Growth characteristics of the cyanobacterium Nostoc flagelliforme in photoautotrophic, mixotrophic and heterotrophic cultivation

Nostoc flagelliforme is a terrestrial cyanobacterium with high economic value. Dissociated cells separated from a natural colony of N. flagelliforme were cultivated for 7 days under either phototrophic, mixotrophic or heterotrophic culture conditions. The highest biomass, 1.67 g L⁻¹ cell concentration, was obtained under mixotrophic culture, representing 4.98 and 2.28 times the biomass obtained in phototrophic and heterotrophic cultures, respectively. The biomass in mixotrophic culture was not the sum as that in photoautotrophic and heterotrophic cultures. During the first 4 days of culture, the cell concentration in mixotrophic culture was lower than the sum of those in photoautotrophic and heterotrophic cultures. However, from the 5th day, the cell concentration in mixotrophic culture surpassed the sum of those obtained from the other two trophic modes. Although the inhibitor of photosynthetic electron transport DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea] efficiently inhibited autotrophic growth of N. flagelliforme cells, under mixotrophic culture they could grow by using glucose. The addition of glucose changed the response of N.flagelliforme cells to light. The maximal photosynthetic rate, dark respiration rate and light compensation point in mixotrophic culture were higher than those in photoautotrophic cultures. These results suggest that photoautotrophic (photosynthesis) and heterotrophic (oxidative metabolism of glucose) growth interact in mixotrophic growth of N. flagelliforme cells.     

Ferric reduction by iron-limited Chlamydomonas cells interacts with both photosynthesis and respiration

Iron limitation led to a large increase in extracellular ferricyanide (Fe[III]) reductase activity in cells of the green alga Chlamydomonas reinhardtii Dangeard. Mass-spectrometric measurement of gas exchange indicated that ferricyanide reduction in the dark resulted in a stimulation of respiratory CO₂ production without affecting the rate of respiratory O₂ consumption, consistent with the previously postulated activation of the oxidative pentose phosphate pathway in support of Fe(III) reduction by iron-limited Chlamydomonas cells (X. Xue et al., 1998, J. Phycol. 34: 939–944). At saturating irradiance, the rate of ferricyanide reduction was stimulated almost 3-fold, and this stimulation was inhibited by 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea. Ferricyanide reduction during photosynthesis resulted in approximately a 50% inhibition of photosynthetic CO₂ fixation at saturating irradiance, and almost 100% inhibition of CO₂ fixation at sub-saturating irradiance. Photosynthesis by iron-sufficient cells was not affected by ferricyanide addition. Addition of 250 μM ferricyanide to iron-limited cells in which photosynthesis was inhibited (either by the presence of glycolaldehyde, or by maintaining the cells at the CO₂ compensation point) resulted in a stimulation in the rate of gross photosynthetic O₂ evolution. Chlorophyll a fluorescence measurements indicated a large increase in non-photochemical quenching during ferricyanide reduction in the light; the increase in nonphotochemical quenching was abolished by the addition of nigericin. These results suggest that reduction of extracellular ferricyanide (mediated at the plasma membrane) interacts with both photosynthesis and respiration, and that both of these processes contribute NADPH in the light. Received: 15 September 1999 / Accepted: 14 October 1999     

Control of carbon partitioning and photosynthesis by the triose phosphate/phosphate translocator in transgenic tobacco plants (Nicotiana tabacum). II. Assessment of control coefficients of the triose phosphate/phosphate translocator

