Limnochemical and phytoplankton studies on Nyumba ya Mungu reservoir, Tanzania

This publication reports on the chemical and phytoplankton aspects of a three month biological survey of Nyumba ya Mungu reservoir, Tanzania.
The lake had a total salt concentration of about 8 meq dm^-3 and specific conductivity of 900 μS cm^-1. The main salt in solution was sodium bicarbonate, and when the lake level fell it sometimes formed a crust on the exposed shore. The concentrations of major nutrient ions were probably not limiting to algal growth and good nutrient replenishment was provided by the two inflow rivers.
Nyumba ya Mungu supports a rich phytoplanton dominated by Melosira and blue-green algae. Acetone extractions gave chlorophyll 'a' concentrations ranging from 20–40 mgm^-3 in the vertical profiles, and light and dark bottle experiments indicated a maximum gross photosynthesis of about 800 mg O₂ m^-3h^-1. There was evidence of chemical stratification in the open water and diurnal stratification in the sheltered bays, but discontinuities were short-lived and the Trade Winds ensured regular mixing of the water. The lake appeared to have a higher primary production than the larger Rift Valley lakes and it was considered that this level of production would continue.     

Taxonomy of the Houbara Bustard Chlamydotis undulata subspecies considered on the basis of sexual display and genetic divergence

The Houbara Bustard Chlamydotis undulata is a polytypic species with three subspecies classified according size, colour and distribution: C. u. undulata, C. u. fuertaventurae and C. u. macqueenii. A comparative study of the male display behaviour of these three subspecies has shown similarities between C. u. undulata and C. u. fuertaventurae , whereas appreciable differences exist in the visual and auditory aspects of the display between C. u. undulata and C. u. macqueenii. These observations make the current taxonomy of Houbara Bustard questionable, particularly in view of the major importance of the sexual display in bird speciation processes. Furthermore, DNA analysis of the cytochrome b gene indicates the existence of a significant differentiation between the C. u. undulata and C. u. macqueenii populations. These findings indicate the need for a revision of the taxonomy of genus Chlamydotis which should separate the macqueenii and undulata populations at species rank. Until further investigations are completed, C. u. fuertaventurae should be kept as a subspecies of undulata since the courtship display is alike in both populations.     

A Novel Experimental System for Studies of Photosynthate Transfer in the Developing Wheat Grain

The aim of this study was to develop a valid and convenientexperimental system for exploring photosynthate transfer inthe developing wheat grain. Structural characteristics relatingto photosynthate transfer and the composition of the endospermcavity sap were examined during the linear stage of grain developmentat 25±3 d after anthesis. Based on the results of thesestudies, an experimental system was devised to permit the directmonitoring and manipulation of photosynthate transfer from theendosperm cavity to the storage endosperm. A novel approachwas used whereby insertions were made into the endosperm cavityby a needle at the embryo end and a piece of microcapillarytubing at the stigma end of the detached grain. By this means,the experimental solution was delivered into and flowed longitudinallyunder gravity through the endosperm cavity to exit at the stigmaend. The composition of the experimental solution reflected the principalsolute concentrations and osmolality of the in vivo endospermcavity contents. With the introduction of the solution intothe cavity, it was found that the viability of grain tissueswas maintained for up to 30 h. During a 24 h period both therate of sucrose uptake and subsequent incorporation into ethanolinsolublecomponents were shown to reproduce the rate of starch biosynthesisand in vivo grain growth. Moreover, the experimental systemeffectively reproduced the in vivo pathway of photosynthatetransfer from the endosperm cavity via the modified aleuronecells into the endosperm. As a result, this system providesa new approach to study photosynthate transfer in the developingwheat grain. Key words: Wheat grain, endosperm cavity, experimental system, photosynthate transport     

An oxygen-mediated positive feedback between elevated carbon dioxide and soil organic matter decomposition in a simulated anaerobic wetland

We examined the effects of elevated atmospheric CO₂ on soil carbon decomposition in an experimental anaerobic wetland system. Pots containing either bare C₄‐derived soil or the C₃ sedge Scirpus olneyi planted in C₄‐derived soil were incubated in greenhouse chambers at either ambient or twice‐ambient atmospheric CO₂. We measured CO₂ flux from each pot, quantified soil organic matter (SOM) mineralization using δ¹³C, and determined root and shoot biomass. SOM mineralization increased in response to elevated CO₂ by 83–218% (P<0.0001). In addition, soil redox potential was significantly and positively correlated with root biomass (P= 0.003). Our results (1) show that there is a positive feedback between elevated atmospheric CO₂ concentrations and wetland SOM decomposition and (2) suggest that this process is mediated by the release of oxygen from the roots of wetland plants. Because this feedback may occur in any wetland system, including peatlands, these results suggest a limitation on the size of the carbon sink presented by anaerobic wetland soils in a future elevated‐CO₂ atmosphere.     

