Tropic Acid Research Articles

Analysis of scopolamine and its eighteen metabolites in rat urine by liquid chromatography-tandem mass spectrometry

A rapid and sensitive method is described for the determination of scopolamine and its metabolites in rat urine by combining liquid chromatography and tandem mass spectrometry (LC–MS/MS). Various extraction techniques (free fraction, acid hydrolyses and enzyme hydrolyses) and their comparison were carried out for investigation of the metabolism of scopolamine. After extraction procedure, the pretreated samples were injected into a reversed-phase C18 column with mobile phase of methanol/ ammonium acetate (2 mM, adjusted to pH 3.5 with formic acid) (70:30, v/v) and detected by an on-line MS/MS system. Identification and structural elucidation of the metabolites were performed by comparing their changes in molecular masses (Δ M), retention-times and full scan MS n spectra with those of the parent drug. The results revealed that at least 18 metabolites (norscopine, scopine, tropic acid, aponorscopolamine, aposcopolamine, norscopolamine, hydroxyscopolamine, hydroxyscopolamine N-oxide, p-hydroxy- m-methoxyscopolamine, trihydroxyscopolamine, dihydroxy-methoxyscopolamine, hydroxyl-dimethoxyscopolamine, glucuronide conjugates and sulfate conjugates of norscopolamine, hydroxyscopolamine and the parent drug) and the parent drug existed in urine after ingesting 55 mg/kg scopolamine to healthy rats. Hydroxyscopolamine, p-hydroxy- m-methoxyscopolamine and the parent drug were detected in rat urine for up 106 h after ingestion of scopolamine.

Acid Citrus Fruit Improvement via Interploid Hybridization Using Allotetraploid Somatic Hybrid and Autotetraploid Breeding Parents

Interploid hybridization was conducted using `Key' lime [Citrus aurantifolia (Cristm.) Swing.], `Lakeland' limequat hybrid [C. aurantifolia × Fortunella japonica (Thumb.) Swing.], Palestine sweet lime (C. limettioides Tan.), `Etrog' citron (C. medica L.), and seven lemon [C. limon (L.) Burm. F.] varieties as female progenitors and five allotetraploid somatic hybrids {`Hamlin' sweet orange [C. sinensis (L.) Osbeck] × `Femminello' lemon (C. limon)]; `Key' lime × `Valencia' sweet orange (C. sinensis); `Valencia' sweet orange × rough lemon (C. jambhiri Lush); Milam lemon (purported C. jambhiri hybrid) × `Femminello' lemon (C. limon); and `Valencia' sweet orange × `Femminello' lemon} and two autotetraploids [`Giant Key' lime (C. aurantifolia) and `Femminello' lemon] as pollen progenitors. A few tetraploid × diploid crosses were also performed. Thirty-five parental cross combinations were accomplished in 2000, 2001, and 2002. The breeding targets were seedlessness, cold-tolerance, and disease resistance. Triploid hybrids were recovered through embryo culture. Generation of triploid citrus hybrids was affected by several factors including sexual compatibility, cross direction, embryo developmental stage, pollen viability, as well as horticultural practices and climatic conditions. Efficiency of triploid hybrid production was higher in diploid × tetraploid crosses than the reciprocal. Many more triploid hybrids were generated from lemon seed progenitors compared to the other acid citrus fruit progenitors. `Todo el Año', `Lisbon', and `Limonero Fino 49' showed the highest sexual compatibility. Embryo germination rate and normal plant recovery were also higher in lemons as compared to the other seed progenitors. Low winter temperatures might have affected the hybrid production efficiency from tropical acid fruit progenitors. A total of 650 hybrids (mostly triploid) were transferred to soil. The novel genetic combinations of these progenies should be valuable for the genetic improvement of acid citrus fruit (lemons and limes).