 Transgenic tobacco (Nicotiana tabacum L.) plants with decreased and increased transport capacities of the chloroplast triose phosphate/phosphate translocator (TPT) were used to study the control the TPT exerts on the flux of starch and sucrose biosynthesis, as well as CO₂ assimilation, respiration and photosynthetic electron transport. For this purpose, tobacco lines with an antisense repression of the endogenous TPT (αTPT) and tobacco lines overexpressing a TPT gene from Flaveria trinervia (FtTPT) were used. In ambient CO₂, there was no or little effect of altered TPT transport activities on either rates of photosynthetic electron transport and/or CO₂ assimilation. However, in elevated CO₂ (1500 μl · l⁻¹) and low O₂ (2%) the TPT exerted strong control on the rate of CO₂ assimilation (control coefficient for the wild type; C^JA _TPT=0.30) in saturating light. Similarly, the incorporation of ¹⁴C into starch in high CO₂ was increased in tobacco plants with decreased TPT activity, but was reduced in plants overexpressing the TPT from F. trinervia. Thus, the TPT exerted negative control on the rate of starch biosynthesis with a C^JStarch _TPT=−0.19 in the wild type estimated from a hyperbolic curve fitted to the data points. This was less than the positive control strength on the rate of sucrose biosynthesis (C^JSuc _TPT=0.35 in the wild type). Theoretically, the positive control exerted on sucrose biosynthesis should be numerically identical to the negative control on starch biosynthesis unless additional metabolic pathways are affected. The rate of dark respiration showed some correlation with the TPT activity in that it increased in FtTPT overexpressors, but decreased in αTPT plants with an apparent control coefficient of C^JRes _TPT=0.24. If the control on sucrose biosynthesis is referred to as “gain of carbon” (positive control) and the control on starch biosynthesis as well as dark respiration as a “loss of carbon” (negative control) for sucrose biosynthesis and subsequent export, the sum of the control coefficients on dark respiration and starch biosynthesis would be numerically similar to the control coefficient on the rate of sucrose biosynthesis. There was also some control on the rate of photosynthetic electron transport, but only at high light and in elevated CO₂ combined with low O₂. The control coefficient for the rate of photosynthetic electron transport was C^JETR _TPT=0.16 in the wild type. Control coefficients were also calculated for plants with elevated and lowered TPT activity. Furthermore, the extent to which starch degradation/glucose utilisation compensates for the lack of triose phosphate export was assessed. The TPT also exerted control on metabolite contents in air. Received: 26 March 1999 / Accepted: 21 August 1999     

Isolation and characterisation of cell wall polysaccharides from cocoa (Theobroma cacao L.) beans

 Cell wall material (CWM) was prepared from sun-dried cocoa (Theobroma cacao L.) bean cotyledons before and after fermentation. The monosaccharide composition of the CWM was identical for unfermented and fermented beans. Polysaccharides of the CWM were solubilised by sequential extraction with 0.05 M trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA), 0.05 M Na₂CO₃, and 1 M, 4 M and 8 M KOH. The non-cellulosic sugar composition for each fraction was similar for unfermented and fermented samples, indicating that fermentation caused no significant modification of the structural features of individual cell wall polysaccharides. Pectic polysaccharides accounted for 60% of the cell wall polysaccharides but only small amounts could be solubilised in solutions of CDTA, Na₂CO₃, and 1 M and 4 M KOH. The bulk of the pectic polysaccharides were solubilised in 8 M KOH and were characterised by a rhamnogalacturonan backbone heavily substituted with side-chains of 5-linked arabinose and 4-linked galactose. Linkage analysis indicated the presence of additional acidic polysaccharides, including a xylogalacturonan and a glucuronoxylan. Cellulose, xyloglucan and a galactoglucomannan accounted for 28%, 8% and 3% of the cell wall polysaccharides, respectively. It is concluded that the types and structural features of cell wall polysaccharides in cocoa beans resemble those found in the parenchymatous tissue of many fruits and vegetables rather than those reported for many seed storage polysaccharides. Received: 29 May 1999 / Accepted: 19 October 1999     

Intraprotoplasmic and wall-localised formation of arabinoxylan-bound diferulates and larger ferulate coupling-products in maize cell-suspension cultures

