiologists have generally agreed that morphogenesis turns on the deformation of existing wall and the deposition of new wall, while turgor pressure produces the work of expansion. In 1990, I summed up consensus in a phrase: “localized compliance with the global force of turgor pressure.” My purpose here is to survey the impact of recent discoveries on the traditional conceptual framework. Topics include the recognition of a cytoskeleton in bacteria; the tide of information and insight about budding in yeast; the role of the Spitzenkörper in hyphal extension; calcium ions and actin dynamics in shaping a tip; and the interplay of protons, expansins and cellulose fibrils in cells of higher plants.

A so called "rudimentary gall" induced by the gall midge Physemocecis hartigi on leaves of Tilia intermedia

The gall midge Physemocecis hartigi Liebel (Cecidomyiidae) induces a pustule gall on the leaves of the linden (Tilia intermedia D.C.). During larval development, the gall is inconspicuous on the host. Once the larva has left the gall (2 weeks after the eggs have been laid) the tissue desiccates and turns brown. We have found that the gall is initiated by the first instar larva, which attacks epidermal cells with sharp mandibles and kills a few precisely localized cells. Cells elongate perpendicularly to the attacked leaf lamina and eventually completely cover the larva. We did not observe cell division. The second instar larva enlarges the small gall cavity by inducing cell wall maceration between the vascular bundle sheath cells and the phloem. The larva feeds on cells that protrude from the open vascular bundles and on the palisade parenchyma. Contrary to earlier observations, we found these cells to be structurally modified into a nutritive tissue. The nutritive cells are hypertrophied and turgid, and have a centrally located enlarged nucleus and small vacuoles; the hydrated cytoplasm contains numerous concentric layers of endoplasmic reticulum, as well as many dictyosomes and autophagic structures. The presence of large pit fields in the cell wall suggests intense symplastic transport of solutes. The larva feeds by puncturing the turgid cells. These punctures may reach deeply into the cells but the cell wall is never ruptured; instead, the wall grows around the mandibles. Starch accumulates around the feeding area. Farther away, the modified leaf tissues contain phenolic substances. The pustule gall of P. hartigi is a highly specialized structure, supporting rapid larval development. The lack of conspicuity and the large larval cavity allow the larva to escape most of the parasitoids. Larval development goes almost without important host defense reactions and, therefore, is of low energy costs for the host. The wounding pattern of the first instar larva is highly species specific and shows a large degree of host adaptation.Key words: gall midge, gall, nutritive tissue, Physemocecis hartigi, Tilia intermedia.

Applications of the compensating pressure theory of water transport

Some predictions of the recently proposed theory of long-distance water transport in plants (the Compensating Pressure Theory) have been verified experimentally in sunflower leaves. The xylem sap cavitates early in the day under quite small water stress, and the compensating pressure P (applied as the tissue pressure of turgid cells) pushes water into embolized vessels, refilling them during active transpiration. The water potential, as measured by the pressure chamber or psychrometer, is not a measure of the pressure in the xylem, but (as predicted by the theory) a measure of the compensating pressure P. As transpiration increases, P is increased to provide more rapid embolism repair. In many leaf petioles this increase in P is achieved by the hydrolysis of starch in the starch sheath to soluble sugars. At night P falls as starch is reformed. A hypothesis is proposed to explain these observations by pressure-driven reverse osmosis of water from the ground parenchyma of the petiole. Similar processes occur in roots and are manifested as root pressure. The theory requires a pump to transfer water from the soil into the root xylem. A mechanism is proposed by which this pump may function, in which the endodermis acts as a one-way valve and a pressure-confining barrier. Rays and xylem parenchyma of wood act like the xylem parenchyma of petioles and roots to repair embolisms in trees. The postulated root pump permits a re-appraisal of the work done by evaporation during transpiration, leading to the proposal that in tall trees there is no hydrostatic gradient to be overcome in lifting water. Some published observations are re-interpreted in terms of the theory: doubt is cast on the validity of measurements of hydraulic conductance of wood; vulnerability curves are found not to measure the cavitation threshold of water in the xylem, but the osmotic pressure of the xylem parenchyma; if measures of xylem pressure and of hydraulic conductance are both suspect, the accepted view of the hydraulic architecture of trees needs drastic revision; observations that xylem feeding insects feed faster as the water potential becomes more negative are in accord with the theory; tyloses, which have been shown to form in vessels especially vulnerable to cavitation, are seen as necessary for the maintenance of P, and to conserve the supplementary refilling water. Far from being a metastable system on the edge of disaster, the water transport system of the xylem is ultrastable: robust and self-sustaining in response to many kinds of stress.

