Cell Length Measurements Research Articles

Role of Amphipathic α-helix and Division-related Proteins in Bacillus Subtilis

In many bacteria, cell division is initiated by a tubulin-like protein FtsZ, which forms a ring structure known as the Z-ring at midcell. FtsA and SepF are important membrane anchor of Z-ring, which exists widely in bacteria species and binds to the membrane by a C-terminal amphipathic α-helix in a membrane potential-dependent manner. It reported that amphipathic α-helix binds to the leading edge of developing septum with an intrinsic preference. These discoveries led to a hypothesis, proteins of amphipathic helix might not only function as membrane anchor of FtsZ, but also participating the regulation of septum synthesis. Several variants were made by genetic techniques, and cell length measurements were performed by fluorescence microscopy and ImageJ. All helix variants were found viable, the amphipathic α-helix does affect the cell division but does not affect the functionality.

GC-MS analysis of Myrtus communis extract and its antibacterial activity against Gram-positive bacteria

BackgroundMyrtus communis is a typical plant of Mediterranean area. The different parts of this plant such as berries, branches, and leaves have been used worldwide as a traditional/folk medicine for the treatment of various ailments and diseases.MethodsEthanolic leaf extract of the plant was prepared by Soxhlet extraction method. Zone of inhibition, minimum inhibitory concentration and minimal bactericidal concentration were determined by well diffusion method and microplate alamar blue assay. GC-MS analysis was carried out to identify the compounds present in the extract. Microscopy and ImageJ software were used respectively for morphology and cell-length measurements. GraphPad Prism was used for statistical analysis.ResultsThe ethanolic extract showed strong inhibitory effect against Gram-positive and acid-fast bacteria with significant inhibition-zone size (9–25 mm), MIC (4.87–78 μg/ml), as well as MBC (0.3–20 mg/ml). However, no effect was observed on the growth of Gram-negative bacteria. The growth inhibition was found to be associated with the damage of cell wall as the extract-treated cells were sensitive to cell wall-targeting antibiotics and displayed the cell wall damage-depicting morphological defects. GC-MS analysis confirmed the presence of novel compounds in addition to the most representative compounds of the essential oils/extracts of M. communis of other country origins.ConclusionThese results demonstrate that M. communis leaf extract could be the source of compounds to be used for the treatment of Gram-positive bacterial infections. This is the first report, which provides insights into the mechanism of action of the extract in inhibiting the growth of Gram-positive bacteria.

Chromatin and Cell Wall Staining of Schizosaccharomyces pombe.

Fission yeasts grow by tip extension, maintaining a constant width until they reach a critical size threshold and divide. Division by medial fission-which gives these yeast their name-generates a new end that arises from the site of cytokinesis. The old end, which was produced during the previous cell cycle, initiates progression of the new cell cycle, and in G2, the new end is activated in a process termed new-end takeoff (NETO). In this protocol, the fluorescent stains calcofluor and 4',6-diamidino-2-phenylindole (DAPI) are used to give a rapid and informative assessment of morphogenesis and cell-cycle progression in the fission yeast Schizosaccharomyces pombe Calcofluor reveals the timing of NETO because it stains the birth scars that are generated at new ends by cytokinesis less efficiently than the rest of the cell wall. Intense calcofluor staining of the septum and measurement of cell length are also widely used to identify dividing cells and to gauge the timing of mitotic commitment. Staining nuclei with DAPI identifies mono- and binucleated cells and complements the calcofluor staining procedure to evaluate the stages of the cell cycle and identify mitotic errors. Equally simple DAPI staining procedures reveal chromatin structure in higher resolution, facilitating more accurate staging of mitotic progression and characterization of mitotic errors.

