Spore germination in Dictyostelium discoideum

Mutant spores of Dictyostelium discoideum, strain SG-10, differ from wild type spores in their ability to spontaneously germinate, to be activated with 5% dimethyl Sulfoxide (DMSO), and to be deactivated with 0.2 M sucrose. Both heat-activated wild type and mutant spores began to swell after a lag of 60–75 min at ambient temperature. Suspension of heat activated spores in 5% DMSO resulted in blockage of spore swelling and a concomitant severe inhibition of respiration; removal of 5% DMSO allowed resumption of respiration and the spores began to swell after a lag of only 15 min. It was concluded that 5% DMSO allowed the early reactions (M) to proceed but blocked the later reactions (R) of post-activation lag.Treatment of one day old spores with 20% DMSO solution for 30–120 min quantitatively activated the population. The post-activation lag time was directly dependent on the time of 20% DMSO treatment. Spores activated with 20% DMSO treatment could be deactivated by incubation at 0°C; the spores most quickly deactivated at 0°C were those within 10 min of swelling. Mitochondrial transport inhibitors such as azide and cyanide caused deactivation in an analogous manner. It is hypothesized that spores proceed to the second portion of the lag phase called (R) before the environment determines if dormancy is reimposed or if germination will proceed. The sensitive strain (SG-10) showed a greater degree of damage than the wild type after supraoptimal treatment with 40% DMSO. The spores became more resistant with age to the damaging action of 40% DMSO. All the observed effects of DMSO treatment were compatible with our multistate model of activation which suggests that the early portion of the lag phase (M) may involve a relative uncoupling of oxidative phosphorylation while the later portion (R) may require tight coupling.     

Lumazine-like fluorescence in a mass of spores of the cellular slime mold,Dictyostelium discoideum

Using a fluorospectrophotometer, we examined the fluorescence of a crude preparation from the spore masses ofDictyostelium discoideum. Fluorescence emission spectra and excitation spectra suggested that the fluorescence of the crude preparation was a lumazine-like fluorescence rather than a pterin-like fluorescence. By using a microspectrophotometer, we observedin situ the fluorescence emission of a lumazine-like substance localized only in the spore mass of the fruiting body.     

Induction of cell fusion by a factor released by the cellular slime mold Polysphondylium pallidum

Heterokaryons and hybrid cells, which are extremely useful for research in cell biology, can be produced artificially by treating cells with either polyethylene glycol or certain inactivated viruses that alter the plasma membrane. We report here a novel cell-fusion inducing factor secreted by CK-8 strain cells of cellular slime mold Polysphondylium pallidum. Treatment of other strains or other species of cellular slime molds, such as NC-4 of Dictyostelium discoideum with the diluted fraction, containing molecules larger than 50 kDa, of the conditioned medium of CK-8 cell culture induces cell fusion at high frequency and produces multinucleated large cells. This cell fusion is inducible between cells of either a single strain or of two different strains of cellular slime molds.Abbreviations BSS Bonner's salt solution - CM conditioned medium - EDTA ethylenediaminetetraacetic acid - F2 fraction containing cell-fusion induction factor - Mr molecular mass     

Inhibitory effects of tunicamycin on cell-cell adhesion and cell reaggregation of the cellular slime mold,Polysphondylium pallidum

To assess the role in cell-cell adhesion of gp64, a putative cell-cell adhesion molecule ofPolysphondylium pallidum, we treated the cells with tunicamycin (TM), a known inhibitor of the synthesis of the N-linked oligosaccharide precursor, and examined TM's effect on cell-cell adhesion. The vegetative growth ofPolysphondylium cells was inhibited with TM in a dose-dependent manner. When cells were treated with TM (2.0 μg/ml) during only the first 4 hr of starvation and further starved for 8 hr without TM, the cells dissociated considerably, although even the growth phase cells ofPolysphondylium normally show EDTA-resistant (Ca²⁺-independent) cell adhesions. In parallel with the above effects, the amounts of intact gp64 decreased considerably in time with the lengths of incubation (0 hr>4 hr >8 hr). When TM-treated cells were washed free of TM, and shaken for a further 12 hr, the cells began to aggregate again, accompanied by an increase of gp64. In conclusion, TM affected cell-cell adhesion ofPolysphondylium cells, but we were not able to distinguish whether the inhibition of cell aggregation was due to defects in glycosylation on glycoproteins and/or due to reduced levels of glycoproteins themselves.     

