A kinetic analysis of cadmium accumulation in a Cd hyper‐accumulator fern,Athyrium yokoscense and tobacco plants

Cadmium (Cd) accumulations in a Cd hyper‐accumulator fern, Athyrium yokoscense (Ay), and tobacco, Nicotiana tabacum (Nt), were kinetically analysed using the positron‐emitting tracer imaging system under two medium conditions (basal and no‐nutrient). In Ay, maximumly 50% and 15% of the total Cd accumulated in the distal roots and the shoots under the basal condition, respectively. Interestingly, a portion of the Cd in the distal roots returned to the medium. In comparison with Ay, a little fewer Cd accumulations in the distal roots and clearly higher Cd migration to the shoots were observed in Nt under the basal condition (maximumly 40% and 70% of the total Cd, respectively). The no‐nutrient condition down‐regulated the Cd migration in both species, although the regulation was highly stricter in Ay than in Nt (almost no migration in Ay and around 20% migration in Nt). In addition, the present work enabled to estimate physical and physiological Cd accumulation capacities in the distal roots, and demonstrated condition‐dependent changes especially in Ay. These results clearly suggested occurrences of species‐/condition‐specific regulations in each observed parts. It is probable that integration of these properties govern the specific Cd tolerance/accumulation in Ay and Nt.     

Maternal information and localized maternal mRNAs in eggs and early embryos of the ascidian Halocynthia roretzi

Summary

The mosaic behavior of blastomeres isolated from ascidian embryos has been taken as evidence that localized ooplasmic factors (cytoplasmic determinants) specify tissue precursor cells during embryogenesis. Experiments involving the transfer of egg cytoplasm have revealed the presence and localization of various kinds of cytoplasmic determinants in eggs of Halocynthia roretzi. Three cell fates, epidermis, muscle and endoderm, are fixed by cytoplasmic determinants. The three kinds of tissue determinants move in different directions during ooplasmic segregation. Prior to the onset of the first cleavage the three kinds of determinants reside in egg regions that correspond to the future fate map of the embryo and then they are differentially partitioned into specific blastomeres. In addition to tissue-specific determinants, there is evidence suggesting that ascidian eggs contain localized cytoplasmic factors that are responsible for controlling the cleavage pattern and morphogenetic movements. Transplantation of posterior-vegetal egg cytoplasm to an anterior-vegetal position causes a reversal of the anterior-posterior polarity of the cleavage pattern. Localized cytoplasmic factors in the posterior-vegetal region are involved in the generation of a unique cleavage pattern. When vegetal pole cytoplasm is transplanted to the animal pole or equatorial position of the egg, ectopic gastrulation occurs at the site of transplantation. This finding supports the idea that vegetal pole cytoplasm specifies the site of gastrulation. Recently, we started a cDNA project to analyze maternal mRNAs. An arrayed cDNA library of fertilized eggs of H. roretzi was constructed, and more than 2000 clones have been partially sequenced so far. To estimate the proportion of the maternal mRNAs that are localized in the egg and embryo, 150 randomly selected clones were examined by in situ hybridization. We found eight mRNAs that are localized in the eight-cell embryo, of which three were localized to the myoplasm (a specific region of the egg cytoplasm that is partitioned into muscle-lineage blastomeres) of the egg, and then to the postplasm of cleavage-stage embryos. These results indicate that the proportion of localized messages is much higher than we expected. These localized maternal messages may be involved in the regulation of various developmental processes.     

Three-dimensional microanatomy of perineuronal proteoglycan nets enveloping motor neurons in the rat spinal cord

Summary. Spinal motor neurons possess reticular coats of extracellular matrix proteoglycans on their somata and proximal dendrites. In order to define the anatomical background of the network, spatial relationships of the perineuronal proteoglycans with synaptic boutons and astrocyte processes were analyzed in rat motor neurons by TEM after histochemical detection of the substances with cationic iron colloid, and by SEM after exposure of the cytoarchitecture with NaOH maceration. Narrow intercellular channels filled with proteoglycan were found to extend along the surface of the neurons to form a homogeneous network of a mesh size of about 1 µm. The system of perineuronal channels consisted of two parts: a primary intervaricose net which meandered among synaptic boutons on the surface of the motor neuron, and secondary subvaricose nets which irrigated interfaces between larger boutons and the neuron. No elements in the perineuronal cytoarchitecture coincided with the meshwork of proteoglycan, indicating the involvement of postsynaptic factors in the distribution of the substance. Thin astrocyte processes surrounding the neurons formed a distinct network with heterogeneous meshes corresponding to boutons of various sizes. The perineuronal glial nets extended their surface area in contact with the intervaricose nets of proteoglycan by complex cellular interdigitations. The subvaricose nets of proteoglycan compartmentalized multiple synapses on large boutons, suggesting an involvement in the division of the synapses during development.     