Contraction of gut smooth muscle cells assessed by fluorescence imaging

Here we discuss the development of a novel cell imaging system for the evaluation of smooth muscle cell (SMC) contraction. SMCs were isolated from the circular and longitudinal muscular layers of mouse small intestine by enzymatic digestion. SMCs were stimulated by test agents, thereafter fixed in acrolein. Actin in fixed SMCs was stained with phalloidin and cell length was determined by measuring diameter at the large end of phalloidin-stained strings within the cells. The contractile response was taken as the decrease in the average length of a population of stimulated-SMCs. Various mediators and chemically identified compounds of daikenchuto (DKT), pharmaceutical-grade traditional Japanese prokinetics, were examined. Verification of the integrity of SMC morphology by phalloidin and DAPI staining and semi-automatic measurement of cell length using an imaging analyzer was a reliable method by which to quantify the contractile response. Serotonin, substance P, prostaglandin E2 and histamine induced SMC contraction in concentration-dependent manner. Two components of DKT, hydroxy-α-sanshool and hydroxy-β-sanshool, induced contraction of SMCs. We established a novel cell imaging technique to evaluate SMC contractility. This method may facilitate investigation into SMC activity and its role in gastrointestinal motility, and may assist in the discovery of new prokinetic agents.

LEAF-E: a tool to analyze grass leaf growth using function fitting.

In grasses, leaf growth is often monitored to gain insights in growth processes, biomass accumulation, regrowth after cutting, etc. To study the growth dynamics of the grass leaf, its length is measured at regular time intervals to derive the leaf elongation rate (LER) profile over time. From the LER profile, parameters such as maximal LER and leaf elongation duration (LED), which are essential for detecting inter-genotype growth differences and/or quantifying plant growth responses to changing environmental conditions, can be determined. As growth is influenced by the circadian clock and, especially in grasses, changes in environmental conditions such as temperature and evaporative demand, the LER profiles show considerable experimental variation and thus often do not follow a smooth curve. Hence it is difficult to quantify the duration and timing of growth. For these reasons, the measured data points should be fitted using a suitable mathematical function, such as the beta sigmoid function for leaf elongation.In the context of high-throughput phenotyping, we implemented the fitting of leaf growth measurements into a user-friendly Microsoft Excel-based macro, a tool called LEAF-E. LEAF-E allows to perform non-linear regression modeling of leaf length measurements suitable for robust and automated extraction of leaf growth parameters such as LER and LED from large datasets. LEAF-E is particularly useful to quantify the timing of leaf growth, which forms an important added value for detecting differences in leaf growth development. We illustrate the broad application range of LEAF-E using published and unpublished data sets of maize, Miscanthus spp. and Brachypodium distachyon, generated in independent experiments and for different purposes. In addition, we show that LEAF-E could also be used to fit datasets of other growth-related processes that follow the sigmoidal profile, such as cell length measurements along the leaf axis.Given its user-friendliness, ability to quantify duration and timing of leaf growth and broad application range, LEAF-E is a tool that could be routinely used to study growth processes following the sigmoidal profile.Electronic supplementary materialThe online version of this article (doi:10.1186/1746-4811-10-37) contains supplementary material, which is available to authorized users.

