Mechanisms and regulation of reduction-based iron uptake in plants

Despite the usually high abundance of iron (Fe) in soils, the low solubility of Fe-bearing minerals restricts the available Fe pools in most aerobic soils to levels that are far below those required for microbial or plant growth. To acquire the necessary amounts of Fe from the environment, organisms have evolved mechanisms that enhance the solubility and dissolution rate of Fe(iii) oxyhydroxides prevailing in aerobic soils. Chemically, these mechanisms are based on weakening of the Fe–O bond by reduction, chelation and protonation. Physiologically, two distinct and in all known cases mutually exclusive strategies can be distinguished: the excretion of siderophores capable of solubilizing external ferric Fe and subsequent uptake of the ferric siderophore complex; and reduction of Fe(iii) prior to uptake of the more soluble Fe²⁺ ion. With the exception of graminaceous species, in which Fe uptake is based on the former mechanism, the latter strategy is found in all cormophytes and certain algae, yeast and bacteria. In higher plants, the increase in their capacity to convert extracellular ferric to ferrous Fe is part of a series of physiological and morphological events that act in concert to achieve appropriate internal levels of Fe. It is this amalgam of features that determines the Fe efficiency of a species or cultivar that in turn affects the yield of economically important plants and the natural distribution of species. Adaptive changes to limited Fe availability have been studied at the molecular, physiological and whole-plant level. This review summarises current knowledge of the components of reduction-based Fe uptake in plants and presents an integrated view of the present understanding of mechanisms that control the rate and extent of Fe absorption by roots.     

Sensory Motor Interfacing in Acoustic Behavior of Anurans

SYNOPSIS. Anurans respond to different acoustic signals in adistinct manner. Moreover, acoustic behavior strongly dependson the inner state of the animal and the social context. Neuroanatomicalstudies as well as extra- and intracellular recordings werecarried out to examine the problem of audio-motor interfacing.Acoustic signals are processed in a partly hierarchical andpartly distributed manner in the anuran central nervous system.Features are represented in a topographical manner. Auditorymaps in the midbrain torus semicircularis are read by a subsetof neurons of the laminar and magnocellular subnuclei, whichinterconnect the auditory pathway and premotor centres. These,in turn, feed into neural networks controlling vocalization,locomotion, or autonomic functions. Our data on the cytoarchitectonicorganization and connectivity of the interfacing neurons giverise to a population coding hypothesis which may explain thedifferential evaluation of acoustic signals. Additionally, immunohistochemicalfindings reveal strong neuromodulatory and hormonal input, especiallyonto interfacing neurons, suggesting intense influence on thephysiological properties of these cells.     

Natural history of the non-solitary sheetweaving spider Anelosimus jucundus (Araneae: Theridiidae)

Field observations were made on one Panamanian population of Anelosimus jucundus. Almost all webs were found in a relatively exposed area, on small shrubs and composites. This is in contrast to A. eximius , a colonial congeneric which in our study site built its large webs along moist, fern-covered banks. Web structure varied with different plant substrates; for example, only some of the webs incorporated a clearly defined lower sheet. Webs were built by penultimate instar females, and perhaps by adult females and males. In some cases, several adult females inhabited a web, but they remained under separate leaf canopies; during census observations co-operative efforts were not noted. Prey consisted mainly of winged insects. Juvenile sex ratio was about equal. The degree of sociality demonstrated by A. jucundus is discussed.     

Cyclic AMP Phosphodiesterase in Leydig Cell Preparations of the Rat Testis

Enzymatic digestion of the interstitial tissue of early juvenile and adult rat testes resulted in an enrichment of the Leydig cell population. The cells of the intertubular preparation from adult testes were separated by centrifugal elutriation, according to differences in sedimentation velocity, a counter-flow centrifugation technique leading to 70% Leydig cell purity. Using this approach, it was possible to demonstrate that Leydig cells from adult testes contain only low affinity isoenzymes of cyclic AMP phosphodiesterase (PDE; E.C.: 3.1.4.17), an intracellular regulator of cAMP. Starch gel electrophoresis showed that the isozyme of cAMP PDE of Leydig cells is masked in crude testis homogenates due to the relatively low level of these cells in the total population. In Leydig cells, there are two different electrophoretic forms expressed which resemble two of eleven different molecular forms of cAMP PDE demonstrated for comparison in 21 different organs of the adult rat.
An interstitial cell preparation from early juvenile testes, with a Leydig cell content of up to 20%, was also investigated electrophoretically with regard to molecular forms of cAMP PDE, the properties of which were characterized by kinetic analysis of cAMP hydrolysis. The results presented are discussed in relation to the onset of testosterone synthesis in Leydig cells of prepubertal rats leading to the initiation of male puberty.     

