Stomatal responses to light in the facultative Crassulacean acid metabolism species, Portulacaria afra

Guard cell responses to light are mediated by guard cell chlorophyll and by a specific blue light photoreceptor. Gas exchange and epidermal peel techniques were employed to investigate these responses in the facultative Crassulacean acid metabolism (CAM) species, Portulacaria afra (L.) Jacq. In P. afra individuals performing C₃ metabolism, red light stimulated an increase in leaf conductance in intact leaves and stomatal opening in isolated epidermal peels, indicating the presence in guard cells of the chlorophyll-mediated response to light. Under a background of continuous red illumination, conductance exhibited transient increases following pulses of blue but not red light, indicating that the specific stomatal response to blue light was also operative. In contrast, in CAM individuals, conductance in gas exchange experiments and stomatal opening in epidermal peel experiments were not stimulated by red light. In CAM plants, conductance did not increase following blue light pulses administered over a range of temperatures, vapor pressure differences (VPD), ambient CO₂ concentrations and background red light intensities. These results indicate that P. afra does possess typical guard cell responses to light when performing C₃ metabolism. The metabolic pathways mediating these responses are either lost or inhibited when CAM is induced.     

A novel magnetic silica support for use in chromatographic and enzymatic bioprocessing

A limited number of support matrices have so far been developed for use in magnetically stabilized fluidized bed (MSFB) applications. We have developed a versatile magnetic silica support which can be derivatized readily for both adsorption chromatography and enzyme immobilization by well-known techniques. A magnetic pellicular bead is prepared by electrostatically depositing alternating layers of colloidal silica and cationic polymer onto macroscopic nickel core particles. The polymer is then burned out and the silica partially sintered to yield a porous shell with 5-80 m(2)/g of surface area. This magnetic composite was tested as a support for immobilizing invertase. Sucrose was continuously converted to its component monosaccharides with nearly constant activity over the first 8 days and retention of 50% of initial activity after 25 days.     

Two- and three-phase mixing in a concentric draft tube gas-lift fermentor

Two- and three-phase mixing studies were carried out in a 44-L concentric draft tube gas-lift fermentor. It was proposed to use the fermentor for the production of solvents using immobilized bacteria. Bubble size, gas holdup, liquid velocities, circulation, and mixing times were determined for various superficial gas velocities in distilled water, starch, carboxymethyl cellulose, and ethanol solutions. The observed trends for two phase mixing were similar to other studies but the results were found to be more sensitive to liquid properties. This was possibly due to the large value of downcomer to riser area used in this study. Mixing in three phases highlighted the difficulty in predicting the effect of adding solids to the gas-liquid system. Results showed that the gas-lift fermentor was ideally suited to dealing with three phases but more work is necessary before accurate models can be developed to account for the effect of solids.     

Circular dichroism detection in HPLC

A circular dichroism-based detection system presents several advantages in the HPLC analysis of chiral compounds because of the selective monitoring of optically active molecules. Its use allows reliable determination of enantiomeric excesses and elution order. To this end, the application of empirical, semiempirical, and nonempirical methods to get stereochemical information from the CD signal is reported. Furthermore, recording the CD spectra on line and evaluation of the dissymetry factor make the CD detection very powerful in characterizing the stereochemistry of chiral eluates.     

Heterocyclic polycyclic aromatic hydrocarbon carcinogenesis: 7H-dibenzo[c,g]carbazole metabolism by microsomal enzymes from mouse and rat liver

The metabolism of dibenzo[c,g]carbazole (DBC), was studied in vitro using microsomal fractions of mouse and rat liver from animals, which were treated with 3-methylcholanthrene (MC). The separation of extractable metabolites by high pressure liquid chromatography (HPLC) and thinlayer chromatography (TLC) as well as identification of most of them by nuclear magnetic resonance, mass spectrometry and comparison with synthetically obtained products are described. The microsomes of both species produced the same twelve compounds of which the following have been identified: five monohydroxylated derivatives (phenols), the product of further oxidation of one of them, and a dihydrodiol. The 5-OH-DBC (60% including its spontaneously-formed dimer) and the 3-OH-DBC (14%) are the main metabolites. Three minor metabolites cochromatographed with synthetically prepared 2-OH-DBC, 4-OH-DBC and 6-OH-DBC. The dihydrodiol detectable in small quantity (4–6%) was tentatively identified as 3,4-dihydroxy-3,4-dihydro-DBC by the sensitivity of its formation to very low concentrations of the inhibitor of microsomal epoxide hydrolase, 1,1,1-trichloropropene oxide, by its molecular ion and major fragment in mass spectrometry and by its dehydration product 3-OH-DBC. No other dihydrodiols were detected. The qualitative and quantitative effects of various modulators of metabolism (enzyme inhibitors, apparently homogeneous epoxide hydrolase, glutathione, supernatant fraction) were investigated. The results are discussed with respect to possible ultimate carcinogens.     

Ellipticines and human liver microsomes: Spectral interaction with cytochrome P-450 and hydroxylation. Inhibition of aryl hydrocarbon metabolism and mutagenicity

Some pharmacological properties of ellipticine (E) and its derivatives linked to their interaction with cytochrome P-450 have been investigated with human liver microsomes. 9-Hydroxyellipticine (9-OHE) interacts with human liver cytochrome P-450 exhibiting a type II spectrum (λ_max: 428 nm, K_s = 1.1 μM). After incubation with human liver microsomes the E was converted to 9-OHE; 7-hydroxyellipticine was not produced. The cytotoxic effect of this biotransformation has been evaluated on leukemic L1210 cells, in vitro, and found to be equal to those elicited by liver microsomes of control or phenobarbital (PB) pretreated rats. Moreover, 9-OHE and 9-fluoroellipticine (9-FE) strongly inhibit the benzo[a]pyrene hydroxylase (AHH) activity of human liver microsomes (I₅₀ = 2.6 μM and 1.6 μM, respectively) as well as the mutagenesis induced by the polycyclic aromatic hydrocarbon 2-acetylaminofluorene (AAF); 1 μg/plate of each of these compounds is able to inhibit by more than 50% the mutagenicity of 5 μg/plate AAF.     

Estimating thermal properties of simulated aquatic soils from their composition

Heat penetration and thermal lag in the submersed soil surrounding the roots of aquatic plants depends on two fundamental thermal properties of the substrate, volumetric heat capacity (C_V) and thermal conductivity (k). The relationship of these parameters to the fractions of organic and mineral matter, gas and water in natural and simulated aquatic soils was investigated. The gas fraction was found to be insignificant and it was possible to make good estimates of C_V and k from a knowledge of substrate water content alone.