Availability, uptake and turnover of glycerol in hypersaline environments

Abstract A sensitive assay for glycerol and other polyols was developed, based on periodate oxidation to formaldehyde, followed by a colorimetric assay with 3-methyl-2-benzothiazolone hydrazone. Apparent glycerol concentrations thus measured in saltern crystallizer ponds were around 20–36 μM, while in the Dead Sea, during a Dunaliella bloom, values were up to 27 μM. However, these values probably overestimate the glycerol concentrations present, as shown by labeled glycerol uptake experiments. Values of [K + S_n] (natural concentration + affinity constant) in saltern ponds were as low as 0.76–1.4 μM, with V_max values of 193–303 nmol 1⁻¹h⁻¹, and turnover times between 2.6–7.2 h at 35°C. Similar measurements in the Dead Sea were: [K + S_n] 0.07–1.41 μM, V_max values 160–426 nmol 1⁻¹h⁻¹, and turnover times in the range of 0.45–3.3 h.     

Hyposensitive canopy conductance renders ecosystems vulnerable to meteorological droughts

Increased meteorological drought intensity with rising atmospheric demand for water (hereafter vapor pressure deficit [VPD]) increases the risk of tree mortality and ecosystem dysfunction worldwide. Ecosystem-scale water-use strategy is increasingly recognized as a key factor in regulating drought-related ecosystem responses. However, the link between water-use strategy and ecosystem vulnerability to meteorological droughts is poorly established. Using the global flux observations, historic hydroclimatic data, remote-sensing products, and plant functional-trait archive, we identified potentially vulnerable ecosystems, examining how ecosystem water-use strategy, quantified by the percentage bias (δ) of the empirical canopy conductance sensitivity to VPD relative to the theoretical value, mediated ecosystem responses to droughts. We found that prevailing soil water availability substantially impacted δ in dryland regions where ecosystems with insufficient soil moisture usually showed conservative water-use strategy, while ecosystems in humid regions exhibited more pronounced climatic adaptability. Hyposensitive and hypersensitive ecosystems, classified based on δ falling below or above the theoretical sensitivity, respectively, achieved similar net ecosystem productivity during droughts, employing different structural and functional strategies. However, hyposensitive ecosystems, risking their hydraulic system with a permissive water-use strategy, were unable to recover from droughts as quickly as hypersensitive ones. Our findings highlight that processed-based models predicting current functions and future performance of vegetation should account for the greater vulnerability of hyposensitive ecosystems to intensifying atmospheric and soil droughts.     

Crystal structure of the collagen alpha1(VIII) NC1 trimer.

Collagen VIII is a major component of Descemet's membrane and is also found in vascular subendothelial matrices. The C-terminal non-collagenous domain (NC1) domain of collagen VIII, which is a member of the C1q-like protein family, forms a stable trimer and is thought to direct the assembly of the collagen triple helix, as well as polygonal supramolecular structures. We have solved the crystal structure of the mouse alpha1(VIII)(3) NC1 domain trimer at 1.9 A resolution. Each subunit of the intimate NC1 trimer consists of a ten-stranded beta-sandwich. The surface of the collagen VIII NC1 trimer presents three strips of partially exposed aromatic residues shown to interact with the non-ionic detergent CHAPS, which are likely to be involved in supramolecular assemblies. Equivalent strips exist in the NC1 domain of the closely related collagen X, suggesting a conserved assembly mechanism. Surprisingly, the collagen VIII NC1 trimer lacks the buried calcium cluster of the collagen X NC1 trimer. The mouse alpha1(VIII) and alpha2(VIII) NC1 domains are 71.5% identical in sequence, with the differences being concentrated on the NC1 trimer surface. A few non-conservative substitutions map to the subunit interfaces near the surface, but it is not obvious from the structure to what extent they determine the preferred assembly of collagen VIII alpha1 and alpha2 chains into homotrimers.     

Isolation of Mutations in the Drosophila Homologues of the Human Neurofibromatosis 2 and Yeast Cdc42 Genes Using a Simple and Efficient Reverse-Genetic Method

Reverse genetic analysis in Drosophila has been greatly aided by a growing collection of lethal P transposable element insertions that provide molecular tags for the identification of essential genetic loci. However, because the screens performed to date primarily have generated autosomal P-element insertions, this collection has not been as useful for performing reverse genetic analysis of X-linked genes. We have designed a reverse genetic screen that takes advantage of the hemizygosity of the X chromosome in males together with a cosmid-based transgene that serves as an autosomally linked duplication of a small region of the X chromosome. The efficacy and efficiency of this method is demonstrated by the isolation of mutations in Drosophila homologues of two well-studied genes, the human Neurofibromatosis 2 tumor suppressor and the yeast CDC42 gene. The method we describe should be of general utility for the isolation of mutations in other X-linked genes, and should also provide an efficient method for the isolation of new alleles of existing X-linked or autosomal mutations in Drosophila.     

Analysis of the gene coding for the murine cellular tumour antigen p53

A genomic clone containing the functional gene for the murine p53 cellular tumour antigen was isolated and structurally characterised. The gene contains at least 11 exons and 10 introns, the first intron possessing a length of 6.1 kb. Attempts to determine the exact 5' end of p53 mRNA were inconclusive, probably due to the presence of a remarkable stem and loop structure (delta G degrees approximately equal to -56 kcal/mol) in the 5' region of the gene. Suggestive similarities were found to exist between p53 and the protein product of the myc oncogene.     

