Phototaxis and Thermotaxis in Some Species of Amphistegina (Foraminifera)*

Positive phototaxis was demonstrated in specimens of Amphistegina radiata within the range of photonic fluxes of 10¹¹ to 10¹⁵ photons × cm^-2× sec^-1. No response was found at lower intensities. Amphistegina radiata has a Dartnall nomogram-shaped action spectrum with a peak at ～500 nm. In addition, A. radiata and A. madagascariensis, which had been maintained at 18 C, moved toward higher temperatures in a horizontal temperature gradient in total darkness. Amphistegina radiata and A. madagascariensis did not move at temperatures ≤ 12 C and ≤ 16 C respectively. An equal number of specimens moved toward the higher and lower temperatures in the gradient when A. radiata was placed at ～29 C and A. madagascariensis at ～22 C. The roles of light and temperature in the distribution of the genus Amphistegina in nature are discussed.     

Regulation of root development in <Emphasis Type="BoldItalic">Arabidopsis thaliana</Emphasis> by phytohormone-secreting epiphytic methylobacteria

In numerous experimental studies, seedlings of the model dicot Arabidopsis thaliana have been raised on sterile mineral salt agar. However, under natural conditions, no plant has ever grown in an environment without bacteria. Here, we document that germ-free (gnotobiotic) seedlings, raised on mineral salt agar without sucrose, develop very short root hairs. In the presence of a soil extract that contains naturally occurring microbes, root hair elongation is promoted; this effect can be mimicked by the addition of methylobacteria to germ-free seedlings. Using five different bacterial species (Methylobacterium mesophilicum, Methylobacterium extorquens, Methylobacterium oryzae, Methylobacterium podarium, and Methylobacterium radiotolerans), we show that, over 9 days of seedling development in a light-dark cycle, root development (hair elongation, length of the primary root, branching patterns) is regulated by these epiphytic microbes that occur in the rhizosphere of field-grown plants. In a sterile liquid culture test system, auxin (IAA) inhibited root growth with little effect on hair elongation and significantly stimulated hypocotyl enlargement. Cytokinins (trans-zeatin, kinetin) and ethylene (application of the precursor ACC) likewise exerted an inhibitory effect on root growth but, in contrast to IAA, drastically stimulated root hair elongation. Methylobacteria are phytosymbionts that produce/secrete cytokinins. We conclude that, under real-world conditions (soil), the provision of these phytohormones by methylobacteria (and other epiphytic microbes) regulates root development during seedling establishment.     

Segregation of the amphitelically attached univalent X chromosome in the spittlebug <Emphasis Type="Italic">Philaenus spumarius</Emphasis>

In meiosis I, homologous chromosomes combine to form bivalents, which align on the metaphase plate. Homologous chromosomes then separate in anaphase I. Univalent sex chromosomes, on the other hand, are unable to segregate in the same way as homologous chromosomes of bivalents due to their lack of a homologous pairing partner in meiosis I. Here, we studied univalent segregation in a Hemipteran insect: the spittlebug Philaenus spumarius. We determined the chromosome number and sex determination mechanism in our population of P. spumarius and showed that, in male meiosis I, there is a univalent X chromosome. We discovered that the univalent X chromosome in primary spermatocytes forms an amphitelic attachment to the spindle and aligns on the metaphase plate with the autosomes. Interestingly, the X chromosome remains at spindle midzone long after the autosomes have separated. In late anaphase I, the X chromosome initiates movement towards one spindle pole. This movement appears to be correlated with a loss of microtubule connections between the kinetochore of one chromatid and its associated spindle pole.     

A quantum chemistry evaluation of the stereochemical activity of the lone pair in Pb<Superscript>II</Superscript> complexes with sequestering ligands

The stereochemical activity of the lone pair on Pb^II complexes is assessed using several theoretical methods, including structural analyses, computations of Fukui functions, natural bond orbitals, electron localization function, investigation of the electron density and of its laplacian. The attention is focused on four octadentate N-carbamoylmethyl-substituted tetraazamacrocycles of various ring sizes ranging from 8 to 14 atoms associated with the Pb^II cation. The theoretical study illustrates the geometrical constraints imposed by the ring structure which limits the spatial development of the lone pair but without fully preventing it. For a given coordination number, the lone pair activity is strongly correlated to the geometry of the ligand and in particular to the size of the cage that the ligand forms around the Pb^II cation. Some limitations of the theoretical tools used are also evidenced, among them the necessity to sample around a critical point instead of just analyzing its nature. In the case of the laplacian of the electron density, a visualization method is introduced to moderate the results based only on the nature of a critical point. These limitations should also be related to the difficulty to extend the lone pair concept for the heaviest atoms of the classification.     