The electrophysiology of plasmolysed cells ofChara australis

The electrophysiology of non-turgid cells of Chara australis was investigated. The data fell into two categories. (i) 20% of cells; these were relatively unaffected by plasmolysis (with the exception of a small depolarization) and retained many aspects of normal electrophysiological behaviour, such as excitation and K + -state I/V characteristics when exposed to 5 mol m -3 K + . (ii) 80% of cells; these showed electrophysiology significantly altered by plasmolysis. These cells exhibited a large depolarization and became highly conductive after plasmolysis. The classic current relaxation kinetics upon voltage step changes diminished. The channels constituting this high conductance state appeared to be weakly anion selective. Application of Ca 2+ channel blocker LaCl 3 did not prevent development of the high conductance. Upon exposure to 5 mol m -3 K + , the negative conductance regions were much less pronounced than those in turgid cells. Excitation was abolished. Cells in both categories showed a steady increase in conductance with time. The effects of plasmolysis on cell membrane conductance were irreversible. The information gathered from turgorless Chara cells can be extrapolated to explain depolarized or positive resting potentials and predominance of weakly anion selective channels in some higher plant cell protoplasts.

Control of sodium influx by calcium and turgor in two charophytes differing in salinity tolerance

ABSTRACTThe effects of Ca2+ and cell turgor on Na+ influx were examined in two charophytes, lamprothamnium papulo‐SUM (salt‐tolerant) and Chara corallina (salt‐sensitive), to try to identify causes of salinity toxicity. Mortality was associated with Na+ influx, with the two species showing similar sensitivities to high Na+ influx. In Lamprothamnium, toxic influxes of Na+ occurred at much higher external Na+ concentrations than in Chara. The differences in Na+ influx at the same Na+ concentration were not due to different responses to external Ca2+. Lamprothamnium adjusts its turgor in response to increasing NaCl whereas Chara cannot. In solutions of KC1 up to at least 200 mol m‐3, however, Chara regulated turgor, and when KC1 was subsequently replaced with NaCl, Na+ influx was low and similar to that in Lamprothamnium at the same Na* concentration. Chara cells which were not turgor‐adjusted in KCI had Na+ influxes 2‐5‐fold higher than the turgid cells. Thus, it appears that turgor is a major determinant of Na+ influx, and therefore of cell survival. We found no evidence that the mechanism of Na+ influx in Chara is different from that in Lamprothamnium. Higher susceptibility of Chara to NaCl seems to result from inability to regulate turgor, in turn leading to toxic Na+ influx.

Water in aerenchyma spaces in roots. A fast diffusion path for solutes

During a study of the diffusivity of sulphorhodamine G in the cortical apoplast of maize roots widely discrepant rates were found between different samples. In roots which had developed large aerenchyma spaces, the diffusion in some regions was very fast, indistinguishable from the rate in water. In other regions the rate was as much as 100 times slower. Examination of frozen intact roots with the cryo-scanning electron microscope showed the presence of liquid filling some of the aerenchyma spaces, while other spaces of the same root contained air. X-ray microanalysis of the liquid (for oxygen) showed that the liquid was water with few detectable ions. Similar liquid was present in small intercellular spaces within the spoke-like radial files of cells between the large spaces, or between remnants of collapsed cell walls at the edges of the large spaces. It is proposed that regions of roots with high diffusivity are those in which some of the aerenchyma spaces are filled with water. In seeking the origin of this liquid, the progress of aerenchyma formation could be followed in the frozen tissues. The first change observed in a group of contiguous cells was a loss of vacuolar solutes and of cell turgor. Next the walls broke apart and collapsed back onto the surrounding turgid cells leaving a volume of ion-poor liquid. The liquid was probably not that found in some aerenchyma spaces of the mature roots, because the final stage of space formation was a loss of the liquid, leaving an air filled cavity surrounded by a composite lining formed from the collapsed walls of the broken cells. It is likely that the liquid in the spaces of mature aerenchyma is exuded from the remaining living cortical cells at times when the root turgor is high. This would be consistent with several recent studies which have shown periodic exudation of water from the surface of turgid roots. The spasmodic occurrence of root cortex tissue with enhanced diffusivity would have important implications for the transport of nutrient ions across the root.

