Field productivity of a CAM plant, Agave salmiana, estimated using daily acidity changes under various environmental conditions

Nocturnal acidity increases of the Crassulaceae acid metabolism succulent Agave salmiana Otto ex Salm. ssp. crassispina (Trel.) Gentry were determined for various photosynthetically active radiation (PAR) levels in the field and various day/night temperatures and soil water potentials in the laboratory. When a particular factor was optimal for nocturnal acid accumulation, it was assigned an index value of unity. The product of the three indices was termed the environmental productivity index (EPI), which summarizes the effect of PAR, temperature, and water status on nocturnal acid accumulation. A monthly value for EPI was determined using microclimatic conditions at the field site near Salinas de Hidalgo, San Luis Potosf, Mexico. EPI was highly correlated with the number of leaves unfolding monthly from plants in the field (r²= 0.95), where monitoring of such leaf unfolding is a non-destructive technique for assessing plant productivity. By using the measured leaf area index for four groups of A. salmiana and a relationship between acid accumulation and net CO₂ up-take, the EPI acidity data were converted to dry weight gain per unit ground area. This measure of productivity closely agreed with the 1.05 kg m⁻² year⁻¹ determined by conventional harvesting techniques. The productivity is also in agreement with studies on other desert agaves, but about 10-fold higher than that generally considered for desert ecosystems.     

Ultraviolet-irradiation induced and spontaneous mutation of Rhizobium trifolii 11B in relation to water-soluble and water-insoluble polysaccharide production ability

Rhizobium trifolii 11B was u.v. irradiated and nine u.v. mutants have been isolated. Among the mutants, only one, R. trifolii 21M11B, produced more (752 mg/100 ml) water-soluble polysaccharide than the parent (704 mg/100 ml). The composition of water-soluble polysaccharide from u.v. mutants differed from that of the parent, R. trifolii 11B, and none of its u.v. mutants produced water-insoluble polysaccharide as detected by the Aniline Blue method. Storage of u.v. mutants for 2 months at 5°C gave four spontaneous variants which acquired the ability to produce water-insoluble polysaccharide. The spontaneous mutants also retained their water-soluble polysaccharide producing ability. The water-soluble polysaccharide produced by these mutants was characterized as curdlan type. The chemistry of water-soluble and water-insoluble polysaccharides was also ascertained.     

Erythrocyte hemolysis by radiofrequency fields

A field-strength-dependent hemolytic effect of continuous-wave radiofrequency (RF) exposure in vitro has been demonstrated. Erythrocytes in whole heparinized rabbit blood were hemolyzed by a 2-h exposure to 50- or 100-MHz RF fields at field strengths of greater than 4 V/cm. An effect of comparable magnitude resulted from exposure to 10-MHz RF at a field strength of 9 V/cm. Sample temperatures were maintained at 22.5 degrees +/- 0.2 degrees C. There was no apparent involvement of heating or temperature gradients, nor were there any RF exposure effects on cellular K+ or Na+ concentration, nor on pH. The mechanism of the hemolytic effect is not known. Since the percentage of lysed erythrocytes was less than 1% and there was an absence of effects on cellular cation concentrations, RF radiation may have irreversibly altered the plasma membrane permeability of a sensitive subpopulation of red cells (possibly aged cells) leading to osmotic lysis. RF radiation at these frequencies appears to affect red cells in a manner that is qualitatively and quantitatively different from microwave radiation.     

Effects of microwave radiation (340 and 900 MHz) on different structural levels of erythrocyte membranes

By use of fluorescence probes 1-anilinonaphthalene-8-sulfonic acid, 2-toluidinylnaphthalene-6-sulfonate, pyrene, perylene and chemical label phosphatidylethanolamine 2,4,6-trinitrobenzele sulfonic acid, the effect of microwave radiation on the erythrocyte membrane was studied. The studies with the fluorescence probes were carried out on erythrocyte ghosts and with 2,4,6-trinitrobenzene sulfonic acid on whole erythrocytes. The fluorescence was measured during irradiation of the membranes with 340-MHz microwaves at an SAR of 100 W/kg. Trinitrophenylation of phosphatidylethanolamine from whole erythrocytes was performed simultaneously with microwave irradiation at 900 MHz (10 mW/cm2). It was shown that the microwave field decreased lipid viscosity, altered the structural state of lipid-protein contact regions, and decreased the protein shielding of lipids. These changes corresponded to those produced by thermal action of microwaves.     

