Localisation of the Site of Action of tube growth stimulation by micro UV-irradiation of pine pollen

Summary Micro-irradiation of pine pollen grains was carried out with different doses at four different dose rates and the tube growth was observed. The irradiation of the whole pollen grains in the dehydrated state and dorsal position and of those in the hydrated state and ventral position induced stimulated tube growth after receiving low doses of UV light. The effect of stimulation depended on the ratio between dose and dose rate. After partial irradiation of pollen grains at low doses, carried out with the technique of blind shot, a stimulation effect could also be observed. It was calculated that the irradiation of the cytoplasm had a strong, the irradiation of the active nucleus (vegetative) had a moderate and the irradiation of the dormant nucleus (generative) had little or no dose rate dependance. The dose effect of the nuclei showed a reverse tendency to the dose effect of the cytoplasm. Experiments with different light filters suggested that the dose rate dependance of the cytoplasm is probably not caused by a repair mechanism. The vegetative nucleus showed an effect of photoreactivation and probably also of a dark repair. The generative nucleus exhibited only an effect of photoreactivation.Dedicated to Prof. Dr. Ing. H. Glubrecht on the occasion of his 60. birthday     

Relative biological effectiveness of 103Pd and 125I photons for continuous low-dose-rate irradiation of Chinese hamster cells

Monolayers of Chinese hamster lung cells (CCL-16) in a polystyrene phantom were irradiated in vitro by 103Pd and 125I sources at dose rates of 6 to 72 cGy/h. Cell survival curves for acute high-dose-rate irradiation (over 30 Gy/h) were also measured using nearly monoenergetic X-ray beams which were designed to simulate the mean energies of photons emitted by 125I and 103Pd and also using a clinical 250 kVp X-ray beam. A profound dose-rate effect is observed over the dose-rate range of 6 to 20 cGy/h. An inverse dose-rate effect was observed for both radionuclides, with its onset occurring at a dose rate of about 20-30 cGy/h. The average RBE of 103Pd relative to 125I was determined to be 1.45 +/- 0.07, 1.41 +/- 0.07, 0.70 +/- 0.07 and 1.49 +/- 0.07 at dose rates of 6.9, 12.6, 19.0 and 26.7 cGy/h, respectively. Because 103Pd implants are generally prescribed at a higher initial dose rate (21 cGy/h) than the corresponding 125I implants (7 cGy/h), the effects of both dose rate and photon energy on biological response must be considered together. For the CCL-16 cells, the RBE of 103Pd at 19.0 cGy/h relative to that of 125I at 6.9 cGy/h was estimated to be 2.3 +/- 0.5.     

Apport du TDM en imagerie multimodalité : le point de vue du physicien médical

The recent introduction of hybrid systems SPECT/CT and PET/CT in nuclear medicine, greatly improved the diagnostic accuracy for particular clinical indications, due to the possible attenuation correction of functional images and the availability of helpful anatomic information. The introduction of CT in the nuclear diagnostic process results in a significant increase of the patient dose. This increase should be justified and optimized considering both the clinical question and the CT settings available on these systems. The choice of CT settings directly affects the effective dose. It varies basically as the square of the tube voltage, linearly with the length of the scan and the product of the current by the rotation time of the tube. It is also inversely proportional to the pitch. For attenuation correction, the literature shows that it is possible to use a low CT tube current without significant effect on tumor FDG uptake or lesion size. Conversely low CT voltage must be used with caution, depending on the algorithm implemented in the CT hybrid device to transform CT Hounsfield units to the attenuation map at the appropriate energy. The radiation dose for anatomic correlation can be substantially lower than for diagnostic-quality CT. It is possible to reduce the patient's radiation dose by a factor of 2 or 3 by acquiring a low-dose PET/CT scan for anatomic correlation of adequate image quality if compared with diagnostic ¹⁸FDG PET/CT. Using specific CT settings, the effective dose can range 7.3–11.3 mSv depending on the patient weight and age.     

