Diurnal variations of amino acids and organic acids in xylem fluid from Lagerstroemia indica: an endogenous circadian rhythm

Diurnal variations in the concentrations of major organic compounds occurred in xylem fluid extracted from Lagerstroemia indica L. The concentration of amino acids and the N/C ratio was at a maximum and that of organic acids was at a minimum between 1230 and 2030 h. Since the concentrations of total organic nitrogen, total amino acids and most individual amino acids (but not organic acids or sugars) were also proportional to xylem tension two experiments were performed to discern whether variations in chemistry were a consequence of diurnal changes in moisture stress. In the first experiment, L. indica , exposed to variable levels of moisture stress during midday, manifested an increase in organic acids and a reduction in the N/C ratio. In the second experiment, chemical profiles of xylem fluid were collected and compared for plants exposed to a natural photoperiod, constant darkness or continuous light at noon and midnight. After 1 day amino acids increased in concentration during midday for all treatments; the variation was greatest (10-fold) for plants in constant darkness where xylem tension varied from 0.20 to 0.25 MPa. Only plants exposed to continuous light lost a diurnal rhythm after 3 days. Thus, the circadian rhythm was endogenous, terminated in continuous light and was not mediated by changes in moisture stress. Glutamine accounted for most of the diurnal variation in total amino acids, organic nitrogen and the N/C ratio in xylem fluid.     

Mobilization of different phosphate fractions in the rhizosphere

Availability of soil P fractions and mechanisms of acquisition by plants were studied. Plants mobilize soil P by desorption via depletion of P solution concentration around roots. In an oxisol, the process was enhanced by nitrate N nutrition of ryegrass, which increased soil pH, and by carboxylate release by white lupin. Ligand exchange and Fe/Al solubilization are assumed to be the mechanisms. Ammonium N nutrition of ryegrass decreased pH and allowed P mobilization in a luvisol but had no such effect in an oxisol, due to acid solubility of P in these soils. Organic P dissolved in soil solution contributed one third to the P uptake of field-grown barley on a luvisol. Laboratory experiments suggest that organic P is hydrolyzed by phosphatases at the root surface and replenished by micro-organisms.     

Estimating regional carbon stocks and spatially covarying edaphic factors using soil maps at three scales

Most estimates of regional and global soil carbon stocks are based on extrapolations of mean soil C contents for broad categories of soil or vegetation types. Uncertainties exist in both the estimates of mean soil C contents and the area over which each mean should be extrapolated. Geographic information systems now permit spatially referenced estimates of soil C at finer scales of resolution than were previously practical. We compared estimates of total soil C stocks of the state of Maine using three methods: (1) multiplying the area of the state by published means of soil C for temperate forests and for Spodosols; (2) calculating areas of inclusions of soil taxa in the 1:5,000,000 FAO/UNESCO Soils Map of the World and multiplying those areas by selected mean carbon contents; and (3) calculating soil C for each soil series and map unit in the 1:250,000 State Soil Geographic Data Base (STATSGO) and summing these estimates for the entire state. The STATSGO estimate of total soil C was between 23% and 49% higher than the common coarse scale extrapolations, primarily because STATSGO included data on Histosols, which cover less than 5% of the area of the state, but which constitute over one-third of the soil C. Spodosols cover about 65% of the state, but contribute less than 39% of the soil C. Estimates of total soil C in Maine based on the FAO map agreed within 8% of the STATSGO estimate for one possible matching of FAO soil taxa with data on soil C, but another plausible matching overestimated soil C stocks. We also compared estimates from the 1:250,000 STATSGO database and from the 1:20,000 Soil Survey Geographic Data Base (SSURGO) for a 7.5 minute quadrangle within the state. SSURGO indicated 13% less total soil C than did STATSGO, largely because the attribute data on depths of soil horizons in SSURGO are more specific for this locality. Despite localized differences, the STATSGO database offers promise of scaling up county soil survey data to regional scales because it includes attribute data and estimates of areal coverage of C-rich inclusions within map units. The spatially referenced data also permit examination of covariation of soil C stocks with soil properties thought to affect stabilization of soil C. Clay content was a poor predictor of soil C in Maine, but drainage class covaried significantly with soil C across the state.     