Nutrient and assimilate partitioning in two tropical maize cultivars in relation to their tolerance to soil acidity

The use of Al-tolerant and P-efficient maize cultivars is an important component of a successful production system on tropical acid soils with limited lime and P inputs. Grain yield and secondary plant traits, including root and aboveground biomass, nutrient content and leaf development, were evaluated from 1996 to 2002 in field experiments on an Oxisol in order to identify maize characteristics useful in genetic improvement. Here we present the results of the 2002 trial and compare them with previous results. The aim of this experiment was to assess the effect of assimilate and nutrient partitioning on the growth and grain yield of two tropical cultivars having different Al tolerance (CMS36, tolerant, Spectral, moderately tolerant). The soil had an Al saturation of 36% in topsoil (pH 4.5) and >45% below 0.3 m depth (pH 4.2). Measurements made from emergence to grain filling included: root, stem and leaf biomass, P and N content, leaf area index (LAI), radiation use efficiency (RUE), soil available N and root profiles at anthesis. The experiments consisted of two P treatments, zero applied or 45 kg P ha −1 (−P and +P). All the treatments received N and K fertilizers. In −P, root biomass and LAI at anthesis were twice as great in CMS36 as in Spectral. In +P the differences between cultivars were negligible. Roots were deeper in CMS36 due to its higher Al tolerance. Total biomass and grain yield were not strongly related to root biomass and LAI. Other factors such as the leaf biomass and the amount of nutrients per unit leaf area were highly correlated with RUE and biomass. In −P, Spectral had the same total biomass but a higher grain yield than CMS36 (2.1 Mg ha −1 versus 1.5 Mg ha −1). This was due to a higher leaf P content (+40%), a greater RUE (+74%), and a lower number of sterile plants. In +P, CMS36 had higher total biomass and grain yield (4.1 Mg ha −1 versus 3.1 Mg ha −1). This was due to its higher leaf P (+25%) and leaf N (+43%) contents, and an increased RUE (+130%) that were associated with higher P and N uptake. Our results indicated that although root tolerance to Al toxicity is necessary for good crop performance on acid soils, assimilate and nutrient partitioning in the aboveground organs play a major role in plant adaptation and may partially compensate for a lower root tolerance.

Effects of glyphosate, chlorsulfuron, and methyl jasmonate on growth and alkaloid biosynthesis of jimsonweed ( Datura stramonium L.)

The troublesome agronomic weed, jimsonweed ( Datura stramonium L.), is also a major poisonous plant. The toxicity of jimsonweed is due to tropane alkaloids, which contain a methylated nitrogen atom ( N-CH 3) and include the anticholinergic drugs atropine, hyoscyamine, and scopolamine, as well as the narcotic cocaine. The enzyme and gene regulatory system of tropane alkaloid in plants is not clearly understood. The effects of the herbicides chlorsulfuron and glyphosate, and the growth regulator methyl jasmonate on the growth and alkaloid biosynthesis of jimsonweed were investigated. The growth responses of jimsonweed were characterized by determining the molar concentration of the herbicides required to inhibit plant root fresh weight by 50% ( I 50). Chlorsulfuron and glyphosate inhibited root growth of jimsonweed seedlings; the I 50 was 8 × 10 −9 and 10 −7 M, respectively. Methyl jasmonate increased root growth of jimsonweed seedlings at 10 −6 and 10 −7 M, but was inhibitory at 10 −5 M. Tropane alkaloids are produced by the condensation of tropine and tropic acid, a phenylalanine-derived intermediate. Phenylalanine levels in jimsonweed seedlings were reduced by glyphosate and chlorsulfuron. Methyl jasmonate at 10 −8 M or greater concentrations induced phenylalanine levels in jimsonweed seedlings. Arginine and ornithine levels in jimsonweed seedlings were increased two to three times by chlorsulfuron and glyphosate, but reduced by methyl jasmonate. Contents of tropinone, ϕ-tropine, and tropine in jimsonweed seedlings were reduced by chlorsulfuron and glyphosate, but increased by methyl jasmonate at 10 −7 and 10 −6 M. Putrescine N-methyltransferase (PMT) is the first committed enzyme, which drives the flow of nitrogen away from polyamine biosynthesis to tropane alkaloid biosynthesis. The expression of PMT mRNA transcripts was reduced in jimsonweed roots treated with 10 −6 M chlorsulfuron and glyphosate. PMT mRNA transcripts of jimsonweed roots were greatly induced following treatment with 10 −7 M methyl jasmonate. These results indicate that methyl jasmonate enhanced PMT activity due to an increase of PMT mRNA. The effects of glyphosate and chlorsulfuron on PMT mRNA’s transcriptional control and the accumulation of amino acid arginine/ornithine contents, coupled with their inhibitory effect on phenylalanine, tropinone, ϕ-tropine, and tropine levels, suggest that these herbicides might cause a decrease in overall tropane alkaloid biosynthesis in jimsonweed. However, the relationship between plant growth and metabolism affected by these compounds is not clear.