梨蒴珠藓孢子萌发与原丝体发育特征研究

为了解梨蒴珠藓（Bartramia pomiformis）孢子萌发和原丝体发育特征,在显微镜下观察室内人工培养的梨蒴珠藓单倍配子体发育过程。结果表明,梨蒴珠藓孢子吸水膨胀5 d后,开始破壁萌发,原丝体系统以丝状绿丝体为主,轴丝体在绿丝体上分化产生。培养22 d后,配子体在轴丝体细胞上分化产生。参照Nishida的标准,梨蒴珠藓孢子萌发类型为真藓型（Bryum-type）。这为梨蒴珠藓的人工扩繁提供了发育学基础资料。     

Speed–accuracy trade-offs during foraging decisions in the acellular slime mould Physarum polycephalum

Speed–accuracy trade-offs (SATs) are thought to be a fundamental feature of biological information processing, yet most evidence of SATs comes from animals. Here, we examine SATs in the foraging decisions of an acellular, amoeboid organism: the slime mould Physarum polycephalum. Slime moulds were given a simple discrimination task: selecting the highest-quality food item from a set of three options. We investigated the effect of two stressors, light exposure and hunger, on the speed and accuracy of decision-making. We also examined the effect of task difficulty. When given a difficult discrimination task, stressed individuals tend to make faster decisions than non-stressed individuals. This effect was reversed in plasmodia given easy discrimination tasks, where stressed individuals made slower decisions than non-stressed individuals. We found evidence of SATs, such that individuals who made fast decisions were more likely to make costly errors by selecting the worst possible food option. Our results suggest that SATs occur in a wider range of taxa than previously considered.     

Effects of nutrients and light pretreatment on phytochrome-mediated fern-spore germination

Spores of the ferns, Dryopteris filix-mas, D. paleacea and Polystichum minutum, sown on plain agar in quartz-distilled water, required several hours of red light in order to germinate. When, however, water agar was replaced by agar made up with a mineral nutrition medium, a single pulse of red light (about 1 min) was able fully to induce germination. Under these conditions spores became light-sensitive a few minutes after sowing. Thus, zero germination in dark controls was obtained only when all light was excluded immediately after sowing or when saturating far-red was given thereafter. The effect of the mineral medium was also obtained using low ion concentrations with an osmolality of less than 100 mol l^–1. Thus, a specific ion effect appears more probable than an unspecific osmotic effect. Species differences in light sensitivity and in dark-germination levels, as reported in the literature, might partly be the consequence of different culture media and of light acting at a very early stage after sowing, which hitherto was assumed to be still insensitive to light. On water agar as well as on mineral agar, the inducing effect of a single red pulse could be increased by the appropriate pretreatment, i.e. by preirradiation with red light for several hours, followed by a saturating pulse of far-red, the latter abolishing the direct inducing effect of the red preirradiation. The nature of both the ion-phytochrome interaction and the phytochrome-phytochrome interaction has not yet been analysed.Abbreviations FR saturating far-red light - Pfr far-red absorbin form of phytochrome - R broad-band red light, acting continuously during several hours This work was performed at the Department of Plant Physiology, University of Lund, Sweden, during a sabbatical leave     

Cell division and morphogenesis in angiosperm embryogenesis

Angiosperm embryogenesis generates the basic body organization of flowering plants. The underlying processes of pattern formation, which establishes the diversity of position-dependent cell fates, and morphogenesis, which brings about the shape of the embryo, may not only involve intercellular communication and controlled cell expansion but also non-random cell divisions. Genetic analysis ofArabidopsisembryogenesis which displays a large invariant pattern of cell divisions suggests that unequal cell divisions segregate cell fates and are thus involved in pattern formation whereas other oriented cell divisions and differential mitotic rates reflect patterning and rather play a role in morphogenesis.     