Feasibility study of the Fricke chemical dosimeter as an independent dosimetric system for the small animal radiation research platform (SARRP)

For the small animal radiation research platform (SARRP) with X-ray beams in the medium energy range (tube operating voltage at 220 kVp), reference dosimetry is based on the AAPM TG-61 recommendations following the in-phantom method. The objective of this study was to evaluate the feasibility of the Fricke solution as a dosimeter to determine the absorbed dose to water. Feasibility studies at this X-ray energy range are not widely available. We evaluated the accuracy, dose linearity and dose rate dependence in a comparison with an NE 2571 Farmer ionization chamber (IC) and measurements in water. The G(Fe³⁺) factor was calculated from the curve fitting of the chemical yields for two radioactive sources (¹⁹²Ir and ⁶⁰Co) and one X-ray system with a tube operating at 150 and 250 kVp. The same methodology was followed for the dependence of the G(Fe³⁺) value on the energy and the dose agreement assessment for 180 and 200 kVp in the SARRP. The Fricke system exhibits a good linear response over the range of 5–70 Gy and an accuracy better than 2% for a 2 Gy/min dose rate. The dose rate dependence is smaller than 1% for dose rates greater than 1 Gy/min. The dependence of the G(Fe³⁺) value on the energy is smaller than 0.41%, with dose agreements better than 2%. The feasibility of the dosimeter for measurements at high doses and high dose rates makes it a suitable tool for dosimetric verifications in several preclinical irradiation configurations.     

Influence of 6 MV and 20 MV X-radiation dose rate on in vitro survive of the K-562 cell line

BackgroundAnalysis of the survival rate of cells after irradiation with a specified dose of X-radiation might be one of the basic foundations for assessment of biological implications of ionizing radiation. Investigation of the influence of X-radiation dose rate on cells was carried out in vitro using the SF2 test.AimThe aim of this study was to investigate the influence of X-radiation dose rate on the surviving fraction of the K-562 cell line for two photon energies of 6 MV and 20 MV.Materials/MethodsTo measure the cells' reaction to X-radiation of variable dose rate human leukaemic K-562 cells were used. In order to fulfil the main aim of the study, the cell line was subjected to irradiation at two different dose rates. Total dose applied at once was 2 Gy. A quantitative evaluation of cell survival rate was carried out at every step of the experiment using a clonogenic assay.ResultsHigh dose rate at the energy of 6 MV decreased the percentage of surviving cells to 23%, while lower dose rate decreased it only to 36%. A similar effect is observed at the energy of 20MV-namely at the higher dose rate the percentage of surviving cells is 18%, whereas at the lower one it is only 34%.ConclusionsThe experiment has shown that when using a lower dose rate, the biological effect of ionizing radiation is less pronounced. However, at a higher dose rate higher radiosensitivity of cells is observed.     

Voluntary food consumption and gastric emptying in rats given intravenous Triton WR-1339

Intravenously administered Triton WR-1339, a nonionic surface active agent, has been used as an endogenous hyperlipemic agent since 1951. We expected Triton to increase food consumption to supply, at least partially, the energy and acetyl groups necessary for producing the hyperlipemic state. In this study, however, we observed that the rats injected intravenously with various dose levels of Triton decreased their voluntary food intake in a dose-related manner. Two other nonionic surface active agents, Tween 20 and Tween 80, given intravenously did not alter food intake. Further studies revealed that Triton WR-1339 administered intravenously 30 min before feeding by stomach tube resulted in a marked delay in the rate of gastric emptying which was also dose related. A delay in gastric emptying has previously been suggested as one mechanism that controls food intake. Tween 20 and Tween 80 did not alter the rate of gastric emptying. We suggest that the mechanism responsible for the decrease in voluntary food consumption in Triton WR-1339 injected rats may be due to the delay of gastric emptying in these animals.     

管电压对下肢CT血管成像辐射剂量及图像质量的影响研究

目的:研究管电压对下肢CT血管成像辐射剂量及图像质量的影响。方法:选取2016年1月-2017年10月于我院行下肢CT血管成像的患者102例,将其以随机数字表法均分成观察组与对照组,每组51例。对照组管电压取120kV,观察组管电压取80kV,其他扫描参数相同。分别比较两组辐射剂量情况、客观图像质量以及主观图像质量情况。结果:观察组CT剂量指数(CTDIvol)、计量长度乘积(DLP)、有效辐射剂量(ED)水平均明显低于对照组,差异均有统计学意义(P0.05)。观察组腹主动脉、髂总动脉、股动脉、腘动脉、胫前动脉、胫后动脉、腓动脉CT值以及图像噪声均明显高于对照组,差异均有统计学意义(P0.05),两组动脉对比噪声比(CNR)和信噪比(SNR)比较差异无统计学意义(P0.05)。观察组血管阶段显示评分、血管细节分支显示评分均明显高于对照组,而血管边缘锐利度评分明显低于对照组,差异均有统计学意义(P0.05)。结论:下肢CT血管成像采用80kV管电压扫描可有效降低患者所接受的辐射剂量,且能获取较为满意的图像,值得临床推广应用。     

