Different Doses Of Γ-rays Research Articles

Induction of novel variants through physical and chemicalmutagenesis in Barbeton daisy (Gerbera jamesonii Hook.)

SummaryGerbera (Gerbera jamesonii) is an attractive ornamental flower of high economic importance. The present investigation was aimed at generating novel flower colour variants in the gerbera cultivar ‘Harley’ through physical and chemical mutagenesis. In vitro-raised shoot cultures of gerbera, established from petiole explants, were exposed to different doses of γ-rays (1.5, 2.0, 2.5, 5.0, 10.0, 15.0, 20.0, or 30.0 Gy) using a Cobalt-60 source emitting 2.51 kGy h–1. To induce mutations through chemical mutagenesis, different concentrations of ethylmethane sulphonate [EMS; 0.1, 0.2, 0.5, 0.8, or 1.0% (v/v)] were administered for 10 min or for 20 min. The LD50 values calculated for shoot survival and the induction of mutations were approx. 6.5 Gy for γ-rays and 0.65% (v/v) EMS for 10 min, or ≤ 0.1% (v/v) EMS for 20 min. Investigations revealed a negative correlation between mutagen dose and plant survival, both in vitro and after acclimatisation. Morphological variants showing changes in leaf shape, leaf size, scape length, flower diameter, and flower colour were obtained. Significantly, early flowering was induced in all mutated plants compared to non-mutated plants.The high frequencies of colour variants obtained using Bγ-rays, or the application of EMS to in vitro-raised shoot cultures could be an effective way to improve gerbera cultivars.

In vitro mutagenesis of rose (Rosa hybrida L.) explants using gamma-radiation to induce novel flower colour mutations

SummaryThe hybrid tea rose (Rosa hybrida L.) cultivar, ‘Pusa Mohit’ was mutagenised under in vitro conditions. Single node cuttings (25 cuttings per treatment with three replications) were irradiated with different doses of γ-rays (0, 5, 10, 15, 25, 40, 55, 65, 70, or 80 Gy) using a 60Co source. The γ-irradiated explants were then cultured aseptically on Murashige and Skoog basal medium supplemented with 15.53 µM 6-benzylaminopurine (BAP) plus 0.54 µM α-naphthaleneacetic acid (NAA) plus 1.44 µM gibberellic acid (GA3) plus 0.8% (w/v) agar-agar to induce sprouting and shoot proliferation.The 40 Gy treatment was determined to be the LD50 dose. Explants treated at higher doses (65, 70, or 80 Gy) showed deleterious effects of ionising radiation. Few explants sprouted, showed poor growth and failed to survive after the first sub-culture. Morphological abnormalities such as fused leaves, leaf albinism, leaves with lower levels of chlorophyll, variegated leaves, and stunted growth were observed at intermediate doses (25, 40, or 55 Gy). Decreased shoot lengths, numbers of roots per shoot, and root lengths were observed at 55 Gy. In vitro-raised mutant plants and non-irradiated (control) plants were transferred to plastic pots 1 month after acclimatisation under laboratory conditions and examined for their morphological traits. Marked variations were recorded between the mutated and control populations. Four flower colour mutants with altered or novel flower colours compared to the original flower colour were isolated. These mutants were multiplied on a large-scale through micropropagation and evaluated for their stability.This study developed a mutagenesis protocol that could be used to develop novel colour mutants in rose.

Thermoluminescence and photoluminescence of ZrO 2 nanoparticles

This work describes the thermoluminescence (TL) and photoluminescence (PL) of zirconium oxide (ZrO 2) nanoparticles synthesized using the propellant chemical combustion method. They were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The XRD result shows a nanocrystalline material with a major tetragonal phase along with a small portion of monoclinic phase, while SEM images display particles of spherical shapes of diameters in the 25–35 nm range. Samples from this powder were exposed to different doses of γ-rays from a 137Cs source in the range of 0.01 Gy–1 kGy. The induced TL glow curve has a single broad peak at around 600 K. TL response curve of this peak shows sublinearity for all the recorded doses, while its fading over two months is negligible. The intensity and structure of the TL glow curve did not change after several cycles of exposures and readout. PL excitation and emission spectra were also recorded and are investigated. When the material was excited by different wavelengths, several emission bands are observed in the range of 300–500 nm. The new nanocrystalline material shows excellent characterization such as good TL sensitivity, low fading and reusability making it a promising TL dosimeter.