Night-time sun-compass behaviour of honey bees at the equator

ABSTRACT. In accordance with the peculiarities of the sun's azimuthal path near the equator, African honey bees observed in their night-time dances apparently allowed for the azimuth moving backwards at night relative to its day-time movement. In several cases the bees evidently inferred the actual azimuthal position of the sun, rather than the one that would result from extrapolating a uniform movement of the sun.     

On a New Microcerberus from the Red Sea and the Relationship of the Microcerberidea to the Anthuridea (Crustacea, Isopoda)

Microcerberus tabai sp.n. from the Gulf of Elat is described in detail. The relationship of the Microcerberida to the Anthuridea is discussed: the Microcerberidea have none of the synapomorphies of the Anthuridea.     

Immobilization of Ciliates by Concanavalin A*

SYNOPSIS. Interaction of several plant lectins with the ciliates Stylonychia mytilus, Euplotes aediculatus, and Tetrahymena pyriformis GL, was investigated. The motility of Stylonychia is specifically inhibited by treatment with concanavalin A, with which the 2 other ciliates react only weakly. Stylonychia can regain its motility by shedding the lectin-loaded surface components and rebuilding a new pellicle. Other lectins used in this study did not interact with these ciliates.     

Modelling the role of agriculture for the 20th century global terrestrial carbon balance

In order to better assess the role of agriculture within the global climate‐vegetation system, we present a model of the managed planetary land surface, Lund–Potsdam–Jena managed Land (LPJmL), which simulates biophysical and biogeochemical processes as well as productivity and yield of the most important crops worldwide, using a concept of crop functional types (CFTs). Based on the LPJ‐Dynamic Global Vegetation Model, LPJmL simulates the transient changes in carbon and water cycles due to land use, the specific phenology and seasonal CO₂ fluxes of agricultural‐dominated areas, and the production of crops and grazing land. It uses 13 CFTs (11 arable crops and two managed grass types), with specific parameterizations of phenology connected to leaf area development. Carbon is allocated daily towards four carbon pools, one being the yield‐bearing storage organs. Management (irrigation, treatment of residues, intercropping) can be considered in order to capture their effect on productivity, on soil organic carbon and on carbon extracted from the ecosystem. For transient simulations for the 20th century, a global historical land use data set was developed, providing the annual cover fraction of the 13 CFTs, rain‐fed and/or irrigated, within 0.5° grid cells for the period 1901–2000, using published data on land use, crop distributions and irrigated areas. Several key results are compared with observations. The simulated spatial distribution of sowing dates for temperate cereals is comparable with the reported crop calendars. The simulated seasonal canopy development agrees better with satellite observations when actual cropland distribution is taken into account. Simulated yields for temperate cereals and maize compare well with FAO statistics. Monthly carbon fluxes measured at three agricultural sites also compare well with simulations. Global simulations indicate a ∼24% (respectively ∼10%) reduction in global vegetation (respectively soil) carbon due to agriculture, and 6–9 Pg C of yearly harvested biomass in the 1990s. In contrast to simulations of the potential natural vegetation showing the land biosphere to be an increasing carbon sink during the 20th century, LPJmL simulates a net carbon source until the 1970s (due to land use), and a small sink (mostly due to changing climate and CO₂) after 1970. This is comparable with earlier LPJ simulations using a more simple land use scheme, and within the uncertainty range of estimates in the 1980s and 1990s. The fluxes attributed to land use change compare well with Houghton's estimates on the land use related fluxes until the 1970s, but then they begin to diverge, probably due to the different rates of deforestation considered. The simulated impacts of agriculture on the global water cycle for the 1990s are∼5% (respectively∼20%) reduction in transpiration (respectively interception), and∼44% increase in evaporation. Global runoff, which includes a simple irrigation scheme, is practically not affected.