Stream ecosystem responses to the 2007 spring freeze in the southeastern United States: unexpected effects of climate change

Some expected changes in climate resulting from human greenhouse gas emissions are clear and well documented, but others may be harder to predict because they involve extreme weather events or heretofore unusual combinations of weather patterns. One recent example of unusual weather that may become more frequent with climate change occurred in early spring 2007 when a large Arctic air mass moved into the eastern United States following a very warm late winter. In this paper, we document effects of this freeze event on Walker Branch, a well‐studied stream ecosystem in eastern Tennessee. The 2007 spring freeze killed newly grown leaf tissues in the forest canopy, dramatically increasing the amount of light reaching the stream. Light levels at the stream surface were sustained at levels considerably above those normal for the late spring and summer months due to the incomplete recovery of canopy leaf area. Increased light levels caused a cascade of ecological effects in the stream beginning with considerably higher (two–three times) rates of gross primary production (GPP) during the late spring and summer months when normally low light levels severely limit stream GPP. Higher rates of stream GPP in turn resulted in higher rates of nitrate (NO₃^?) uptake by the autotrophic community and lower NO₃^? concentrations in stream water. Higher rates of stream GPP in summer also resulted in higher growth rates of a dominant herbivore, the snail Elimia clavaeformis. Typically, during summer months net NO₃^? uptake and snail growth rates are zero to negative; however, in 2007 uptake and growth were maintained at moderate levels. These results show how changes in forest vegetation phenology can have dramatic effects on stream productivity at multiple trophic levels and on nutrient cycling as a result of tight coupling of forest and stream ecosystems. Thus, climate change‐induced changes in canopy structure and phenology may lead to large effects on stream ecosystems in the future.     

Molecular Aspects of Fibrin Clot Solubilization

THE human plasma protein, fibrinogen, is a disulphide bonded¹ dimer², each unit containing an Aα, Bβ and 8 chain^*, interconnected by disulphide bridges³. Thrombin (E.C.3.4.4.-13) releases fibrinopeptides A and B from the Aα and Bβ chains respectively⁴ to form fibrin monomer (α₂β₂γ₂) ? which polymerizes to form fibrin polymer or clotted fibrin. This polymer, following factor XIII (plasma transglutaminase, fibrin stabilizing factor) mediated crosslinking among the α chains and among the γ chains⁵, is one of the major and initiating constituents of a thrombus. Fibrinolytic activators, for example, streptokinase (SK) and urokinase (UK), are of thrombolytic value as they convert the thrombus plasminogen to plasmin (E.C.3.4.4.14) which by fibrinolytic action dissolves the thrombus. Whereas the interaction of fibrinogen and plasmin has been well studied^6–9, little is known concerning the mechanism of plasmin mediated fibrin clot lysis. I report here on the mechanism of non-cross-linked fibrin clot solubilization in near physiological conditions.     

Linked Genes for Calmodulin and E2 Ubiquitin-Conjugating Enzyme in Trichomonas vaginalis

ABSTRACT In searching the genomes of early-diverging protists to study whether the possession of calmodulin is ancestral to all eukaryotes, the gene for calmodulin was identified in Trichomonas vaginalis. This flagellate is a member of the Parabasalia, one of the earliest lineages of recognized eukaryotes to have diverged. This sequence was used to isolate a homologous 1.250-kb fragment from the T. vaginalis genome by inverse polymerase chain reaction. This fragment was also completely sequenced and shown to contain the 3' end of the single-copy calmodulin gene and the 3' end of a gene encoding a protein with high similarity to E2 ubiquitin-conjugating enzymes, a family which has previously only been identified in animals, plants, and fungi. Phylogenetic analysis of 50 members of the E2 family distinguishes at least nine separate subfamilies one of which includes the T. vaginalis E2-homologue and an uncharacterized gene from yeast chromosome XII.     

Metal cation binding by the hyperthermophilic microorganism,Archaea Methanocaldococcus Jannaschii,and its effects on silicification

Abstract: A series of experiments was conducted to determine the capacity of an archaeal strain, Methanocaldococcus jannaschii, to bind metals and to study the effects of metal binding on the subsequent silicification of the microorganisms. The results showed that M. jannaschii can rapidly bind several metal cations (Fe³⁺, Ca²⁺, Pb²⁺, Zn²⁺, Cu²⁺). Considering the lack of silicification of this strain without metal binding, these experiments demonstrate that Fe(III) ion binding to the cell wall components was of fundamental importance for successful silicification and, especially, for the excellent preservation of the cell wall. This study brings new elements to the understanding of fossilization processes, showing that the positive effect of Fe(III) on silicification, already known for Bacteria, can also apply to Archaea and that this preliminary binding can be decisive for the subsequent fossilization of these organisms. Knowledge of these mechanisms can be helpful for the search and the identification of microfossils in both terrestrial and extraterrestrials rocks, and in particular on Mars.