Effects of ultraviolet-B radiation on common bean (Phaseolus vulgaris L.) plants grown under nitrogen deficiency

This work reports on the significance of UV-B absorbing compounds and DNA photorepair in protecting bean plants from UV-B radiation under nitrogen restriction. Bean plants grown in sterile vermiculite and irrigated periodically with a nutrient solution containing 12 or 1 mM of nitrate were irradiated with 22 μW cm⁻² of UV-B, 4 h daily during 10 days after the first trifoliate leaf was developed. This intensity was equivalent to 3.2 kJ m⁻² per day, approximately. PAR fluence rate was 350 ± 50 μmol quanta m⁻² s⁻¹. Control plants did not receive UV-B irradiation. Leaf expansion was negatively affected by both nitrate restriction and UV-B irradiation. This decrease was paralleled by a significant increase in starch, which was exacerbated by the combined action of both factors. Combined action of low nitrogen and UV-B also negatively affected the CO₂ assimilation rate and the stomatal conductance. Formation of UV-B absorbing compounds was significantly increased by both UV-B irradiation and nitrogen restriction and this increase was exacerbated by the combination of both factors. No significant increase in dimer formation was detected in irradiated plants at the UV-B dose used. Significant dimer formation was only obtained by using very high UV-B intensities. This suggests that under an irradiation level of 22 μW cm⁻² of UV-B, which is close to natural conditions, protective mechanisms such as pigment screening and DNA photorepair were probably sufficient to prevent any dimer formation in leaves.     

Structure and thermal decomposition of methylamine borane

The crystal structure of methylamine borane has been determined and contains parallel chains of dihydrogen-bonded CH₃NH₂BH₃ molecules. Thermal decomposition takes place from the melt (ΔH_fusion = 8.5 kJ mol⁻¹) and begins with the formation of an ionic borohydride. Hydrogen is liberated in two stages, at ca. 100 and 190 °C, with the observed rates during the first stage (ΔH = −25 kJ mol⁻¹, E_a = 115 kJ mol⁻¹) strongly dependent on temperature and time. cis- and trans-N-trimethylcyclotriborazane are formed during the first stage and subsequently cross-link to yield a non-volatile solid. Before this cross-linking, the system exhibited a high degree of volatility, with weight losses in excess of 80% observed in TG experiments using flowing gas.     

Anaerobic digestion of solid slaughterhouse waste (SHW) at laboratory scale: Influence of co-digestion with the organic fraction of municipal solid waste (OFMSW)

Mesophilic anaerobic digestion of slaughterhouse waste (SHW) and its co-digestion with the organic fraction of municipal solid waste (OFMSW) have been evaluated. These processes were carried out in a laboratory plant semi-continuously operated and two set-ups were run. The first set-up, with a hydraulic retention time (HRT) of 25 days and organic loading rate (OLR) of 1.70 kg VS m⁻³ day⁻¹ for digestion, and 3.70 kg VS m⁻³ day⁻¹ for co-digestion, was not successful. The second set-up was initiated with an HRT of 50 days and an OLR of 0.9 kg VS m⁻³ day⁻¹ for digestion and 1.85 kg VS m⁻³ day⁻¹ for co-digestion. Under these conditions, once the sludge had been acclimated to a medium with a high fat and ammonia content, it was possible to decrease the HRT while progressively increasing the OLR to the values used in the first set-up until an HRT of 25 days and OLRs of 1.70 and 3.70 kg VS m⁻³ day⁻¹, for digestion and co-digestion, respectively (the same conditions of the digesters failures previously). These digesters showed a highly stable performance, volatile fatty acids (VFAs) were not detected and long chain fatty acids (LCFAs) were undetected or only trace levels were measured in the analyzed effluent. Fat removal reached values of up to 83%. Anaerobic digestion was thus found to be a suitable technology for efficiently treating lipid and protein waste.     