Alternative method for rapidly screening microbial isolates for their potential to degrade volatile contaminants

Summary A method is described for rapidly screening the metabolic potential of bacteria to oxidize semivolatile and volatile compounds as a sole carbon source. The method is based on automated system that utilizes Microplates^TM manufactured by Biolog, Inc. (Hayward, CA, USA). This system detects bacterial respiratory activity from the oxidation of a carbon source introduced in volatile form. This is in contrast to the original design, which is based on inoculating a carbon source directly into each well. The 96-well (MT) microtiter plates contain nutrients and a tetrazolium dye. When a bacterial species is capable of oxidizing a volatile carbon substrate, the dye turns purple, and a spectrophotometric plate reader quantifies the response. As a test of this method 150 isolates, including isolates known to degrade some of the test compounds and negative controls were evaluated for their potential to oxidize carbon tetrachloride, toluene, ando-xylene. Thirty-seven isolates (25%) were qualitatively identified as contaminant oxidizers, and thirteen of these (35%) showed significant degradation capabilities for both toluene ando-xylene.Environmental Sciences Division Publication Number 4277.     

Remote sensing of sea surface and coastal features in the area of the Golfe d'Arguin,Mauritania

The analysis of a series of NOAA AVHRR satellite data recorded between July and September 1986 shows the interaction between northerly and southerly water masses during summer as well as the northern limit of the northward advance of water masses originating from the South Equatorial Current. Two upwelling situations analysed by means of NOAA data show the intrusion of suspended matter from the ocean into the Golfe d'Arguin and illustrate the water circulation within the coastal zone. This circulation pattern is detailed by LANDSAT and SPOT data. A SPOT picture from October 1987 shows the structure of the intertidal and coastal geomorphology.     

Dramatic enhancement of enzymatic activity in organic solvents by lyoprotectants

When seven different hydrolytic enzymes (four proteases and three lipases) were lyophilized from aqueous solution containing a ligand, N-Ac-L-Phe-NH(2), their catalytic activity in anhydrous solvents was far greater (one to two orders of magnitude) than that of the enzymes lyophilized without the ligand. This ligand-induced activation was expressed regardless of whether the substrate employed in organic solvents structurally resembled the ligand. Furthermore, nonligand lyoprotectants [sorbitol, other sugars, and poly(ethylene glycol)] also dramaticaliy enhanced enzymatic activity in anhydrous solvents when present in enzyme aqueous solution prior to lyophilization. The effects of the ligand and of the lyoprotectants were nonadditive, suggesting the same mechanism of action. Excipient activated and nonactivated enzymes exhibited identical activities in water. Also, addition of the excipients directly to suspensions of nonactivated enzymes in organic solvents had no appreciable effect on catalytic activity. These observations indicate that the mechanism of the excipient-induced activation is based on the ability of the excipients to alleviate reversible denaturation of enzymes upon lyophilization. Activity enhancement induced by the excipients is displayed even after their removal by washing enzymes with anhydrous solvents. Subtilisin Carlsberg, lyophilized with sorbitol, was found to be a much more efficient practical catalyst than its "regular" counterpart. (c) 1993 John Wiley & Sons, Inc.     

Optimization of alkyl beta-D-galactopyranoside synthesis from lactose using commercially available beta-galactosidases

Commercially available lactase (beta-D-galactoside galactohydrolase, EC 3.2.1.23) enzymes produced from Kluyveromyces fragilis and Kluyveromyces lactis were accessed as catalysts for use in the production of beta-galactopyranosides of various alcohols using lactose as galactosyl donor. The yield of galactoside was enhanced by using the highest practical concentrations of both lactose and alcohol acceptor. The concentrations and thus yield, were limited by the solubility of the substrates. The increase in galactoside yield with increasing lactose concentration appeared to be specific to the lactose substrate and not due to water activity alterations, because addition of maltose to a fixed concentration of lactose had no effect. During the course of the reaction, the yield of galactoside peaked after around 70% to 80% of the lactose was consumed, due to hydrolysis of the product by the enzyme. A wide variety of compounds with primary or secondary hydroxyl groups could act as acceptors, the essential requirement being at least some water solubility. Addition of organic cosolvents had little effect on galactoside yield except when it increased the water solubility of sparingly soluble alcohols. Some galactosides were synthesized on a gram scale to determine practical product recoveries and improve purification methods for large-scale synthesis. Initial purification by hydrophobic chromatography (for galactosides of hydrophobic alcohols) or strong anion-exchange chromatography (for galactosides of hydrophilic alcohols) separated galactosides, galactobiosides, and higher oligomers from reducing sugars. A facile separation of the galactoside and galactobioside could then be effected by flash chromatography on silica gel. (c) 1993 John Wiley & Sons, Inc.     