Cyclopentenylcytosine does not enhance cisplatin-induced radiosensitization in human lung tumour cells

The search for agents that enhance the effect of ionizing radiation has been an object of study for decades. In this study, the sensitizing properties of cyclopentenylcytosine (CPEC) on radiation and cisplatin-induced radiosensitization in human squamous lung carcinoma cells were investigated. Human lung tumour SW-1573 cells (SWp, parental; SWg, gemcitabine-resistant) were incubated with CPEC and cisplatin and subsequently irradiated with different doses of γ-rays. Clonogenic survival was determined to measure the effectiveness of the treatments. CPEC (1 or 2 μM) treatment for 4 h decreased the plating efficiency to 75 and 50% in SWp and SWg cells, respectively. In the SWg cells, 0.1 and 1 μM CPEC for 4 h enhanced the cell killing effect of cisplatin. However, an increase was not noted in the SWp cells. Due to the moderate toxicity of 1 μM for 4 h, this CPEC dose was used in the radiosensitization experiments. However, CPEC neither radiosensitized the lung tumour cells nor enhanced the radiosensitizing effect of cisplatin. A 2-h incubation with 4 μM cisplatin also decreased the plating efficiency to 75-80% in the two cell lines. Using this cisplatin dose, radiosensitization was obtained in the two cell lines. Although cisplatin treatment clearly radiosensitized the lung tumour cells, CPEC treatment did not. Cisplatin-induced radiosensitization was also not enhanced by CPEC.

Structural and electrical properties of γ-irradiated TiO 2/Al 2O 3 composite prepared by sol–gel method

TiO 2/Al 2O 3 system was prepared by sol–gel method and subjected to heating at 400 and 1000 °C. The obtained solids were irradiated at different doses of γ-rays (10–150) kGy. Structural and electrical properties of the solids investigated have been studied using XRD, EDX, SEM and electrical conductivity measurements. The results revealed that the system calcined at 400 °C consisted mainly of nanocrystalline rutile phase which turned by heating at 1000 °C to well crystallized rutile as major phase together with AlTiO 3 and α-Al 2O 3 as minor phases. γ-Irradiation of, the system precalcined at 400 and 1000 °C exerted a small increase in the d-value of the main diffraction line of rutile phase in the system calcined at 400 °C. This treatment resulted in a significant increase in the electrical conductivity of calcined solids (10 2 to 10 3-fold). Furthermore, γ-rays created some holes (evidenced by SEM investigation). These created holes might increase the mobility of charge carriers (positive holes) increasing thus the electrical conductivity of irradiated solids.

Effect of gamma-irradiation on guanyl specific ribonuclease from Trichoderma harzianum

Sensitivity of aqueous solutions of fungal guanyl specific RNase Th to irradiation with different doses of γ-rays was studied. Enzyme activity, aggregation, amino acid composition, UV-absorption and difference spectra of native and irradiated enzyme were investigated. Inactivation of RNase Th after irradiation occurred with all doses used and alterations in the spectral properties of the enzyme were observed. The reasons of these deviations most likely are changes in the conformation as a result of breaking of hydrogen and disulfide bonds and destroying of one molecule of tyrosine. The data received for the sensitivity of this enzyme to gamma-irradiation could contribute to more detail characterization of this family of proteins.