Annual biomass and production of epiphytes in three monospecific seagrass communities of Thalassia hemprichii (Ehrenb.) Aschers

The biomass of epiphytes and seagrasses has been measured in relation to leaf age in three monospecific seagrass stands of Thalassia hemprichii (Ehrenb.) Aschers. in Papua New Guinea. From June 1981 through August 1982, biomass values for epiphytes at the three sites ranged from 5 to 70 g ADW m⁻² sediment surface at site 1, from 5 to 14 g ADW m⁻² at site 2, and from 3.5 to 7.0 g ADW m⁻² at the site 3. Annual mean epiphyte biomass values for the different sites were 1.3 g ADW m⁻² leaf surface at site 1, 1.7 g ADW m⁻² leaf surface at site 2, and 1.5 g ADW m⁻² leaf surface at site 3.

The annual mean standing crop of T. hemprichii leaves was highest at site 1 (103 g ADW m⁻². Values for site 2 and site 3 were 60 g ADW m⁻² and 41 g ADW m⁻², respectively.

Production of epiphytes was calculated in three different ways: firstly, by using biomass values for each specific leaf-age group, with corrections for colonization; secondly, by fitting the biomass values with a specific growth curve; and thirdly, by estimated the rate of biomass accumulation. On an area basis, production of epiphytes on leaves of T. hemprichii ranged from 0.55 to 3.97 g ADW m⁻² day⁻¹ at site 1, from 0.17 to 0.73 g ADW m⁻² day⁻¹ at site 2, and from 0.24 to 0.68 g ADW m⁻² day⁻¹ at site 3.     

Morphological and physiological responses of canola (Brassica napus) siliquas and seeds to UVB and CO2 under controlled environment conditions

Combined effects of UVB radiation and CO₂ concentration on plant reproductive parts have received little attention. We studied morphological and physiological responses of siliquas and seeds of canola (Brassica napus L. cv. 46A65) to UVB and CO₂ under four controlled experimental conditions: UVB radiation (4.2 kJ m⁻² d⁻¹) with ambient level of CO₂ (370 μmol mol⁻¹) (control); UVB radiation (4.2 kJ m⁻² d⁻¹) with elevated level of CO₂ (740 μmol mol⁻¹); no UVB radiation (0 kJ m⁻² d⁻¹) with ambient level of CO₂ (370 μmol mol⁻¹); and no UVB radiation (0 kJ m⁻² d⁻¹) with elevated level of CO₂ (740 μmol mol⁻¹). UVB radiation affected the outer appearance of siliquas, such as colour, as well as their anatomical structures. At both CO₂ levels, the UVB radiation of 4.2 kJ m⁻² d⁻¹ reduced the size of seeds, which had different surface patterns than those from no UVB radiation. At both CO₂ levels, 4.2 kJ m⁻² d⁻¹ of UVB decreased net CO₂ assimilation (A_N) and water use efficiency (WUE), but had no effect on transpiration (E). Elevated CO₂ increased A_N and WUE, but decreased E, under both UVB conditions. At both CO₂ levels, the UVB radiation of 4.2 kJ m⁻² d⁻¹ decreased chlorophyll fluorescence, total chlorophyll (Chl), Chl a and Chl b, but had no effect on the ratio of Chl a/b and the concentration of UV-screening pigments. Elevated CO₂ increased total Chl and the concentration of UV-screening pigments under 4.2 kJ m⁻² d⁻¹ of UVB radiation. Neither UVB nor CO₂ affected wax content of siliqua surface. Many significant relationships were found between the above-mentioned parameters. This study revealed that UVB radiation exerts an adverse effect on canola siliquas and seeds, and some of the detrimental effects of UVB on these reproductive parts can partially be mitigated by CO₂.     