Comparison of chemical properties of purified plasma membranes and secretory vesicle membranes from the bovine adrenal medulla

Summary A highly enriched fraction of plasma membranes from the bovine adrenal medulla has been isolated by differential and sucrose gradient centrifugation. The membranes were found to occur as 0.1–0.5 diameter vesicles and to equilibrate at a density of 1.13–1.14 g/ml. This fraction was characterized by 4-fold elevated levels of adenylate cyclase and 20-fold elevated levels of 5-nucleotidase. Secretory vesicle membranes, isolated by repeated hypotonie and hypertonic shocks of whole vesicles, were found to equilibrate between d = 1.08 and d = 1.12 on a sucrose density step gradient. These membranes were highly enriched in cytochrome b₅₆₂ and dopamine--hydroxylase. Proteins in the two membranes were compared by SDS gel electrophoresis. All protein size classes found in the vesicle membrane fraction were also represented in the plasma membrane fraction, though in different proportions on the basis of staining intensity. The plasma membrane fraction contained prominent bands co-migrating with the - and -bands of tubulin, as well as a component co-migrating with actin. These bands were absent from the vesicle membranes. Fingerprint analysis of stained bands from the membrane fraction demonstrated that the components were indeed tubulin and actin. The plasma membranes contained twice as much sialic acid residues as did the chromaffin granule membranes, but had only half the cholesterol content on a weight basis. The cholesterolphospholipid ratio in the plasma membranes was 0.63, while in the secretory vesicle membranes it was 1.04. These results show that plasma membranes and secretory vesicle membranes are functionally and structurally different.Supported, in part, by a stipend to O.Z. from The Grant Foundation, New York     

Occurrence of facultative anoxygenic photosynthesis among filamentous and unicellular cyanobacteria.

Eleven of 21 cyanobacteria strains examined are capable of facultative anoxygenic photosynthesis, as shown by their ability to photoassimilate CO2 in the presence of Na2S, 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 703-nm light. These include different cyanobacterial types (filamentous and unicellular) of different growth histories (aerobic, anaerobic, and marine and freshwater). Oscillatoria limnetica, Aphanothece halophytica (7418), and Lyngbya (7104) have different optimal concentrations of Na2S permitting CO2 photoassimilation, above which the rate decreases: 3.5, 0.7, and 0.1 mM, respectively. In A. halophytica, for each CO2 molecule photoassimilated two sulfide molecules are oxidized to elemental sulfur, which is excreted from the cells.The ecological and evolutionary significance of anoxygenic photosynthesis in the cyanobacteria is discussed.     

Estimation of Sediment Denitrification Rates at In Situ Nitrate Concentrations

The denitrification rates in a marine sediment, estimated by using ¹⁵N-nitrate, V_max, K_m, and sediment nitrate concentrations, were 12.5 and 2.0 nmol of N₂-N cm⁻³ day⁻¹ at 0 to 1 and 1 to 3 cm, respectively, at 12°C. The total rate was 165 nmol of N₂-N m⁻² day⁻¹.     

ATP synthesis catalyzed by the ATPase complex from Rhodospirillum rubrum reconstituted into phospholipid vesicles together with bacteriorhodopsin

The coupling factor ATPase complex extracted by Triton X-100 from the photosynthetic bacterium Rhodospirillum rubrum could be incorporated into phospholipid vesicles after removal of the Triton. Vesicles reconstituted with this F₀ · F₁-type ATPase together with bacteriorhodopsin were found to catalyze, in the light, net ATP synthesis which was inhibited by the energy transfer inhibitors oligomycin and N,N-dicyclohexylcarbodiimide as well as by uncouplers. In vesicles reconstituted with the crude ATPase up to 50% of the observed rate of phosphorylation was independent on light and bacteriorhodopsin and insensitive to the above-listed inhibitors. This dark activity was, however, completely blocked by the adenylate kinase inhibitor, p¹,p⁵-di(adenosine-5′)pentaphosphate, which did not affect at all the net light-dependent phosphorylation nor the ATP-³²P_i exchange reaction. Vesicles reconstituted with the purified ATPase catalyzed only the light- and bacteriorhodopsin-dependent diadenosine pentaphosphate-insensitive phosphorylation. The rate of this photophosphorylation was found to be proportional to the amount of ATPase and bacteriorhodopsin, and linear for at least 20 min of illumination. These results indicate that the purified ATPase contains the complete assembly of subunits required to transduce electrochemical gradient energy into chemical energy.     

Bacteriorhodopsin in a bloom of halobacteria in the Dead Sea

A dense bloom of red halobacteria developed in the Dead Sea in the summer 1980, bacterial densities of up to 1.9 x10⁷ cells ml^-1 were observed. The population consisted of two types: pleomorphic, cup-shaped cells and rod-shaped cells. A high content of bacteriorhodopsin was found in the bloom (up to 0.4 nmol per mg protein). The rod-shaped Halobacterium was isolated and was shown to contain bacteriorhodopsin.Abbreviations 20 specific gravity at 20°C - Tris Tris-(hydroxymethyl)-aminomethane