Global classification of natural terrestrial ecosystems

Summary A global classification system of natural terrestrial ecosystems (including systematic notation), based on the climate zones of Walter, is presented. The basic units of the system are the ecological units biome and biogeocoene. The zonobiomes, which are climate zones corresponding to the largest vegetation units, are subdivided into subzonobiomes and these into individual biomes. The biomes are thus natural, geographical units within the climate zones. They are in turn subdivided into individual biogeocoenes and their constituent synusiae. In addition, the coordinate concepts of pedobiome and orobiome are introduced. These are distinguished from the zonobiomes as follows:1. the pedobiomes by extreme edaphic conditions which cause azonal vegetation.2. the orobiomes, as mountain ranges, by their vertical climate zonation and the altitudinal belts of vegetation.These relationships are explained, and two subseries of pedo-and oro-subunits are established. Transitional zones (zono-ecotones) between individual zonobiomes are also distinguished. The classification system is summarized in a schematic, and a world map of zonobiomes and zono-ecotones is included. More details are presented in Walter (1976).

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Zusammenfassung Ein globales Gliederungssystem der natürlichen terrestrischen Ökosysteme (einschließlich systematischen Bezeichnungen) wird in Beziehung zu den Walter'schen Klimazonen gesetzt. Grundeinheiten des Systems sind die ökologischen Einheiten Biom und Biogeozön. Die Zonobiome werden unterteilt in Subzonobiome und diese in Biome. Die Zonobiome sind Klimazonen und entsprechen den größten Vegetationseinheiten. Die Biome sind natürliche, geographische Einheiten innerhalb der Klimazonen. Sie werden bis zu einzelnen Biogeozönen und ihren Synusien (Teilsytemen) unterteilt. Parallel dazu werden die Begriffe Pedobiom und Orobiom eingeführt. Diese heben sich aus den Zonobiomen heraus: die Pedobiomen durch extreme Böden, die eine azonale Vegetation bedingen, die Orobiome als Gebirge durch die vertikale Klimagliederung und die Höhenstufen der Vegetation. Diese Beziehungen werden erklärt, und zwei Nebenreihen der Pedo- bzw. Orobiom-Untereinheiten werden aufgestellt. Zwischen den einzelnen Zonobiomen werden Übergangszonen (Zonoökotone) unterschieden. Das Gliederungssytem wird bereits in einem Schema zusammengefaßt, und eine Weltkarte der Zonobiome und Zonoökotone wird beigefügt. Ausführlich werden alle diese Fragen bei WALTER (1976) behandelt.

     

Possible role in uptake of water vapour by ixodid tick salivary glands

The mouth is confirmed as the site of water vapor uptake in the lone star tick, Amblyomma americanum. It was shown that the level of chloride (³⁶Cl) increased in the mouthparts of desiccated ticks. The highest levels of ³⁶Cl were found in the mouthparts, salivary glands, and gut tissue during rehydration. It is suggested that ions are secreted by the salivary glands into the mouth where water is picked up hygroscopically by the secretion. It is further suggested that the water and ions are then swallowed and absorbed from the lumen of the gut.     

Mathematical analysis of multienzyme systems. II. Steady state and transient control.

The control theory of steady states, previously presented for linear enzymatic systems (Heinrich and Rapoport, 1974) is extended to nonlinear systems. On the basis of three theorems a new procedure for the calculation of the control strength and of the control matrix is developed. The theory is applied to the extended model of glycolysis of erythrocytes, which includes also ATP-consuming processes. Also in this model the glycolytic flux is mainly controlled by the hexokinase-phosphofructokinase-system. The control strengths of the pyruvate kinase and of the enzymes of the 2.3 P2G-bypass are negligibly small. The control strength of the ATPase is negative, i.e. an activation of this enzyme leads to a decrease of the flux. For transition states of multienzyme systems definitions are given for the mean time required for the transition of the metabolites and for the "transient control" of enzymes. Enzymes with a pronounced influence on the transition time are called time-limiting enzymes. Enzymes which excert strong control on the time-dependent processes may have little influence under steady state conditions and vice versa. The transition times of ATP have been calculated for transient states of glycolysis.     

Tetrahydromethanopterin methyltransferase, a component of the methane synthesizing complex of Methanobacterium thermoautotrophicum

A new enzyme, tetrahydromethanopterin methyltransferase, which catalyzes the transfer of methyl groups from methyl-tetrahydromethanopterin to 2-mercaptoethane-sulfonate, has been found in the methane synthesizing complex of Methanobacterium thermoautotrophicum. The enzyme is oxygen sensitive and has a well defined pH optimum at pH 6.7. There was no methyl group transfer when the enzyme was heated to 100 degrees for 5 min. The product of the forward reaction, methyl-CoM, was positively identified by TLC and high voltage paper electrophoresis. The demethylation of methyl-CoM, in the absence of methane synthesis, was dependent on the addition of H4MPT which suggests that the enzyme reaction is reversible.     