Emulsion liquid membrane extraction of lactic acid from aqueous solutions and fermentation broth

Studies on the batch extraction of lactic acid using an emulsion liquid membrane system are reported. The membrane phase consists of the tertiary amine carrier Alamine 336 and the surfactant Span 80 dissolved in n-heptane/paraffin and aqueous solutions of sodium carbonate in the internal phase. The effects of internal phase reagent, extraction temperature, and initial external phase pH on the extraction efficiency and the emulsion swelling are examined. A statistical factorial experiment on extraction from clarified lactic acid fermentation broth was carried out to obtain knowledge of the performance of the extraction system from a broth. The extraction efficiency from the fermentation broth is found to be lower as compared to aqueous solutions of pure lactic acid. The effect of pH and the presence of other ionic species on selectivity are discussed. (c) 1993 John Wiley & Sons, Inc.     

Lipase catalyzed esterification of glycidol in organic solvents

We studied the resolution of racemic glycidol through esterification with butyric acid catalyzed by porcine pancreatic lipase in organic media. A screening of seven solvents (log P values between 0.49 and 3.0, P being the n-octanol-water partition coefficient of the solvent) showed that neither log P nor the logarithm of the molar solubility of water in the solvent provides good correlations between enantioselectivity and the properties of the organic media. Chloroform was one of the best solvents as regards the enantiomeric purity (e. p.) of the ester produced. In this solvent, the optimum temperature for the reaction was determined to be 35 degrees C. The enzyme exhibited maximum activity at a water content of 13 +/- 2% (w/w). The enantiomeric purity obtained was 83 +/- 2% of (S)-glycidyl butyrate and did not depend on the alcohol concentration or the enzyme water content for values of these parameters up to 200 mM and 25% (w/w), respectively. The reaction was found to follow a BiBi mechanism. (c) 1993 John Wiley & Sons, Inc.     

Enantioselective synthesis of ibuprofen esters in AOT/isooctane microemulsions by Candida cylindracea lipase

The enantioselective esterification of racemic ibuprofen, catalyzed by a Candida cylindracea lipase, was studied in a water-in-oil microemulsion (AOT/isooctane). By using n-propanol as the alcohol, an optimal W(0) ([H(2)O]/[AOT] ratio) of 12 was found for the synthesis of n-propyl-ibuprofenate at room temperature. The lipase showed high preference for the S(+)-enantiomer of ibuprofen, which was esterified to the corresponding S(+)-ibuprofen ester. The R(-)-ibuprofen remained unesterified in the microemulsion. The calculated enantioselectivity value (E) for S-ibuprofen ester was greater than 150 (conversion 0.32). The enzyme activities of n-alcohols with different chain lengths (3-12) were compared, and it appeared that short- (propanol and butanol) and long-chained (decanol and dodecanol) alcohols were better substrates than the intermediate ones (pentanol, hexanol, and octanol). However, unlike secondary and tertiary alcohols, all of the tested primary alcohols were substrates for the lipase. The reversible reaction (i.e., the hydrolysis of racemic ibuprofen ester in the microemulsion) was also carried out enantioselectively by the enzyme. Only the S form of the ester was hydrolyzed to the corresponding S-ibuprofen. The reaction yield was, however, only about 4% after 10 days of reaction. The corresponding yield for the esterification of ibuprofen was about 35% (10 days). The high enantioselectivity displayed by the lipase in the microemulsion system was seen neither in a similar esterification reaction in a pure organic solvent system (isooctane) nor in the hydrolysis reaction in an aqueous system (buffer). The E value for S-ibuprofen ester in the isooctane system was 3.0 (conversion 0.41), and only 1.3 for S-ibuprofen in the hydrolysis reaction (conversion 0.32). The differences in enantioselectivity for the lipase in various systems are likely due to interfacial phenomena. In the microemulsion system, the water in which the enzyme is dissolved is separated from the solvent by a layer of surfactant molecules, thus creating an interface with a relatively large area. Such interfaces are not present in the pure organic solvent systems (no surfactant) nor in aqueous systems. (c) 1993 John Wiley & Sons, Inc.