Structure of the cell surface of the yeast Candida tropicalis and its relation to hydrocarbon transport

The surface structure of the hypdrocarbon-utilizing yeast Candida tropicalis was investigated by scanning and transmission electron microscopy (SEM and TEM respectively). The sample preparation technique was based on a rapid cryofixation without any addition of cryoprotectants. In subsequently freeze-dried samples the surface structure was analysed by scanning electron microscopy. Thin sections were prepared from freeze substituted samples. Both techniques revealed hair-like structures at the surface of hydrocarbon-grown cells. The hairy surface structure of the cells was less expressed in glucose-grown cells and it was absent completely after proteolytic digestion of the cells. When cells were incubated with hexadecane prior to cyryofixation a contrast-rich region occured in the hair fringe of thin sections as revealed by TEM. Since these structures were characteristic for hexadecane-grown cells and could not be detected in glucose-grown or proteasetreated cells it was concluded that they originate from hexadecane adhering to the cell surface and are functionally related to hexadecane transport. The structure of the surface and its relation to hydrocarbon transport are discussed in view of earlier results on the chemical composition of the surface layer of the cell wall.Abbreviations SEM Scanning electron microscopy - TEM transmission electron microscopy     

Localization of fluorescent substances in the cellular slime moldDictyostelium discoideum cells during growth and development

The localization of fluorescent substance was observed microscopically in livingDictyostelium discoideum cells. The fluorescence was localized in the vacuoles of the vegetative cells. The fluorescent vacuoles were not observed in the dead cells. The fluorescent vacuoles in the cytoplasm were lost in starved cells which are able to form an aggregate and to differentiate. The fluorescent vacuoles were not lost but decreased slightly in the cytoplasm of full grown cells and of cells grown in liquid nutrient medium for an extended period of time (stationary phase cells). On a solid substratum, fluorescent vacuoles were also lost from the cells, where the vegetative cells aggregate and form a slug-shaped mass of cells. The whole slug showed homogeneous fluorescence. In a finally constructed fruiting body, the spore mass showed fluorescence. In a spore mass, the fluorescence was not observed in the spores but in the interspore space of the spore mass. It is suggested that vegetative cells secrete fluorescent substance into the inter-cellular space in the mass of cells during development.     

Calcium requirement of phytochrome-mediated fern-spore germination: No direct phytochrome-calcium interaction in the phytochrome-initiated transduction chain

Phytochrome-mediated germination of fern spores of Dryopteris paleacea Sw. was initiated by a saturating red-light (R) irradiation after 20 h of imbibition. For its realization external Ca²⁺ was required, with a threshold at a submicromolar concentration, and an optimum was reached around 10^-4 M. At concentrations 10^-1 M only a reduced response was obtained, based probably on an unspecific osmotic or ionic effect. The germination response was inhibited by La³⁺, an antagonist of Ca²⁺. From these results it is concluded that Ca²⁺ influx from the medium into the spores may be an important event in phytochrome-mediated germination. In the absence of Ca²⁺ the R-stimulated system remained capable of responding to Ca²⁺, added as late as 40 h after R. Moreover, Ca²⁺ was effective even if added after the active form of phytochrome, Pfr, had been abolished by far-red (FR) 24 h after R. Thus, the primary effect of Pfr, that initiates the transduction chain, does not require calcium. Coupling of Pfr to subsequent dark reactions has been investigated by R-FR irradiations with various dark intervals. The resulting escape kinetics were characterized by a lag phase (6 h) and half-maximal escape from FR reversibility (19 h). These kinetics were not significantly changed by the presence or absence of calcium. Thus, direct interaction of Pfr and calcium is not a step in the transduction chain initiated by the active form of photochrome.Abbreviations EGTA ethyleneglycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid - FR far-red light - Pr red-light-absorbing form of phytochrome - Pfr far red-light-absorbing form of phytochrome - Pipes piperazine-1,4-bis(2-ethanesulfonic acid) - R red light A preliminary report of this work was presented at the XIV Int. Bot. Congr., Berlin (West), Germany, Book of Abstracts, 2-116a-5 (1987)     

Microtubule and actin filament organization during stomatal morphogenesis in the fernAsplenium nidus