Hydrocracking of cumene over Ni/Al 2O 3 as influenced by CeO 2 doping and γ-irradiation

Cumene hydrocracking was carried out over pure and doped Ni/Al 2O 3 solids and also, on these solids after exposure to different doses of γ-rays between 0.4 and 1.6 MGy. The dopant concentration was varied between 1 and 4 mol% CeO 2. Pure and doped samples were subjected to heat treatment at 400°C and cumene hydrocracking reaction was carried out using various solids at temperatures between 250°C and 400°C by means of micropulse technique. The results showed that both CeO 2 doping and γ-irradiation of the investigated system brought about an increase in its specific surface area. γ-irradiation of pure samples increased their catalytic activities effectively. However, the doping caused a decrease in the catalytic activity. γ-irradiation of the doped samples brought about a net decrease in the catalytic activity. The catalytic reaction products over different investigated solids were ethylbenzene as a major product together with different amounts of toluene, benzene and C 1–C 3 gaseous hydrocarbons. The selectivity towards the formation of various reaction products varies with the reaction temperature, doping and γ-irradiation.

Effects of γ-Irradiation on the Surface and Catalytic Properties of Co3O4/MgO Systems Aged for One Year

The effects of γ-rays (20–160 Mrad) on the surface and catalytic properties of two Co3O4/MgO systems were investigated. The formulae of the investigated solids were 0.05Co3O4/MgO and 0.2Co3O4/MgO, respectively, both prepared by the impregnation method and calcined at 500°C. The irradiated samples were left for one year in sealed tubes before any measurements were undertaken. γ-Irradiation of the investigated solids resulted in a progressive decrease in the particle size of the Co3O4 and MgO phases. This treatment also led to a measurable increase in the specific surface area of the treated solids to an extent proportional to the γ-ray dosage. Treatment of the Co3O4/MgO system with different doses of γ-rays brought about a significant increase in the catalytic activity expressed both as the reaction rate constant and as the reaction rate constant per unit surface area. However, the curve relating to the catalytic activity and dosage of γ-rays showed maxima located at 40 and 80 Mrad for samples having the formula 0.05Co3O4/MgO and 0.2Co3O4/MgO, respectively. Furthermore, samples exposed to 160 Mrad showed a larger catalytic activity than the unirradiated samples. The results demonstrate the role of γ-rays in inhibiting the deterioration of the catalytic activity of the investigated systems as a function of aging time. The irradiation process did not modify the activation energy of the catalyzed reaction but altered the concentration of active centres on the surfaces of the solids without changing their energetic nature.

γ-Ray and hydrogen peroxide induction of gene amplification in hamster cells deficient in DNA double strand break repair

To investigate the role of DNA double strand breaks (DSBs) and of their repair in gene amplification, we analyzed this process in the V3 Chinese hamster cell line and in the parental line AA8, after exposure to γ-rays and to hydrogen peroxide (H 2O 2). V3 is defective in DSB repair because of a mutation in the DNA-dependent protein kinase catalytic subunit ( DNA-PKcs) gene, a gene involved in the non-homologous end-joining pathway. As a measure of gene amplification we used the frequency of colonies resistant to N-(phosphonacetyl)- l-aspartate (PALA), since in rodent cells PALA resistance is mainly achieved through the amplification of the CAD (carbamyl- p-synthetase, aspartate transcarbamylase, dihydro-orotase) gene. After treatment with different doses of γ-rays and of H 2O 2, we found a dose related increase in the frequency of gene amplification and of chromosome aberrations. When the same doses of damaging agents were used, these increments were higher in V3 than in AA8. These results indicate that DSBs that are not efficiently repaired can be responsible for the induction of gene amplification. H 2O 2 stimulates gene amplification as well as γ-rays, however, at similar levels of amplification induction, chromosome damage was about 50% lower. This suggests that gene amplification can be induced by H 2O 2 through pathways alternative to a direct DNA damage. Stimulation of gene amplification by H 2O 2, which is one of the products of the aerobic metabolism, supports the hypothesis that cellular metabolic products themselves can be a source of genome instability.

