Studies of protonemal morphogenesis in mosses. IX. Discelium nudum: exquisite pioneer of unstable clay banks

Abstract

The protonemal system of Discelium nudum produces a sward of unicellular, colourless, starch-filled rhizoidal tubers ca 1 cm below the surface of unstable clay banks. These short-lived and desiccation-intolerant diaspores are exposed on new clay surfaces following winter exfoliation of the original substratum. Their abundance and rapid germination appears to be a reproductive strategy giving Discelium a competitive advantage in this highly unstable habitat. The rounded, thin-walled, non-gemmiferous chloronemal filaments and colourless rhizoids of Discelium suggest affinities with the Funariaceae and the Gigaspermaceae. An early report of multicellular tubers in Discelium is most probably due to misinterpretion of the large starch grains, up to 20 μm in diameter, as cells within the unicellular tubers.     

Studies of protonemal morphogenesis in mosses. XII. Ephemeropsis,the zenith of morphological differentiation

Abstract

This light and scanning electron microscope study of freshly collected material confirms that the protonemal system of Ephemeropis is the most highly differentiated so far found in mosses and reveals hitherto unsuspected roles for its unique features. Whereas substrate attachment in the Hypnales, illustrated here in Homalothecium sericeum, is by clusters of irregular terminal mucilage-secreting ramifications on long otherwise unbranched rhizoids and in other mosses is via otherwise unmodified rhizoids, the anchoring structures or hapteres in Ephemeropsis are very regular side branch systems that also secrete copious mucilage. This last feature, only clearly visible in living specimens, also invests the bristle-like appendages similarly unique to Ephemeropsis. Abundant cyanobacteria in this mucilage may be an important nitrogen source for Ephemeropsis. Other features most likely linked to growth on twigs, the leaf bases of ferns and tree ferns and epiphylly are the absence of food-conducting cytology from the main protonemal axes and the rapid absorption of water by the much-branched chloronemata. Gemmae are produced at the tips of attenuated filaments that grow downwards in a spiral pattern and are rapidly anchored to the subjacent leaves by means of short side branches at their bases that also secrete copious mucilage.     

A new species of Cheilolejeunea (Spruce) Schiffn. from Panama

Abstract

Cheilolejeunea (subgen. Strepsilejeunea) norisiae G. Dauphin & Gradst. sp. nov. is described and illustrated. The new species differs from other members of the genus Cheilolejeunea by the laciniate leaf margins and the large pre-apical tooth.     

Studies in aquatic fungi of varanasi. X. Additional new or interesting records of aquatic phycomycetes

Summary Four species of the genusSaprolegnia Nees, viz.,Saprolegnia diclina, S. delica, S. mixta, S. monoica var.glomerata, and three from the achlyoid group, viz.,Achlya colorata, A. racemosa, andA. americana were isolated on various substrata used as baits from the vicinity of University campus. ExcludingS. diclina andA. americana, all the above fungi are reported as occurring new from this country.     

Studies on the physiological bases of morphogenesis in fungi; the respiratory metabolism of dimorphic pathogenic fungi

The interconversions of mycelial and yeast-like forms (M right harpoon over left harpoon Y) in Blastomyces dermatitidis and in Blastomyces brasiliensis are characterized as examples of thermal dimorphism since the phenomena are apparently dependent only on the temperature of incubation of these two species. The change in morphology consequent upon Y --> M conversion is considered to result from the selective inhibition of cell division, without the simultaneous inhibition of growth. Such selective inhibition is viewed in a wider context as an example of the differential operation of the physicochemical apparatus of the cell in the control of form development by an organism. To analyze this differential operation, which is here dependent only on temperature, we have studied the effect of temperature on oxygen consumption by each of the dimorphic forms. In the absence of external substrate the yeast forms consume 5 to 6 times more oxygen per unit dry weight than do the M forms.The Y forms exhibit an exogenous oxidation of acetate and of glucose, as well as an oxidative assimilation of these substrates, whereas the M forms exhibit no exogenous metabolism in either a resting or starved condition. A study of the effect of a wide range of temperatures on oxygen consumption by the M forms indicates the operation of two rate-limiting processes: (a) one with an activation energy of 13,250 calories/gm. molecule over the range 5-30 degrees , and (b) reversible enzyme inactivation; the latter process assuming importance in the higher temperature range. On abrupt, large changes in temperature the balance between these two rate-limiting reactions (which it is suggested characterizes the steady state) is apparently disrupted as a result of a lag in the assumption of a rate of reversible enzyme inactivation characteristic of the new temperature. This disruption of balance is evidenced in overshoot phenomena. The effect of an analogous disruption of balance, and of increasing enzymic inactivation; on a competition between enzyme systems, competing for substrate for cell elongation and for cell division, is considered in explanation of the observed dependence of the cell division mechanism on the maintenance of an elevated temperature.     

