Phototropic Curvature in Phycomyces

The distribution of curvature and of bending speed along the cell's growing region are studied during steady state phototropic bending. At the start, elemental bending speed parallels the known axial distribution of growth rate. Hence regional phototropic sensitivity is initially determined by the local growth rate, and unilateral visible light acts proportionally at all levels of the growth zone. In the later course of bending, the bending speed distribution shifts downward instead of progressing upward in step with the cell's elongation. Furthermore, during phototropic inversion reversed bending begins high in the growth zone and progresses downward while normal bending continues below. These spatial and temporal changes in the distribution of differential growth are considered to be due to a fixed rate of supply of material used in growth that is transported from lower regions of the cell and asymmetrically distributed within the growth zone.     

Differentiation capabilities of mouse optic stalk in isolation of its immediate in vivo environment

During normal in vivo development, the optic stalk gives rise only to macroglial cells. When we cultured optic stalks isolated from their immediate in situ environment, we found that optic stalks obtained from embryos at Theiler stages 16 to 19 gave rise to both neurons and glial precursor cells, whereas optic stalks obtained from embryos at stages 20 to 23 gave rise to only glial precursor cells. Between stages 19 and 20 (a period of 12 hr of development) the optic stalk changes from a pseudostratified to a simple epithelium, and concomitant with these changes is the growth of the neural retinal axons along the optic stalk. An attractive hypothesis to explain these observations is that the environmental cues that restrict the differentiation capability of the optic stalk ventricular cell population in vivo emanate from the retinal axons. Whether this is due to a restriction in the differentiation capability of a pleuripotential ventricular cell or to a selective cell death of a subpopulation of ventricular cells already committed to the neuronal lineage of differentiation is not yet resolved.     

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 (ψ_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 × FRMo 17) to manipulation of ABA levels at low ψ_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 ψ_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 ψ_w. In the root, low ψ_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 ψ_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 ψ_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 ψ_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 ψ_w appears to decrease with increasing distance from the apex. In the mesocotyl, in contrast, the accumulation of ABA at low ψ_w appears to become increasingly inhibitory to expansion as cells are displaced away from the meristematic region.     

Tissue dynamics of steady state growth in Hydra littoralis. II. Patterns of tissue movement

In the column of hydra, tissues continually move away from a region located just underthe whorl of tentacles. Above this subtentacular region, tissues proceed into the hypostome and tentacles; below it tissues pass into the buds or continue down the stalk. These movements represent a steady state pattern of tissue renewal in which column growth is balanced by tissue loss at the body extremities. But the existence of a subtentacular zone in which tissue appears stationary does not necessarily indicate that growth is restrictedto this region, as is commonly stated. The body column of hydra can be viewed as an expanding cylinder whose elongation is balanced by tissue loss at the two ends. In such a body there must be one region from whichtissue appears to emanate, regardless of how growth is distributed along the cylinder. Only the rates at which tissues move will be characteristic of the underlying growthpattern. In Hydra littoralis, the measured rates of tissue movement down the gastric column are consistent with the distributions of mitotic figures, which indicate that growth is spread out along the column.     

A retinoblastoma ortholog controls stalk/spore preference in Dictyostelium

We describe rblA, the Dictyostelium ortholog of the retinoblastoma susceptibility gene Rb. In the growth phase, rblA expression is correlated with several factors that lead to 'preference' for the spore pathway. During multicellular development, expression increases 200-fold in differentiating spores. rblA-null strains differentiate stalk cells and spores normally, but in chimeras with wild type, the mutant shows a strong preference for the stalk pathway. rblA-null cells are hypersensitive to the stalk morphogen DIF, suggesting that rblA normally suppresses the DIF response in cells destined for the spore pathway. rblA overexpression during growth leads to G1 arrest, but as growing Dictyostelium are overwhelmingly in G2 phase, rblA does not seem to be important in the normal cell cycle. rblA-null cells show reduced cell size and a premature growth-development transition; the latter appears anomalous but may reflect selection pressures acting on social ameba.     