Microinjection of fungal cells: a powerful experimental technique

Microinjection is an effective method for introducing membrane-impermeant molecules into cells. As yet however, mycologists have made only limited use of this technique. Recent improvements in both equipment and methodology may change this situation as it is now possible to routinely microinject small turgid cells. In this paper I will review microinjection techniques and evaluate these with regard to fungal cells. The potential of microinjection for furthering our knowledge of fungal biology will be discussed. Key words: microinjection, fungi, oomycetes, F-actin, calcium.

The gas vesicles, buoyancy and vertical distribution of cyanobacteria in the Baltic Sea

The mean pressures required to collapse gas vesicles in turgid cells of cyanobacteria from the Baltic Sea were 0·91 MPa (9·1 bar) in Aphanizomenon flos-aquae, 0·83 MPa in Nodularia sp. collected from the main deep basins and 0·34 MPa in Nodularia from shallower coastal regions. The gas vesicles were strong enough to withstand the depth of winter mixing, down to the permanent halocline (60 m in the Bornholm Sea, 90 m in the Eastern Gotland Sea) or to the sea bottom (30 m or less in the shallow Arkona Sea and Mecklenburg Bight). The cyanobacteria had low cell turgor pressures, within the range 0·08–0·18 MPa. The colonies were highly buoyant: the Aphanizomenon colonies floated up at a mean velocity of 22 m per day and the Nodularia colonies at 36 m per day. The colonies remained floating when up to half of the gas vesicles had been collapsed. In summer the cyanobacteria were mostly restricted to the water above the thermocline and in calm conditions their concentration increased towards the top of the water ...

Measurements of Ca 2+ fluxes in intact plant cells

Owing to the central role of Ca 2+ in signal transduction processes, it is important to measure membrane fluxes of Ca 2+ in cells which are as undisturbed as possible, particularly when studying the control of these fluxes. To this end, techniques have been developed to measure Ca 2+ fluxes in intact, turgid plant cells. The measurements are principally of influx across the plasma membrane where Ca 2+ transport is likely to occur through cation-selective channels. The most direct method measures tracer fluxes of Ca 2+ , but special procedures are required to distinguish between influx and extracellular binding of Ca 2+ . Unfortunately, such techniques are currently only applicable to giant cells where surgical separation of the intracellular contents from the cell wall is possible. The influx of Ca 2+ into normal, resting cells of the green alga Chara corallina is usually about 0.3 nmol m -2 s -1 (at an external Ca 2+ concentration of 0.5 mol m -3 ). This flux is up to 5 times higher in actively growing cells, 20 times higher in cells depolarized by 20 mol m -3 K + and 1000 times higher during an action potential. Reducing cell turgor by a wide range of solutes increases Ca 2+ influx, especially near plasmolysis. Ca 2+ influx is sensitive to alterations in both external and cytosolic pH, but is inhibited by complete darkness and by low concentrations of La 3+ . Various organic Ca 2+ channel antagonists had mixed effects on Ca 2+ influx into Chara . The work described in this paper should enable further study of the control of Ca 2+ fluxes into intact, turgid plant cells, and their role in signal transduction and the control of cellular activities.

Nephelometric determination of turgor pressure in growing gram-negative bacteria.

Gas vesicles were used as probes to measure turgor pressure in Ancylobacter aquaticus. The externally applied pressure required to collapse the vesicles in turgid cells was compared with that in cells whose turgor had been partially or totally removed by adding an impermeable solute to the external medium. Since gram-negative bacteria do not have rigid cell walls, plasmolysis is not expected to occur in the same way as it does in the cells of higher plants. Bacterial cells shrink considerably before plasmolysis occurs in hyperosmotic media. The increase in pressure required to collapse 50% of the vesicles as external osmotic pressure increases is less than predicted from the degree of osmotically inducible shrinkage seen with this organism or with another gram-negative bacterium. This feature complicates the calculation of the turgor pressure as the difference between the collapse pressure of vesicles with and without sucrose present in the medium. We propose a new model of the relationship between turgor pressure and the cell wall stress in gram-negative bacteria based on the behavior of an ideal elastic container when the pressure differential across its surface is decreased. We developed a new curve-fitting technique for evaluating bacterial turgor pressure measurements.