Methylenecyclopropene: local vision of the first <Superscript>1</Superscript>B<Subscript>2</Subscript> excited state

The ¹A₁ ground and the first ¹B₂ excited states of the methylenecyclopropene (triafulvene) are described by localized wave functions, based on 20 structures valence bond structures. The results are compared to CASSCF(4,4) calculations for both the energetics and the dipole moment. Additional calculations with partial electronic delocalization are presented, and it is shown that the dipole moment modification does not correspond to a situation where the antiaromatic situation prevails (with 4n electrons in the cycle). Part of the analysis uses a “trust factor” that helps to decide if a wave function is appropriate to describe a given state. The trust factor compares the VB wave function to the CASSCF’s with their overlap. Finally, the valence bond density is used to produce density maps that illustrate the electron transfer upon excitation.

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Graphical Abstract A projector-based method compares CASSCF wave functions to local wave functions, including Lewis structures as shown in the picture. A “trust factor” (τ) is obtained. Both the ground state and the first excited state of the methylenecyclopropene are discussed

     

Side effects of atypical antipsychotics: a brief overview

This paper reviews the available evidence concerning the side effects of atypical antipsychotics, including weight gain, type II diabetes mellitus, hyperlipidemia, QTc interval prolongation, myocarditis, sexual side effects, extrapyramidal side effects and cataract. Some recommendations about how to prevent and manage these side effects are also provided. It is concluded that atypical antipsychotics do not represent a homogeneous class, and that differences in side effects should be taken into account by clinicians when choosing an antipsychotic for an individual patient.     

Temperature and the metabolic balance of streams

1. It is becoming increasingly clear that fresh waters play a major role in the global C cycle. Stream ecosystem respiration (ER) and gross primary productivity (GPP) exert a significant control on organic carbon fluxes in fluvial networks. However, little is known about how climate change will influence these fluxes. 2. Here, we used a ‘natural experiment’ to demonstrate the role of temperature and nutrient cycling in whole‐system metabolism (ER, GPP and net ecosystem production – NEP), in naturally heated geothermal (5–25 °C) Icelandic streams. 3. We calculated ER and GPP with a new, more accurate method, which enabled us to take into account the additional uncertainties owing to stream spatial heterogeneity in oxygen concentrations within a reach. ER ranged 1–25 g C m^?2 day^?1 and GPP 1–10 g C m^?2 day^?1. The median uncertainties (based on 1 SD) in ER and GPP were 50% and 20%, respectively. 4. Despite extremely low water nutrient concentrations, high metabolic rates in the warm streams were supported by fast cycling rates of nutrients, as revealed from inorganic nutrient (N, P) addition experiments. 5. ER exceeded GPP in all streams (with average GPP/ER = 0.6) and was more strongly related to temperature than GPP, resulting in elevated negative NEP with warming. We show that, as a first approximation based on summer investigations, global stream carbon emission to the atmosphere would nearly double from 0.12 Pg C year^?1 at 13 °C to 0.21 (0.15–0.33) Pg C year^?1 with a 5 °C warming. 6. Compared to previous studies from natural systems (including terrestrial ecosystems), the temperature dependence of stream metabolism was not confounded by latitude or altitude, seasonality, light and nutrient availability, water chemistry, space availability (water transient storage), and water availability. 7. Consequently, stream nutrient processing is likely to increase with warming, protecting downstream ecosystems (rivers, estuaries, coastal marine systems) during the summer low flows from nutrient enrichment, but at the cost of increased CO₂ flux back to the atmosphere.     

Vacuolated plant cells as ideal osmometer: reversibility and limits of plasmolysis, and estimation of protoplasm volume in control and water-stress-tolerant cells

Abstract. The osmotic behaviour of vacuolated plant cells (adaxial epidermal cells of Allium cepa bulb scales, and epidermal as well as chloroplast containing subepidermal stem base cells of Pisum sativum) was studied over a wide range of CaCl₂ concentrations. The following results were obtained.

• a. Allium cepa and Pisum sativum plant cells behave as an ideal osmometer as far as plasmolytic contraction of the protoplast is concerned.
• b. The protoplasts of these cells could be plasmolysed to 15–45% of their original volume without the loss of membrane semi-permeability.
• c. Cells plasmolysed in 1.0 kmol m^?3 CaCl₂ could be completely deplasmolysed and upon deplasmolysis the cells resumed protoplasmic streaming.
• d. The above findings (a-c) indicate that during gradual plasmolysis and deplasmolysis membrane semi-permeability is maintained.
• e. At very high plasmolysing concentrations vacuoles covered with the tonoplast separated from the rest of the protoplasm in some cells whereas others showed systrophy. Extruded vacuoles were able to respond to osmotic shrinkage.
• f. The non-solvent space in Allium cells of about 3% also corresponded to the protoplasm volume calculated from the protoplast geometry (mean from results of direct measurement method and subtraction method).
• g. Subepidermal stem base cells of water-stress-tolerant Pisum plants had a 75% greater non-solvent space than the control cells indicating that a water-stress-tolerant cell may contain a larger amount of protoplasm and/or a vacuole with a higher content of colloidal material in the vacuole.
• h. Water-stress-tolerant cells showed greater tolerance to osmotic dehydration (volume reduction) than control cells.