Maize (Zea mays L.) cell cultures incorporated radioactivity from [¹⁴C]cinnamate into hydroxycinnamoyl-CoA derivatives and then into polysaccharide-bound feruloyl residues. Within 5–20 min, the CoA pool had lost its ¹⁴C by turnover and little or no further incorporation into polysaccharides then occurred. The system was thus effectively a pulse–chase experiment. Kinetics of radiolabelling of diferulates (also known as dehydrodiferulates) varied with culture age. In young (1–3 d) cultures, polysaccharide-bound [¹⁴C]feruloyl- and [¹⁴C]diferuloyl residues were both detectable within 1 min of [¹⁴C]cinnamate feeding. Thus, feruloyl residues were dimerised <1 min after their attachment to polysaccharides. For at least the first 2.3 h after [¹⁴C]cinnamate feeding, polysaccharide-bound [¹⁴C]diferuloyl residues remained almost constant at ≈7% of the total polysaccharide-bound [¹⁴C]ferulate derivatives. Since feruloyl residues are attached to polysaccharides <1 min after the biosynthesis of the latter, and >10 min before secretion, the data show that extensive feruloyl coupling occurred intra-protoplasmically. Exogenous H₂O₂ (1 mM) caused little additional feruloyl coupling; therefore, wall-localised coupling may have been peroxidase-limited. In older (e.g. 4 d) cultures, less intraprotoplasmic coupling occurred: during the first 2.5 h, polysaccharide-bound [¹⁴C]diferuloyl residues were a steady 1.4% of the total polysaccharide-bound [¹⁴C]ferulate derivatives. In contrast to the situation in younger cultures, exogenous H₂O₂ induced a rapid 4- to 6-fold increase in all coupling products, indicating that coupling in the walls was H₂O₂-limited. In both 2- and 4-d-old cultures, polysaccharide-bound ¹⁴C-trimers and larger coupling products exceeded [¹⁴C]diferulates 3- to 4-fold, but followed similar kinetics. Thus, although all known dimers of ferulate can now be individually quantified, it appears to be trimers and larger products that make the major contribution to cross-linking of wall polysaccharides in cultured maize cells. We argue that feruloyl arabinoxylans that are cross-linked before and after secretion are likely to loosen and tighten the cell wall, respectively. The consequences for the control of cell expansion and for the response of cell walls to an oxidative burst are discussed. Received: 19 January 2000 / Accepted: 13 April 2000     

Effects of salinity on photosynthetic characteristics in photomixotrophic cell-suspension cultures from Alternanthera philoxeroides

We studied the effect of NaCl salinity on the development of cellular photosynthesis using a green, photomixotrophic, cell-suspension culture of Alternanthera philoxeroides (Mart.) Griseb. For these cells, increasing the concentration of sucrose in the media produces a rapid drop in net photosynthetic rate, which recovers as sucrose is depleted from the media. This predictable recovery provides a simple system to examine cellular photosynthetic development. Cells, unadapted to high salinity, were transferred to nutrient media with 30 mM sucrose (Control) or nutrient media with 30 mM sucrose and 100 mM NaCl (Salt). A dramatic increase in the dark respiration rate of Control and Salt cells during the first 6 d of the experiment produced net oxygen consumption in the light. The high dark respiration rates during this period were accompanied by a decline in total Chl and the amounts of two photosynthetic proteins, the light harvesting Chl a/b binding protein of photosystem II (LHCP) and the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco SSU). The dark respiration rate of Salt cells was greater than that of Control cells on days 4–8. After day 4, dark respiration rates decreased and net photosynthesis increased to stable values in both treatments at day 11 after media sucrose concentration reached a minimum. As dark respiration rates decreased and net photosynthetic rates increased, total Chl and the amounts of LHCP and rubisco SSU increased in both Control and Salt cells. The slower development of photosynthetic capacity in salt cells was correlated with a fresh weight that was 20% lower than that of control cells at the end of the experiment.     

