ULTRASTRUCTURE OF THE DEVELOPING MEGASPORE MOTHER CELL OF GINKGO BILOBA

The immature megaspore mother cell of Ginkgo biloba is essentially spherical and is surrounded by a thick, complex wall. A large nucleus occupies the central region of the cell, and the organelles appear to be randomly arranged in the cytoplasm. With approaching maturity and the onset of meiosis, the cell elongates in the direction of the ovular axis. An extensive system of ER develops at the micropylar pole of the cell during elongation, and the plastids and mitochondria migrate to the opposite or chalazal pole. The micropylar end of the mature megaspore mother cell is usually devoid of plastids and mitochondria, but these organelles are densely packed in the chalazal end of the cell below the nucleus. The dictyosomes and dense spherosome-like bodies do not show such polarity in their distribution. At meiosis I plastids and mitochondria are, as a rule, restricted to the chalazal dyad cell that is destined to produce the functional megaspore. The wall of the megaspore mother cell consists of a middle lamella which is irregularly thickened, an outer wall layer resembling the walls of the surrounding nutritive cells, and an inner layer resembling the middle lamella in appearance.     

OBSERVATIONS ON THE FINE STRUCTURE OF THE CRYPTOPHYCEAE. I. THE GENUS CRYPTOMONAS1,2

The fine structure of 3 members of the genus Cryptomonas, C. rostrella, C. reticulata, and C. calceiformis, has been examined. These species exhibit the features typical of the class Cryptophyceae. The presence of subpellicular trichocysts causes a regular folding of the periplast, and larger trichocysts are present within the gullet. The plastid contains thylacoids arranged in pairs and a prominent pyrenoid; both structures are enclosed in 4 membranes, the outermost of which is a rough endoplasmic reticulum. The nucleus, Golgi apparatus and the Corps de Maupas occupy characteristic positions within the cell, and are the most characteristic features. All these structures indicate that this algal class occupies a unique phylogenetic position.     

ULTRASTRUCTURE OF THE CONCHOCELIS STAGE OF THE MARINE RED ALGA PORPHYRA LEUCOSTICTA1

The ultrastructure of the Conchocelis or filamentous stage of Porphyra leucosticta was investigated. Each cell contains 1 or 2 parietal, stellate chloroplasts with a single pyrenoid in each chloroplast. The centrally located nucleus is irregularly shaped and contains 1–2 nucleoli. The cytoplasm has typical floridean starch grains and nonmernbrane-bound lipid bodies. The cell wall is divided into an outer and an inner wall. Many lomasomes are associated with the cell membrane. Pit connections are found between cells, and their taxonomic significance is discussed.     

GROWTH INDUCTION IN CULTURES OF HAPLOPAPPUS GRACILIS. II. THE BEHAVIOR OF THE NUCLEUS

Mitra , J., and F. C. Steward . (Cornell U., Ithaca, New York.) Growth induction in cultures of Haplopappus gracilis. II. The behavior of the nucleus. Amer. Jour. Bot. 48(5): 358–368. Illus. 1961.—Cells of Haplopappus, which have been stimulated to grow under the influence of coconut milk and such synergists as naphthalene or 2,4-dichlorophenoxy acetic acid, can be cultivated as free cells, as small cell clusters, or as peripheral cells on a cultured colony or mass. Such cells display forms and cell lineages, the general pattern of which is reminiscent of those that may occur in early embryogeny. To this extent, Haplopappus resembles what has previously been observed in the growth of free cells of carrot. The form of the normal chromosome of Haplopappus (2n = 4) is described with respect to root tip cells. The range of effects which may be observed in the nuclei of the cultured cell is also described. Such variations as the following were encountered: (1) multinucleate giant cells which may divide by internal segmentation; (2) polyploidy, giving rise to highly polyploid nuclei up to, and even in excess of, 64 chromosomes; (3) somatic pairing; (4) haploidy; (5) pseudochiasmata, with the evident implication of somatic “crossing-over”; (6) chromosome breaks, reunions and bridges, such as are commonly associated with effects of radiation and with chemical mutagens. Attention is drawn to the usefulness of this material for the further experimental investigation of the biochemical basis for the cytological events which are here described, and, if the variant cells may be cloned, of the relationship between the aberrant nuclear cytology and the ability of the cells or colonies to differentiate or to undergo morphogenesis.     