Enantioseparation of alkyl tropate by high performance liquid chromatography using (2 R, 3 R)-di- n-propyl tartrate

Optically active tartaric acid and its diester derivatives are well known as effective chiral selectors. In the current studies, a self-prepared diester of tartaric acid (2 R, 3 R)-di- n-propyl tartrate (DPT) was used as a chiral mobile-phase additive (CMPA) for the enantioseparation of seven kinds of alkyl tropate on a silica gel column by high performance liquid chromatography (HPLC). Four kinds of alkyl tropate were successfully enantioseparated using this chiral system, indicating that DPT is a novel useful chiral selector. The influences of mobile-phase composition and solute structure on enantioseparation were extensively studied. Although different types of alcoholic additive or various concentrations of alcoholic additive, DPT and dichloromethane in the mobile phase had great influence on the retention factor ( k′) and resolution ( R s), the mobile-phase composition essentially had no effect on the separation factor ( α). In contrast, the structure of alkyl tropate greatly influenced the separation factor ( α). The results revealed that an increase in the bulkiness of the O-alkyl groups of tropic acid esters reduced the separation factors ( α), indicating that inhibition of the formation of effective hydrogen-bond interaction between DPT and solutes by the bulkiness of the O-alkyl group decreases the retentivity difference between the transient diasterieomeric complex pairs. Our observations suggested that the hydrogen-bond interactions between chiral additives and solutes might be the major chiral recognition mechanism for DPT as CMPA.

Comparative Enantioseparation of 2‐Arylpropionic Acid Esters on Cellulose Derivative and (S,S)‐Whelk‐O 1 Columns

Cellulose‐derivative chiral stationary phases (CSPs) have been proven to be the most useful CSPs because of their versatility and capability. However, the exact chiral recognition mechanism on these CSPs is still unclear due to the complexity of these CSPs. In the present study, we attempt to compare the difference of the chiral recognition mechanism between cellulose‐derivative CSPs and (S,S)‐Whelk‐O 1 using ketoprofen esters, tropic acid esters, and racemic naproxen esters. The results revealed that alkoxy groups have great influence on the chiral recognition of 2‐arylpropionic acid esters on cellulose‐derivative CSPs or (S,S)‐Whelk‐O 1. From methyl ester to sec‐butyl ester, the chiral selectivity (α) is systematically changed on (S,S)‐Whelk‐O 1, whereas it does not follow any particular trend on cellulose‐derivative CSPs, suggesting that the attractive interactions between CSP and solute were the predominant factor for the chiral recognition on (S,S)‐Whelk‐O 1, although the inclusion and steric fitness of solutes into the chiral cavities might be the dominant chiral recognition mechanism for cellulose‐derivative CSPs. With several exceptions, there exists some kind of correlation between the ester kind and a different kind of cellulose‐derivative CSP. The influence of mobile phase modifier on the enantioseparation of 2‐arylpropionic acid esters on the cellulose‐derivative chiral columns was also extensively studied. Four types of influence resulting from using different alcoholic modifier in mobile phase were observed. The influence of alcoholic modifier on the enantioseparation was mainly through the alteration of steric environment of chiral cavities and this influence is solute dependent. Furthermore, the results suggested that the hydrogen‐bonding interaction between solute and CSP might not be important for the chiral recognition of ketoprofen esters, tropic acid esters, or racemic naproxen esters on cellulose tris(3,5‐dimethylphenylcarbamate) (CDMPC).

