Radiation Resistance of the Microflora Associated with Amniotic Membranes

Summary Amniotic membrane is widely used in the treatment of burn wounds and ulcers of various etiology. As it comes into contact with open wounds, it needs to be perfectly sterile to avoid the transmission of any disease. Accordingly, amniotic membrane needs to bear a high sterility assurance level (SAL). Conventionally, a radiation dose of 25 kGy is the generally accepted dose for sterilization. But to keep intact the biomechanical and other properties, it is sometimes proposed to use a lower dose without compromising an SAL of 10⁻⁶. The initial microbial contamination level and the radiation resistance of the contaminants determine the dose required for sterilization. The microbial species associated with the amniotic membrane from about 70 different batches were isolated. Twenty-two representative bacterial isolates were characterized and tested for survival in an incremental series of radiation doses from 0.5 to 5.0 kGy. The radiation decimal reduction dose (D₁₀) values for the strains were determined. Relatively higher D₁₀ values were recorded for the gram-positive isolates. The D₁₀ values of microbial isolates ranged from 0.16 to 1.3 kGy, and most resistant Bacillus strain had a D₁₀ value of 2.1 kGy. The radiation dose necessary to achieve an SAL of 10⁻⁶ was calculated based on the D₁₀values of the isolated strains. For a bioburden of 1000 Bacillus organism, the sterilization dose of 18.9 kGy is obtained. However, based on the experimental determination of D₁₀ of the radiation-resistant reference strain Bacillus pumilus, the adequate dose for radiation sterilization is found to be 19.8 kGy if bioburden level of 1000 is granted. The results substantiate that radiation dose of 25 kGy assures sterilization of amniotic membranes with bioburden level of 1000 colony forming units.     

Influence of Gamma Radiation on the Transport of Indolyl-3-Acetic Acid in Bark Tissue from Apple Trees

The influence of gamma radiation on the polarity of IAA translocation was investigated. Pieces of apple tree shoots, taken from 3-year-old trees, were irradiated in a dark irradiation chamber BK-⁶⁰Co source, 10 kCi. Doses from 20 to 150 krad were given. Strips of bark were peeled off both irradiated and control shoots. The middle parts of the bark strips were placed on agar blocks loaded with IAA-1-¹⁴C. The radioactivity of basal and acropetal segments was determined after about 20 h and results expressed as polarity quotient. It has been shown that irradiation with 20 krad (200 Gy) decreases the polarity quotient remarkably (polarity quotient of control equals 7; for 20 krad—2.9; 100 krad—1.6). The decrease in polarity results from inhibition of the basipetal translocation of IAA. Irradiated tissue shows a decrease in IAA uptake. Possible mechanisms of gamma irradiation effects on polar translocation of IAA are discussed.     

Lysozyme Modification by the Fenton Reaction and Gamma Radiation

A comparative study was performed on lysozyme modification after exposure to Fenton reagent (Fe(II)/H 2 O 2 ) or hydroxyl radicals produced by &#110 radiation. The conditions were adjusted to obtain, with both systems, a 50% loss of activity of the modified ensemble. &#110 radiation modified almost all types of amino acid residues in the enzyme, with little specificity. The modification order was Tyr > Met=Cys > Lys > Ile+Leu > Gly > Pro=Phe>Thr+Ala>Trp=Ser>Arg>Asp+Glu, with 42 mol of modified residues per initial mole of native enzyme. In contrast, when the enzyme was exposed to the Fenton reaction, only some types of amino acids were modified. Furthermore, a smaller number of residues (13.5) were damaged per initial mole of enzyme. The order of the modified residues was Tyr > Cys > Trp > Met >His > Ile+Leu > Val > Arg. These results demonstrate that the modifications elicited by these two free radical sources follow different mechanisms. An intramolecular free radical chain reaction is proposed to play a dominant role in the oxidative modification of the protein promoted by &#110 radiation.     