On Prandtl's Formulas for Supersonic Jet Cell Length

In 1904 Prandtl developed a pioneering small perturbation theory to obtain the well-known “Prandtl Formula” λ = 1.306 d√(( wm/ c)2 − 1) for the wavelength (cell length) of an almost perfectly expanded circular supersonic jet, uniform everywhere and notably so on the bounding streamlines, where d = jet diameter, wm/ c = mean (unperturbed) speed (Mach number) of the jet. To relate to experiment and possibly provide a means of estimating jet speed from cell length measurements, he very tersely made a comparison of the results of his formula with those of Emden's formula, λ = 0.88 d√( R - Rc). This was based on extensive experiments with choked jets, with R = pressure ratio (critical value Rc), He rewrote his formula as λ = 1.306 dw√(( w/c)2 − 1), called herein “Prandtl's Formula II, where now dw = minimum diameter of the nozzle duct, i.e. exit diameter for Emden's choked jets, but the throat diameter of the convergent-divergent nozzle of uniform supersonic jets. He rewrote the foregoing equation, “my relationship,”” clearly considering that the nozzle exit diameter dw for the fully expanded flow would vary (according to the one-dimensional gas flow equations) so as to be consistent with the pressure ratio in Emden's formula. Unfortunately these simple but important notational changes for the comparison were made without comment and appear to have been totally ignored. Then converting his Formula II into Emden's form gave the well-known λ = 1.2 d√( R - Rc), a good approximation over a wide range of R. This fully satisfied Prandtl's objective, the discrepancy (1.2 vs. 0.88) being a constant factor easily taken into account, its magnitude apparently being of no particular significance considering the radically different jet flow structures. The coefficient 1.306 was improved to 1.22 by Pack who was able to compute up to 40 terms of the series solution, for which Prandtl had taken just the first term. Pack also provided the full series solution for the two-dimensional case. The circumstances of the origin of these formulas and their subsequent history over the next half-century are discussed in some detail, but a more general discussion of cell length is beyond the scope of this account.

Low extracellular K + increases intracellular Ca 2+ oscillation and injury by activating the reverse mode Na +–Ca 2+ exchanger and inhibiting the Na +, K + ATPase in rat cardiomyocytes

Background The effects of low K + on post-ischemic reperfused heart cells are not clearly understood. Calcium overload is one of the major causes for myocardial reperfusion injury, the present study was to investigate the role of intracellular calcium oscillations in the effects of reperfusion with low K + on rat myocytes. Methods Ischemic myocytes were reperfused with Tyrode solution containing K + at 5.4 (control) or 3.0 mM (low K +) for 10 min. the changes of intracellular calcium was recorded by spectrofluorometry. The exclusion of trypan blue by myocytes served as indices of viability. Measurements of cell length, reverse-mode Na +–Ca 2+ exchanger (NCX) and Na +, K + ATPase activity were performed. Results Compared to control, myocytes reperfused with low K + had greater number of calcium oscillations and reverse-mode NCX activity, which were accompanied with decreased cell length recovery and cell viability. Reperfusion with KB-R7943, an inhibitor of reverse-mode NCX, attenuated the effects of low K + on all the parameters. Inhibition of Na +, K + ATPase with Ouabain increased the susceptibility to calcium oscillations in myocytes reperfused with low K +, which was accompanied with cell length shortening and decreased cell viability. Reperfusion with K + at 9.0 mM, which activated Na +, K + ATPase, attenuated calcium oscillations, protected cell length recovery, and increased cell viability. Conclusions These results suggest that increased calcium oscillations mediate the exacerbating reperfusion injury with low K + on myocytes, and inhibition of Na +, K + ATPase activity and increase of reverse-mode NCX activity contribute to these effects.

H-ras Inhibits RhoA/ROCK Leading to a Decrease in the Basal Tone in the Internal Anal Sphincter

The present studies evaluated the role of H-ras and its implications in the RhoA/Rho kinase (ROCK) pathway in regulating basal tone in the internal anal sphincter (IAS). Studies were performed in the IAS from the wild-type (H-ras(+/+)) and knock-out (H-ras(-/-)) mice. The basal tone of smooth muscle strips was measured by isometric force transducers. Length of smooth muscle cells (SMC) isolated from the IAS in the basal state was determined by phase contrast microscopy. Experiments were repeated in the presence of Y 27632, a ROCK inhibitor. Involvement of the RhoA/ROCK machinery was analyzed by reverse-transcription polymerase chain reaction, Western blot, and immunocytochemistry. Reversal of H-ras knock-out effect was evaluated by transfection of SMCs with the constitutively activated (G12V) mutant. Basal tone of the H-ras(-/-) IAS was significantly higher and resistant to relaxation by Y 27632, compared with the H-ras(+/+) IAS. Similarly, the length of SMCs from H-ras(-/-) IAS was significantly shorter. Y 27632 eliminated this difference. RhoA immunoreactivity shifted from cytoplasm to plasma membrane in H-ras(-/-) SMCs, a change typically associated with contraction. Further, SMCs from H-ras(-/-) mice exhibited higher levels of the contractile proteins ROCK II, phosphorylated-MYPT(1) and phosphorylated-MLC(20). Transfection with the G12V mutant increased the length of H-ras(-/-) cells. Conversely, the dominant negative H-ras (S17N) mutant decreased the length of H-ras(+/+) cells. H-ras negatively regulates basal tone in the IAS by inhibiting RhoA/Rho-kinase machinery. Studies may have significant relevance in the pathophysiology and therapy of certain anorectal motility disorders associated with the IAS dysfunction.