Cell division in caffeine-induced binucleate protonemal cells ofAdiantum. I. Asynchronous mitosis of two nuclei in a single cell

Coordination of karyokinesis of two nuclei in individual filamentous binucleate cells of the fern,Adiantum capillus-veneris was investigated. To induce binucleate cells, the protonemata were treated with caffeine, which is known as an inhibitor of plant cytokinesis, during the first synchronous division of cells that was induced by blue light (BL). The next synchronous division of cells in the resultant binucleate cells was analysed. In most cases, the two nuclei were associated with each other and were located in the apical region of the long protonemal cells (approximately 400–600 μm in length, 20 μm in width). In some cells, one nucleus was located in the apical region and the other was located in the middle of the cylinderical region. In such cells, karyokinesis of the apical nucleus preceded that of the basal nucleus, even though karyokinesis of associated nuclei progressed synchronously. Mitotic binucleate cells were centrifuged in order to gather two dissociated heterophasic nuclei. Progression of karyokinesis in the re-associated nuclei became coordinated within 1 h in most cells. These results suggest that mitosis-regulating factor(s) may diffuse to only limited distances inAdiantum protonemata.     

Mussaenda lancipetala X. F. Deng & D. X. Zhang,a new species of Rubiaceae from China

Mussaenda lancipetala X. F. Deng & D. X. Zhang, a new species of Rubiaceae from Yunnan Province, Southwestern China, is described and illustrated. The new species is characterized by its reverse herkogamous sexual system, its ovate-lanceolate corolla lobes with caudate apex, and corolla tube covered with sparse farinose pubescence, by which it is clearly distinguished from other species of Mussaenda.     

中国玉叶金花属(茜草科)植物一新种

报道了在云南发现的玉叶金花属Mussaenda一新种——狭瓣玉叶金花M. lancipetala X. F. Deng ＆ D. X. Zhang。狭瓣玉叶金花的性系统为柱头缩入式雌雄异位; 花冠裂片卵状披针形且具有细长的长尖头, 花冠管外被有粉末状的毛被, 可以很容易与玉叶金花属其他种类相区别。     

Studies of X inactivation and isodisomy in twins provide further evidence that the X chromosome is not involved in Rett syndrome.

Rett syndrome (RS), a progressive encephalopathy with onset in infancy, has been attributed to an X-linked mutation, mainly on the basis of its occurrence almost exclusively in females and its concordance in female MZ twins. The underlying mechanisms proposed are an X-linked dominant mutation with male lethality, uniparental disomy of the X chromosome, and/or some disturbance in the process of X inactivation leading to unequal distributions of cells expressing maternal or paternal alleles (referred to as a "nonrandom" or "skewed" pattern of X inactivation). To determine if the X chromosome is in fact involved in RS, we studied a group of affected females including three pairs of MZ twins, two concordant for RS and one uniquely discordant for RS. Analysis of X-inactivation patterns confirms the frequent nonrandom X inactivation previously observed in MZ twins but indicates that this is independent of RS. Analysis of 29 RS females reveals not one instance of uniparental X disomy, extending the observations previously reported. Therefore, our findings contribute no support for the hypothesis that RS is an X-linked disorder. Furthermore, the concordant phenotype in most MZ female twins with RS, which has not been observed in female twins with known X-linked mutations, argues against an X mutation.