A new type of stalk articulation in the sea lily genus Vityazicrinus (Echinodermata,Crinoidea) and its ontogeny

A new stalk articulation named pseudo-synarthry is here described from the mesistele of Vityazicrinus petrachenkoi, a rare deep-sea crinoid from the Central Pacific Ocean. Pseudo-synarthries have an articulation facet displaying a general structure closely resembling the morphology of the true synarthry, i.e., with a strong bilateral symmetry and deep ligament depressions. Pseudo-synarthries differ from synarthries in lacking a hinge-like fulcral ridge and developing two additional depressions bordered by prominent crescent ridges at opposite sides of the bilateral symmetry axis. Pseudo-synarthries develop in the mesistele below a proxistele articulated by symplexies of 6–8 crenular units. Distally, subsidiary radial ridges appear on the outer edge of ligamentary depressions and tend to multiply, transforming pseudo-synarthries into multiradiate syzygies, as previously observed in the genus Guillecrinus. A chaotic polymeric pattern locally appears in the proxistele and mesistele, which tends to develop into a holomeric pattern during growth, devoid of any visible trace of ossicle fusion. Both early columnal ontogeny in comatulid larvae and the transition from a polymeric to a holomeric pattern in the guillecrinid stalk lead to the rejection of the hypothesis that the monomeric columnal results from the fusion of pre-existing ossicles. Among Guillecrinidae, pseudo-synarthries constitute derived characters that are unique to the Vityazicrinus mesistele. The development of radial subsidiary ridges in the distal stalk corresponds to a synapomorphy shared by Vityazicrinus and Guillecrinus, the two only genera currently attributed to this family. Pseudo-synarthries in Vityazicrinus appear as advanced stalk articulations adapted to the deep-sea environment, which are unknown from the fossil record.     

Effects of red light on the growth of intact wheat and barley coleoptiles

The final lengths of intact dark-grown coleoptiles vary with species and cultivar. The growth distribution pattern in the apical 25-mm growing zone and the absolute amount of growth in each zone depend on the age and species of the coleoptile. A comparative study of several cultivars of wheat, Triticum vulgare, and barley, Hordeum vulgare, indicates that the growth distribution pattern in 30- to 38-mm coleoptiles varies with the species and cultivar. In barley, there are two patterns of growth distribution among the several cultivars, whereas in wheat, all cultivars exhibit a common zonal growth pattern. The total growth of coleoptiles, initially 30 to 38 mm in length, during a 24-hour dark incubation period is the same in dark-grown coleoptiles as in those irradiated with 3 minutes of red (660 nm) light prior to the incubation period. The growth distribution pattern in the growing zone of this 30- to 38-mm coleoptile is, however, altered by red light. Growth of the apical 5-mm zone is stimulated by red light and the zonal growth 5 to 10 mm below the apex is only slightly affected, whereas growth in the zones 10 to 15 to 20, and 20 to 25 mm below the apex is inhibited. This growth distribution pattern in irradiated coleoptiles changes as the coleoptile increases in length. The response of a zone following exposure to red light is dependent upon the age of the seedlings irradiated. The over-all effect of red light on growth of the intact coleoptile varies with the length of the coleoptile. In young seedling 20 to 29 mm in length, the cells of the coleoptile can compensate for the effects of red light, with the over-all growth of the dark-grown and irradiated coleoptile about the same. As the seedling grows older, the cells of the coleoptile can no longer make up for the effects of red light, and the over-all effect changes from compensation to pronounced inhibition.     

The analysis of spiral growth in phycomyces using a novel optical method

A conical mirror was designed and used to measure simultaneously the elongational and rotational displacement of a number of markers on the growing zone of the sporangiophore of Phycomyces. The results obtained by this new optical method demonstrate that the rotational rate is roughly proportional to the elongational rate, except in the lower region of the growing zone where a significant amount of rotation occurs without measurable elongation. From the data presented in this report, we have constructed a model that appears to explain the mechanism responsible for the left-handed spiral growth of the developing sporangiophore.     

A genetic melanotic neoplasm of Drosophila melanogaster

The construction of mature fruiting bodies occurs during the culmination stage of development of Dictyostelium discoideum. These contain at least two different cell types, spores and stalks, which originate from an initially homogenous population of vegetative amoebas. As an attempt to identify proteins whose synthesis is regulated in each cell type during differentiation, we have analyzed the two-dimensional profiles of proteins synthesized by spore and stalk cells during the culmination stage. We have identified 5 major polypeptides which are specifically synthesized by spore cells during culmination and 9 which are only made by stalk cells. Furthermore, synthesis of about 20 polypeptides appears to be enriched either in the spore or in the stalk cells. We also show that synthesis of actin, a major protein synthesized during Dictyostelium development, is specifically inhibited in the spore cells during culmination. Synthesis of most of the cell type-specific proteins initiates at 19–20 hr, during culmination. Moreover, the proteins whose synthesis is induced after formation of tight aggregates, the time when the major change in gene expression occurs, are not specifically incorporated into spores or stalk cells, and appear to be synthesized by both cell types. We conclude that a new class of genes is expressed during the culmination stage in Dictyostelium, giving rise to specific patterns of protein synthesis in spore and stalk cells.     

