Combined effects of CO2 enrichment,diurnal light levels and water stress on foliar metabolites of potato plants grown in naturally sunlit controlled environment chambers

Experiments were conducted in outdoor, naturally sunlit, soil–plant–atmosphere research (SPAR) chambers using plants grown in pots. Drought treatments were imposed on potato plants (Solanum tuberosum cv. Kennebec) beginning 10 days after tuber initiation. A total of 23 out of 37 foliar metabolites were affected by drought when measured 11 days after initiating water stress treatments. Compounds that accumulated in response to drought were hexoses, polyols, branched chain amino acids (BCAAs) and aromatic amino acids, such as proline. Conversely, leaf starch, alanine, aspartate and several organic acids involved in respiratory metabolism decreased with drought. Depending upon harvest date, a maximum of 12 and 17 foliar metabolites also responded to either CO₂ enrichment or diurnal treatments, respectively. In addition, about 20% of the measured metabolites in potato leaflets were simultaneously affected by drought, CO₂ enrichment and diurnal factors combined. This group contained BCAAs, hexoses, leaf starch and malate. Polyols and proline accumulated in response to water stress but did not vary diurnally. Water stress also amplified diurnal variations of hexoses and starch in comparison to control samples. Consequently, specific drought responsive metabolites in potato leaflets were dramatically affected by daily changes of photosynthetic carbon metabolism.     

Potential sites of bioactive gibberellin production during reproductive growth in Arabidopsis

Gibberellin 3-oxidase (GA3ox) catalyzes the final step in the synthesis of bioactive gibberellins (GAs). We examined the expression patterns of all four GA3ox genes in Arabidopsis thaliana by promoter-beta-glucuronidase gene fusions and by quantitative RT-PCR and defined their physiological roles by characterizing single, double, and triple mutants. In developing flowers, GA3ox genes are only expressed in stamen filaments, anthers, and flower receptacles. Mutant plants that lack both GA3ox1 and GA3ox3 functions displayed stamen and petal defects, indicating that these two genes are important for GA production in the flower. Our data suggest that de novo synthesis of active GAs is necessary for stamen development in early flowers and that bioactive GAs made in the stamens and/or flower receptacles are transported to petals to promote their growth. In developing siliques, GA3ox1 is mainly expressed in the replums, funiculi, and the silique receptacles, whereas the other GA3ox genes are only expressed in developing seeds. Active GAs appear to be transported from the seed endosperm to the surrounding maternal tissues where they promote growth. The immediate upregulation of GA3ox1 and GA3ox4 after anthesis suggests that pollination and/or fertilization is a prerequisite for de novo GA biosynthesis in fruit, which in turn promotes initial elongation of the silique.     

A hydrogeomorphological context for ecological research on alpine glacial rivers

1. This paper presents a framework for the analysis of glacial stream ecosystems based upon the hierarchy of physical processes that operate over timescales varying from diel to millennial. Linked conceptual models propose interrelationships between climate, hydrology and fluvial geomorphology in alpine catchments.
2. These conceptual models are illustrated using data from the Taillon/Gabiétous catchment, French Pyrénées. Secondary sources provide information concerning the long-term sequence of climatic and geomorphological controls on contemporary catchment processes. Detailed hydrogeomorphological field data collected over three consecutive summer melt seasons (1995–97) permit identification of marked changes in shorter-term (diel, seasonal and inter-annual) physical processes.
3. Clear differences in the response of water quality and quantity variables were observed between years as climatic conditions varied. In two of the three study years, a precipitation-driven regime was imposed upon the typical ablation-driven river discharge pattern in alpine streams. Clear changes in water quality and quantity were evident with increasing distance from the glacier: (i) discharge increased although specific discharge decreased markedly, (ii) the mean and variability in water temperature increased, and (iii) base concentrations of suspended solids decreased.
4. The physical processes incorporated in the conceptual models presented in this paper have ecological implications because they underpin a nested suite of disturbance regimes operating over timescales from diel to millennial.     

