Channel-mediated permeation of ammonia gas through the peribacteroid membrane of soybean nodules

Ammonia permeability of the peribacteroid membrane (PBM) from N(2)-fixing soybean nodules was measured (8x10(-5) m/s) using isolated PBM in a stopped-flow spectrofluorimeter. Ammonia (NH(3)) uptake into PBM vesicles was inhibited by up to 42% by HgCl(2) (EC(50)=2.9 microM, mercaptoethanol-reversible) and reduced by ATP pre-incubation. The activation energy of NH(3) uptake (52 kJ/mol) increased (118 kJ/mol) with HgCl(2). Water transport was also HgCl(2)-sensitive (EC(50)=52.6 microM), but increased by ATP pre-incubation. NH(3) and H(2)O may permeate via different pathways through Nodulin 26 or there is another protein on the PBM that is permeable to NH(3).     

The capsule polysaccharide structure and biogenesis for non-O1 Vibrio cholerae NRT36S: genes are embedded in the LPS region

Background  

In V. cholerae, the biogenesis of capsule polysaccharide is poorly understood. The elucidation of capsule structure and biogenesis is critical to understanding the evolution of surface polysaccharide and the internal relationship between the capsule and LPS in this species. V. cholerae serogroup O31 NRT36S, a human pathogen that produces a heat-stable enterotoxin (NAG-ST), is encapsulated. Here, we report the covalent structure and studies of the biogenesis of the capsule in V. cholerae NRT36S.     

The effect of different growing conditions on water relations parameters of leaf epidermal cells of Tradescantia virginiana L.

Summary Tradescantia virginiana L. plants were cultivated under contrasting conditions of temperature, humidity, light quality and intensity, and nutrient status in order to investigate the effect of growth conditions on the water relations parameters of the leaf epidermal cells. Turgor pressure (P), volumetric elastic modulus (), half-time of water potential equilibration (T _1/2), hydraulic conductivity (L _p ) were measured with the miniaturized pressure probe in single cells of the upper and lower epidermis of leaves. Turgor differed (range: 0.1 bar to 7.2 bar) between treatments with lowest values under warm and humid conditions and additional supply of fertilizer, and highest values under conditions of low air humidity and low nutrient supply. The volumetric elastic modulus changed by 2 orders of magnitude (range: 3.0 bar to 350 bar, 158 cells), but was only affected by the treatments, in as much as it was dependent on turgor. The turgor dependence of , measured on intact leaves of T. virginiana, was similar to that for cells of the isolated (peeled) lower epidermis, where as a function of turgor was linear over the whole range of turgors. This result has implications for the discussion of pressure/volume curves as measured by the pressure bomb where changes in bulk leaf are frequently discussed as adaptations to certain treatments. The measurements of the hydraulic conductivity indicate that this parameter varies between treatments (range of means: 2.4×10^-6 cm s^-1 bar^-1 to 13.4×10^-6 cm s^-1 bar^-1). There was a negative correlation for L _p in cells of intact leaves as a function of turgor which was altered by the growing conditions. However, a correlation with turgor could not be found for cells from isolated epidermis or cells from a uniform population of plants. The large variation in L _p from cell to cell observed in the present and in previous studies was accounted for in a study of 100 cells from a uniform population of plants by the propagation of measurement errors in calculating L _p . The results suggest that in T. virginiana cellular water relations are changed mainly by the turgor dependence of .     

Genomics and the renaissance of generalism

A meeting report of the sessions on human, eukaryotic and bacterial genome sequencing at the American Society for Microbiology and Institut Pasteur joint conference: Genomes 2000 International Conference on Microbial and Model Genomes, Paris, April 11-15, 2000     

A novel method based on combination of semi-in vitro and in vivo conditions in Agrobacterium rhizogenes-mediated hairy root transformation of Glycine species