Differentiation of Various Cell Types during Fruiting Body Formation of Dictyostelium Discoideum*

The processes of differentiation of the presumptive cells (prespore and prestalk cens) into mature spores, stalk and basal-disc cells in Dictyotelium discoideum was investigated. The number of stalk and disc cells in pre-labeled culminating cell masses was estimated by determining the radioactivity of the undissociable fraction separated by filtration from the dissociable fraction containing presumptive cells and spores. Changes in the proportion of amoeboid cells stainable with fluorescein-conjugated antispore serum and encapsulated spores were also followed in the dissociable fraction. Formation of stalk and disc cells began at 17 hr of development and was completed at 26 hr, while formation of morphologically identifiable spores began at 18 hr and was completed at 20 hr, long before completion of stalk formation. At the onset of culmination, unstained cells abruptly increased with an accompanying decrease of stained cells, when unstained rear-guard cells appeared in the hind region. Although some of the rear-guard cells soon differentiated into basal-disc cells, the rest remained amoeboid in the upper part of the spore mass (sorus) after complete formation of a fruiting body. Despite the presence of the amoeboid cells in mature sori, the proportion of the sorus to the stalk and disc of a fruiting body was approximately equal to that of stained (prespore) to unstained (prestalk) cells in a migrating slug.     

A POSSIBLE MECHANISM FOR THE MORPHOGENESIS OF LAMELLAR SYSTEMS IN PLANT CELLS

A mechanism for the formation of lamellar systems in the plant cell has been proposed as a result of electron microscope observations of young and mature cells of Nitella cristata and the plastids of Zea mays in normal plants, developing plants, and certain mutant types. The results are compatible with the concept that lamellar structures arise by the fusion or coalescence of small vesicular elements, giving rise initially to closed double membrane Structures (cisternae). In the chloroplasts of Zea, the cisternae subsequently undergo structural transformations to give rise to a compound layer structure already described for the individual chloroplast lamellae. During normal development, the minute vesicles in the young chloroplast are aggregated into one or more dense granular bodies (prolamellar bodies) which often appear crystalline. Lamellae grow out from these bodies. In fully etiolated leaves lamellae are absent and the prolamellar bodies become quite large, presumably because of inhibition of the fusion step which appears to require chlorophyll. Lamellae develop rapidly on exposure of the plant to light, and subsequent development closely parallels that seen under normal conditions. The plastids of white and very pale green mutants of Zea similarly lack lamellae and contain only vesicular elements. A specialized peripheral zone immediately below the double limiting membrane in Zea chloroplasts appears to be responsible for the production of vesicles. These may be immediately converted to lamellae under normal conditions, but accumulate to form a prolamellar body if lamellar formation is prevented, as in the case of etiolation and chlorophyll-deficient mutation, or when the rate of lamellar formation is slower than that of the production of precursor material (as appears to be the case in the early stages of normal development).     

THE DEVELOPMENT OF CELLULAR STALKS IN BACTERIA

Extensive stalk elongation in Caulobacter and Asticcacaulis can be obtained in a defined medium by limiting the concentration of phosphate. Caulobacter cells which were initiating stalk formation were labeled with tritiated glucose. After removal of exogenous tritiated material, the cells were subjected to phosphate limitation while stalk elongation occurred. The location of tritiated material in the elongated stalks as detected by radioautographic techniques allowed identification of the site of stalk development. The labeling pattern obtained was consistent with the hypothesis that the materials of the stalk are synthesized at the juncture of the stalk with the cell. Complementary labeling experiments with Caulobacter and Asticcacaulis confirmed this result. In spheroplasts of C. crescentus prepared by treatment with lysozyme, the stalks lost their normal rigid outline after several minutes of exposure to the enzyme, indicating that the rigid layer of the cell wall attacked by lysozyme is present in the stalk. In spheroplasts of growing cells induced with penicillin, the stalks did not appear to be affected, indicating that the stalk wall is a relatively inert, nongrowing structure. The morphogenetic implications of these findings are discussed.     