Inoculation and nitrate alter phytohormone levels in soybean roots: differences between a supernodulating mutant and the wild type

 The levels of different cytokinins, indole-3-acetic acid (IAA) and abscisic acid (ABA) in roots of Glycine max [L.] Merr. cv. Bragg and its supernodulating mutant nts382 were compared for the first time. Forty-eight hours after inoculation with Bradyrhizobium, quantitative and qualitative differences were found in the root's endogenous hormone status between cultivar Bragg and the mutant nts382. The six quantified cytokinins, ranking similarly in each genotype, were present at higher concentrations (30–196% on average for isopentenyl adenosine and dihydrozeatin riboside, respectively) in mutant roots. By contrast, the ABA content was 2-fold higher in Bragg, while the basal levels of IAA [0.53 μmol (g DW)⁻¹, on average] were similar in both genotypes. In 1 mM NO₃ ⁻-fed Bragg roots 48 h post-inoculation, IAA, ABA and the cytokinins isopentenyl adenine, and isopentenyl adenosine quantitatively increased with respect to uninoculated controls. However, only the two cytokinins increased in the mutant. High NO₃ ⁻ (8 mM) markedly reduced root auxin concentration, and neither genotypic differences nor the inoculation-induced increase in auxin concentration in Bragg was observed under these conditions. Cytokinins and ABA, on the other hand, were little affected by 8 mM NO₃ ⁻. Root IAA/cytokinin and ABA/cytokinin ratios were always higher in Bragg relative to the mutant, and responded to inoculation (mainly in Bragg) and nitrate (both genotypes). The overall results are consistent with the auxin-burst-control hypothesis for the explanation of autoregulation and supernodulation in soybean. However, they are still inconclusive with respect to the inhibitory effect of NO₃ ⁻. Received: 16 April 1999 / Accepted: 13 December 1999     

O-Acetylation of plant cell wall polysaccharides: identification and partial characterization of a rhamnogalacturonan O-acetyl-transferase from potato suspension-cultured cells

 A microsomal preparation from suspension-cultured potato stem cells (Solanum tuberosum L. cv. AZY) was incubated with [¹⁴C]acetyl-CoA resulting in a precipitable radiolabeled product. Analysis of the product revealed that it consisted mostly of acetylated proteins and cell wall polysaccharides, including xyloglucan, homogalacturonan and rhamnogalacturonan I. Thus, acetyl-CoA is a donor-substrate for the O-acetylation of wall polysaccharides. A rhamnogalacturonan acetylesterase was used to develop an assay to measure and characterize rhamnogalacturonan O-acetyl transferase activity in the microsomal preparation. Using this assay, it was shown that the transferase activity was highest during the linear growth phase of the cells, had a pH-optimum at pH 7.0, a temperature optimum at 30 °C, an apparent K _m of 35 μM and an apparent V _max of 0.9 pkat per mg protein. Further analysis of the radiolabeled acetylated product revealed that it had a molecular mass >500 kDa. Received: 3 July 1999; Accepted: 27 September 1999     

High photosynthetic photon flux and high CO2 concentration under increased number of air exchanges promote growth and photosynthesis of four kinds of orchid plantlets in vitro

Summary In vitro plantlets of Phalaenopsis ‘Happy Valentine’, Neofinetia falcate Hu, Cymbidium kanran Makino, and Cymbidium goeringii Reichb. f. were grown under photoautotrophic [high photosynthetic photon flux (PPF), high CO₂ concentration, and increased number of air exchanges] and heterotrophic (low PPF, low CO₂ concentration, no air exchanges) culture conditions. After 40 d of culture, a significant difference in plantlet growth was observed between the two cultures. Total fresh and dry mass were on average 1.5 times greater in photoautotrophic culture than in heterotrophic culture. Higher net photosynthetic rates were also observed for Phalaenopsis in photoautotrophic culture. In photoautotrophic culture, little difference was observed in air temperature between the inside and outside of the culture vessel, whereas in heterotrophic culture, air temperature inside the culture vessel was 1–2°C higher than that outside the culture vessel. Relative humidity inside the culture vessel was remarkably different between the two cultures: 83–85% in photoautotrophic culture and 97–99% in heterotrophic culture. These results indicated that growth and net photosynthetic rate of in vitro orchid plantlets were susceptible to the culture environments such as PPF, CO₂ concentration, relative humidity (RH), and the number of air exchanges, which would allow a more efficient micropropagation system for these orchid plants.     