The response of an emergent sedge Bolboschoenus medianus to salinity and nutrients

The potential for nutrient load (30, 100 and 350 g N m⁻² per year) to alter plant performance under saline conditions (control, 4.5, 9 and 13 dS m⁻¹) was examined in the sedge Bolboschoenus medianus. Relative growth rates (RGR) across nutrient loadings ranged from 30.2 to 41.8 mg g⁻¹ per day in controls and were reduced to 20.9–28.5 mg g⁻¹ per day by salinities of 13 dS m⁻¹. Whilst higher nutrient loads generally increased RGR, the response was smaller at higher salinities. Responses to salinity and nutrient load were specific. Nutrient load increased the RGR via increases in the leaf area ratio (LAR). The LAR ranged from 1.9 to 2.1 m² kg⁻¹ across salinity treatments at 30 g N m⁻² per year, and increased to 2.5–2.8 m² kg⁻¹ at 350 g N m⁻² per year. Salinity reduced the RGR via a reduction in the net assimilation rate (NAR). The NAR in control plants ranged from 14.7 to 16 g m⁻² per day across nutrient loadings and decreased to 11–12 g m⁻² per day at 13 dS m⁻¹. Carbon isotope discrimination of leaves decreased by 2–3‰ in response to 13 dS m⁻¹ at the lower nutrient loadings. A prominent response of B. medianus to salinity was a change in biomass allocation from culms to tubers. In contrast, the response to nutrient load was characterised by a shift in biomass allocation from roots to leaves.     

Study of the interaction of artemisinin with bovine serum albumin

The study on the interaction of artemisinin with bovine serum albumin (BSA) has been undertaken at three temperatures, 289, 296 and 303 K and investigated the effect of common ions and UV C (253.7 nm) irradiation on the binding of artemisinin with BSA. The binding mode, the binding constant and the protein structure changes in the presence of artemisinin in aqueous solution at pH 7.40 have been evaluated using fluorescence, UV–vis and Fourier transform infrared (FT-IR) spectroscopy. The quenching constant K_q, K_sv and the association constant K were calculated according to Stern–Volmer equation based on the quenching of the fluorescence of BSA. The thermodynamic parameters, the enthalpy (ΔH) and the entropy change (ΔS) were estimated to be −3.625 kJ mol⁻¹ and 107.419 J mol⁻¹ K⁻¹ using the van’t Hoff equation. The displacement experiment shows that artemisinin can bind to the subdomain IIA. The distance between the tryptophan residues in BSA and artemisinin bound to site I was estimated to be 2.22 nm using Föster's equation on the basis of fluorescence energy transfer. The decreased binding constant in the presence of enough common ions and UV C exposure, indicates that common ions and UV C irradiation have effect on artemisinin binding to BSA.     

Effects of Acacia nilotica, A. polyacantha and Leucaena leucocephala leaf meal supplementation on performance of Small East African goats fed native pasture hay basal forages

Optimal utilisation of tannin-rich browse tree fodders including Acacia spp. foliages as crude protein (CP) supplements to ruminants in the tropics is limited by less available information on their feed nutritive potential. Two studies were conducted to: (1) determine rate and extent of ruminal dry matter (DM) degradability (DMD) and (2) investigate effect of sun-dried Acacia nilotica (NLM), A. polyacantha (PLM) and Leucaena leucocephala leaf meal (LLM) supplementation on growth performance of 20 growing (7–9 months old) Small East African male goats (14.6 ± 0.68 kg) fed on native pasture hay (NPH) basal diet for 84 days in a completely randomised design experiment in north-western Tanzania. The goats were randomised into four treatment groups consisting of five animals each. Three supplement diets: 115.3 g NLM (T₂), 125.9 g PLM (T₃) and 124.1 g LLM (T₄), which was used as a positive control, were supplemented at 20% of the expected DM intake (DMI; i.e., 3% body weight) to the three animal groups fed on NPH (basal diet) compared to the animals in a control group that were fed on NPH without browse supplementation (T₁).