Surface and catalytic properties of γ-irradiated Fe 2O 3Cr 2O 3/Al 2O 3 solids

An iron, chromium, aluminium mixed oxides specimen having the nominal molar composition 0.125 Fe 2O 3 0.06 Cr 2O 3/Al 2O 3 was prepared and subjected to thermal treatment at 700°C. The calcined sample was exposed to different doses of γ-rays varying between 20 and 160 Mrad. The surface and catalytic properties of the different irradiated solids were studied using nitrogen adsorption at −196°C and catalysis of CO oxidation by O 2 at 225–300°C. The results showed that γ-irradiation at doses between 20 and 80 Mrad resulted in a progressive increase of specific surface area (10–36%), total pore volume (55–175%) and mean pore radius (41–105%) of treated adsorbents. Irradiation at doses above this limit led to a significant decrease in the magnitudes of different surface parameters which still measured higher values than those found for the un-irradiated sample. The catalytic activity increased monotonically as a function of the dose absorbed. The catalytic reaction rate constant, measured at 225, 250 and 300°C increased by 400, 170 and 115%, respectively by exposure to a dose of 160 Mrad. The increase in the reaction rate constant per unit surface area measured at the same reaction temperatures due γ-irradiation at 160 Mrad was 370, 155 and 102%. This treatment did not modify the mechanism of the catalytic reaction, but increased the number of catalytically active sites taking part in chemisorption and catalysis of CO oxidation reaction without changing their energetic nature.

Determination of DNA single-strand breaks by low-energy heavy ion and analysis of dose-effect curves

Calf thymus DNA was exposed to low-energy heavy ions (N+) and 60Co-γ-rays, and the dose-effect on DNA single-strand breaks (SSB) has been investigated. The results indicate that the dose-effect curve by N+ irradiation is different from that of conventional ionizing radiation. While the curve from γ-irradiation follows exponential type, the effect curve produced by N+ ion is of saddle type. The yield of DNASSB per dose unit per DNA unit remained at a certain level under different doses of γ-rays. In contrast, the DNASSB at low dosage region of N+ showed an obvious peak before it decreased rapidly to a lower level.

The herbal preparation abana protects against radiation-induced micronuclei in mouse bone marrow

The induction of micronuclei was studied in mouse bone marrow treated or not with 5, 10 and 20 mg/kg b.wt. of abana (a herbal preparation) before exposure to 0–3 Gy of γ-radiation. Whole-body irradiation of mice resulted in a dose-dependent increase in the frequency of micronuclei. Treatment of mice with various doses of abana before exposure to different doses of γ-rays resulted in a significant reduction of the micronucleus frequency at all exposure doses. The highest decline in the frequencies of micronuclei was observed after administration of 20 mg/kg abana, where the frequency of micronuclei was approximately 4-fold less than that of the concurrent control. The PCE/NCE ratio was significantly higher in the drug-treated group compared to DDW+irradiated control and it was almost restored to normal level after administration of 20 mg/kg abana. Our results demonstrate that abana protects mice against radiation-induced micronucleus formation and radiation-induced decline in cell proliferation.

Surface and Catalytic Properties of γ-Irradiated Cr2O3/Al2O3 Solids

Two samples of Cr2O3/Al2O3 were prepared by mixing a known mass of finely powdered Al(OH)3 with a calculated amount of CrO3 solid followed by drying at 120°C and calcination at 400°C. The amounts of chromium oxide employed were 5.66 and 20 mol% Cr2O3, respectively. The calcined solid specimens were then treated with different doses of γ-rays (20–160 Mrad). The surface and catalytic properties of the different irradiated solids were investigated using nitrogen adsorption at −196°C and the catalysis of CO oxidation by O2 at 300–400°C. The results revealed that γ-rays brought about a slight decrease in the BET surface area, SBET (15%), and in the total pore volume, Vp (20%), of the adsorbent containing 5.66 mol% Cr2O3. The same treatment increased the total pore volume, Vp (36%), and the mean pore radius, r̄ (43%), of the other adsorbent sample without changing its BET surface area. The catalytic activities of both catalyst samples were found to increase as a function of dose, reaching a maximum value at 80–160 Mrad and 40 Mrad for the solids containing 5.66 and 20 mol% Cr2O3, respectively. The maximum increase in the catalytic activity measured at 300°C was 59% and 100% for the first and second catalyst samples, respectively. The induced effect of γ-irradiation on the catalytic activity was an increase in the concentration of catalytically active sites taking part in chemisorption and in the catalysis of CO oxidation by O2 without changing their energetic nature. This was achieved by a progressive removal of surface hydroxy groups during the irradiation process.