The time-profile of the PBMC HSP70 response to in vitro heat shock appears temperature-dependent

Summary. Heat shock proteins (HSPs) are synthesised by cells subsequent to a stress exposure and are known to confer protection to the cell in response to a second challenge. HSP induction and decay are correlated to thermotolerance and may therefore be used as a biomarker of thermal history. The current study tested the temperature-dependent nature of the heat shock response and characterised its time profile of induction. Whole blood from 6 healthy males (Age: 26 ± (SD) 2 yrs; Body mass 74.2 ± 3.8 kgs; VO_2max: 49.1 ± 4.0 ml·kg⁻¹·min⁻¹) were isolated and exposed to in vitro heat shock (HS) at 37, 38, 39, 40, and 41 °C for a period of 90 min. After HS the temperature was returned to 37 °C and intracellular HSP70 was quantified from the leukocytes at 0, 2, 4, and 6 h after heat treatment. The concentration of HSP70 was not different between temperatures (P > 0.05), but the time-profile of HSP70 synthesis appeared temperature-dependent. At control (37 °C) and lower temperatures (38–39 °C) the mean HSP70 concentration increased up to 4 h post HS (P < 0.05) and then returned towards baseline values by 6 h post HS. With in vitro hyperthermic conditions (40–41 °C), the time-profile was characterised by a sharp rise in HSP70 levels immediately after treatment (P < 0.05 for 40 °C at 0 h), followed by a progressive decline over time. The results suggest a temperature-dependent time-profile of HSP70 synthesis. In addition, the temperature at which HSP70 is inducted might be lower than 37 °C.     

The Rhodococcus fascians-plant interaction: morphological traits and biotechnological applications

Rhodococcus fascians is a Gram-positive bacterium that infects dicotyledonous and monocotyledonous plants, leading to an alteration in the normal growth process of the host. The disease results from the modulation of the plant hormone balances, and cytokinins are thought to play an important role in the induction of symptoms. Generally, on the aerial parts of the plants, existing meristems were found to be most sensitive to the action of R. fascians, but, depending on the infection procedure, differentiated tissues as well gave rise to shoots. Similarly, in roots not only actively dividing cells, but also cells with a high competence to divide were strongly affected by R. fascians. The observed symptoms, together with the determined hormone levels in infected plant tissue, suggest that auxins and molecules of bacterial origin are also involved in leafy gall formation. The complexity of symptom development is furthermore illustrated by the necessary and continuous presence of the bacteria for symptom persistence. Indeed, elimination of the bacteria from a leafy gall results in the further development of the multiple embryonic buds of which it consists. This interesting characteristic offers novel biotechnological applications: a leafy gall can be used for germplasm storage and for plant propagation. The presented procedure proves to be routinely applicable to a very wide range of plants, encompassing several recalcitrant species. Received: 14 January 1999 / Accepted: 19 June 1999     

Isoforms of chalcone synthase in Daucus carota L. and their differential expression in organs from the European wild carrot and in ultraviolet-A-irradiated cell cultures