SOME EFFECTS OF RADIUM RADIATIONS ON WHITE MICE

It has been estimated that 92 per cent of the total radiation emitted by radium in equilibrium with its subsequent products is given off in the form of α-rays. This, however, cannot be utilized when the source is enclosed in an ordinary container, because the α-rays are absorbed completely by even a small thickness of glass. About 3.2 per cent of the total radiation is emitted in the form of β-rays, and 4.8 per cent as gamma radiation. The effects produced on the radiated mice of these experiments were due mainly to the β-rays, which are easily absorbed by tissue. The γ-rays, being only slightly absorbed by organic matter, probably contributed very little to the observed effects. It is interesting to correlate the different effects produced by the same dose of radiation. The mice which received a dose of 1.9 millicurie hours showed no local effects on the skin or hair. Neither females nor males were sterilized, and the time at which they opened their eyes or reached sexual maturity was not affected, as far as we could tell. The only difference noted between the radiated animals and the controls was in the body weight. This dose accelerated the growth of the young mice, that is, while initially of the same weight, soon after irradiation they became distinctly bigger than the controls, but finally the animals of each group had substantially the same average weight. That this variation in body weight should be accidental is unlikely, since it was observed also in the animals treated by a slightly larger dose (2.4 millicurie hours). The number of animals (seven) which showed this effect is too small to prove conclusively the accelerating effect of small doses of radiation on the body growth of mice. But considering that similar results have been. obtained by radiating plants and beetles, it is reasonable that the observed increase in weight might be attributed, at least in part, to the effects of radiation. Since this paper was first written Russ, Chambers, and Scott have shown that small doses of x-rays accelerate the body growth of rats. In view of this additional evidence there can be little doubt that the increase in weight observed in our experiments was due to the radiation. A dose of 2.4 millicurie hours applied over the backs of the animals produced no local skin effects, but it accelerated the growth of the mice as in the previous case. In addition it caused permanent sterilization of all the females. A similar result was obtained with 4.9 millicurie hours, except that the effect on the rate of growth was uncertain. A dose of 6.8 millicurie hours produced a definite but mild skin erythema and retarded the development of lanugo hair. But since in this instance the emanation was applied over the heads of the animals, the dose reaching the ovaries was not sufficient to cause sterilization, as already explained. No other definite effect was noted. In connection with the sterilization of the females it should be noted that a dose of radiation which produced no visible skin changes was sufficient to cause permanent sterility. On account of the greater distance of the ovaries from the source of radiation as compared with that of the skin directly below the tube, and the depth of tissue which the rays had to traverse to reach the ovaries, the amount of radiation acting on the latter was much smaller than the amount falling on the skin. The radiation emitted by the emanation tube is reduced to about 50 per cent of its initial value after traversing 1 mm. of tissue. Still, while the skin was not visibly affected, the mice were sterilized. This shows that the ovaries are influenced very easily by radiation of this type. We can estimate the amount of radiation reaching the ovaries which is sufficient to cause sterility to be less than 25 per cent of the amount necessary to produce visible skin changes in the mice. It should be noted also that whenever sterility of the female mice was induced, it was permanent. Furthermore, those mice which were not rendered sterile by radiation were, as far as the experiments enable us to say, as prolific as the controls. Remembering that a dose of 1.9 millicurie hours had no apparent effect on the ovaries, while a slightly larger dose, 2.4 millicurie hours, caused permanent sterility, it might be concluded that it is not possible to produce temporary sterility by radiation. We know, however, that temporary sterility can be produced, at least when the animals are radiated at a later stage in their development. The mice in our experiments were radiated for the first time soon after birth, and it is not improbable that under these conditions temporary sterility cannot be obtained. Large sublethal doses produced severe skin burns, retarded the body growth of the animals, but failed to sterilize the males. About one-third of the total skin area of the mice showed marked effects from the radiation. The animals were very sick for a time, and their growth was temporarily stunted. But nevertheless they recovered and finally became apparently normal except for the narrow hairless strip of skin which had been closest to the emanation tube. Only the females were rendered permanently sterile. The males did not show even temporary sterility when the doses of radiation were close to the lethal dose. While the testes of mammals are known to be very easily affected by radiation, still they are more resistant than the ovaries. In addition, in these experiments they were at a greater distance from the source of radiation than the ovaries, and they were better protected by the thicker layer of tissue in the path of the rays. The fact that no sublethal dose in these experiments sterilized the males shows that under the conditions of irradiation adopted the amount of radiation reaching the testes was not sufficient to affect them noticeably. If the source of radiation had been applied closer to the reproductive organs of the males, they would have been sterilized by millicurie hour doses much smaller than the lethal dose. Some of the radiated animals were killed with ether, and macroscopic and microscopic examinations of the reproductive organs were made. The ovaries of the sterile females were generally atrophied and colored yellow. The normal histological structure was altered. The characteristic findings were the destruction of the Graafian follicles, with absence of ovum cells. The testes and the epididymis of the radiated mice of the present experiment appeared macroscopically and histologically normal, with the presence of abundant spermatozoa. Owing to the method adopted for the irradiation of the mice, the testes were too far from the source of radiation, and too well protected by the intervening tissue to be definitely affected by the rays.     