Turgor‐ dependent membrane permeability in relation to calcium level

The relationship between the inhibiting effect of Ca2+ and of low turgor pressure on K+ release from fresh‐cut discs of carrot (Daucus carota var. Nantes) storage tissue was studied. A range of Ca2+ concentrations in the tissue was obtained by adding 0.5 mM EDTA or CaSO4 at different concentrations to the medium. Calcium inhibited K+ release in fully turgid cells (2.5 μmol K+ g−1 h−1 in 0.5 mM EDTA vs 0.4 μmol K+ g−1 h−1 in 10 mM CaSO4). Less turgid cells, obtained by equilibration with 0.2 M mannitol, released K+ at only 30% of the rate of the turgid cells, yet the pattern of K+ release as a function of Ca2+ level was similar in both turgid and non‐turgid cells. Removal of calcium by EDTA occasionally injured cell membranes in the fully turgid discs but never in the less turgid ones. In view of the additive effect of Ca2+ and low turgor on K+ release regardless of the treatment order, it is suggested that the two factors exert their effect on membrane permeability independently of each other.

Generation of Torque by the Column of Stylidium

The gynostemium or column of the flower of Stylidium, when stimulated mechanically, flips through an angle of about 4 rad in 15-20 ms and then resets to its original position in 300-600 s. The torque causing this movement is produced in a specialized motor tissue when the angular displacement, 8, of the column from its set position exceeds a threshold value of about 4 x lo-' rad. An experimental apparatus has been developed to change 0 in a controlled manner and measure the resultant torque, 7, exerted by the column. For subthreshold angular displacement, the column opposes the applied torque and the stiffness of the column, defined as d~/dOi,s 1.5 x 10' pN m rad-'. At threshold displacement, 7 reverses in direction and the stiffness decreases to about 0.5 % of this value in about 2-4 ms. The stiffness remains low for the remainder of the fast movement and slow recovery, but returns to the original high value after the column has been set for about 20-30 min. Most of the stiffness of the set colunln seems to reside in very turgid cells within the concave or anterior side of the motor tissue. The cells when turgid could provide a holding torque, maintaining the column in the set position against an equal and opposite torque in the posterior layer. On stimulation, the anterior cells apparently cease to exert torque, with subsequent movement of the column caused by a torque within cells in the opposite, posterior, layer. The mechanism by which the column loses stiffness in the short time of 2-4 ms is not clearly understood; two possibilities are considered.

Rhythmic and phytochrome-regulated changes in transmembrane potential in Samanea pulvini

NYCTINASTIC plants such as Albizzia julibrissin, Mimosa pudica and Samanea saman have compound leaves with paired leaflets which are usually horizontal (open) during daylight and vertical (closed) at night, oscillating between these positions with a circadian rhythm during long dark periods1–3. The angle of a leaflet is determined by the relative turgour of motor cells on opposite sides of the pulvinus, an organ which subtends the leaflet. Extensor cells are turgid and flexor cells are flaccid when leaflets are open and vice versa when they are closed. This is regulated by movements of potassium2,4–8, which is high in turgid cells and low in flaccid cells. Inhibitors of oxidative phosphorylation and low temperatures impede opening and promote closure, suggesting that active transport predominates during opening, while diffusion is favoured during closure4,8–10.

Plant cell-wall microfibril disposition revealed by freeze-fractured plasmalemma not treated with glycerol

The plasmalemmata of root tip cells of Phaseolus vulgaris L. appear to be well preserved in freeze-fractured material in which no glycerol pre-treatment has been used. The plasmalemmata retain the impressions made by the microfibrils and pit-fields of the cell walls against which these membranes are pressed in turgid cells. Material freeze-fractured in this way is therefore more suitable than glycerol-treated material (in which these impressions are not retained) for the study of membrane features which may be related to microfibril synthesis.

Spore projection in Epicoccum and Arthrinium

Conidia of Epicoccum nigrum are projected from their sporodochia. Evidence is presented that projection is due to the rounding off of turgid cells. A similar mechanism may separate the conidia of Arthrinium cuspidatum from their conidiophores.