 Two isoforms of chalcone synthase (CHS) were isolated from cDNA libraries derived from UV-A-irradiated anthocyanin-accumulating (DCb) and non-accumulating (DCs) cell cultures of carrot (Daucus carota L.). The clones designated as DcCHS1, which were present only in the DCb library, had a deduced primary sequence of 389 amino acids and an expected molecular mass of 42.7 kDa, and seem to be alleles of those cloned by Ozeki et al. (1993). The second isoform (DcCHS2) was present in both libraries. It had the highest degree of similarity (97.7%) to parsley CHS over all 397 amino acids. The expected molecular mass of the corresponding protein was 43.6 kDa. Results obtained from Southern blot analysis indicated the existence of at least two CHS genes in carrot. A transient enhancement of the DcCHS1 mRNA level after continuous irradiation with UV-A light could only be observed in anthocyanin-accumulating cultures, whereas an increase in DcCHS2 mRNA was seen in both cell lines. The maximum accumulation of CHS mRNA occurred 48 h after the onset of UV-A irradiation. In the European wild carrot the accumulation of DcCHS1 mRNA was restricted to the red central flowers, whereas the DcCHS2 mRNA was detectable in all red and white petals, as well as leaves, but was absent in stems and roots. The expression of DcCHS1 was restricted to anthocyanin-accumulating cells or organs. The heterologous expression of both cDNAs in Escherichia coli resulted in immunostainable bands of different sizes on the Western blot and high levels of catalytic CHS activity. Received: 2 September 1999 / Accepted: 30 November 1999     

Somatic embryogenesis induced by the simple application of abscisic acid to carrot (Daucus carota L.) seedlings in culture

Seedlings of carrot (Daucus carota L. cv. Red Cored Chantenay) formed somatic embryos when cultured on medium containing abscisic acid (ABA) as the sole source of growth regulator. The number of embryos per number of seedlings changed depending on the concentration of ABA added to the medium, with a maximum embryo number at 1 × 10⁻⁴M ABA. Seedling age was critical for response to exogenous ABA; no seedling with a hypocotyl longer than 3.0 cm was able to form an embryo. Removal of shoot apices from seedlings completely inhibited the embryogenesis induced by application of exogenous ABA, suggesting that the action of ABA requires some substance(s) that is translocated basipetally from shoot apices through hypocotyls. Histologically, somatic embryos shared common epidermal cells and differentiated not through the formation of embryogenic cell clumps, but directly from epidermal cells. These morphological traits are distinct from those of embryogenesis via formation of embryogenic cell clumps, which has been found in embryogenic carrot cultures established using 2,4-dichlorophenoxyacetic acid or other auxins. These results suggest that ABA acts as a signal substance in stress-induced carrot seedling somatic embryogenesis. Received: 22 April 2000 / Accepted: 8 June 2000     

An alternative stochastic model of generation of oligodendrocytes in cell culture

According to our previous model, oligodendrocyte – type 2 (O-2A) astrocyte progenitor cells become competent for differentiation in vitro after they complete a certain number of critical mitotic cycles. After attaining the competency to differentiate, progenitor cells divide with fixed probability p in subsequent cycles. The number of critical cycles is random; analysis of data suggests that it varies from zero to two. The present paper presents an alternative model in which there are no critical cycles, and the probability that a progenitor cell will divide again decreases gradually to a plateau value as the number of completed mitotic cycles increases. In particular all progenitor cells have the ability to differentiate from the time of plating. The Kiefer-Wolfowitz procedure is used to fit the new model to experimental data on the clonal growth of purified O-2A progenitor cells obtained from the optic nerves of 7 day old rats. The new model is shown to fit the experimental data well, indicating that it is not possible to determine whether critical cycles exist on the basis of these experimental data. In contrast to the fit of the previous model, which suggested that the addition of thyroid hormone increased the limiting probability of differentiation as the number of mitotic cycles increases, the fit of the new model suggests that the addition of thyroid hormone has almost no effect on the limiting probability of differentiation. Received: 6 March 2000 / Revised version: 18 September 2000 / Published online: 30 April 2001     

The application of atomic force microscopy to topographical studies and force measurements on the secreted adhesive of the green alga Enteromorpha