ULTRASTRUCTURE OF THE DINOFLAGELLATE PERIDINIUM CINCTUM F. OVOPLANUM. I. VEGETATIVE CELL ULTRASTRUCTURE

Vegetative cells of Peridinium cinctum f. ovoplanum have a dense cytoplasm containing those organelles characteristic of eukaryotic cells. Thecal plates have a fibrillar substructure with numerous 200-nm pores. Chloroplasts are radially arranged and contain a simple internal pyrenoid. An eyespot is associated with the chloroplast. The large, centrally located nucleus contains over 100 chromosomes dispersed in a granular nucleoplasm. Chromosomal bands with a periodicity of 86 nm are present perpendicular to the long axis of the chromosome. Numerous chromosomes are attached to the nuclear envelope. Peridinium cinctum vegetative cell morphology is compared to other dinoflagellates examined.     

OBSERVATIONS ON THE FINE STRUCTURE OF OEDOGONIUM. II. THE SPERMATOZOID OF O. CARDIACUM

Hoffman , L. R., and Irene Manton . (U. Leeds, England.) Observations on the fine structure of Oedogonium. II. The spermatozoid of O. cardiacum. Amer. Jour. Bot. 50(5): 455–463. Illus. 1963.—Salient features of the fine structure of the spermatozoid of Oedogonium cardiacum are described and illustrated as they appear in whole mounts and in sections. There is a close resemblance to the zoospore of the same species (Hoffman and Manton, 1962) though the gamete is smaller and in some respects simpler. The flagella, though similar in length to those on the zoospore, are fewer (ca. 30 instead of ca. 120 per cell). The construction of the flagellar ring is similar though there is less mechanical material associated with the flagellar bases in the gamete. Compound “roots” alternating with the flagellar bases are identical in structure and relative position in both types of motile cells; there is no direct connection with the nucleus. Other details of resemblance and difference between the spermatozoid and the zoospore are discussed.     

THE FLAGELLAR APPARATUS OF THE ZOOSPORE OF UROSPORA PENICILLIFORMIS(CHLOROPHYTA)1

The flagellar apparatus of Urospora penicilliformis (Roth) Aresch. is unique, or at least very unusual among green algae. The flagellar axonemes are rigid, and contain wing-like projections. There are no central microtubules in the most proximal part of the axoneme. The transition region contains a series of electron dense transverse lamellae rather than a single septum, and lacks a stellate pattern. There is no cartwheel pattern in the proximal part of the basal bodies. The latter are associated with four different types of fibrous elements: ascending striated fibers that attach to an electron dense plate in the papillar center, lateral striated fibers that parallel microtubular roots, fibrous elements that link adjacent basal bodies, and finally two massive striated fibers that descend into the cell, passing closely along the nucleus (system II fibers, or rhizoplasts). Each of the four microtubular flagellar roots is sandwiched between two system I striated structures. The roots are probably equal; they contain proximally four, and distally up to eight microtubules. Based on the zoospore flagellar apparatus, it is concluded that the multinucleate U. penicilliformis is related to the Ulvaphyceae. Finally, a possible explanation in functional terms is given for the peculiar external morphology and behavior of the zoospore.     

DIFFERENTIATION OF INTRACAPSULAR CELLS IN THE SPOROPHYTE OF SPHAEROCARPOS DONNELLII

Ultrastructural and histochemical changes during intracapsular cell differentiation in the premeiotic sporophyte of the liverwort Sphaerocarpos donnellii Austin were studied. From an initially undifferentiated meristematic tissue, spore mother cells and nutritive cells become differentiated. The first indications of ultrastructural differentiation into two cell types are the accumulation of lipid within spherosomes and the occurrence of plastid tubules in the presumptive spore mother cells. Once differentiated the two cell types are clearly distinguishable on the basis of cytoplasmic vacuolation, stored food reserve, and cell and nuclear size. The mature spore mother cell contains many spherosomes, small vacuoles, starch-containing plastids, and a large central nucleus. The mature nutritive cell, on the other hand, is extremely vacuolate and contains large, starch-filled plastids, a few spherosomes, and a small nucleus. A previously undescribed type of cell was observed in developing sporophyte capsules. This cell is located peripherally in the capsule and degenerates during differentiation of spore mother cells and nutritive cells.     