NPH had significantly the lowest (P < 0.05) CP of 45.5 g kg⁻¹ DM compared to NLM, PLM and LLM (159, 195 and 187 g kg⁻¹ DM, respectively). NPH had higher (P < 0.05) fibre fractions; lower ruminal DM degradability characteristics and ME than NLM, PLM and LLM. Supplementation of the animals with browse resulted to (P < 0.05) higher average daily weight gains (ADG) of 157.1 g day⁻¹ in T₄ than the animals fed on T₂ (114.3 g day⁻¹) and T₃ (42.9 g day⁻¹), and even to those fed on T₁ (control), which lost weight (−71.4 g day⁻¹). Improved weight gains were mainly due to corrected feed nitrogen (N) or CP due to supplementation of the animals with browse fodder. Too low CP of the NPH would not meet the normal requirements of CP (80 g CP kg⁻¹ DM) for optimal rumen microbial function in ruminants. Higher ADG due to LLM (T₄) and NLM (T₂) supplementation suggest optimised weight gains due to browse supplementation (20% of expected DMI); while lower weight gains from supplementation with PLM (T₃) indicate the possible utilisation of A. polyacantha leaves to overcome weight losses especially during dry seasons.     

Experimental and theoretical study of a truly functional biomimetic molybdenum oxotransferase analogue system

Density functional theory (DFT) computations at the B3LYP/Lanl2DZ level were used to elucidate the oxygen atom transfer (OAT) and coupled electron proton transfer (CEPT) reaction steps involved in the biomimetic catalytic cycle performed by polymer-supported Mo^VIO₂(NN′)₂ complexes [NN′ = phenyl-(pyrrolato-2-ylmethylene)-amine] with water as oxygen source, trimethyl-phosphane as oxygen acceptor and one-electron oxidising agents. The DFT method employed has been validated against experimental data [X-ray crystal structures of a NN′ ligand and a Mo^VIO₂(NN′)₂ complex as well as kinetic data]. The rate-limiting step in the forward-OAT from [Mo^VIO₂] to PMe₃ is the attack of PMe₃ at an oxo ligand with ΔG^≠ (298 K) = 64.6 kJ mol⁻¹. Dissociation of the product OPMe₃ is facile with ΔG^≠ (298 K) = 26.3 kJ mol⁻¹ giving a mono-oxo [Mo^IVO] complex which fills its coordination sphere with a further PMe₃ substrate with ΔG^≠ (298 K) = 39.2 kJ mol⁻¹. One-electron oxidation to a Mo(V) phosphane complex precedes the coordination of water/hydroxide. Additionally, the comproportionation of [Mo^VIO₂] and [Mo^IVO] to dinuclear oxo-bridged [OMo^V–O–Mo^VO] species has been calculated as the thermodynamic sink in this system and the back-OAT from dmso to mono-oxo [Mo^IVO] to give [Mo^VIO₂] has been shown to involve an equilibrium between stereoisomeric [Mo^VIO₂] complexes with an activation barrier of ΔG^≠ (298 K) = 113.1 kJ mol⁻¹.     

Role of mutation Y6F on the binding properties of Schistosoma japonicum glutathione S-transferase

The role of the hydroxyl group of tyrosine 6 in the binding of Schistosoma japonicum glutathione S-transferase has been investigated by isothermal titration calorimetry (ITC). A site-specific replacement of this residue with phenylalanine produces the Y6F mutant, which shows negative cooperativity for the binding of reduced glutathione (GSH). Calorimetric measurements indicated that the binding of GSH to Y6F dimer is enthalpically driven over the temperature range investigated. A concomitant net uptake of protons upon binding of GSH to Y6F mutant was detected carrying out calorimetric experiments in various buffer systems with different heats of ionization. The entropy change is favorable at temperatures below 26 °C for the first site, being entropically favorable at all temperatures studied for the second site. The enthalpy change of binding is strongly temperature-dependent, arising from a large negative ΔC°_p1=−3.45±0.62 kJ K⁻¹ mol⁻¹ for the first site, whereas a small ΔC°_p2=−0.33±0.05 kJ K⁻¹ mol⁻¹ for the second site was obtained. This large heat capacity change is indicative of conformational changes during the binding of substrate.     