Manganese Solubility and Phytotoxicity Affected by Soil Moisture, Oxygen Levels, and Green Manure Additions

Manganese (Mn) toxicity is common in tropical acid soils, second only to aluminum toxicity. Changes in soil pH and redox potential (Eh) caused by soil moisture conditions and organic amendments certainly affect Mn solubility and toxicity to plants grown in soils with high Mn reserves. Laboratory incubation and greenhouse experiments were conducted to quantify such effects using a high-Mn Oxisol and a moderate-Mn Mollisol from Hawaii, with soybean (Glycine max L. cv. Kahala) being a test crop. The soils were mixed with a green manure (leucaena leaf) at 0, 10, and 20 g kg−1, and were incubated at 24 ± 1°C at 80% of field water holding capacity—equilibrated with air (FC), or N2 gas (N2)—or submerged under 8 cm of water. Soil pH, Eh, and soluble Mn as measured in saturated paste extract, Mehlich-3 and hydroxylamine hydrochloride (NH2OH) solutions were periodically determined over 56 days of incubation. The submergence and N2 treatments increased soil pH towards 7.0 and decreased soil Eh from 600 mV to between 300 and 400 mV, indicating a more reducing environment, which seemed to be controlled by the MnO2-Mn2+ and/or FeOOH-Fe2+ redox couples. Green manure additions had similar effects, but to a lesser extent. Consequently, soluble soil Mn concentrations increased by 100–1000 fold relative to those of the controls (no manure, at FC). There was a marked decrease in soybean growth and a marked increase in leaf Mn concentration in the treatments of submergence and green manure additions. A 10% reduction in dry matter yield was expected when leaf Mn exceeded 200 mg kg−1, leaf Ca/Mn (weight-to-weight) <80, saturated paste Mn >0.50 mg L−1, Mehlich3 Mn >200 mg kg−1, and NH2OH Mn >1100 mg kg−1. The effects were most evident at 14–28 days after incubation.

Kinetic resolution of tropic acid ethyl ester and its derivatives by lipase PS

The first kinetic resolution of tropic acid ethyl ester (TAEE) with lipase PS and vinyl acetate as an acylating agent is reported. The resulting ( S)-(−)-3-acetoxy tropic acid ethyl ester and ( R)-(+)-tropic acid ethyl ester are produced in high yields and in excellent ee (87–94%). The method has been extended to resolve a variety of tropic acid ester derivatives. In addition, an improved method for the preparation of racemic mixtures of tropic acid ethyl ester and its derivatives from 3-hydroxy-2-phenylacrylic acid ethyl ester using NaBH 4 in methanol is reported. This procedure is better than the previous ones because it is cleaner, safer and can be worked up easily. An improved method of deacylating the chiral 3-acetoxy tropic acid ethyl ester without any loss of stereochemical integrity using HCl/CH 3OH is also reported.

Evaluation of diabetes-related short-chain organic acids in rat plasma by capillary electrophoresis

A capillary zone electrophoresis method was optimised to analyse low-molecular-mass organic acids for the purpose of monitoring diabetes in rat plasma. The method included acetoacetic, 2-hydroxybutyric, lactic and uric acids. A variation in the background electrolyte allowed us to measure pyruvic acid in the same sample. Conditions have been optimised for measuring a large number of plasma samples corresponding to control and diabetic rats. Samples were mixed with acetonitrile (1:1, v/v) to precipitate proteins, centrifuged, diluted and injected. Tropic acid was chosen as an adequate internal standard. Separation was developed with reversed voltage by using a column cartridge pre-treated with polyacrylamide. Two electrophoretic buffers were employed: 0.150 M H 3PO 4 made up pH 6.20 with NaOH and 0.3 mM CaCl 2 for acetoacetic, hydroxybutyric, lactic and uric acids, and 200 mM phosphate–10 mM acetate pH 4.0 for pyruvic acid, both with direct detection at 200 nm. The method was validated for linearity, accuracy and precision and the limits of quantification were calculated. The method was successfully applied to analyse these organic acids in control and diabetic animals. Acetoacetic and hydroxybutyric acids were clearly increased in diabetic rats, meanwhile no statistically significant difference has been found with the other acids.