Neoaplectana carpocapsae: Movements of nematode populations on a thermal gradient

To gain information on factors which could affect the nematode Neoaplectana carpocapsae's, dispersion and infection of insect larvae in the field, nematode populations were tested on a thermal gradient (0.5 C/cm). Infective juveniles grown at 15, 20, and 25 C migrated on the gradient toward their respective growth temperatures when tested immediately after harvesting from their medium. This migration by juveniles, grown at 20 or 25 C, was altered within 12 hr by shifting incubation temperature. The nematodes' tendency to migrate toward warmer temperatures, when placed below incubation temperature, decreased during 6–7 days incubation at 20 or 25 C and the nematodes reversed direction: incubation at 2–5 C inhibited this reversal. Nematodes incubated at 20 C, then applied to a gradient zone at 12–13 C, had a greater tendency (P < 0.05) to remain aggregated in that zone within a 3-hr period than those applied at 17–18, 22–23, or 27–28 C. Their tendency to migrate from the 12–13 C zone was significantly (P < 0.05) increased by shifting them to 15 C for 14–138 hr.     

Über Strukturierungen der Wuchszonen vonAcetabularia mediterranea

Summary On the surface of the apical protoplast of growing cells ofAcetabularia mediterranea structured fibrils are stainedwith the basic dye azure-I after digestion of protein with trypsin.The structured fibrils are very probably composed of anionic polysaccharides, may be of the polyuronide type. Normally these polysaccharides are masked by unknown protein.The synthesis of the structured substances in the stalk tip is strongly related to the action of active morphogenetic substances under light conditions.In normal growing cells the density of the structure is polarly distributed. In the stalk tip the texture is close. In more basal stalk-regions it becomes widened and in stalk-regions about 3–4 mm below the stalk tip no structure can be demonstrated.The protoplast structure seems to be related to growth processes concerning surface growth. Growth, however, is not induced by the structure, as shown at enucleate anterior cell parts or darkened cells.

---

---

Mit 13 Textabbildungen

---

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Evidence that the fertilization envelope blocks sperm entry in eggs of Xenopus laevis: interaction of sperm with isolated envelopes.

Single-celled myxamoebae undergo differentiation into either stalk cells or spore cells during a 24-hr period in Dictyostelium discoideum. This study employed ultramicrochemical techniques and enzymatic cycling to assess the presence of cell-specific events in spore and stalk cells. Freeze-dried sections of one organism were assayed in 0.1 μl of reaction mixture. This method was used to determine the extent of localization of trehalose in spore cells and stalk cells during development.Trehalose was low in the early stages of differentiation to about 20 hr when the level started to increase. In developing spore cells, the trehalose level increased sixfold during the last 5 hr of development. Likewise, the entire stalk contained trehalose when the stalk was first formed. At mature sorocarp, trehalose levels were the same in spores and the apex of the stalk. There was a decreasing gradient of trehalose down the stalk. The bottom one-fourth of the stalk was devoid of this disaccharide. Therefore, trehalose was degraded from an area of the stalk where it was localized earlier in development.The results of this investigation negate the assumption that trehalose is never present in the stalk. Although trehalose was found in spore cells, prestalk cells also contained high trehalose levels. The stalk cell-specific trehalose was not retained during differentiation, however, but was apparently degraded in the mature stalk cell.     

Extreme growth plasticity in the early branching sauropodomorph Massospondylus carinatus

There is growing evidence of developmental plasticity in early branching dinosaurs and their outgroups. This is reflected in disparate patterns of morphological and histological change during ontogeny. In fossils, only the osteohistological assessment of annual lines of arrested growth (LAGs) can reveal the pace of skeletal growth. Some later branching non-bird dinosaur species appear to have followed an asymptotic growth pattern, with declining growth rates at increasing ontogenetic ages. By contrast, the early branching sauropodomorph Plateosaurus trossingensis appears to have had plastic growth, suggesting that this was the plesiomorphic condition for dinosaurs. The South African sauropodomorph Massospondylus carinatus is an ideal taxon in which to test this because it is known from a comprehensive ontogenetic series, it has recently been stratigraphically and taxonomically revised, and it lived at a time of ecosystem upheaval following the end-Triassic extinction. Here, we report on the results of a femoral osteohistological study of M. carinatus comprising 20 individuals ranging from embryo to skeletally mature. We find major variability in the spacing of the LAGs and infer disparate body masses for M. carinatus individuals at given ontogenetic ages, contradicting previous studies. These findings are consistent with a high degree of growth plasticity in M. carinatus.     

Structure and growth activities of the mandibular condyle in monkeys (Macaca fascicularis): II. Synergistic behavior of cell dynamics and metabolism

The mandibular condyles of eight growing male monkeys (Macaca fascicularis) were analyzed by using a combination of radioautographic and morphometric techniques. This was done with the aim of examining the dynamics in the structure and growth activities of the articular tissue covering as well as of the subchondral zone of erosion. The animals received 1 mCi/kg body weight 3H-proline 24 hr and 0.5 mCi/kg body weight 3H-thymidine 3 hr prior to death. Their age was estimated on the basis of skeletal maturation as recorded from radiographs of the hand and wrist. Consistently, the proliferative activity in the intermediate layer, the rates of cell turnover and growth of chondroblasts and chondrocytes, the rates of extracellular matrix production in the intermediate and chondral layers, as well as the resorptive and appositional activities in the zone of erosion were characterized by an in-concert behavior. This behavior suggests a general synergistic control of the various cell dynamic and metabolic processes affecting the rate of normal condylar growth.     