Viscosity-dependent structural fluctuations in enzyme catalysis.

The effect of viscosity on the rate of catalysis of carboxypeptidase A has been tested. By use of the tripeptide carbobenzoxy-l-alanyl-l-alanyl-l-alanine [Z(L-Ala)3] as substrate, it was shown that most of the effect on the hydrolysis rate caused by the presence of 30 or 40% methanol or glycerol in aqueous solution can be ascribed to a contribution of viscosity to the catalytic rate constant, kcat. Arrhenius plots of kcat in 30 and 40% glycerol or methanol are linear and almost parallel. When the rate constants are "corrected" for the viscosity of various media, the difference between the various Arrhenius plots is considerably reduced; it vanishes, within experimental error, when the effect of the dielectric constant of the solutions is taken into account as well. It is proposed that the viscosity of the medium can influence the rate-limiting step of the enzymic reaction, which is the rate of transitions over the energy barrier preceding product formation. According to the suggested mechanism, the enzyme--substrate complex can overcome this energy barrier by viscosity-dependent structural fluctuations. The quantitative agreement between the theory and the experimental results suggests that (a) due to the temperature dependence of the viscosity of the solution, the potential energy barrier of the reaction is about 5 kcal/mol lower than the observed activation energy and (b) information about the structural flexibility of the complex can be obtained by kinetic measurements.     

A new less toxic polymer gel dosimeter: Radiological characteristics and dosimetry properties

PurposeA new polymer gel dosimeter recipe was investigated that may be more suitable for widespread applications than polyacrylamide gel dosimeters, since the extremely toxic acrylamide has been replaced with the less harmful monomer 2-Acrylamido 2-Methyl Propane Sulfonic acid (AMPS).MethodsThe new formulation was named PAMPSGAT. The MRI response (R2) of the dosimeters was analyzed for conditions of varying dose, dose rate, and temperature during scanning. Radiological properties of the PAMPSGAT polymer gel dosimeter were investigated.ResultsThe dose-response (R2) of AMPS/Bis appears to be linear over a dose range 10–40 Gy. The percentage of difference between the R2 values for imaging at 15 °C and MRI room temperature is about 4.6% for vial with 40 Gy absorbed dose which decreased to less than 1% for imaging at 20 °C. The percentage difference of Zeff of PAMPSGAT gel and soft tissue was less than 1% in the practical energy range (100 KeV–100 MeV). The electron density of the PAMPSGAT polymer gel was 2.9% higher than that of muscle. Results showed that the sensitivity of PAMPSGAT polymer gel dosimeter irradiated by ⁶⁰Co (energy = 1.25 MeV) is about 27.7% higher than that of irradiated using a 6 MeV Linac system.ConclusionsTemperature during MRI scanning has a small effect on the R2 response of the PAMPSGAT polymer gel dosimeter. Results confirmed tissue equivalency of the PAMPSGAT polymer gel dosimeter in most practical energy range. The PAMPSGAT polymer gel dosimeter response depends on energy and dose rate.     