Cleavage specificity of the subtilisin-like protease C1 from soybean

The cleavage specificity of protease C1, isolated from soybean (Glycine max (L.) Merrill) seedling cotyledons, was examined using oligopeptide substrates in an HPLC based assay. A series of peptides based on the sequence Ac-KVEKEESEEGE-NH2 was used, mimicking a natural cleavage site of protease C1 in the alpha subunit of the storage protein beta-conglycinin. A study of substrate peptides truncated from either the N- or C-terminus indicates that the minimal requirements for cleavage by protease C2 are three residues N-terminal to the cleaved bond, and two residues C-terminal (i.e. P3-P2'). The maximal rate of cleavage is reached with substrates containing four to five residues N-terminal to the cleaved bond and four residues C-terminal (i.e. P4 or P5 to P4'). The importance of Glu residues at the P1, P1', and P4 positions was examined using a series of substituted nonapeptides (P5-P4') with a base sequence of Ac-KVEKEESEE-NH2. At the P1 position, the relative ranking, based on kcat/Km, was E>Q>K>A>D>F>S. Substitutions at the P1' position yield the ranking E congruent withQ>A>S>D>K>F, while those at P4' had less effect on kcat/Km, yielding the ranking F congruent with S congruent with E congruent withD>K>A congruent withQ. These data show that protease C1 prefers to cleave at Glu-Glu and Glu-Gln bonds, and that the nature of the P4' position is less important. The fact that there is specificity in the cleavage of the oligopeptides suggests that the more limited specific cleavage of the alpha and alpha' subunits of beta-conglycinin by protease C1 is due to a combination of the sequence cleavage specificity of the protease and the accessibility of appropriate scissile peptide bonds on the surface of the substrate protein.     

Incorporation of N-fluoroacetyl-d-glucosamine into hyaluronate by rabbit tracheal explants in organ culture

1. Incubation of rabbit tracheal explants with N-[(3)H]acetyl-d-glucosamine and N-acetyl-d-[1-(14)C]glucosamine led to labelling of a number of soluble macromolecular products separable from the medium, after papain digestion, by ion-exchange chromatography. 2. With N-acetyl-d-[1-(14)C]glucosamine in the incubation medium, a neutral glycoprotein, two acidic glycoprotein fractions, hyaluronic acid and a glycosaminoglycan fraction were obtained and all were radioactively labelled. Similar labelling occurred with N-fluoroacetyl-d-[1-(14)C]glucosamine or N-fluoro[(3)H]acetylglucosamine as precursor. 3. Maximal labelling was obtained at 96h after incubation of cultures. N-Fluoroacetyl-glucosamine under these conditions was incorporated into hyaluronate less efficiently than N-acetylglucosamine. 4. With N-fluoroacetyl-d-[1-(14)C]glucosamine as precursor, a hyaluronate component was separated that on enzymic degradation by glycosidases (hyaluronidase, beta-glucuronidase and N-acetyl-beta-hexosaminidase) yielded a (14)C-labelled oligosaccharide fraction together with N-acetyl-d-[1-(14)C]glucosamine and N-fluoroacetyl-d-[1-(14)C]glucosamine, consistent with some exchange of N-acetyl groups having occurred. 5. The results on enzymic degradation of labelled macromolecules by glycosidases suggest that the presence of incorporated N-fluoroacetyl side chains may render the hyaluronate analogue more resistant to hyaluronidase.     

Myosin VI regulates endocytosis of the cystic fibrosis transmembrane conductance regulator

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cyclic AMP-regulated Cl(-) channel expressed in the apical plasma membrane in fluid-transporting epithelia. Although CFTR is rapidly endocytosed from the apical membrane of polarized epithelial cells and efficiently recycled back to the plasma membrane, little is known about the molecular mechanisms regulating CFTR endocytosis and endocytic recycling. Myosin VI, an actin-dependent, minus-end directed mechanoenzyme, has been implicated in clathrin-mediated endocytosis in epithelial cells. The goal of this study was to determine whether myosin VI regulates CFTR endocytosis. Endogenous, apical membrane CFTR in polarized human airway epithelial cells (Calu-3) formed a complex with myosin VI, the myosin VI adaptor protein Disabled 2 (Dab2), and clathrin. The tail domain of myosin VI, a dominant-negative recombinant fragment, displaced endogenous myosin VI from interacting with Dab2 and CFTR and increased the expression of CFTR in the plasma membrane by reducing CFTR endocytosis. However, the myosin VI tail fragment had no effect on the recycling of endocytosed CFTR or on fluid-phase endocytosis. CFTR endocytosis was decreased by cytochalasin D, an actin-filament depolymerizing agent. Taken together, these data indicate that myosin VI and Dab2 facilitate CFTR endocytosis by a mechanism that requires actin filaments.     