Interactions of chlorine with tropical aquatic fulvic acids and formation of intermediates observed by fluorescence spectroscopy

The interactions of tropical aquatic fulvic acids (AFA) with chlorine and formation of trihalomethanes were characterized by fluorescence spectroscopy. The aquatic humic substances (AHS) were isolated from a dark-brown stream (located in a environmental protection area near Cubatão city in São Paulo State, Brazil) by means of the collector XAD 8 according the procedure recommended by the International Humic Substances Society. The photoluminescence measurements were made by using a Perkin Elmer spectrometer; AHS, aquatic humic acids (AHA) and AFA samples were assayed. The interactions of AFA and chlorine were characterized by using different reaction times (1, 24, 48, 72 and 168 h) and chlorine concentrations (2.5, 5.0, 10.0 and 20.0 mg L-1). The relative fluorescence intensity for AFA was significantly decreased with the increasing of chlorine concentration and reaction time. The reduction of fluorescence intensity in the region of longer wavelength was interpreted as an indicative of interaction between condensed aromatic groups of AFA and chlorine.

Utilisation by upland rice of plant residue- and fertiliser-phosphorus in two tropical acid soils

A dual isotopic technique was used to assess the effects of soil type, and residues of Gliricidia sepium, without and with added fertiliser-P on the utilisation of P. Upland rice (Oryza sativa) was grown for 70 days in two tropical acid soils of different P sorbing capacity and P status. Uniformly 32P-labelled soils were treated with inorganic fertiliser-P tagged with 33P, Gliricidia sepium residue applied at planting and 3 weeks earlier, and in a combination of fertiliser-P and Gliricidia applied at and 3 weeks before planting. There were significant responses of shoot and root weights, and total P uptake to Gliricidia- and/or fertiliser-P addition in the Ultisol (low P status) but not the Oxisol (high P status), suggesting that P in the latter soil was not yield limiting, despite the high standard P requirement. Similarly, incorporation of Gliricidia three weeks before planting further increased shoot weight only in the Ultisol. There were generally higher proportions, quantities and percent utilisations of the Gliricidia-P and fertiliser-P in the Ultisol than in the Oxisol. Gliricidia significantly increased the utilisation of fertiliser-P only in the Ultisol. However, early application of Gliricidia increased Gliricidia-P but not fertiliser-P utilisation in the Ultisol. Added fertiliser-P did not influence Gliricidia-P utilisation.

The dynamics of protons, aluminium, and calcium in the rhizosphere of maize cultivated in tropical acid soils: experimental study and modelling

The goals of this work were to understand the dynamics of H+, Al and Ca in the rhizosphere of maize cultivated in tropical acid soils, and to evaluate the contribution of the dissolution kinetics of the Al-hydroxides to Al dynamics. The study of the dissolution kinetics was based on a comparison between experimental and simulated data, using a model of the chemical processes in the rhizosphere. Two Oxisols, pH 5.1 and 4.6, and one Ultisol, pH 5.2, were studied. An Al-tolerant maize variety (Zea mays L.) was grown for 14 days on a 3-mm thick soil layer. The composition of the soil and the soil solution, together with the concentration of Al in the roots, were determined throughout the experiment. The results showed that root growth (i) decreased the soil solution pH, up to one pH unit, (ii) increased Al concentration in the soil solution, (iii) increased exchangeable Al, and (iv) decreased exchangeable Ca. Soil solution pH, exchangeable Al, and exchangeable Ca were closely linked. Exchangeable Al increased 1.5 – 3.0 times, due to the dissolution of easily mobilised Al components. In addition, Al accumulation in roots depended mainly on Al in the soil solution. Modelling the interactions between H+, Al, and Ca proved that the main factor determining Al in the soil solution was the kinetic reactivity of the easily mobilised Al components. These components, probably poorly crystallised Al-hydroxides, are key players in the functioning of the rhizosphere in tropical acid soils.

Adsorption and translocation of sulfur in some tropical acid soils

AbstractIn view of growing concern about sulfur (S) deficiency, we attempted to study the effect of soil characteristics on the adsorption and translocation of S in soils. Laboratory experiments were conducted with five surface soils collected from three regions in the state of Orissa (Eastern India). In an adsorption study, all the soils were equilibrated with graded doses of potassium sulfate (K2SO4). Freundlich adsorption isotherms provided good fit to S adsorption data. Free Fe2O3 and Al2O3 in the soils were primarily responsible for retaining added S in soils. Further, studies on the movement of sulfate‐S in 30‐cm plexiglass columns, where radio‐labeled S along with water (5 cm) was applied as gypsum and K2SO4, showed that K2SO4‐S migrated deeper than gypsum‐S. Sulfur moved deeper in case of initially water‐saturated soils than in initially air‐dry soils.