A Method for Estimating Cell Volume of Amoebae Based on Measurements of Cell Length of Motile Forms: Physiological and Ecological Applications

A novel method of estimating the cell volume of non-testate, free-living amoebae is presented. Measurements of the length (L) of motile forms of some amoebae, obtained by applying some basic rules, can be used to calculate diameter (D) using a relatively simple formula, derived from regression analysis (N=39): D=0.6L. Important physiological and ecological variables, including carbon content and respiratory rate, can then be easily calculated using this estimated cell volume.

Dynamics study of detonation-wave cellular structure 1. Statistical properties of detonation wave front

We have investigated the evolution of cellular detonation-wave structure as a gaseous detonation travels along a round tube and measured cell lengths as a function of the initial pressure of the gas. We have tested acetylene-containing combustible gas mixtures with different degrees of regularity. Along with the smoked-foil technique, an emission method has been used to the measure current and average values of the detonation cell length. The method is based on the detection of an emission spectrum behind the detonation front in the spectral range corresponding to local gas temperatures that are much higher than those for the Chapman-Jouguet equilibrium condition. This technique provides quasi-continuous cell-length measurements along the normal to the detonation front over the length of several factors of ten times the tube.

The peri-cell-cycle in Arabidopsis.

The root systems of plants proliferate via de novo formed meristems originating from differentiated pericycle cells. The identity of putative signals responsible for triggering some of the pericycle cells to re-enter the cell cycle remains unknown. Here, the cell cycle regulation in the pericycle of seedling roots of Arabidopsis thaliana (L.) HEYNH: is studied shortly after germination using various strategies. Based on the detailed analysis of the promoter-beta-glucuronidase activity of four key cell cycle regulatory genes, combined with cell length measurements, microdensitometry of DNA content, and experiments with a cell cycle-blocking agent, a model is proposed for cell cycle regulation in the pericycle at the onset of lateral root initiation. The results clearly show that before the first lateral root is initiated, the pericycle consists of dissimilar cell files in respect of their cell division history. Depending on the distance behind the root tip and on position in relation to the vascular tissue, particular pericycle cells remain in the G(2) phase of the cell cycle and are apparently more susceptible to lateral root initiation than others.

Pericycle cell proliferation and lateral root initiation in Arabidopsis.

In contrast with other cells generated by the root apical meristem in Arabidopsis, pericycle cells adjacent to the protoxylem poles of the vascular cylinder continue to cycle without interruption during passage through the elongation and differentiation zones. However, only some of the dividing pericycle cells are committed to the asymmetric, formative divisions that give rise to lateral root primordia (LRPs). This was demonstrated by direct observation and mapping of mitotic figures, cell-length measurements, and the histochemical analysis of a cyclin-GUS fusion protein in pericycle cells. The estimated duration of a pericycle cell cycle in the root apical meristem was similar to the interval between cell displacement from the meristem and the initiation of LRP formation. Developmentally controlled LRP initiation occurs early, 3 to 8 mm from the root tip. Thus the first growth control point in lateral root formation is defined by the initiation of primordia in stochastic patterns by cells passing through the elongation and young differentiation zones, up to where lateral roots begin to emerge from the primary root. Therefore, the first growth control point is not restricted to a narrow developmental window. We propose that late LRP initiation is developmentally unrelated to the root apical meristem and is operated by a second growth control point that can be activated by environmental cues. The observation that pericycle cells divide and lateral root primordia form without intervening mitotic quiescence suggests that lateral organ formation in roots and shoots might not be as fundamentally different as previously thought.