Protein-based complex medium design for recombinant serine alkaline protease production

This work reports on the design of a complex medium based on simple and complex carbon sources, i.e. glucose, sucrose, molasses, and defatted-soybean, and simple and complex nitrogen sources, i.e. (NH₄)₂HPO₄, casein, and defatted-soybean, for serine alkaline protease (SAP) production by recombinant Bacillus subtilis carrying pHV1431::subC gene. SAP activity was obtained as 3050 U cm⁻³ with the initial defatted-soybean concentration C_soybean^o=20 kg m⁻³ and initial glucose concentration C_G^o=8 kg m⁻³; whereas, addition of the inorganic nitrogen source (NH₄)₂HPO₄ decreased SAP production considerably. Further increase in SAP production (3850 U cm⁻³) was obtained when sucrose was replaced with glucose at C_sucrose^o=15 kg m⁻³ and C_soybean^o=20 kg m⁻³. Nevertheless, when molasses was replaced with sucrose, the maximum activity was obtained with molasses having 10 kg m⁻³ initial sucrose concentration and C_soybean^o=15 kg m⁻³as 2130 U cm⁻³; moreover, when casein was replaced with defatted-soybean SAP production decreased considerably (ca. 250 U cm⁻³). Thereafter, the effects of inorganic ionic compounds were investigated; and except phosphate, inorganic compounds supplied from defatted-soybean were found to be sufficient for the bioprocess. The highest SAP activity was obtained as 5350 U cm⁻³ in the medium that contained (kg m⁻³): C_soybean^o=20, C_sucrose^o=15, C_Na2HPO4^o=0.021, and C_NaH2PO4^o=2.82, that was 6.5-fold higher than that of the SAP produced in the defined medium. By using the designed complex medium, oxygen transfer characteristics of the bioprocess were investigated; and, Damköhler number that is the oxygen transfer limitation increases with the cultivation time until t=14 h; and, at t>20 h both mass transfer and biochemical reaction resistances were effective. Overall oxygen transfer coefficient varied between 0.010 and 0.044 s⁻¹; volumetric oxygen uptake rate varied between 0.001 and 0.006 mol m⁻³ s⁻¹; and specific oxygen uptake rate varied between 0.0001 and 0.0022 mol kg⁻¹ DW s⁻¹ throughout the bioprocess.     

Production d'NH4 par la crevette Crangon crangon L. dans deux écosystémes côtiers. approche expérimentale et étude de l'influence du sédiment sur le taux d'excrétion

Estimation of the ammonia production of the shrimp C. crangon in two littoral ecosystems (oligotrophic sand and eutrophic mud) was determined in winter and summer conditions from laboratory observations in experimental microcosms. The ammonia excretion rate of C. crangon was not influenced by either the sediment type or the ammonia concentration of the overlying water; on the other hand, the mean excretion rate and the response to initial handling stress increased markedly as shrimp were deprived of soft substratum.

The daily ammonia production of C. crangon was 16 μmol NH₃ · g ⁻¹ wet wt · day ⁻¹ in winter and 40 μmol in summer. A gross production of 12 μmol NH₃ · m⁻² · day ⁻¹ and 300–700 μmol μ m⁻² · day⁻¹, respectively, could be expected in the two ecosystems studied. This would account for 5% (winter) and 2–4% (summer) of the total NH⁺₄ flux at the sediment-water interface. The contribution of the excretion of all macrofauna to the NH⁺₄ flux from the sediment is discussed.     

Effect of light-path length in outdoor flat plate reactors on output rate of cell mass and of EPA in Nannochloropsis sp.