Molecular localization of a redox-modulated process regulating plant mitochondrial electron transport

Using in organellar assays, we found that significant tobacco alternative oxidase (AOX) activity is dependent on both reduction of a putative regulatory disulfide bond and the presence of pyruvate, which may interact with a Cys sulfhydryl. This redox modulation and pyruvate activation thus may be important in determining the partitioning of electrons to AOX in vivo. To investigate these regulatory mechanisms, we generated tobacco plants expressing mutated AOX proteins. Mutation of the most N-terminal Cys residue (Cys-126) to an Ala residue produced an AOX that could not be converted to the disulfide-linked form, thus identifying this Cys residue as being responsible for redox modulation. Although this mutation might be expected to produce an AOX with constitutive high activity in the presence of pyruvate, we found it to have minimal in organellar activity in the presence of pyruvate. Nonetheless, the Cys-126 mutation did not appear to have compromised the catalytic function of AOX, given that cells expressing the protein displayed high rates of cyanide-resistant respiration in vivo. The striking difference between in vivo and in organellar results suggests that an additional mechanism(s), as yet unidentified by in organellar assays, may promote activity in vivo. Mutation of the Cys residue nearest the presumptive active site (Cys-176) to an Ala residue did not prevent disulfide bond formation or affect the ability of AOX to be stimulated by pyruvate, indicating that this Cys residue is involved in neither redox modulation nor pyruvate activation.     

Reflooding the Faguibine floodplain system,northern Mali: potential benefits and challenges

The Faguibine system, northern Mali, consists of a series of interconnected floodplains of which the flooded surface area declined from about 1 000 km² in the late 19th century to only some 90 km² in 2010. Flood extent depends on the height of the Niger River flood peak at Diré. Satellite imagery analysis indicated that a phase shift may have occurred in the year 2000, probably as a delayed consequence of the Sahelian drought of the 1970s compounded by the collapse of societal controls on water use during recent civil conflict. An economic evaluation of the system in 2011 showed US$100 000 per year of net income per flooded km² in Lake Faguibine, allowing vulnerable people to practise recession agriculture, to fish and to graze livestock. An intensive investment phase, combined with an approach of rebuilding local governance systems and environmental management capacity, could yield net benefits to the user communities of the order of ten times the maintenance costs, contributing to human well-being. The system is currently threatened by the building of the Fomi Dam in Guinea and by the planned expansion of irrigation upstream. There is also a risk of the return of a prolonged drought linked to the Atlantic multi-decadal oscillation index.     

Expression,localization and possible functions of aquaporins 3 and 8 in rat digestive system

Although aquaporins (AQPs) play important roles in transcellular water movement, their precise quantification and localization remains controversial. We investigated expression levels and localizations of AQP3 and AQP8 and their possible functions in the rat digestive system using real-time polymerase chain reactions, western blot analysis and immunohistochemistry. We investigated the expression levels and localizations of AQP3 and AQP8 in esophagus, forestomach, glandular stomach, duodenum, jejunum, ileum, proximal and distal colon, and liver. AQP3 was expressed in the basolateral membranes of stratified epithelia (esophagus and forestomach) and simple columnar epithelia (glandular stomach, ileum, and proximal and distal colon). Expression was particularly abundant in the esophagus, and proximal and distal colon. AQP8 was found in the subapical compartment of columnar epithelial cells of the jejunum, ileum, proximal colon and liver; the most intense staining occurred in the jejunum. Our results suggest that AQP3 and AQP8 play significant roles in intestinal function and/or fluid homeostasis and may be an important subject for future investigation of disorders that involve disruption of intestinal fluid homeostasis, such as inflammatory bowel disease and irritable bowel syndrome.     

Monomethylarsonous Acid (MMAIII) Has an Adverse Effect on the Innate Immune Response of Human Bronchial Epithelial Cells to Pseudomonas aeruginosa

Arsenic is the number one contaminant of concern with regard to human health according to the World Health Organization. Epidemiological studies on Asian and South American populations have linked arsenic exposure with an increased incidence of lung disease, including pneumonia, and chronic obstructive pulmonary disease, both of which are associated with bacterial infection. However, little is known about the effects of low dose arsenic exposure, or the contributions of organic arsenic to the innate immune response to bacterial infection. This study examined the effects on Pseudomonas aeruginosa (P. aeruginosa) induced cytokine secretion by human bronchial epithelial cells (HBEC) by inorganic sodium arsenite (iAs^III) and two major metabolites, monomethylarsonous acid (MMA^III) and dimethylarsenic acid (DMA^V), at concentrations relevant to the U.S. population. Neither iAs^III nor DMA^V altered P. aeruginosa induced cytokine secretion. By contrast, MMA^III increased P. aeruginosa induced secretion of IL-8, IL-6 and CXCL2. A combination of iAs^III, MMA^III and DMA^V (10 pbb total) reduced IL-8 and CXCL1 secretion. These data demonstrate for the first time that exposure to MMA^III alone, and a combination of iAs^III, MMA^III and DMA^V at levels relevant to the U.S. may have negative effects on the innate immune response of human bronchial epithelial cells to P. aeruginosa.