Effects of anoxia on intracellular Ca2+ and contraction in isolated guinea pig cardiac myocytes.

Single, enzymatically isolated guinea pig ventricular myocytes were exposed to 3-min periods of anoxia with glucose-free Tyrode solution containing 1 mM sodium dithionite (Na2S2O4) and were then reoxygenated for 10 min. The myocytes were exposed to rapid applications of 10 mM caffeine during the control, anoxic, and reoxygenation periods. Intracellular Ca2+ concentration ([Ca2+]i) was measured ratiometrically using indo 1 with simultaneous measurements of cell length. The effects of anoxia on Ca2+ were compared with those of hypoxia and metabolic inhibition. The amplitude of the electrically stimulated (Ca transient) and caffeine-evoked Ca2+ (Caff-Ca) transients decreased during anoxia and recovered after reoxygenation. Diastolic [Ca2+]i did not change during 3 min of anoxia but rose progressively after prolonged anoxia and remained at this higher level on reoxygenation. During metabolic inhibition the Ca transients decreased, while the Caff-Ca transients showed no change in amplitude. During hypoxia the Ca transients decreased. Anoxia slowed the time to peak of the Ca transient, the time to 50% relaxation, and the time to 90% relaxation. The decline of indo 1 fluorescence on rapid caffeine application was slowed during anoxia, metabolic inhibition, and hypoxia and partially recovered after reoxygenation.

Effects of K+ and the K+ Ionophore Valinomycin on the Post-Conjugational Nuclear Differentiation of Paramecium caudatum: (determination/macronucleus/Paramecium/potassium/valinomycin).

For determination of the effect of K+ on macro- and micronuclear differentiation Paramecium caudatum exconjugants were transferred to medium with various concentrations of Valinomycin and/or K+ at the critical stage of nuclear differentiation. The differentiation was not disturbed by transfer to medium containing 1.5 mM to 50 mM KCl. Injection of KCl solution at the critical stage also did not affect differentiation of the macronucleus appreciably. But change of the KCl concentration in the medium at the critical stage interrupted of normal development of the macronucleus. Macro- and micronuclear differentiations after conjugation are known to be determined by the antero-posterior localization of postzygotic micronuclei. This nuclear localization is achieved by elongation of mitotic spindles and marked shortening of the cell length at the time of micronuclear division. Successive measurements of cell length at 25°C showed that cells began to shorten 1.5 hr after mating-pair separation, reaching to half the initial length about 2.5 hr after the separation, and then returning to recover their initial length within about 50 min. In a solution of K+ (50 mM) plus Valinomycin (1μg/ml or more), cell shortening was inhibited. It is not known whether elongation of mitotic spindles at the time of critical nuclear division was disordered by this treatment, but the macronuclear anlagen developed in the treated cells. Thus shortening in the cell length is not indispensable for nuclear differentiation.

Distribution of diploid and tetraploidLotus pedunculatusplants in moist, North Island hill country

Abstract The proportions of diploid (2n) and tetraploid (4n) Lotus pedunculatus lines were determined at different hill country sites in southern North Island hill pastures by stomatal cell length measurements and by counting chromosome numbers. The area had been oversown 10–15 years earlier with both diploid G4703 (now ‘Grasslands Sunrise’) lotus and tetraploid ‘Grasslands Maku’ lotus seed. There was a greater frequency of diploid than tetraploid plants in the 506 plants sampled from different slope, aspect, and fertility classes. Tetraploid plants were more common on steeper slopes and north-facing aspects but the proportion of diploid:tetraploid plants was not affected by fertiliser treatments. These data are consistent with the hypothesis that plants with a large DNA content per cell nucleus and large cell size have a superior ability to grow in seasonally dry sites.