Despite numerous advantages of the many tissue culture-independent hairy root transformation protocols, the process is often compromised in the initial in vitro culture stage where inability to maintain high humidity and the delivery of nourishing culture medium decrease cellular morphogenesis and organ formation efficiency. Ultimately, this influences the effective transfer of produced plantlets during transfer from in vitro to in vivo conditions, where low survival rates occur during the acclimation period. We have developed an intermediate protocol for Agrobacterium rhizogenes transformation in Glycine species by combining a two-step in vitro and in vivo process that greatly enhances the efficiency of hairy root formation and which simplifies the maintenance of the transformed roots. In this protocol, cotyledonary nodes of Glycine max and Glycine canescens seedlings were infected by A. rhizogenes K599 carrying a reporter gene construct constitutively expressing green fluorescent protein (GFP). Glass containers containing sand and nutrient solution were employed to provide a moist clean microenvironment for the generation of hairy roots from inoculated seedlings. Transgenic roots were then noninvasively identified from nontransgenic roots based on the detection of GFP. Main roots and nontransgenic roots were removed leaving transgenic hairy roots to support seedling development, all within 1 mo of beginning the experiment. Overall, this protocol increased the transformation efficiency by more than twofold over traditional methods. Approximately 88% and 100% of infected plants developed hairy roots from G. max and G. canescens, respectively. On average, each infected plant produced 10.9 transformed hairy roots in G. max and 13–20 in G. canescens. Introduction of this simple protocol is a significant advance that eliminates the long and genotype-dependent tissue culture procedure while taking advantage of its optimum in vitro qualities to enhance the micropropagation rate. This research will support the increasing use of transient transgenic hairy roots for the study of plant root biology and symbiotic interactions with Rhizobium spp.     

Calcium storage in plants and the implications for calcium biofortification

Calcium (Ca) is an essential nutrient for plants and animals, with key structural and signalling roles, and its deficiency in plants can result in poor biotic and abiotic stress tolerance, reduced crop quality and yield. Likewise, low Ca intake in humans has been linked to various diseases (e.g. rickets, osteoporosis, hypertension and colorectal cancer) which can threaten quality of life and have major economic costs. Biofortification of various food crops with Ca has been suggested as a good method to enhance human intake of Ca and is advocated as an economically and environmentally advantageous strategy. Efforts to enhance Ca content of crops via transgenic means have had promising results. Overall Ca content of transgenic plants has been increased but in some cases adverse affects on plant function have been observed. This suggests that a better understanding of how Ca ions (Ca²⁺) are stored and transported through plants is required to maximise the effectiveness of future approaches.     

Design and baseline characteristics of the ParkFit study,a randomized controlled trial evaluating the effectiveness of a multifaceted behavioral program to increase physical activity in Parkinson patients

Background  

Many patients with Parkinson's disease (PD) lead a sedentary lifestyle. Promotion of physical activities may beneficially affect the clinical presentation of PD, and perhaps even modify the course of PD. However, because of physical and cognitive impairments, patients with PD require specific support to increase their level of physical activity.     

Fairy, tadpole, and clam shrimps (Branchiopoda) in seasonally inundated clay pans in the western Mojave Desert and effect on primary producers

Background

Fairy shrimps (Anostraca), tadpole shrimps (Notostraca), clam shrimps (Spinicaudata), algae (primarily filamentous blue-green algae [cyanobacteria]), and suspended organic particulates are dominant food web components of the seasonally inundated pans and playas of the western Mojave Desert in California. We examined the extent to which these branchiopods controlled algal abundance and species composition in clay pans between Rosamond and Rogers Dry Lakes. We surveyed branchiopods during the wet season to estimate abundances and then conducted a laboratory microcosm experiment, in which dried sediment containing cysts and the overlying algal crust were inundated and cultured. Microcosm trials were run with and without shrimps; each type of trial was run for two lengths of time: 30 and 60 days. We estimated the effect of shrimps on algae by measuring chlorophyll content and the relative abundance of algal species.

Results

We found two species of fairy shrimps (Branchinecta mackini and B. gigas), one tadpole shrimp (Lepidurus lemmoni), and a clam shrimp (Cyzicus setosa) in our wet-season field survey. We collected Branchinecta lindahli in a pilot study, but not subsequently. The dominant taxa were C. setosa and B. mackini, but abundances and species composition varied greatly among playas. The same species found in field surveys also occurred in the microcosm experiment. There were no significant differences as a function of experimental treatments for either chlorophyll content or algal species composition (Microcoleus vaginatus dominated all treatments).

Conclusions

The results suggest that there was no direct effect of shrimps on algae. Although the pans harbored an apparently high abundance of branchiopods, these animals had little role in regulating primary producers in this environment.