Biochemical and egg size evolution of freshwater fishes in the Rhinogobius brunneus complex (Pisces, Gobiidae) in Okinawa, Japan

Many colour morphs have been recognized in the Rhinogobius brunneus complex. A recent electrophoretic study has revealed that some of the colour morphs are well differentiated from each other genetically. In Okinawa, egg-size and life-history variation has been found in addition to the colour variation in this species complex. To clarify the nature of this life-history variation, gobies of a fluviatile morph with large eggs as well as three other amphidromous morphs with small eggs, inhabiting a single stream sympatrically in Okinawa, were analysed by electrophoresis and the females were also used for comparison of egg and clutch sizes. Electrophoretic data for 34 loci showed that each morph was separated by a fixed-allele difference for at least one locus, indicating that the four morphs which occurred sympatrically are reproductively isolated from each other. However, Nei's genetic distance between the fluviatile morph and one of the amphidromous morphs was much smaller (0.026) than distances among amphidromous gobies (0.323-0.480). Egg size of the former was by far the largest among the four. These results imply that speciation of the fluviatile morph accompanied by the egg-size increase has been completed rapidly without considerable genetic differentiation.     

NITRATE REDUCTASE IN PHOTOSYNTHETIC BACTERIUM, RHODOSPIRILLUM RUBRUM. PURIFICATION AND PROPERTIES OF NITRATE REDUCTASE IN NITRATE-ADAPTED CELLS

1. From nitrate-adapted cells of Rhodospirillum rubrum, an activepreparation of nitrate reducing enzyme was isolated in partiallypurified state. The enzyme was found to be localized in thechromatophores of the cell and, on sonication, readily releasedinto the upernatant fraction. The purified enzyme, catalyzingthe electron transfer between DPNH and nitrate, contained ab-type cytochrome, flavin and non-heme iron, which was removedon dialysis in the presence of cyanide. Besides DPNH, only methylviologen(reduced form) was effective as electron donor. 2. The effects of pH and the addition of various activatorsand inhibitors on the rate of nitrate reduction were investigated,using DPNH or reduced methylviologen as the electron donor.The oxidation-reduction of the flavin and the heme in the enzymewas followed spectrophotometrically. A pathway of electron inthe nitrate reduction through this enzyme was proposed. 3. The nitrate reductase of this bacterium was compared withother nitrate reductases obtained from other sources, and themetabolic roles of this enzyme were discussed. In the nitrate-adaptedcells of Rsp. rubrum, only one and the same enzyme was obtainedunder different growth conditions of nitrate assimilation (i.e., nitrate as N-source; light as energy source) and nitrate-respiration(i. e., in the dark; nitrate as hydrogen acceptor and N-source). ¹ Dedicated to Prof. H. TAMIYA on the occasion of his 60th birthday.This paper was submitted to the University of Tokyo to fulfillthe requirement for the author's doctorate. ² Present address; Botanical Institute, Kyoto University. (Received December 14, 1962; )     

STUDIES ON ALGAL CYTOCHROME II PHYSICO-CHEMICAL PROPERTIES OF CRYSTALLINE PORPHYRA TENERA CYTOCHROME 553

The Physico-chemical properties of an algal cytochrome, Porphyratenera cytochrome 553 were investigated, using a crystallinepreparation of the substance. The cytochrome was found to behighly resistant to heat and preservation. The stability ofthe cytochrome was also prominent in a wide range of pH. Absorption spectra as: well as data concerning the extinctioncoefficients of the oxidized and reduced forms are presented. The oxidation-reduction potential of the cytochrome was determinedat various pH. The value for the normal potential was foundto decrease gradually with increasing pH; from 355 mV at pH5.0, to 270 mV at pH 11.0. Electrophoretic investigation revealedthat this cytochrome is a markedly acidic protein, with an isoelectricpoint of pH 3.5. The molecular weight of the cytochrome wasdetermined from ultracentrifugal and diffusion experiments tobe 13,600. The values for the minimum molecular weight calculatedfrom the heme- and iron-contents are, respectively, 12,000 and11,000. (Received April 20, 1960; )     

Involvement of Pteridines in the Body Coloration of the Isopod Armadillidium vulgare

The pteridine content was measured as a function of age in Armadillidium vulgare, and the fine structure of the pteridine-containing granules in the integument was examined in relation to pteridine content. Yellow chromatophores are an essential component of the cream-markings, which are a defining feature of the female A. vulgare. Four kinds of pteridines in the integument including a yellow pigment (sepiapterin) were determined by HPLC. The body color of the red phenotype of A. vulgare varies from dark red to yellowish red and was formerly thought to be due to the quality and quantity of ommochrome pigment. Our analysis of the pteridine content in the integument of this phenotype revealed a significant change in sepiapterin content per body weight with age. Sepiapterin content per body weight decreased gradually with age, while that of biopterin tended to increase with age. Ultrastructural observations of the pigment granules in the yellow chromatophores revealed a corresponding change in the fine structure of pigment granules. In the older adults, some of the electron-dense fibrous materials in the pteridine-containing granules was concentrically arranged, and in the younger adults, most of pteridine-containing granules were electron-lucent. The role of pteridine quality in determining the structure of pteridine-containing granules is discussed.