The effect of light-path length (i.e. reactor width or thickness) of flat plate glass reactors on outdoor production of eicosapentaenoic acid (EPA) and cell mass of Nannochloropsis sp. was tested, using a range of light-paths from 1.3 to 17.0 cm. Volumetric productivity of cell mass and optimal, as well as maximal cell density which represents the highest sustainable cell density under the experimental conditions, decreased with increase in light-path. Daily areal output rate (g dry weight m⁻² day⁻¹) increased with increased light-path, in contrast with results obtained in similar reactors with Spirulina cultures, in which areal output rates increased when the light-path was reduced. Maximal areal productivity of Nannochloropsis sp. (12.8 and 22.4 g ash-free dry weight per day per m² of irradiated reactor surfaces, in winter and summer, respectively), reflecting maximal efficiency in light utilization, was obtained with the long light-paths, i.e. 10.4 and 17.0 cm. Increasing the light-path from 1.3 to 17.0 cm resulted in an increase in areal EPA productivity, from 66.7 to 278.2 mg m⁻² day⁻¹ in winter and from 232.1 to 515.7 mg m⁻² day⁻¹ in summer. This enhancement in areal productivity of EPA stems from increased productivity of cell mass which was associated with the increase in light-path. We concluded that the optimal light-path, which must be defined for each algal species, represents an important parameter which determines optimal culture density (i.e. resulting in the highest output rate of cell mass per irradiated reactor surface), as well as productivity of cell mass and cell products. Under our conditions the optimal light-path for culturing Nannochloropsis in vertical reactors was ca 10 cm.     

Determination of the maximum and minimum lethal temperatures (LT50) for Loxosceles intermedia Mello-Leitão, 1934 and L. laeta (Nicolet, 1849) (Araneae, Sicariidae)

In this study, the maximum and minimum lethal temperatures (LT₅₀) of L. intermedia and L. laeta were determined in two treatments: gradual heating (25–50°C) and cooling (25°C to −5°C), and 1 h at a constant temperature. In gradual temperatures change, L. intermedia mortality started at 40°C and the LT₅₀ was 42°C; for L. laeta, mortality began at 35°C and the LT₅₀ was 40°C. At low temperatures, mortality was registered only at −5°C for both species. In the constant temperature L. intermedia showed a maximum LT₅₀ at 35°C and L. laeta at 32°C; the minimum LT for both species was −7°C.     

Photosynthetic photon flux effects on bean response to nitrogen dioxide

Phaseolus vulgaris L. cv. Kinghorn Wax seedlings, supplied with nutrient solution containing either 0 or 5 mM nitrate as sole N source, were exposed to 0.25 μl/l NO₂ for 6 hr each day for 10 days at continuous photosynthetic photon flux (PPF) of 100, 300, 500 or 700 μmol m⁻² sec⁻¹. There was a significant interaction of PPF and nitrate. Shoot and root dry weights increased with increasing PPFs only when nitrate was supplied. The main effects of NO₂ on plant growth were significant; none of the interactions involving NO₂ were significant. Exposure to NO₂ decreased shoot and root dry weight in both the presence and absence of nutrient N and at all PPF levels. All interactions were significant for in vitro leaf nitrate reductase activity (NRA), which increased markedly at PPFs above 100 μmol m⁻² sec⁻¹ when nitrate was supplied. Treatment with NO₂ strongly inhibited enzyme activity in the presence of nitrate, particularly at the 300 μmol m⁻² sec⁻¹ PPF level. These experiments demonstrated that PPF level does not modify the effect of NO₂ on growth but does have a major effect on NRA and on NO₂ effects on NRA in the presence of nutrient nitrate.     