The Impact of Gamma Radiation on Sediment Microbial Processes

Microbial communities have the potential to control the biogeochemical fate of some radionuclides in contaminated land scenarios or in the vicinity of a geological repository for radioactive waste. However, there have been few studies of ionizing radiation effects on microbial communities in sediment systems. Here, acetate and lactate amended sediment microcosms irradiated with gamma radiation at 0.5 or 30 Gy h⁻¹ for 8 weeks all displayed NO₃⁻ and Fe(III) reduction, although the rate of Fe(III) reduction was decreased in 30-Gy h⁻¹ treatments. These systems were dominated by fermentation processes. Pyrosequencing indicated that the 30-Gy h⁻¹ treatment resulted in a community dominated by two Clostridial species. In systems containing no added electron donor, irradiation at either dose rate did not restrict NO₃⁻, Fe(III), or SO₄²⁻ reduction. Rather, Fe(III) reduction was stimulated in the 0.5-Gy h⁻¹-treated systems. In irradiated systems, there was a relative increase in the proportion of bacteria capable of Fe(III) reduction, with Geothrix fermentans and Geobacter sp. identified in the 0.5-Gy h⁻¹ and 30-Gy h⁻¹ treatments, respectively. These results indicate that biogeochemical processes will likely not be restricted by dose rates in such environments, and electron accepting processes may even be stimulated by radiation.     

Some Properties of Cucumber Fruit Streak Virus

An isometric virus c. 30 nm in diameter with a single RNA species (mol.wt 1.45 × 10⁶) isolated from cucumber plants from the island of Crete (Greece) is described under the name of cucumber fruit streak virus (CFSV). The most evident symptom on naturally infected plants consisted of longitudinal chlorotic streak of the fruits. In glasshouse, the virus was soil-transmitted to C. sativus, and, mechanically, to a wide range of herbaceous hosts, most of which were infected only locally. Purified virus preparations sedimented as a single component with sedimentation coefficient of 132S. At equilibrium these preparations were homogeneous in CsCl gradients but formed two bands in Cs₂SO₄ gradients. Virus particles were stabilized by forces involving divalent cations, pH-dependent bonds and salt links between protein and RNA. Although some of the properties of CFSV are similar to those of other small spherical viruses with single RNA species there are differences which do not allow for the assignment of the virus to any of established taxonomic group of plant viruses.     

Biochemical Effects of Gamma Radiation on Potato and Sweet Potato Tissues

Relationship between the chemical constituents of tobacco leaves and the gaseous constituents of cigarette smoke from which K value¹⁾ was computed was discussed and the following presuppositions were demonstrated to be correct.

1. Fibrous substances in tobacco leaves are the main precursors of acetaldehyde, propionaldehyde, acrolein, acetone, methylethylketone, diacetyl, methanol, furan, an unknown compound, No. 6 and an unknown compound, No. 16 in cigarette smoke.

2. Sugars in tobacco leaves are the main precursors of 2-methylfuran and 2,5-dimethyl- furan in cigarette smoke.

3. Resinous substances in tobacco leaves are the main precursors of isoprene and an unknown compound, No. 2 in cigarette smoke.

     

Inactivation of Thirty Viruses by Gamma Radiation

Decimal reduction values (D value) for 30 viruses were determined. The weighted D values of the viruses suspended in Eagle's minimum essential medium ranged from 0.39 to 0.53 Mrads. It was necessary to increase the radiation dose by a factor of >3 to inactivate virus suspended in Eagle's minimum essential medium as compared to the same virus suspended in distilled water. The destruction rate curves were of a first-order reaction.     

Gamma Radiation Inactivation of Coxsackievirus B-2

The radioresistance of coxsackievirus B-2 was studied when the virus was suspended in Eagle minimal essential medium, distilled water, cooked ground beef, and raw ground beef and irradiated at various temperatures in a cobalt-60 gamma radiation source. The number of surviving viruses at given doses of radiation was determined by a plaque assay system. All destruction curves indicated a first-order reaction. When the virus was irradiated in minimal essential medium at temperatures of -30, -60, and -90 C, D values (in Mrad) were 0.69, 0.59, and 0.64, respectively. When the virus was suspended in water and irradiated at -90 C, the D value was 0.53. Cooked ground beef containing the virus was irradiated at temperatures ranging from 16 to -90 C. The D values were 0.70 (16 C), 0.76 (0.5 C), 0.68 (-30 C), 0.78 (-60 C), and 0.81 (-90 C). Raw ground beef containing the virus was irradiated at -30, -60, and -90 C, and the D values were respectively 0.75, 0.71, and 0.68. The D values indicate that the rate of viral inactivation was dependent on the suspending menstrum.     