Increase in plasmid transformation efficiency in SOS-induced Escherichia coli cells

Summary UV irradiation of competent cells of Escherichia coli K12 produced an increase in the efficiency of transformation with plasmid DNA. This phenomenon has been called IPTE (increase in plasmid transformation efficiency) and is dependent on the activated state of the RecA protein. IPTE is independent of the lexA, recB recC, and recF genes. It is not related to the size or the replicon type of the plasmid. Furthermore, it is also induced in cells which have been previously treated with other SOS system-inducing agents such as bleomycin, mitomycin C, or nalidixic acid. IPTE is therefore similar to other repair (SOS) functions inducible by DNA damage since all of them are dependent upon activation of the RecA protein. IPTE differs from other SOS functions in the absence of a direct control by the LexA repressor.     

Selenium content and distribution in rat tissues irradiated with gamma rays

The effects of supplementation with selenous yeast and ionizing radiation on selenium (Se) content and distribution were evaluated in rat tissues (liver, kidney, spleen, heart, muscle, blood, front brain, hind brain, hypothalamus, pituitary, adrenal glands, testes, and hair). This study had 16 Se-supplemented (0.5 μg Se/d) and 16 placebo adult male Wistar rats. One half of the animals (eight Se-supplemented and eight placebos) were irradiated with a single dose of 4.2 Gy from a Co-60 source and sacrificed 7 d after irradiation along with nonirradiated animals and analyzed for Se content determination. The data obtained showed that selenous yeast supplementation increased Se levels in rat tissues (highest increases in hypothalamus, 161%; hind brain, 126%; spleen, 110%; and adrenal gland, 105%). Ionizing radiation induced significant changes in Se content and distribution (decrease in liver, blood, hair, femoral muscle, spleen, and hypothalamus; increase in kidney, testes, adrenal glands, and brain of placebo group). Supplementation with selenous yeast reduces changes in Se content and distribution after irradiation. It seems that the animal tissue susceptibility to oxidative damage may be correlated to their ability to retain Se in tissues.     

Shielding disk position in intra-operative electron radiotherapy (IOERT): A Monte Carlo study

PurposeIn IOERT breast treatments, a shielding disk is frequently used to protect the underlying healthy structures. The disk is usually composed of two materials, a low-Z material intended to be oriented towards the beam and a high-Z material. As tissues are repositioned around the shield before treatment, the disk is no longer visible and its correct alignment with respect to the beam is guaranteed. This paper studies the dosimetric characteristics of four possible clinical positioning scenarios of the shielding disk. A new alignment method for the shielding disk in the beam is introduced. Finally, it suggests a new design for the shielding disk.MethodsAs the first step, the IOERT machine “Mobetron 1000” was modeled by using Monte Carlo simulation, tuning the MC model until an excellent match with the measured PDDs and profiles was achieved. Four possible shielding disk positioning scenarios were considered, determining the dosimetric impact. Furthermore, in our center, to prevent beam misalignment, we have developed a shielding disk equipped with guiding rods. Having ascertained a correct alignment between the disk and the beam, we can propose a new internal design of the shielding disk that can improve the dose distribution with a better coverage of the treated area.ResultsAll MC simulations were performed with a 12 MeV beam, the maximum energy of Mobetron 1000 and a 5.5 cm diameter flat tip applicator, this applicator being the most clinically used. The simulations were compared with measurements performed in a water phantom and showed good results within 2.2% of root mean square difference (RMSD). The misplacement positions of the shielding disk have dosimetric impacts in the treatment volume and a small translation could have a significant influence on healthy tissues. The D-scenario is the worst which could happens when the shielding disk is flipped upside down, giving up to 144% dose instead of 90% at the surface of the Pb/Al shielding disk. A new shielding design used, together with our alignment tool, is able to give a more homogeneous dose in the target area.ConclusionsThe accuracy of shielding disk position can still be problematic in IOERT dosimetry. Any method that can ascertain the good alignment between the shielding disk and the beam is beneficial for the dose distribution and is a prerequisite for an optimized shield internal design that could improve the coverage of the treated area and the protection of healthy tissues.