Isolation, configuration and contractile responses of single smooth muscle cells

In studies on the intrinsic contraction mechanisms of smooth muscle, various factors such as cell-to-cell interaction, penetration of chemicals to the trigger regions, or extracellular spaces in the tissue may influence the results. The use of single smooth muscle cells in such investigations may help to eliminate these factors. Single smooth muscle cells can be isolated from guinea pig taenia coli by digesting the minced tissue with a combination of collagenase and soybean trypsin inhibitor. The cells are spindle shaped, 100-200 microns in length and 10 microns in diameter. Three kinds of techniques for determination of contractile responses of single smooth muscle cells have been established: 1) fixation method, 2) perfusion method, and 3) capillary adhesion method. Using these techniques, the cells appeared to be contracted in a dose-dependent manner (graded response), while another mode of the contractile response, the "all-or-none response", has also been proposed. Scanning and transmission electron micrographs of the single cells revealed several evaginations of various sizes and shapes on the surface and electron dense bodies at the neck of the evaginations. ED50 obtained with the single cells, prepared from taenia coli of guinea pigs with collagenase in the presence of trypsin inhibitor was similar to that obtained with the intact tissue. Digestion of the tissue with highly purified collagenase and papain yields a large number of single cells with higher sensitivity to agonists. Characteristics of cells isolated from ileal longitudinal muscle of guinea pig are similar to those of cells isolated from taenia coli. The magnitude of contraction and sensitivity to acetylcholine were different in each cell. Incubation of isolated tissues with various concentrations of agonists followed by measurement of cell length in the tissue showed that the heterogeneous responses of the cells were intrinsic characteristics of smooth muscle cells and not due to damage incurred during the isolation procedure. Since isolated smooth muscle cells possess contractility, these might preserve the characteristics of smooth muscle, so they can be used for smooth muscle research. It must be considered, however, that each cell in the smooth muscle tissue has different contractility.

Cell length measurements in longitudinal smooth muscle strips of the pig urinary bladder.

In this study the length of smooth muscle cells in muscle bundles of pig urinary bladder wall was determined after dissection in Tyrode buffers with different calcium concentrations ([Ca2+]). Previous studies have shown that the length of isolated smooth muscle cells decreases with an increase in [Ca2+] in the buffer. Unlike the results in isolated cells, no significant differences in length were found between cells in strips subjected to different [Ca2+]. Cells in bundles dissected from filled bladders were significantly larger than those dissected from emptied bladders. Cells in strips from emptied bladders dissected in 1.8 mM Ca(2+)-Tyrode buffer were shorter than those obtained in Ca(2+)-free buffer. From the measurements it was concluded that: (1) Cell length in intact tissue is directly related to tissue length; series elastic structures external to the cells do not allow significant shortening of the cells. (2) Passive parallel elasticity outside the cells accounts for passive shortening when bladders are emptied manually. (3) Cell length is not related to empty bladder weight. (4) A positive relation exists between empty bladder weight and bladder capacity.

Effect of Inhibition of Abscisic Acid Accumulation on the Spatial Distribution of Elongation in the Primary Root and Mesocotyl of Maize at Low Water Potentials