Physical mapping studies on the human X chromosome in the region Xq27-Xqter

We have characterized three terminal deletions of the long arm of the X chromosome. Southern analysis using Xq27/q28 probes suggests that two of the deletions have breakpoints near the fragile site at Xq27.3. Flow karyotype analysis provides an estimate of 12 X 10(6) bp for the size of the deleted region. We have not detected the deletion breakpoints by pulsed-field gel electrophoresis (PFGE) using the closet DNA probes, proximal to the fragile site. The physical distance between the breakpoints and the probes may therefore be several hundred kilobases. The use of the deletion patients has allowed a preliminary physical map of Xq27/28 to be constructed. Our data suggest that the closest probes to the fragile site on the proximal side are 4D-8 (DXS98), cX55.7 (DXS105), and cX33.2 (DXS152). PFGE studies provide evidence for the physical linkage of 4D-8, cX55.7, and cX33.2. We have also found evidence for the physical linkage of F8C, G6PD, and 767 (DXS115), distal to the fragile site.     

The efficiency of water use in water stressed plants is increased due to ABA induced stomatal closure

Gas exchange and abscisic acid content of Digitalis lanata EHRH. have been examined at different levels of plant water stress. Net photosynthesis, transpiration and conductance of attached leaves declined rapidly at first, then more slowly following the withholding of irrigation. The intercellular partial pressure of CO₂ decreased slightly. The concentration of 2-cis(S)ABA increased about eight-fold in the leaves of non-irrigated plants as compared with well-watered controls. A close linear correlation was found between the ABA content of the leaves and their conductance on a leaf area basis. In contrast, the plot of net assimilation versus ABA concentration was curvilinear, leading to an increased efficiency of water use during stress. After rewatering, photosynthesis reached control values earlier than transpiration, leaf conductance and ABA content. From these data it is concluded that transpiration through the stomata is directly controlled by the ABA content, whereas net photosynthesis is influenced additionally by other factors.Possible reasons for the responses of photosynthesis and water use efficiency to different stress and ABA levels are discussed.Abbreviations A net CO₂ assimilation - ABA abscisic acid - C_i intercellular CO₂ concentration - g stomatal conductance - T transpiration - WUE water use efficiency     

Purification and properties of urease from bovine rumen.

Urease (urea amidohydrolase, EC 3.5.1.5) was extracted from the mixed rumen bacterial fraction of bovine rumen contents and purified 60-fold by (NH4)2SO4 precipitation, calcium phosphate-gel adsorption and chromatography on hydroxyapatite. The purified enzyme had maximum activity at pH 8.0. The molecular weight was estimated to be 120000-130000. The Km for urea was 8.3 X 10(-4) M+/-1.7 X 10(-4) M. The maximum velocity was 3.2+/-0.25 mmol of urea hydrolysed/h per mg of protein. The enzyme was stabilized by 50 mM-dithiothreitol. The enzyme was not inhibited by high concentrations of EDTA or phosphate but was inhibited by Mn2+, Mg2+, Ba2+, Hg2+, Cu2+, Zn2+, Cd2+, Ni2+ and Co2+. p-Chloromercuribenzenesulfphonate and N-ethylmaleimide inhibited the enzyme almost completely at 0.1 mM. Hydroxyurea and acetohydroxamate reversibly inhibited the enzyme. Polyacrylamide-gel electrophoresis showed that the mixed rumen bacteria produce ureases which have identical molecular weights and electrophoretic mobility. No multiple forms of urease were detected.     

Recognition of 5-hydroxymethylcytosine by the Uhrf1 SRA domain

Recent discovery of 5-hydroxymethylcytosine (5hmC) in genomic DNA raises the question how this sixth base is recognized by cellular proteins. In contrast to the methyl-CpG binding domain (MBD) of MeCP2, we found that the SRA domain of Uhrf1, an essential factor in DNA maintenance methylation, binds 5hmC and 5-methylcytosine containing substrates with similar affinity. Based on the co-crystal structure, we performed molecular dynamics simulations of the SRA:DNA complex with the flipped cytosine base carrying either of these epigenetic modifications. Our data indicate that the SRA binding pocket can accommodate 5hmC and stabilizes the flipped base by hydrogen bond formation with the hydroxyl group.