Summary The newly-formed guard cell mother cells (GMCs) ofAsplenium nidus are small, lens-shaped and are formed by one or two asymmetrical divisions. Their growth axis is parallel to the plane of their future division, a process during which the internal periclinal wall (IPW) is detached from the partner wall of the underlying cell(s). This oriented GMC expansion occurs transversely to a microfibril bundle, which is deposited externally to a U-like microtubule (Mt) bundle and a co-localized actin filament (Af) bundle. They line the IPW and the major part of the anticlinal walls. The deposition of the microfibril bundle is followed by the slight constriction of the internal part of the GMCs and the broadening of the substomatal cavity. The IPW forms a distinct bulging distal to the neighbouring leaf margin, as well as a less defined proximal one. During the IPW bulging, the Mts and Afs under the external periclinal wall (EPW) attain a radial organization. This is followed by thinning of the central EPW region, which becomes impregnated with a callose-like glucan. The rest of the EPW becomes unequally thickened. The disintegration of the U-like Mt bundle is succeeded by the organization of radial Mt and Af arrays under the IPW. The radial Mt systems, controlling the alignment of the newly-deposited microfibrils, allow the GMC to assume a round paradermal profile. The GMCs form a preprophase Mt band (PPB) perpendicular to the interphase U-like Mt bundle. The anticlinal PPB portions appear first and those lining the periclinal walls later. The cytoplasm adjacent to the latter walls retain the radial Mt systems during early preprophase, simultaneously with the anticlinal PPB portions. The observations suggest that the GMCs of the fernA. nidus obtain a unique form, as a result of a particular polarity established in the cortical cytoplasm of the periclinal walls, in which Mts and Afs appear involved. This polarity persists in cell division and is inherited to guard cells (GCs). It provides primary morphogenetic information not only to GMCs but also to GCs.Abbreviations Af actin filament - EPW external periclinal wall - GC guard cell - GMC guard cell mother cell - IPW internal periclinal wall - Mt microtubule - MTOC microtubule organizing centre - PPB preprophase microtubule band     

Nonsymbiotic hemoglobins in rice are synthesized during germination and in differentiating cell types

Summary Nonsymbiotic hemoglobins (ns-Hbs) previously have been found in monocots and dicots; however, very little is known about the tissue and cell type localization as well as the physiological function(s) of these oxygen-binding proteins. We report the immunodetection and immunolocalization of ns-Hbs in rice (Oryza sativa L.) by Western blotting and in situ confocal laser scanning techniques. Ns-Hbs were detected in soluble extracts of different tissues from the developing rice seedling by immunoblotting. Levels of ns-Hbs increased in the germinating seed for the first six days following imbibition and remained relatively constant thereafter. In contrast, ns-Hb levels decreased during leaf maturation. Roots and mesocotyls contained detectable, but low levels of ns-Hbs. Split-seed experiments revealed that ns-Hbs are synthesized de novo during seed germination and are expressed in the absence of any signal originating from the embryo. Immunolocalization of ns-Hbs by confocal microscopy indicated the presence of ns-Hbs primarily in differentiated and differentiating cell types of the developing seedling, such as the aleurone, scutellum, root cap cells, sclerenchyma, and tracheary elements. To our knowledge, this is the first report of the specific cellular localization of these proteins during seedling development.Abbreviations Hbs hemoglobins - Ns nonsymbiotic     

碎米藓属两种藓类植物孢子萌发与原丝体发育特征研究

为获取其孢子萌发类型与该属植物系统发育、生态选择以及生殖策略选择的相关性,该研究通过室内人工培养的方式,在微米量级下观察并描述了碎米藓属(Fabronia)碎米藓(F.pusilla)和东亚碎米藓(F.matsumurae)两种藓类植物孢子萌发、原丝体发育和配子体发生的过程.结果表明:(1)两种藓类植物孢子均为壁外萌发...     

Physiology and fine structure of sporangiospore germination in Piptocephalis unispora prior to infection

Germination of the sporangiospore of Piptocephalis unispora Benjamin, observed by means of light and electron microscopy, involved the formation of a new inner wall which became continous with the inner layer of the wall of the germ tube. The outer wall layer of the germ tube was continous with the original inner wall layer of the dormant spore. Preliminary details of appressorium structure were noted. Nutritional experiments indicated that sporangiospores required external sources of utilisable nitrogen and carbon compounds for maximal swelling and germ tube production. Limited development occurred when either nutrient was supplied singly. Comparison of germination of the asexual spore with that in other Mucorales, especially the Kickxellaceae, has been made, and the merosporangial status in P. unispora discussed.Non-Standard Abbreviations CH casein hydrolysate - Q spore quotient     

Light and nitrate interaction in phytochrome-controlled germination ofPaulownia tomentosa seeds