Atomic force microscopy (AFM) enables the topographical structure of cells and biological materials to be resolved under natural (physiological) conditions, without fixation and dehydration artefacts associated with imaging methods in vacuo. It also provides a means of measuring interaction forces and the mechanical properties of biomaterials. In the present study, AFM has been applied for the first time to the study of the mechanical properties of a natural adhesive produced by a green plant cell. Swimming spores of the green alga Enteromorpha linza (L.) J. Ag. (7–10 μm) secrete an adhesive glycoprotein which provides firm anchorage to the substratum. Imaging of the adhesive in its hydrated state revealed a swollen gel-like pad, approximately 1 μm thick, surrounding the spore body. Force measurements revealed that freshly released adhesive has an adhesion strength of 173 ± 1.7 mN m⁻¹ (mean ± SE; n=90) with a maximum value for a single adhesion force curve of 458 mN m⁻¹. The adhesive had a compressibility (equivalent to Young's modulus) of 0.54 × 10⁶ ± 0.05 × 10⁶ N m⁻² (mean ± SE; n=30). Within minutes of release the adhesive underwent a progressive `curing' process with a 65% reduction in mean adhesive strength within an hour of settlement, which was also reflected in a reduction in the average length of the adhesive polymer strands (polymer extension) and a 10-fold increase in Young's modulus. Measurements on the spore surface itself revealed considerably lower adhesion-strength values but higher polymer-extension values than the adhesive pad, which may reflect the deposition of different polymers on this surface as a new cell wall is formed. The study demonstrates the value of AFM to the imaging of plant cells in the absence of fixation and dehydration artefacts and to the characterisation of the mechanical properties of plant glycoproteins that have potential utility as adhesives. Received: 22 February 2000 / Accepted: 20 April 2000     

A dynamical model for plant cell wall architecture formation

We discuss a dynamical mathematical model to explain cell wall architecture in plant cells. The highly regular textures observed in cell walls reflect the spatial organisation of the cellulose microfibrils (CMFs), the most important structural component of cell walls. Based on a geometrical theory proposed earlier [A. M. C. Emons, Plant, Cell and Environment 17, 3–14 (1994)], the present model describes the space-time evolution of the density of the so-called rosettes, the CMF synthesizing complexes. The motion of these rosettes in the plasma membrane is assumed to be governed by an optimal packing constraint on the CMFs plus adherent matrix material, that couples the direction of motion, and hence the orientation of the CMF being deposited, to the local density of rosettes. The rosettes are created inside the cell in the endoplasmatic reticulum and reach the cell-membrane via vesicles derived from Golgi-bodies. After being inserted into the plasma membrane they are assumed to be operative for a fixed, finite lifetime. The plasma membrane domains within which rosettes are activated are themselves also supposed to be mobile. We propose a feedback mechanism that precludes the density of rosettes to rise beyond a maximum dictated by the geometry of the cell. The above ingredients lead to a quasi-linear first order PDE for the rosette-density. Using the method of characteristics this equation can be cast into a set of first order ODEs, one of which is retarded. We discuss the analytic solutions of the model that give rise to helicoidal, crossed polylamellate, helical, axial and random textures, since all cell walls are composed of (or combinations of) these textures. Received: 10 July 1999 / Revised version: 7 June 2000 / Published online: 16 February 2001     

Intracellular chloroplast photorelocation in the moss Physcomitrella patens is mediated by phytochrome as well as by a blue-light receptor

 The light-induced intracellular relocation of chloroplasts was examined in red-light-grown protonemal cells of the moss Physcomitrella patens. When irradiated with polarized red or blue light, chloroplast distribution in the cell depended upon the direction of the electrical vector (E-vector) in both light qualities. When the E-vector was parallel to the cross-wall (i.e. perpendicular to the protonemal axis), chloroplasts accumulated along the cross-wall; however, no accumulation along the cross-wall was observed when the E-vector was perpendicular to it (i.e. parallel to the protonemal axis). When a part of the cell was irradiated with a microbeam of red or blue light, chloroplasts accumulated at or avoided the illumination point depending on the fluence rate used. Red light of 0.1–18 W m⁻² and blue light of 0.01–85.5 W m⁻² induced an accumulation response (low-fluence-rate response; LFR), while an avoidance response (high-fluence-rate response; HFR) was induced by red light of 60 W m⁻² or higher and by blue light of 285 W m⁻². The red-light-induced LFR and HFR were nullified by a simultaneous background irradiation of far-red light, whereas the blue-light-induced LFR and HFR were not affected at all by this treatment. These results show, for the first time, that dichroic phytochrome, as well as the dichroic blue-light receptor, is involved in the chloroplast relocation movement in these bryophyte cells. Further, the phytochrome-mediated responses but not the blue-light responses were revealed to be lost when red-light-grown cells were cultured under white light for 2 d. Received: 7 September 1999 / Accepted: 15 October 1999     