Blood D-(-)-3-hydroxybutyrate concentrations after oral administration of trioctanoin, trinonanoin, or tridecanoin to newborn rhesus monkeys (Macaca mulatta)

Premature newborn infants are born with limited stores of glycogen and fat. Energy, such as medium-chain triglycerides (MCT), which can spare the use of body protein as metabolic energy, may be beneficial. This study compares MCT containing C8, C9, or C10 fatty acids as oral sources of energy for newborn rhesus monkeys (Macaca mulatta). On day 1 of life, 4 groups of 5 monkeys were given a single dose of water or MCT by nasogastric tube. The dose provided approximately 80% of the expected energy requirement. Plasma C8:0, C9:0, and C10:0 fatty acids and whole-blood D-(-)-3-hydroxybutyrate (3HB) concentrations were measured at 0, 1, and 3 h after dosing. Concentrations of free fatty acids (C8, C9, or C10) and ketone (3HB) increased with time after the dose. At 1 and 3 h, concentrations of C8 and C9 did not differ, but C9 was greater than C10. At 1 h, blood 3HB concentrations due to C8 triglyceride were higher than C9 or C10 (503 versus 174 and 225 μmol/L respectively). As MCT chain length increased from C8 to C10, blood concentration of 3HB decreased. Odd-chain MCT (C9 versus C8) resulted in lower whole-blood ketone (3HB), perhaps due to C9 metabolism or the rate of release or uptake of fatty acids. These results have implications for the use of MCT in nutritional supplements for preterm infants.     

Untersuchungen über das Pollenschlauchwachstum von Pisum sativum und einiger mutanten

Summary When the pollen tubes of Pisum sativum (initial line) and of its mutants are grown on a standard medium containing only sucrose, boric acid and agar-agar, no difference in maximum length was observed. But, while pollen tubes of the initial line took nine hours to reach this length, pollen tubes of the mutants needed only six hours. Growth seems to be faster in pollen tubes of the mutants than in those of the initial line.Further investigations examined the influence of twenty-one amino acids on pollen tube growth. With the initial line, these substances can be classified into three groups: those that promote pollen tube growth; those which have no influence upon its growth; and those which reduce its growth. The amino acids of each group are characterized by special structural properties. Those amino acids which accelerate pollen tube growth of the initial line show variable effects on the pollen tubes of the mutants. In some cases the same behaviour of pollen tubes can be observed whether amino acids are added or not, in others the addition of amino acids has a positive effect on pollen tube growth, though less than on pollen tubes of the initial line, and in a single case the addition of an amino acid is followed by a negative effect on growth.     

Energy acquisition and allocation in an ectothermic predator exposed to a common environmental stressor

Stressors are commonly encountered by organisms and often prove to be energetically costly. Certain stressors can simultaneously affect multiple components of an animal's energy budget and can either exacerbate energetic costs to the individual or offset one another. Here we used a commonly encountered stressor, the pesticide carbaryl, to examine the complex effects that acute environmental disturbances can have on energy expenditure, allocation, and acquisition, important processes that influence growth and reproduction. After exposing lizards (Sceloporus occidentalis) to carbaryl, we measured their metabolism over a 48 h period and assessed their food consumption over 96 h. We found no difference in total energy expenditure among treatment groups, but lizards exposed to the highest dose of carbaryl allocated energy differently than other groups. Compared to controls, these lizards exhibited a 16-30% increase in standard metabolic rate (SMR), which was offset by a 45-58% decrease in additional energy expenditures. Lizards in the highest dose group also exhibited a 30-34% decrease in energy acquisition compared to controls. The net result was a 1.83 kJ decrease in energy assimilation, equivalent to 5 times their daily SMR requirements. Our results indicate that energetic consequences of stressors may result in complex energetic trade-offs, and emphasize the need to simultaneously examine the effect of stressors on multiple portions of an animal's energy budget.     