PHLOEM OF PRIMITIVE ANGIOSPERMS. I. SIEVE-ELEMENT ONTOGENY IN THE PETIOLE OF LIRIODENDRON TULIPIFERA L. (MAGNOLIACEAE)

As part of a continuing study of sieve elements in primitive angiosperms, a study of this cell type was undertaken in Liriodendron tulipifera. A typical ontogenetic sequence was observed in which synthetic processes such as wall thickening are followed in time by cellular lysis of nucleus, ribosomes, microtubules, vacuoles, and dictyosomes. This lysis is selective in that certain cellular components (e.g., the plasmalemma) remain unaffected. Concomitant with lysis is the formation of sieve-area pores from plasmodesmata. Comparison of pore size on end and lateral walls indicates that the use of the term “sieve tube” rather than “sieve cell” to describe these elements is appropriate.     

STRUCTURE AND FUNCTION OF THE ALGAL PYRENOID. I. ULTRASTRUCTURE AND CYTOCHEMISTRY DURING ZOOSPOROGENESIS OF TETRACYSTIS EXCENTRICA1

The fine structure of the pyrenoid in the mature vegetative cell of Tetracystis excentrica Brown and Bold is described. During zoosporogenesis, the pyrenoid undergoes regression, and the ultrastructure of this process is described in detail. The ground substance undergoes dissolution, and reticulate fibrillar structures appear as well as intruding chloroplast thylakoids. Pyrenoid-associated starch plates diminish, and quantities of starch not associated with the pyrenoid are produced. New pyrenoids appear late in the division cycle after all other major organelles associated with the motile cell have been formed. Zoospore pyrenoids develop in thylakoid-free spaces of the chloroplast which are similar to the DNA-containing regions. The new pyrenoid ground substance, which is loosely fibrillar, arises in close proximity to starch grains which may be formed in the stroma. Then the zoospore pyrenoid produces 2 hemispherical starch plates identical to those in the mature vegetative cell. Zoospore pyrenoids lack the 2 convoluted thylakoids between the starch plates and the ground substance characteristic of those in the mature vegetative cell. Instead, the thylakoids are identical to those of the chloroplast at first, and then develop into a convoluted state in the vegetative cell. Cytochemical tests for DNA, RNA, and protein were made for the cytoplasm, nucleus, nucleolus, and pyrenoid. Conclusive evidence is presented for the presence of RNA in the cytoplasm and nucleolus, DNA in the nucleus, and protein in the pyrenoid. The tests did not conclusively demonstrate the presence or absence of DNA and RNA in the pyrenoid; however, they suggested that small amounts of both DNA and RNA may be present.     

THE FEMALE GAMETOPHYTE OF MACHAERANTHERA PATTERSONII (ASTER PATTERSONII) AND OF M. TANACETIFOLIA

The nucellus of Machaeranthera pattersonii (A. Gray) Greene (Aster pattersonii A. Gray) contains only one megaspore mother cell, and the female gametophyte develops from the chalazal megaspore of a row of four, thus conforming to the Polygonum type of development. These observations are contrary to the older work of Palm. Three nuclear divisions produce the typical eight nuclei with the egg apparatus, primary endosperm cell with two polar nuclei, and two antipodal cells, the micropylar one containing two nuclei. Usually no more antipodal cells are formed, although there is further nuclear division, apparently followed by nuclear fusion. The antipodal cells remain about the same size without forming an antipodal haustorium. Cell division accompanies the first division of the primary endosperm nucleus. The early stages of the embryo resemble those of other Compositae. Machaeranthera tanacetifolia (HBK) Nees also shows the Polygonum type of development of the female gametophyte. It is suggested that Palm may have been working on some species of Erigeron that had been wrongly identified, which would account for the difference in observations.     

EMBRYOLOGY OF CALYPSO BULBOSA. I. OVULE DEVELOPMENT

Calypso bulbosa is a terrestrial orchid that grows in north temperate regions. Like many orchids, the Calypso has ovules that are not fully developed at anthesis. After pollination, the ovule primordia divide several times to produce a nucellar filament which consists of five to six cells. The subterminal cell of the nucellar filament enlarges to become the archesporial cell. Through further enlargement and elongation, the archesporial cell becomes the megasporocyte. An unequal dyad results from the first meiotic division. A triad of one active chalazal megaspore and two inactive micropylar megaspores are the end products of meiotic division. Callose is present in the cell wall of the megaspore destined to degenerate. In the mature embryo sac the number of nuclei is reduced to six when the chalazal nuclei fail to divide after the first mitotic division. The chalazal nuclei join the polar nucleus and the male nucleus near the center of the embryo sac subsequent to fertilization.     