SCHIZODICTYON, A NEW GENUS IN THE PALMELLACEAE

American Journal of BotanyVolume 38, Issue 10 p. 780-783 Article SCHIZODICTYON, A NEW GENUS IN THE PALMELLACEAE R. H. Thompson, R. H. Thompson Department of Botany, University of Kansas, Lawrence, KansasSearch for more papers by this author R. H. Thompson, R. H. Thompson Department of Botany, University of Kansas, Lawrence, KansasSearch for more papers by this author First published: 01 December 1951 https://doi.org/10.1002/j.1537-2197.1951.tb14893.xCitations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume38, Issue10December 1951Pages 780-783 RelatedInformation

Unrolling of Leaves of Musa sapientum and Some Related Plants and Their Reactions to Environmental Aridity

1. An experimental study was made of the mechanics of the unrolling of the leaves of Musa and Heliconia (Musaceae), Alpinia (Zingiberaceae), Canna (Cannaceae), and Calathea (Marantaceae), representing each of the four families of the tropical order Scitamineae. 2. The large laminae of all the species studied are convolute in vernation. They are practically full-grown at the time they begin to emerge from the top of the false stem, which, to a greater or less degree, is characteristic of most of the genera of this order. At this time, if the lamina is unrolled, it is found to be smoothed and flat, without the transverse ribs so characteristic of these plants. 3. Unrolling is effected by the timely enlargement of the cells of the upper water tissue above and immediately adjacent to the principal veins. The localized enlargement of these cells results in raising the principal veins above the general surface of the lamina, thus forming the ribs. In the coiled position of the leaf they are pushed inward, come to occupy a curvature of smaller radius, and are thus (with the turgid cells which lie above them) brought into a state of compression. In this compressed state they force the lamina to unroll. 4. In Musa the fibers on the dorsal side of the veins are thick walled and become lignified somewhat before the portion of the leaf in which they lie begins to unroll. The fibers on the ventral side remain thin walled until the leaf has unfolded, and never become lignified. 5. Enlargement of the expansion cells proceeds inward from the outer margin of the lamina, and from the apex toward the base. 6. If the unrolling of the leaf is prevented by binding it with cord, the expansion cells in all species studied except Alpinia become greatly enlarged, and occupy over half the entire cross-section of the lamina. In Alpina the hypertrophy is relatively slight, apparently because the water tissue is interrupted by thick walled cells which are not able to stretch. Only in Canna does the hypertrophy extend completely across the lamina half; in most cases it is strictly limited to the region of the principal and the stronger subordinate veins. 7. Leaves of Musa and Canna were found to unroll in complete absence of light. In darkness, however, the hypertrophy of the water cells of bound leaves is much less than of those in the light. 8. If the lamina of Musa is prematurely unrolled and held in a plane, the expansion cells fail to enlarge. They enlarge only when in a state of compression. 9. The ribs are essential to impart rigidity to the lamina halves, which are otherwise without lateral support. 10. In addition to the unrolling of each side of the lamina, a special arrangement is necessary to bend it outward from the midrib. This is effected by great development of expansion cells along the edges of the midrib (Musa, Heliconia, Calathea), or in the center of the midrib (Alpinia). 11. In most members of the Scitamineae, when the leaf suffers great water loss and the expansion cells lose their turgidity, the process of unfolding is in part reversed. each side of the lamina bends upward along the midrib, exposing the stomata, which are situated principally in the lower surface. This non-adaptive movement is a necessary result of the structure and method of unfolding of the leaf. 12. In Musa the sides of the lamina fold downward in dry weather. This is a result of the formation of a rather massive tissue of prismatic ells in a strip along either side of the midrib, which thus becomes a pulvinar band. The rising and falling of the lamina halves are brought about by differential changes in the turgor of two antagonistic tissues, the expansion cells on the upper side and the prismatic cells on the lower. 13. The prismatic cells begin to develop only after complete expansion of the leaf, when stimulated by the compression to which they are subjected after the expansion cells on the upper side of the pulvinar band bend it downward. Hence they do not develop in leaves which are prevented from unfolding by binding. They develop only in the light.

The Anatomy and the Histology of Bud-formation in the Serpulid Filograna implexa, together with some Cytological Observations on the Nuclei of the Neoblasts.*

The Anatomy and the Histology of Bud-formation in the Serpulid Filograna implexa, together with some Cytological Observations on the Nuclei of the Neoblasts.*