Previous work showed that accumulation of endogenous abscisic acid (ABA) acts both to maintain primary root growth and inhibit shoot growth in maize seedlings at low water potentials (psi(w)) (IN Saab, RE Sharp, J Pritchard, GS Voetberg [1990] Plant Physiol 93: 1329-1336). In this study, we have characterized the growth responses of the primary root and mesocotyl of maize (Zea mays L. cv FR27 x FRMo 17) to manipulation of ABA levels at low psi(w) with a high degree of spatial resolution to provide the basis for studies of the mechanism(s) of ABA action. In seedlings growing at low psi(w) and treated with fluridone to inhibit carotenoid (and ABA) biosynthesis, ABA levels were decreased in all locations of the root and mesocotyl growing zones compared with untreated seedlings growing at the same psi(w). In the root, low psi(w) (-1.6 megapascals) caused a shortening of the growing zone, as reported previously. The fluridone treatment was associated with severe inhibition of root elongation rate, which resulted from further shortening of the growing zone. In the mesocotyl, low psi(w) (-0.3 megapascal) also resulted in a shortened growing zone. In contrast with the primary root, however, fluridone treatment prevented most of the inhibition of elongation and the shortening of the growing zone. Final cell length measurements indicated that the responses of both root and mesocotyl elongation to ABA manipulation at low psi(w) involve large effects on cell expansion. Measurements of the relative changes in root and shoot water contents and dry weights after transplanting to a psi(w) of -0.3 megapascal showed that the maintenance of shoot elongation in fluridone-treated seedlings was not attributable to increased water or seed-reserve availability resulting from inhibition of root growth. The results suggest a developmental gradient in tissue responsiveness to endogenous ABA in both the root and mesocotyl growing zones. In the root, the capacity for ABA to protect cell expansion at low psi(w) appears to decrease with increasing distance from the apex. In the mesocotyl, in contrast, the accumulation of ABA at low psi(w) appears to become increasingly inhibitory to expansion as cells are displaced away from the meristematic region.

Restoring forces in cardiac myocytes. Insight from relaxations induced by photolysis of caged ATP

Concentration jumps of intracellular ATP were produced by photolysis of P3-1-(2-nitrophenyl)ethyl (NPE)-caged ATP and were used to investigate the passive relengthening properties in unloaded cardiac myocytes. Patch-clamp pipettes in the whole-cell mode were used to voltage-clamp the myocytes and to load the cells with caged ATP while optical methods were applied to record sarcomere length or cell length simultaneously. Cell length was varied using energy deprivation contractures while intracellular Ca2+ was controlled with EGTA. At sarcomere lengths between 1.8 and 1.4 microns cellular relengthening after photolysis of caged ATP was rapid (t1/2 approximately 100 ms) and could be well described by a simple mechanical model. However, ATP jumps made at sarcomere lengths approximately 1.1 microns led to slow relengthening (t1/2 approximately seconds), comparable to the slow reextensions observed in skinned myocytes after bulk solution changes. We attribute the slow and incomplete relengthening of intact and skinned myocytes after severe rigor shortening to deformation and alteration of structural elements inside the cell. Relengthening from intermediate sarcomere lengths in intact cells is elastic and provides information about the underlying relengthening forces inside the cell. The data do not support the presence of a significant discontinuity in elastic modulus at a sarcomere length of approximately 1.6 microns expected from ultrastructural features of the sarcomeres and from observations in skinned myocytes. Our results suggest that the cell length measurements usually performed in this preparation provide an adequate description of the force produced by the unloaded cell in the steady state. The results also provide a way to estimate the error arising from viscous forces during rapid shortening.

Diffuse growth, a new pattern of cell wall deposition for the Rhodophyta

Abstract By means of calcofluor staining, cell elongation measurements, and microspectrofluorometry, diffuse cell wall deposition is demonstrated for the first time in the red algae in Audouinella dasyae (Acrochaetiaceae, Acrochaetiales), Spermothamnion repens and Tiffaniella snyderae (Ceramiaceae, Ceramiales). Measurements of cell length indicate that cell elongation is occurring, but neither visual inspection nor microspectrofluorometry of cells stained with calcofluor show band deposition. The Rhodophyta thus possess all three mechanisms of cell wall deposition known to operate in plants: apical cell wall deposition in all apical cells examined to date, and either band deposition or diffuse deposition in intercalary cells. These results suggest that patterns of wall deposition may be a useful systematic character in Ceramiaceae, with the tribe Spermothamnieae possessing diffuse growth, and other tribes investigated to date exhibiting band growth.