MORPHOLOGY AND SYSTEMATICS OF SCIUROTHAMNION STEGENGAE GEN. ET SP. NOV. (CERAMIACEAE,RHODOPHYTA) FROM THE INDO‐PACIFIC1

A new ceramiaceous alga, Sciurothamnion stegengae De Clerck et Kraft, gen. et sp. nov., is described from the western Indian Ocean and the Philippines. Sciurothamnion appears related to the tribe Callithamnieae on the basis of the position and composition of its procarps and by the majority of post‐fertilization events. It differs, however, from all current members of the tribe by the presence of two periaxial cells bearing determinate laterals per axial cell. Additionally, unlike any present representative of the subfamily Callithamnioideae, no intercalary foot cell is formed after diploidization of the paired auxiliary cells. The genus is characterized by a terminal foot cell (“disposal cell”), which segregates the haploid nuclei of the diploidized auxiliary cell from the diploid zygote nucleus. The nature of three types of foot cells reported in the Ceramiaceae (intercalary foot cells containing only haploid nuclei, intercalary foot cells containing haploid nuclei and a diploid nucleus, and terminal foot cells containing only haploid nuclei) is discussed.     

INFLUENCE OF THE MULTILAYERED STRUCTURE ON THE MORPHOGENESIS OF MARCHANTIA SPERMATIDS

The multilayered structure (MLS) in a spermatid of Marchantia is the morphogenetic blueprint of the headpiece in a mature sperm. As the nucleus begins elongation, a curved, tapered nuclear projection follows the path of microtubules extending from the MLS and becomes inserted into an indented zone at the rear of the asymmetric organelle. The indented zone defines the most forward penetration of the nucleus into the sperm headpiece. Partial disorganization of MLS lower strata nearest the nuclear projection facilitates overlapping of the nucleus with the rearward part of the anterior mitochondrion. At the front of the nascent headpiece, the mitochondrion is stabilized against microtubules following total disorganization of intervening MLS strata. Penetration of the nuclear projection along the MLS and directed disorganization of MLS lower strata control ultimate disposition of headpiece components. The headpiece is isolated and molded into final shape by undercutting and constriction of the cell membrane.     

THE FLAGELLAR APPARATUS OF GYMNODINIUM SP. (DINOPHYCEAE)1

The detailed structure of the flagellar apparatus has been determined in a small dinoflagellate of the genus Gymnodinium. Although diminutive, this dinoflagellate possesses a complex flagellar apparatus consisting of a posteriorly directed microtubular root, a transverse striated fibrous root, several striated fibrous connectives that attach the basal bodies to one another as well as to the different roots, and a conspicuous non-striated fibrous connective that directly links the posteriorly directded microtubular root with the extended lobe of the nucleus. This represents the second discovery of a nuclear connective linked to the flagellar apparatus in the Dinophyceae but is the first report to elucidate the spatial relationships of the connective with the flagellar apparatus and the cell. A detailed diagrammatic reconstruction is provided and the similarities between these flagellar apparatus features are compared with those known for other dinoflagellates. Additionally, the structure and displacement of the nuclear connective are compared with nuclear connectives described in other protists.     

ULTRASTRUCTURE OF SPERMATIUM LIBERATION IN THE MARINE RED ALGA PTILOTA DENSA1

The differentiation of male gametes of the marine red alga Ptilota densa was studied by electron microscopy. Mature primary spermatangia are enveloped by a single cell wall and possess a clearly polar subcellular organization. The nucleus is situated apical to large, striated, fibrous vacuoles which are apparently formed by the repeated fusion of dictyosome vesicles. The transformation and liberation of spermatia from spermatangia involve both the secretion of the fibrous vacuoles at the base of the cell and the subsequent rupturing of the spermatangial cell wall. Liberated spermatia are coated with a thin mucilage layer and contain numerous small vesicles and several mitochondria and dictyosomes. The nucleus is cup-shaped and generally lacks a limiting envelope. These findings are discussed in relation to other light and electron microscopic studies of differentiating spermatangia in red algae.     