Effect of gamma-irradiation on surface and catalytic properties of CuO−ZnO/Al2O3 system

A copper, zinc and aluminium mixed oxides sample having the nominal composition 0.25 CuO/0.03 ZnO/Al2O3 was prepared by impregnating Al(OH)3 with copper and zinc nitrate solutions, drying at 100 °C then heating in air at 600 °C. The obtained solid was exposed to different doses of γ-rays (20–160 Mrad). The surface characteristics namelySBETVP andr of different treated adsorbents were determined from N2 adsorption isothems measured at −196 °C. The catalytic activity of various irradiated solids was determined by following up the kinetics of CO-oxidation by O2 at 150–200 °C. The results showed that the doses up to 80 Mrad resulted in no significant change in theSBET but increased slightly theVP (20%) of the treated adsorbents. The irradiation at 160 Mrad caused an increase of 20% in theSBET of the irradiated solid sample. The catalytic activity increased progressively by increasing the dose, a dose of 160 Mrad brought about an increase of 140% in the catalyst's activity. The apparent activation energy of the catalytic reaction decreased monotonically by increasing the absorbed dose of γ-rays which was attributed to a parallel induced decrease in the value of pre-exponential term of the Arrhenius equation. The observed increase in the catalytic activity due to γ-irradiation has been interpreted as a result of increasing the concentration of catalytically-active sites contributing in chemisorption and catalysis of CO-oxidation via a possible fragmentation of CuO crystallites.

Study of optical properties of pure and MoO3-doped polyvinyl alcohol films irradiated with γ-rays

Cast thin films of pure and MoO3-doped polyvinyl alcohol (PVA) have been prepared. The optical transmission spectra in ultraviolet to near-infrared regions are investigated before and after irradiation by different doses of γ-rays in the range 102 to 107 Gy. The analysis of transmission spectra showed that the intensity of the bands is remarkably affected by both dopant concentration and γ-irradiation doses. The disappearance of the transmission band at 265 nm in 1.0 wt% and 2.0 wt% MoO3 is attributed to the structural change due to dopant. It was found that doping with molybdenum oxide results in an additional band at 600 nm. The optical energy gap and band tail of pure and MoO3-doped PVA samples at different γ-doses are estimated.

Surface and catalytic properties of gamma-irradiated CuO and NiO catalysts

The effects of gamma-irradiation (20–160 Mrad) on surface and catalytic properties of CuO and NiO were investigated. The surface characteristics namely S BET, V p , and r ̄ of various solids were determined from nitrogen adsorption isotherms conducted at −196 °C and their catalytic activities were measured by following up the kinetics of CO-oxidation by O 2 using a static method. The results showed that gamma rays brought about a small increase (24%) in the S BET of CuO till a dose of 40 Mrad, and a dose of 80 Mrad was found to increase considerably its S BET (224%) due to narrowing of its pores ( r ̄ decreased from 110 to61Å). In the case of NiO solid its S BET was found to vary in a complex manner up on exposure to different doses of γ-rays. Gamma rays modified the catalytic activity of CuO catalyst in a complex manner. The catalytic activity of NiO, being expressed as the reaction rate constant k, was found to decrease progressively by increasing the dose in the range 20–120 Mrad. However, the reaction rate constant per unit surface area ( k ̄ ) of NiO decreased slightly (18%) by exposure to a dose of 20 Mrad. By increasing the dose to 40 Mrad a maximum specific catalytic activity ( k ̄ ) was observed. The further increase of the dose to 80 Mrad resulted in a sudden drop (69%) in the specific catalytic activity ( k ̄ ) of the treated solid. Irradiation at 120 Mrad brought about an increase (14%) in the value of k ̄ .