Determination of L-hyoscyamine in atropine and D-hyoscyamine in L-hyoscyamine by chiral capillary electrophoresis as an alternative to polarimetry.

A method for the separation of atropine enantiomers, D- and L-hyoscyamine by capillary electrophoresis (CE) has been developed and validated. The advantages of the CE method compared with polarimetry include smaller amounts of analytes and a lower limit of detection of the unwanted enantiomer. Moreover, the present method enables a baseline separation of the analytes and tropic acid, one of the typical impurities of atropine. The developed enantioseparation of atropine was performed using a commercially available sulfated beta-cyclodextrin and was validated for the determination of L-hyoscyamine in atropine as well as for the enantiomeric purity of L-hyoscyamine.

Application of the STICS crop model to predict nitrogen availability and nitrate transport in a tropical acid soil cropped with maize

Oxisols have a high likelihood of NO3 − leaching which may strongly reduce N availability for tropical crops. The aim of this work was to evaluate the N and the water submodels of the STICS crop model for its ability to estimate N availability in N-fertilised field maize crops on two oxisols in Guadeloupe (French West Indies) with and without Al toxicity: a non-limed plot (NLI, pHKCl 3.9, 2.1 cmol Al3+ kg−1), and a limed plot (LI, pHKCl 4.5, 0 cmol Al3+ kg−1). An uncropped plot (UC, pHKCl 4.5, 0 cmol Al3+ kg−1) was used in order to fit some model parameters for soil evaporation, nitrification and NO3 − transport. The model was modified in order to describe nitrification as a partially inhibited process in acid soils, and to take into account NO3 − retention in oxisols. Nitrification was described as the result of the multiplicative effects of soil acidity, temperature and soil water content. Soil moisture and NO3 − and NH4 + content up to 0.8 m soil depth, above-ground biomass and N uptake by crops, and their leaf area index (LAI), were measured from sowing to the beginning of grain filling. The model described correctly the changes in soil water content during the moist and the dry periods of the experiment, and there was some evidence that capillary rise occurred in the dry period. Nitrogen mineralization, nitrification in UC, NO3 − transport and plant uptake were satisfactorily simulated by the model. Because of the effect of Al toxicity on plant growth, LAI at flowering was three times higher in LI than in NLI. Some discrepancies between observed and simulated data were found for the distribution of NO3 − and NH4 + in the cropped plots. This was probably due to the change of the ionic N form absorbed by the crops as a function of soil acidity and available P in the soil. No leaching was observed below 0.8 m depth and this was associated with NO3 − retention in the soil. The results showed that partial inhibition of nitrification and NO3 − retention should be taken into account by crop models to obtain realistic estimates of N availability for plants in tropical acid soils.

The Role of Particulate Organic Matter in Phosphorus Cycling

In tropical cropping systems, a better understanding of P transformations and short-term P cycling during decomposition of incorporated residues is pertinent. The primary objectives of this study were (i) to assess P immobilization in decomposing residues of sorghum (Sorghum bicolor (L.) Moench.) and crotalaria (Crotalaria juncea L.), (ii) to establish the role of soil fungi in the process, and (iii) to determine the contribution of P immobilization in explaining differences in soil P availability from plant residues in two weathered soils (Ultisol and Alfisol). Phosphorus associated with particulate organic matter (POM-P) was measured at different residue decomposition stages. Irradiated and nonirradiated residues were utilized to evaluate the origin of fungal colonization of particulate organic matter (POM). Results indicate a significant release of P from the residues at early stages of decomposition. An average of 93 and 76% of the initial POM-P was released after 5 d of decomposition in the Ultisol and Alfisol, respectively; and no significant differences were found between the residue types. After this initial 5-d period, significantly higher values of POM-P were observed for sorghum (5.8 and 7.9 mg P kg−1) as compared with crotalaria (1.9 and 2.8 mg P kg−1) in the two soils, suggesting a higher P immobilization in decomposing sorghum residue. Phosphorus immobilization represented up to 30% of the P in the residues and it could account for observed differences in P availability in the amended soils. A correspondence between patterns of P accumulation and fungal colonization of POM suggested that soil fungi might be responsible for this P immobilization. Further research is required however, to identify the mechanisms regulating this fungal colonization and P immobilization of plant residues in tropical acid soils.