EXPERIMENTAL MODIFICATION OF THE MORPHOGENETIC BEHAVIOR OF THE ISOLATED SUB-APICAL CELL OF THE APEX OF SPHACELARIA CIRROSA (PHAEOPHYCEAE)1

Experimental isolation of the terminal cells of the apex of Sphacelaria cirrosa (Roth) C. Agardh shows that the isolated apical cell retains a self-maintained mode of functioning. The isolated sub-apical cell, however, gives rise to a newly-formed axis after undergoing a different type of developmental sequence. An experimental scheme allowing one to defer isolation of the sub-apical cell after killing the apical cell shows that the maintenance, for a few hours only, of connections with subjacent cells is sufficient to induce an apical type mode of functioning in the sub-apical cell. The sequential analysis of the first cytological events in this phenomenon allows one to relate this modification of the morphogenetic program to a functional and polarized arrangement of organelles within the cell reconstituting the apical. The morphogenetic program is characterized by a migration of the nucleus to a distal position prior to an asymmetrical mitosis characteristic of the apical mode of functioning.     

A MORPHOMETRIC STUDY OF THE ULTRASTRUCTURE OF ECHINOCEREUS ENGELMANNII (CACTACEAE). III. SUBAPICAL AND MATURE TISSUES

A stereological, morphometric study of the ultrastructure of subapical cells, xylem parenchyma, and cortical chlorenchyma of Echinocereus engelmannii shows that each of these cell types has a unique organellar composition. The cells of any of these tissues are unique not only in vacuolation (which is visible at the light microscope level), but also in the nucleus/cytoplasm ratio and the concentrations of mitochondria, chloroplasts, and dictyosomes. Furthermore, the differences between each of these cell types were large and statistically significant. It had previously been found that the cells of each zone of the shoot apical meristems of E. engelmannii are different from those of the other zones, but the present study suggests that, considering the large ranges of structure possible in the nonapical cells of this species, the apical meristem variation should be considered as only a minor difference and that the meristem zones are really quite similar to each other.     

ULTRASTRUCTURE OF THE MATURE UNGERMINATED RICE (ORYZA SATIVA) CARYOPSIS. THE CARYOPSIS COAT AND THE ALEURONE CELLS

The results of a light and electron microscopic study of the caryopsis coat and aleurone cells in ungerminated, unimbibed rice (Oryza sativa) caryopses are presented. Surrounding the rice grain is the caryopsis coat composed of the pericarp, seed coat and nucellar layers. The outermost layer, the pericarp, consists of crushed cells and is about 10 μm thick. The seed coat, interior to the pericarp, is one cell thick and has a thick cuticle. Between the seed coat cuticle and endosperm are the remains of the nucellus. The nucellus is about 2.5 μm thick and has a thick cuticle adjacent to the seed coat cuticle. Interior to the caryopsis coat is the aleurone layer of the endosperm. The aleurone completely surrounds the rice grain and is composed of two cell types—aleurone cells that surround the starchy endosperm and modified aleurone cells that surround the germ. The aleurone cells of the starchy endosperm contain many aleurone grains and lipid bodies around a centrally located nucleus. The modified aleurone cells lack aleurone grains, have fewer lipid bodies than the other aleurone cells, and contain filament bundles (fibrils). Plastids of aleurone cells exhibit a unique morphology in which the outer membranes invaginate to form tubules and vesicles within the plastid. Transfer aleurone cells are not observed in the mature rice caryopsis.     

DOPAMINE IN THE MESOLIMBIC SYSTEM OF THE RAT BRAIN: ENDOGENOUS LEVELS AND THE EFFECTS OF DRUGS ON THE UPTAKE MECHANISM AND STIMULATION OF ADENYLATE CYCLASE ACTIVITY

Abstract— High concentrations of dopamine were found in the nucleus accumbens and olfactory tubercle of the rat brain using a radiochemical enzymatic assay technique. An active uptake system for [³H]dopamine that is temperature sensitive and dependent on external sodium ions is present in synaptosome-rich homogenates of these two brain areas. This uptake process is potently inhibited by benztropine (IC₅₀= 2.0 × 10^-7m ). Dextroamphetamine d was 4.5 times more potent than 1-amphetamine in inhibiting dopamine uptake in the nucleus accumbens and six times more potent in the olfactory tubercle and corpus striatum. Low concentrations of dopamine caused an increase in adenosine 3′5′-monophosphate (cyclic AMP) formation in homogenates of both the nucleus accembens and olfactory tubercle. This effect was potently blocked by chlorpromazine. The α-adrenoceptor antagonist phentolamine weakly antagonized the stimulation of this adenylate cyclase by dopamine, but the β-adrenoceptor antagonist propranolol did not.