Local NO3- or NH4+ supply modifies the root system architecture of Cedrus atlantica seedlings grown in a split-root device

To study the effects of local nitrate or ammonium supply on the architecture of the Cedrus atlantica root system, cedar seedlings were grown in split-root boxes in a growth chamber. In each box-compartment, roots were fertilized with a solution containing nitrogen, either as nitrate [Ca(NO₃)₂] or ammonium (NH₄Cl), supplied at 0.1 or 5.0 mM. For each seedling, the shoot growth was measured twice a week for 3 months. The root system architecture was also recorded twice a week by tracing the root elongation through the transparent face of the root observation boxes. The apical diameter of the tap-root relay and that of a representative sample of lateral roots were recorded once a month using a monocular magnifier.

The increase of ammonium or nitrate concentration in the nutrient solution has significantly enhanced the production of lateral roots on the tap-root relay. After 90 days of culture, percentages of short lateral roots obtained with nitrate were higher than those obtained using ammonium. A preferential carbon allocation to the shoots was also obtained with an increasing nitrogen supply. Until the 40th day of culture, the elongation of lateral roots was similar for all treatments and ranged from 0.25 to 0.5 cm day⁻¹. From the 40th day to the 95th day, significant differences were observed between the compared modes and maximum elongation rates were obtained with 5 mM NH₄⁺ (2.18 cm day⁻¹) and 5 mM NO₃⁻ (1.18 cm day⁻¹). Local applications of nitrate and ammonium at a low or a high concentration had local effects on elongation and branching of the root system in the fertilized compartment. Contrasting effects of ammonium and nitrate were observed on the apical diameter of tap-roots and lateral roots. The root-split culture device confirmed that nitrate had local effects on the architecture of the C. atlantica root system.     

Thermodynamic and kinetic analysis of the interaction between hepatitis B surface antibody and antigen on a gold electrode modified with cysteamine and colloidal gold via electrochemistry

Hepatitis B surface antibody (HBsAb) was immobilized to the surface of a gold electrode modified with cysteamine and colloidal gold as matrices to detect hepatitis B surface antigen (HBsAg). Differential pulse voltammetry (DPV) method was used for the investigation of the specific interaction between the immobilized HBsAb and HBsAg in solution, which was followed as a change of peak current in DPV with time. With the modified gold electrode, the differences in affinity of HBsAb with HBsAg at the temperatures of 37 and 40 °C were easily distinguished and the kinetic rate constants (k_ass and k_diss) and kinetic affinity constant K were determined from the curves of current versus time. In addition, the thermodynamic constants, ΔG, ΔH and ΔS, of the interaction at 37 °C were calculated, which were −56.65, −64.54 and −25.45 kJ mol⁻¹, respectively.     

Kinetics and mechanism of the stoichiometric oxygenation of [Cu(fla)(idpa)]ClO4 [fla=flavonolate, IDPA=3,3′-imino-bis(N,N-dimethylpropylamine)] and the [Cu(fla)(idpa)]ClO4-catalysed oxygenation of flavonol

Oxygenation of [Cu^II(fla)(idpa)]ClO₄ (fla=flavonolate; IDPA=3,3′-iminobis(N,N-dimethylpropylamine)) in dimethylformamide gives [Cu^II(idpa)(O-bs)]ClO₄ (O-bs=O-benzoylsalicylate) and CO. The oxygenolysis of [Cu^II(fla)(idpa)]ClO₄ in DMF was followed by electronic spectroscopy and the rate law −d[{Cu^II(fla)(idpa)}ClO₄]/dt=k_obs[{Cu^II(fla)(idpa)}ClO₄][O₂] was obtained. The rate constant, activation enthalpy and entropy at 373 K are k_obs=6.13±0.16×10⁻³ M⁻¹ s⁻¹, ΔH^‡=64±5 kJ mol⁻¹, ΔS^‡=−120±13 J mol⁻¹ K⁻¹, respectively. The reaction fits a Hammett linear free energy relationship and a higher electron density on copper gives faster oxygenation rates. The complex [Cu^II(fla)(idpa)]ClO₄ has also been found to be a selective catalyst for the oxygenation of flavonol to the corresponding O-benzoylsalicylic acid and CO. The kinetics of the oxygenolysis in DMF was followed by electronic spectroscopy and the following rate law was obtained: −d[flaH]/dt=k_obs[{Cu^II(fla)(idpa)}ClO₄][O₂]. The rate constant, activation enthalpy and entropy at 403 K are k_obs=4.22±0.15×10⁻² M⁻¹ s⁻¹, ΔH^‡=71±6 kJ mol⁻¹, ΔS^‡=−97±15 J mol⁻¹ K⁻¹, respectively.     