Untersuchungen zur individuellen Entwicklungskinetik vonGallionella ferruginea in statischer Mikrokultur

The velocity of individual development of the iron bacteriumGallionella jerruginea starting from the point of stalk elongation was determined quantitatively in microculture. In vivo measurements were done by determining stalk elongation, generation time and velocity of cell rotation on individualGallionella-stalks with apical cells developing up to 3-4 generations. The experiments led to the following results:

1. In the presence of ferrous iron and under microaerophilic growth conditions, the development ofGallionella-stalks in microcultures starts immediately after closing the small culture chambers (slide culture). TheGallionella individuals grow in one-layered microzones nearly parallel to the surface of the liquid.
2. The velocity of stalk elongation, up to the first cell division, is 40 to 60 μm/h; in well growing cultures it increases to 80–90 μm/h. The velocity of development in microculture is 2–4 times greater than in natural environments (Hanert, 1973).
3. The stalk development starting from an individualGallionella-thread with apical cell is highest limited to the 3rd–4th generation. It stops after 22–26 h. The maximal total length of all stalk branches formed during this time is 2200–2900 μm.
4. The limitation of individual stalk development after 3–4 division cycles is not caused by limited nutrition or exocellular products in the batch cultures. It is not a function of the special environment because it was found that the stalk development in a natural flowing system is also limited to 2 generations (unpublished). Therefore the limitation must be effected by a special intracellular limiting factor.
5. The average generation time of individualGallionella development requires 5–7 h. In the first generation the cells divide nearly synchronously, in the second there are differences of 2–5 h even among daughter cells. The period up to the first cell division is 1.5–2 h on an average. Compared with development under natural conditions, cell division in microculture occurs more rapidly.
6. It was shown that the developingGallionella-stalks with apical cells elongate only unipolarly at the free non-sessile end of the stalks which extends into the culture medium. The apical cell rotates round its y-axis. At each rotation of 360°, the stalk elongates in a length of λ, i.e. twice the distance between two twists of a stalk.

     

Polarization of fucoid eggs by steady electrical fields.

Pelvetia eggs were exposed to steady electric fields from 5 hr after fertilization until their rhizoids began to grow out some 6 to 10 hr later. Eleven batches of eggs responded by initiating rhizoids towards the positive electrode; two batches responded by growing towards the negative electrode; and three grew towards the negative one in small fields and towards the positive one in higher fields. Polarization, defined as the average cosine of the outgrowth directions, was proportional to field strength up to polarization values of 50% for the positive responses and 75% for the negative ones. A voltage drop of 6 mV/cell induced 10% polarization in the positively galvanotropic batches, while 3 mV/cell did this in the negative ones. We reason that both responses are mediated by faster calcium entry at the future growth point. It is supposed to be faster there in positively galvanotropic eggs because the membrane potential, hence the driving force, is highest; in negatively galvanotropic eggs because depolarization induces an overbalancing increase in calcium permeability there.     

Growth of the morphological,piloboloid mutants ofPhycomyces blakesleeanus

The sporangiophore of a growth zone-defective mutant, piloboloid (genotypepil), ofPhycomyces gradually ceases longitudinal elongation and radially expands until the growth zone becomes nearly spherical, shortly after the sporangiophore has reached the final developmental stage. The growth of 23pil mutants, obtained by mutagenesis withN-methyl-N′-nitro-N-nitrosoguanidine (NTG), 2-methoxy-6-chloro-9-[3-(ethyl-2-chloroethyl)aminopropylamino]acridine-2HCl (ICR-170), or 4-nitroquinoline-1-oxide (NQO), was studied under different conditions. Allpil mutants obtained were genetically homokaryotic. Expansion in the growth zone and degree of synchrony ofpil sporangiophore length were both greater at low temperature (10°C) and under white light (10 μW/cm²) than at high temperature (20, 25°C) and in the dark. Dwarf sporangiophores of about 1-mm length, which characteristically stop growing immediately after sporangium formation, did not expand radially. The mycelial morphology ofpil mutants was almost normal compared with that of the wild type, though growth was some-what slower in the former than the latter.