黄瓜果实扩张蛋白基因克隆与分析

以非单性结实的全雌黄瓜为实验材料,利用cDNA-AFLP技术比较了授粉前后黄瓜幼果的基因表达差异。以ASE-AT/TAQ-CAG为引物对从授粉后黄瓜幼果组织中分离到1条特异片段,该片段仅在授粉后黄瓜幼果组织中表达,将该片段回收测序并翻译成氨基酸序列,用blastp程序在NCBI GenBank数据库中进行同源性检索和相似性比对,结果发现该片段推导的氨基酸序列与黄瓜扩张蛋白CsEXP1~9的相似性依次分别为71%、58%、63%、75%、85%、82%、67%、68%和85%,可能是一个新的黄瓜扩张蛋白基因,命名为CsEXP10,表明扩张蛋白基因可能与黄瓜果实膨大生长有密切关系。     

不同基质种植对黄瓜植株生理及果实品质的影响

以不同材料(岩棉、粗砂、刨花)为基质栽培黄瓜,于不同的生长时期对黄瓜叶片、根系及果实进行分析。结果表明,岩棉栽培黄瓜具有较大的优越性:其叶片叶绿素含量较高,果实Vc、淀粉含量最高;生长中期和后期叶片抗逆性强,叶片中硝酸还原酶活性和根系活力保持较高;产量比其它两种基质栽培的高45%以上。     

Investigation of DNA Damage Induced by Proton and Gamma Radiation

Biophysics - In this study, we compared the effects of gamma and high-energy proton radiation (1000 MeV) on DNA in aqueous saline solutions (5 and 150 mM NaCl) at doses of 30 and 50 Gy. We used...     

Influence of Thermoperiod on Growth and Development in Cucumber

We studied the influence of gradient temperature regimes on various parameters of the formation of shoots and roots of cucumber plants, such as rate of leaf appearance, rate of growth, duration of growth and length of leaves, and the rate of growth shoots organs and roots. The plants were grown under the controlled conditions: at different combinations of day and night temperature, illumination 100 W/m², and 12 h photoperiod. The comparison of constant and fluctuating diurnal temperature regimes has shown that in the optimal area for all studied indices, the highest values were recorded at the constant daily temperature (25°C for all growth indices of shoots and 20°C for growth of roots), while all gradient regimes either did not affect, or exerted inhibitory effects on the plant. Outside the optimum area, the effects of gradient temperatures differed. The main acting fluctuating temperatures, that exerted stimulating effects, combined low hardening (15°C) and optimal temperatures (25°C), which was earlier described for animals. The 15/35 and 35/15°C combinations were unambiguously inhibitory, since both temperatures are hardening for the cucumber. A lesser stimulating effect of gradient temperatures on the developmental rate in a plant, as compared to poikilothermic animals, could be due to a greater autonomy of plant ontogenesis because of autotrophy and, correspondingly, a greater degree of homeostasis. The mechanisms accounting for the responses to temperature gradients are similar in different groups of ectotherms.     

山东黄瓜地方品种资源果实外观品质的评价

对山东黄瓜地方品种资源的瓜奈形状、皮色、刺、瘤、刺色、棱沟、瓜长、把长、横径、单瓜重、把瓜比、果型指数等12个果实外观性状进行了调查分析,结果表明,山东黄瓜地方品种资源果实外观性状具有丰富的遗传多样性,平均多样性指数为1．58。华北型种质果实外观性状的平均多样性指数高于华南型种质。根据生产上对果实外观性状的要求,对两种生态类型中优良种质资源进行了评价。从外观形态上筛选出各自的代表性种质,在两种生态类型中筛选了长瓜短把型种质和短重型种质,为资源的利用和品种的选育提供了信息。