Establishment and validation of a dose-effect curve for γ-rays by cytogenetic analysis

A dose-effect curve obtained by analysis of dicentric chromosomes after irradiation of peripheral blood samples, from one donor, at 11 different doses of γ-rays is presented. For the elaboration of this curve, more than 18 000 first division metaphases have been analyzed. The results fit very well to the linear-quadratic model. To validate the curve, samples from six individuals (three controls and three occupationally exposed persons) were irradiated at 2 Gy. The results obtained, when compared with the curve, showed that in all cases the 95% confidence interval included the 2 Gy dose, with estimated dose ranges from 1.82 to 2.19 Gy.

Crosslinking studies of poly(dimethylsiloxane) networks: a comparison of inverse gas chromatography, swelling experiments and mechanical analysis

Finite concentration inverse gas chromatography (i.g.c.) was used to determine the crosslink density of three poly(dimethylsiloxane) (PDMS) samples, which were crosslinked with different doses of γ-rays. Crosslink density data of the same materials were also obtained in swelling measurements and, in one case, in stress-strain mechanical analysis. Results yielded by the different techniques agreed very well considering the different nature of the approximations made in the various experiments. Information obtained by i.g.c. also included the Flory-Huggins interaction parameters of the linear and crosslinked PDMS samples.

Effect of γ-irradiation on the catalytic activity and selectivity of γ-alumina II. Conversion of isopropanol

The catalytic conversion of isopropanol was conducted over a poorly crystalline γ-alumina irradiated with different doses of γ-rays (25–150 Mrad). The catalytic reaction was carried out at 180–400°C in a flow technique under atmospheric pressure. The results showed that the dose of 25 Mrad resulted in a decrease of about 50% of the dehydration activity which suffered a further slight decrease upon irradiation at a dose of 50 Mrad. Increasing the dose in the range of 50–150 Mrad effected an increase in the dehydration activity reaching a maximum limit at 100 Mrad, then decreased abruptly by a dose of 150 Mrad. γ-irradiation led also to creation of some active sites contributing in dehydrogenation of isopropanol to producing acetone. These results were discussed in terms of removal of Bronsted acidity (25–50 Mrad), responsible for the dehydration reaction and to transformation of Lewis to Bronsted acidity (100 Mrad) by the action of liberated water from the dehydration reaction. The drop in dehydration activity due to irradiation at 150 Mrad might result from an efficient removal of the Bronsted acid sites created. The induced dehydrogenation activity of irradiated aluminas was attributed to creation of some electron-donor centers.

Effect of gamma-irradiation on the catalytic activity and selectivity of gamma-alumina

Methanol conversion reaction was carried out in contact with a poorly crystalline γ-alumina pre-irradiated with different doses of γ-rays. The reaction was conducted at 140–440°C using a flow technique under atmospheric pressure. The results obtained revealed that γ-irradiation of Al2O3 resulted in drastic modifications of its activity and selectivity in methanol conversion reaction. The dose of 15 Mrad was sufficient to suppress completely the formation of dimethyl ether (DME) and stimulated the formation of methane, which started at 200°C instead of 300°C in the case of the unirradiated alumina specimen. However, the rate of CH4 formation was found to decrease as a function of the dose employed. When the dose reached 140 Mrad, DME was reproduced with a rate comparable to that measured for the unirradiated catalyst sample. These results permitted us to conclude that DME is produced on the weak acidic sites (Bronsted acidity of Al2O3) and is not necessarily an intermediate compound for methane formation that takes place directly from methanol on strong acidic sites (Lewis acidity). The doses of 15–75 Mrad expelled completely the Bronsted acidic sites from Al2O3 surface, and the doses above this limit brought about a transformation of Lewis acidic sites into Bronsted acidity that is responsible for dimethyl ether formation. This transformation occurs by the action of liberated water from the dehydration of methyl alcohol.