Symplastic communication between the central cell and the egg apparatus cells in the embryo sac of Torenia fournieri Lind. before and during fertilization

 Various membrane-impermeable, water-soluble fluorescent tracers with different molecular weights were microinjected into the central cell of the embryo sac of Torenia fournieri Lind. before and during fertilization. Before anthesis, there was high symplastic permeability between the central cell and the egg apparatus cells. In this stage, fluorescent tracers up to 10 kDa could pass from the central cell into the egg apparatus cells, whereas those with larger molecular weight remained in the central cell. As the embryo sac matured, symplastic permeability decreased such that 2 d after anthesis only tracers less than 3 kDa could spread from the central cell into the egg cell. There appeared to be no symplastic permeability between the primary endosperm and zygote after fertilization, since tracers as small as 521 Da could not pass into the zygote in about half of the microinjected embryo sacs. This is the first report of a change in cell-to-cell communication among the cells of the female germ unit before and after fertilization. Received: 16 December 1999 / Accepted: 4 February 2000     

The effect of taurine depletion on the contractile properties and fatigue in fast-twitch skeletal muscle of the mouse

Summary. Taurine as well as tauret (retinyliden taurine) levels were measured in locust Locusta migratoria compound eyes. HPLC measurements revealed relatively low taurine levels (1.9 ± 0.16 mM) in dark-adapted eyes. Glutamate, aspartate and glycine levels were 2.0 ± 0.2, 2.7 ± 0.4 and 3.0 ± 0.37 mM, respectively, while GABA was present only in trace amounts. After about 4 h of light adaptation at 1500–2000 lx, amino acid levels in the compound eye were as follows: taurine, 1.8 ± 0.17 mM; glutamate, no change at 2.1 ± 0.2 mM; aspartate sharply increased to 4.7 ± 0.7 mM; glycine slightly decreased to 2.8 ± 0.3 mM; and GABA trace levels. In the compound eye of locust Locusta migratoria, the existence of endogenous tauret in micro-molar range was established. In the dark, levels were several times higher compared with compound eye after light adaptation 1500 lx for 3 h, as estimated by TLC in combination with spectral measurements. Existence of tauret in compound eye is of special interest because in the compound eye, rhodopsin regeneration is based on photoregeneration.     

Inactivation of DNA replication origins by the cell cycle regulator, trigonelline, in root meristems of Lactuca sativa

 The effects of trigonelline (TRG) on the cell cycle in root meristems of Lactuca sativa L. were examined in the knowledge that TRG is a cell cycle regulator that causes cell arrest in G2, and prevents ligation of replicons in S-phase. The hypothesis was tested that continuous exposure to TRG would perturb DNA replication which, in turn, would lengthen the cell cycle and impair root elongation. Using DNA fibre autoradiography, mean replicon size was 31 and 13 μm in the TRG (3 mM) and control treatments, respectively. Trigonelline also resulted in a lengthening of both S-phase and the cell cycle and a decrease in primary root elongation. Hence, replicon inactivation was responsible for the protracted S-phase. Trigonelline treatment also resulted in a 1.6-fold increase in fork rate (13.8 μm h⁻¹) compared with the control (8.4 m h⁻¹). The faster fork rate in the larger replicons is in accord with the highly significant positive relationship already established between fork rate and replicon size for various unrelated higher plants. Received: 11 October 1999 / Accepted: 23 December 1999