Pulsed light and nitrate exhibit an interactive effect on the germination ofPaulownia tomentosa Steud. seeds that require long periods of light irradiation. Two pulses of red light (R), separated by an adequately long dark interval, substitute for continuous prolonged irradiation. A far-red (FR) pulse given at the beginning of the dark interval inhibits germination, while it has no effect if given at the end. The requirement for certain ratios of the far-red-absorbing form of phytochrome/total phytochrome (P_fr/P_tot) differs when a FR+R-pulse is given as the first or second of two pulses (FR+R or R) separated by a dark interval. An equal decrease of the P_fr/P_tot ratio leads to a more pronounced decrease in germination when the pulse of the same FR+R ratio is given as the second pulse at the end of the dark interval. The length of dark interval between light pulses needed for maximal germination, differed in (i) seeds with a natural requirement for long periods of light irradiation from that in (ii) seeds with their long light requirement imposed by two weeks of imbibition in darkness or by (iii) imbibition in 40% heavy water. However, a single R pulse was sufficient to induce a high percentage of germination if the seeds were supplied with KNO₃ (10 mM) from the onset of imbibition up to the onset of light. This effect decreased with a delayed time of application, and was prevented if FR preceded the KNO₃ application. We dedicate this paper to Professor Hans Mohr on the occasion of his 60th birthday     

Ultrastructure and histochemical analysis of extracellular matrix surface network in kiwifruit endosperm-derived callus culture

The study used Actinidia deliciosa endosperm-derived callus to investigate aspects of the morphology, histology and chemistry of extracellular matrix (ECM) structures in morphogenically stable tissue from long-term culture. SEM showed ECM as a membranous layer or reticulated fibrillar and granular structure linking the peripheral cells of callus domains. TEM confirmed that ECM is a distinct heterogeneous layer, up to 4 mum thick and consisting of amorphous dark-staining material, osmiophilic granules and reticulated fibres present outside the outer callus cell wall. ECM covered the surface of cells forming morphogenic domains and was reduced during organ growth. This structure may be linked to acquisition of morphogenic competence and thus may serve as a structural marker of it in endosperm-derived callus. ECM was also observed on senescent cells in contact with the morphogenic area. Treatment of living calluses with chloroform and washing with ether-methanol led to partial destruction of the extracellular layer. Digestion with pectinase removed the membranous layer almost completely and exposed thick fibrillar strands and granular remnants. Digestion with protease did not visibly affect the surface layer. Indirect immunofluorescence showed low-methylesterified pectic epitopes labelled by JIM5 monoclonal antibody. Immunolabelling, histochemistry, and solvent and enzyme treatments suggested pectins and lipids as components of the surface layer. These compounds may indicate protective, water retention and/or cell communication functions for this external layer.     

The outer segments of photoreceptive pinealocytes in the pineal organ of the funa,Carassius gibelio langsdorfi

Summary The form and size of the outer segments of photoreceptive pinealocytes in the pineal organ of the funa, Carassius gibelio langsdorfi, were observed with the scanning electron microscope. The height of the outer segments measures between 1 and 3 m and the diameter varies widely from 1.5 to 8 m. Various forms of outer segments, i.e. a slender type, a dome-like type, a cap-like type and a helical type, were demonstrated. The parallel-oriented filamentous processes of the inner segments have the same length as the outer segments and a diameter of approximately 100 nm; they are projections from the apical border of the inner segment and surround the cone-like outer segments. The processes make a right angle with the lamellar disks. The distance between two processes averages 100 nm. The lamellar disks of the outer segments are oriented at right angles to the modified cilium in the basal part, but the angle often changes in the peripheral part, where the lamellar disks are raised and become parallel to the cilium.Supported by a fellowship from the Japan Society for the Promotion of Science and a grant from the Deutsche Forschungsgemeinschaft to M. UeckSupported by a grant from the Ministry of Education of Japan to K.Wake     

Scanning electron microscopy of photoreceptor cells in the light- and dark-adapted retina of Haplochromis burtoni (Cichlidae,Teleostei)

Summary The photoreceptor layer in the retina of Haplochromis burtoni (Cichlidae, Teleostei) was studied by scanning electron microscopy. Three types of receptors were identified: rods, single-cones and double-cones. The three-dimensional arrangement of these photoreceptors is described in the light- and dark-adapted retina. The surface of the inner segment of the photoreceptor cells displays fine vertical fissures which give rise to slender processes. These so called calycal processes which are of different lengths in rods and cones, surround the beginning of the smooth-surfaced outer segment. The myoid, the contractile part of the receptor, which is located beneath the ellipsoid, was examined in the single-cones of the dark-adapted retina. It is a slender structure with surface infoldings. The myoid, studied by transmission electron microscopy, contains bundles of parallel myofilaments, which are thought to be contractile.This investigation was supported by grants of the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 51-E/10)