Power spectrum,growth velocities and cross-correlations of longitudinal and transverse oscillations of individual Nicotiana tabacum pollen tube

We report on our results concerning growth rate and oscillation modes of the individual pollen tube apex. The observed volumetric growth and growth rate periodicity in the longitudinal (axial) direction are accompanied by transverse oscillations with similar frequencies but higher energies than the axial modes. Examination of the time-domain coherence between oscillations in mutually perpendicular directions revealed minimal energy dissipation in the unperturbed (isotonic) case, opposite to the two remaining cases (hypertonic, hypotonic) with notable correlations. We conjecture that the minimal energy loss is therefore optimal in the natural growth conditions. The longitudinal growth velocity is also found to be the fastest in the unperturbed case. As a result, the isolated system (pollen tube tip) is conserving energy by transforming it from elastic potential energy of extending apical wall to the kinetic energy of periodical motion. The energy dissipation is found to be about 20 % smaller in axial direction than in lateral one, indicating that the main energy consumption is dedicated to the elongation. We further observe that the hypertonic spectrum is shifted towards lower and the hypotonic towards higher frequencies with respect to the isotonic spectrum. In consequence, the turgor pressure inside the growing cell influences monotonically the frequency of both modes of oscillations. The calculated power spectrum seen as a measure of the overall energy efficiency of tip growth under hypertonic, hypotonic and isotonic conditions implies that the biochemistry has been fine tuned to be optimal under normal growth conditions, which is the developmental implication of this work. A simple theoretical extension of the Ortega equation is derived and analysed with respect to its contribution to power spectrum. We show that the plastic term, related to the effective turgor pressure, with maximum contribution at frequency f = 0 is responsible for the steady growth. In turn, the elastic contribution dependent on the time derivative of pressure fluctuations tends to move the system into oscillatory mode (f > 0). None of those mechanisms is privileged over another. The coupling mechanism is naturally generated through a convolution of those two terms and will decide about the overall character of the growth for each particular case.     

Cell to Cell Variability of Radiation-Induced Foci: Relation between Observed Damage and Energy Deposition

Most studies that aim to understand the interactions between different types of photon radiation and cellular DNA assume homogeneous cell irradiation, with all cells receiving the same amount of energy. The level of DNA damage is therefore generally determined by averaging it over the entire population of exposed cells. However, evaluating the molecular consequences of a stochastic phenomenon such as energy deposition of ionizing radiation by measuring only an average effect may not be sufficient for understanding some aspects of the cellular response to this radiation. The variance among the cells associated with this average effect may also be important for the behaviour of irradiated tissue. In this study, we accurately estimated the distribution of the number of radiation-induced γH2AX foci (RIF) per cell nucleus in a large population of endothelial cells exposed to 3 macroscopic doses of gamma rays from ⁶⁰Co. The number of RIF varied significantly and reproducibly from cell to cell, with its relative standard deviation ranging from 36% to 18% depending on the macroscopic dose delivered. Interestingly, this relative cell-to-cell variability increased as the dose decreased, contrary to the mean RIF count per cell. This result shows that the dose effect, in terms of the number of DNA lesions indicated by RIF is not as simple as a purely proportional relation in which relative SD is constant with dose. To analyse the origins of this observed variability, we calculated the spread of the specific energy distribution for the different target volumes and subvolumes in which RIF can be generated. Variances, standard deviations and relative standard deviations all changed similarly from dose to dose for biological and calculated microdosimetric values. This similarity is an important argument that supports the hypothesis of the conservation of the association between the number of RIF per nucleus and the specific energy per DNA molecule. This comparison allowed us to calculate a volume of 1.6 μm³ for which the spread of the specific energy distribution could explain the entire variability of RIF counts per cell in an exposed cell population. The definition of this volume may allow to use a microdosimetric quantity to predict heterogeneity in DNA damage. Moreover, this value is consistent with the order of magnitude of the volume occupied by the hydrated sugar-phosphate backbone of the DNA molecule, which is the part of the DNA molecule responsible for strand breaks.     

Abscisic acid induced decay of strawberry transpiration

The effect of 0–7.5 × 10⁻³μmol abscisic acid (ABA) on the transpiration of strawberry ( Fragaria grandiflora Duch. ev. Red gauntlet), both under illumination and in darkness, was investigated with the use of an infrared gas analyser. Mathematical analysis of the results suggests that the decrease in transpiration after darkening can be described by a series of first-order processes with continuous distribution of rate constants k. Application of ABA makes the rate constant distribution narrower, so that one single rate constant occurs at the highest doses. ABA accelerates the decrease of transpiration more in darkness than under illumination. This suggests that the process of efflux of osmotically active particles from guard cells is influenced more than influx. For ABA doses greater than 7.5 × 10⁴μmol, the transpiration decreases in two stages, of which only the first one seems to be affected by ABA: but above this dose further acceleration of decay of transpiration after darkening is not observed. The observations may indicate that above this critical dose of ABA the rate determining step consists in guard cell wall relaxation rather than in efflux of osmotica.     