The Role of Particulate Organic Matter in Phosphorus Cycling

In tropical cropping systems, a better understanding of P transformations and short‐term P cycling during decomposition of incorporated residues is pertinent. The primary objectives of this study were (i) to assess P immobilization in decomposing residues of sorghum (Sorghum bicolor (L.) Moench.) and crotalaria (Crotalaria juncea L.), (ii) to establish the role of soil fungi in the process, and (iii) to determine the contribution of P immobilization in explaining differences in soil P availability from plant residues in two weathered soils (Ultisol and Alfisol). Phosphorus associated with particulate organic matter (POM‐P) was measured at different residue decomposition stages. Irradiated and nonirradiated residues were utilized to evaluate the origin of fungal colonization of particulate organic matter (POM). Results indicate a significant release of P from the residues at early stages of decomposition. An average of 93 and 76% of the initial POM‐P was released after 5 d of decomposition in the Ultisol and Alfisol, respectively; and no significant differences were found between the residue types. After this initial 5‐d period, significantly higher values of POM‐P were observed for sorghum (5.8 and 7.9 mg P kg−1) as compared with crotalaria (1.9 and 2.8 mg P kg−1) in the two soils, suggesting a higher P immobilization in decomposing sorghum residue. Phosphorus immobilization represented up to 30% of the P in the residues and it could account for observed differences in P availability in the amended soils. A correspondence between patterns of P accumulation and fungal colonization of POM suggested that soil fungi might be responsible for this P immobilization. Further research is required however, to identify the mechanisms regulating this fungal colonization and P immobilization of plant residues in tropical acid soils.

Analysis of tropane and related alkaloids.

The current methods for tropane alkaloid chromatographic separation and determination are summarised. The alkaloids included are: the medicinally applied tropic acid esters hyoscyamine and scopolamine and their derivatives, cocaine and derivatives, the metabolites and degradation products of these compounds occurring in plant material, calystegines as nortropane alkaloids, anatoxins as homonortropane alkaloids, pelletierines and pseudopelletierines as alkaloids with isomeric structures. Developments in GC, HPLC, CE and TLC are presented and the advantages of each method for plant analysis are discussed. A summary for each chromatographic method lists the instrumentation and parameters applied for tropane alkaloids.

Nitric acid concentrations near the tropical tropopause: Implications for the properties of tropical nitric acid trihydrate clouds

In situ measurements of NOy, NOx, and temperature confirm that nitric acid trihydrate (NAT) particles could form at the tropical tropopause. The HNO3 mixing ratio near the tropical tropopause is typically no larger than about 0.2–0.3 ppbv, and the corresponding equilibrium mass of nitric acid trihydrate (NAT) is no larger than 0.3 μg m−3. Considerably larger NAT condensed masses are required to explain the HALOE extinctions; however, localized regions of enhanced HNO3 produced by oxidation of lightning‐generated NO might exist. NAT layers would only be identified as clouds by SAGE II if the particle diameters are in the optimum range of about 0.6 to 2 μm and the condensed NAT mass is larger than about 0.2 μg m−3. The SAGE II extinction ratio measurements (0.5 μm/1.0 μm) cannot distinguish NAT clouds from mixtures of optically thin ice clouds and background aerosols.

Tropical nitric acid clouds

The presence of nitric acid clouds near the tropical tropopause was proposed over a decade ago, although little has been learned about them since. Particle extinction measurements at three wavelengths from the Halogen Occultation Experiment offer compelling evidence for the existence of nitric acid clouds near the tropical tropopause. Most of these clouds are consistent with nitric acid trihydrate, and a small fraction can be explained by liquid ternary H2SO4‐H2O‐HNO3 aerosols.