A study in UF-membrane reactor on activity and stability of nitrile hydratase from Microbacterium imperiale CBS 498-74 resting cells for propionamide production

The bioconversion of propionitrile to propionamide was catalysed by nitrile hydratase (NHase) using resting cells of Microbacterium imperiale CBS 498-74 (formerly, Brevibacterium imperiale). This microorganism, cultivated in a shake flask, at 28 °C, presented a specific NHase activity of 34.4 U mg_DCW⁻¹ (dry cell weight). The kinetic parameters, K_m and V_max, tested in 50 mM sodium phosphate buffer, pH 7.0, in the propionitrile bioconversion was evaluated in batch reactor at 10 °C and resulted 21.6 mM and 11.04 μmol min⁻¹ mg_DCW⁻¹, respectively. The measured apparent activation energy, 25.54 kJ mol⁻¹, indicated a partial control by mass transport, more likely through the cell wall.

UF-membrane reactors were used for kinetic characterisation of the NHase catalysed reaction. The time dependence of enzyme deactivation on reaction temperature (from 5 to 25 °C), on substrate concentrations (from 100 to 800 mM), and on resting cell loading (from 1.5 to 200 μg  ml⁻¹) indicated: lower diffusional control (E_a=37.73 kJ mol⁻¹); and NHase irreversible damage caused by high substrate concentration. Finally, it is noteworthy that in an integral reactor continuously operating for 30 h, at 10 °C, 100% conversion of propionitrile (200 mM) was attained using 200 μg  ml⁻¹ of resting cells, with a maximum volumetric productivity of 0.5 g l⁻¹ h⁻¹.     

Physiological causes of cotton fruit abscission under conditions of high temperature and enhanced ultraviolet-B radiation

An experiment was conducted in sunlit controlled environment growth chambers to determine the physiological mechanisms of fruit abscission of cotton ( Gossypium hirsutum L. cv. NuCOTN 33B) grown in high temperature and enhanced ultraviolet (UV)-B radiation. Six treatments included two levels of optimum (30/22°C) and high (36/28°C) day/night temperatures and three levels of biologically effective UV-B radiation (0, 7, and 14 kJ m⁻² per day). Both the temperature and UV-B treatments were imposed from seedling emergence through 79 days after emergence (DAE). High temperature did not negatively affect either leaf net photosynthetic rates (Pn) or abscission of cotton squares (floral buds with bracts) but significantly decreased boll retention. Plants exposed to 7 kJ UV-B radiation retained 56% less bolls than the 0 kJ UV-B control plants at 79 DAE, despite no significant differences in leaf Pn measured at squaring and flowering. At 53 DAE, leaf Pn of plants grown in high UV-B radiation (14 kJ m⁻² per day) decreased by 11%, whereas total non-structural carbohydrate (TNC) concentrations in the leaves, floral buds, and young bolls decreased by 34, 32, and 20%, respectively, compared with the control plants. The high UV-B radiation significantly increased square abscission. Square abscission was not related to leaf TNC concentration but closely correlated with TNC in floral buds ( r  = −0.68, P  < 0.001). Young boll abscission was highly correlated with TNC concentrations in both the leaves ( r  = −0.40, P  < 0.01) and the bolls ( r  = −0.80, P  < 0.001). Our results indicate that non-structural carbohydrate limitation in reproductive parts was a major factor associated with fruit abscission of cotton grown under high temperature and enhanced UV-B radiation conditions.