The Effect of a Perforated Mouthpiece Tube on Cigarette Smoke Reduction

Cigarette smoke reduction due to a perforated mouthpiece tube was measured, and its results were compared with the reduction caused by conventionally vented acetate filters. The reduction of nicotine and tar increased with the ventilation rate through the perforated tube. In the absence of a filter material, the difference between the reduction of tar and nicotine was found to be greater than that observed for conventionally vented filters, and the concentration of nicotine in tar was enhanced. The reduction of carbon monoxide, carbon dioxide, acetaldehyde, isoprene and acetone were all proportional to the ventilation rate through the perforated tube. The presence of a filter material had no effect on the gas and vapor phase components.     

Pollen tube competition as a mechanism of prezygotic reproductive isolation between Mimulus nasutus and its presumed progenitor M. guttatus

This paper considers the extent to which differences in pollen tube growth rates can provide prezygotic reproductive isolation between Mimulus nasutus and its presumed progenitor, Mimulus guttatus . Mimulus nasutus is partially cleistogamous, but its larger chasmogamous flowers offer appreciable opportunity for outcrossing. Mimulus nasutus was found to have smaller pollen grains and shorter styles than M. guttatus . No differences were observed in pollen grain germination on conspecific and heterospecific stigmas. However, pollen tube growth rates of M. nasutus were found to be much slower than those of M. guttatus in the styles of that species. Consequently, any M. nasutus pollen transferred to an M. guttatus stigma was found to be competitively disadvantaged in an M. gutattus style. By contrast, no difference in pollen tube growth rate was detected between the species when growing in M. nasutus styles, possibly because M. nasutus styles are unable to support fast pollen tube growth. We tested the prediction from the pollen tube studies that a 50:50 mix of M. guttatus and M. nasutus pollen would produce 50% hybrid seeds when M. nasutus was the maternal parent, and near to 0% hybrid seed when M. guttatus was the maternal parent. The results were found to support this prediction. We conclude that pollen–pistil interactions can effect strong reproductive isolation between these species, as M. guttatus pollen tubes have a competitive advantage over those of M. nasutus in an M. guttatus style, but not in an M. nasutus style.     

甜柿巨大花粉萌发特征及辐射敏感性研究

以‘禅寺丸’（Diospyros kakiL.f)为试材,对巨大花粉萌发率,花粉管伸长,亲和性及辐射敏感性进行了研究。结果表明：（1）巨大花粉在培养基和柱头上正常萌发,不存在萌发及亲和性障碍;（2）巨大花粉萌发迟缓及低萌发率造成其与普通花粉受精竞争中处于劣势;（3）巨大花粉和普通花粉对^60Coγ-射线辐射敏感性有差异。巨大花粉的敏感性低于普通花粉,1200Gy为刺激巨大花粉萌发的适合剂量,同时可抑制普通花粉萌发,从而可相对提高巨大花粉的受精竞争力;（4）辐射延迟效应造成巨大花粉的萌发率在一定期间内有下降趋势。但自身的修复机制可部分恢复其生活力。     

Monte Carlo simulation of eye lens dose reduction from CT scan using organ based tube current modulation

PurposeTo investigate lens dose reduction with organ based tube current modulation (TCM) using the Monte Carlo method.MethodsTo calculate lens dose with organ based TCM, 36 pairs of X-ray sources with bowtie filters were placed around the patient head using a projection angle interval of 10° for one rotation of Computed Tomography (CT). Each projection was simulated respectively. Both voxelized and stylized eye models and Chinese reference male phantoms were used in the simulation, and tube voltages 80, 100, 120 and 140 kVp were used.ResultsDose differences between two eye models were less than 20%, but large variations were observed among dose results from different projections of all tube voltages investigated. Dose results from 0° (AP) directions were 60 times greater than those from 180° (PA) directions, which enables organ based TCM reduce lens doses by more than 47%.ConclusionsOrgan based TCM may be used to reduce lens doses. Stylized eye models are more anatomically realistic compared with voxelized eye models and are more reliable for dose evaluation.