氚水在模拟水稻－水－土壤生态系统中的行为

采用模拟污染物的同位素示踪技术研究HTO(流水)在水稻-水-土壤模拟生态系统中的迁移、消长行为,并应用三库室开系统模型和非线性回归方法确定了水稻、水和土壤分室的拟合方程．结果表明,田表水中的HTO不仅在系统各分室间转移和分配,而且迅速向系统外散逸;HTO中的流以自由水氚和结合态流形式存在于水稻中,以吸湿性水流和结晶水氚存在于土壤,其中自由水氚(或吸湿性水氚)的比活度大于结合态流(或结晶水氚);水稻植株和土壤中HTO比活度随时间增加至最大值后又趋于下降,而结合态氚则呈缓慢增加;水稻茎秆中的总氚比活度高于其它各部位,而后逐渐趋于动态平衡．对实验数据进行回归分析得：田表水、土壤和水稻植株中的总氚比活度分别为Cw(t)=32.19c^-0.0353t 99.94c^-0.330t、Cs(t)=20.42(e^-0.0353t-e^-0.330t)和Cr(t)=38.49c^-0.0353t-10.13e^-0.330t-28.36c^-2.5744t。方差分析结果表明,各回归方程较好地反映了HTO在水稻-水-土壤生态系统中的行为．     

A metabolic derivation of tritium transfer coefficients in animal products

Tritium is a potentially important environmental contaminant originating from the nuclear industry, and its behaviour in the environment is controlled by that of hydrogen. Animal food products represent a potentially important source of tritium in the human diet and a number of transfer coefficient values for tritium transfer to a limited number of animal products are available. In this paper we present an approach for the derivation of tritium transfer coefficients which is based on the metabolism of hydrogen in animals. The derived transfer coefficients separately account for transfer to and from free (i.e. water) and organically bound tritium. A novel aspect of the approach is that tritium transfer can be predicted for any animal product for which the required metabolic input parameters are available. The predicted transfer coefficients are compared to available independent data. Agreement is good (R ²=0.97) with the exception of the transfer coefficient for transfer from tritiated water to organically bound tritium in ruminants. This may be attributable to the particular characteristics of ruminant digestion. We show that tritium transfer coefficients will vary in response to the metabolic status of an animal (e.g. stage of lactation, diet digestibility etc.) and that the use of a single transfer coefficient from diet to animal product is inappropriate. It is possible to derive concentration ratio values from the estimated transfer coefficients which relate the concentration of tritiated water and organically bound tritium in an animal product to their respective concentrations in the animals diet. These concentration ratios are shown to be less subject to metabolic variation and may be more useful radioecological parameters than transfer coefficients. For tritiated water the concentration ratio shows little variation between animal products ranging from 0.59 to 0.82. In the case of organically bound tritium the concentration ratios vary between animal products from 0.15 (goat milk) to 0.67 (eggs). Received: 28 May 2001 / Accepted: 20 August 2001     

The transfer of tritium-labeled organic material from grass into cow's milk

Two lactating cows were given tritiated hay containing organically bound tritium (OBT) only for about 4 weeks. Tritium activity was determined in milk fat, casein, lactose, milk water, and whole milk. In one cow, milk was sampled for approximately 450 days, covering two lactation periods. At steady state, specific tritium activities in casein, lactose, and milk water were 58, 10, and 11%, respectively, of those in milk fat. Some OBT was converted into THO during catabolism and entered the body water pool. This 3H source accounted for nearly 40% of tritium in lactose, but in casein and milk fat about 97% of tritium was derived from ingested OBT. Comparison of the specific activity of milk constituents with the specific activity of ingested hay showed the following values: 0.84 for milk fat, 0.49 for casein, 0.05 for lactose, 0.10 for milk water. About one-half of the tritium transferred to milk was found in organic milk constituents and the other half in milk water. Decrease of tritium activity with time could be represented by three components with different half-lives for the organic milk constituents. Those for milk fat and casein were quite similar, with a slow component of nearly 3 months.     

Tritium in plants: A review of current knowledge

The aim of this paper is to provide an overview of the literature regarding the fate of tritium in plants. At first, some prerequisites about the sources, chemical and physical characteristics, biological effects and potential risks associated to tritium are presented. The general scheme of tritium transport and cycling in the environment, the different tritium fractions in biological organisms and the corresponding techniques for sampling and measurement are discussed. Then, the main processes of uptake, incorporation and conversion of tritium into plants are described, based on experimental data. As tritium incorporated into the organic fraction may be the major contributor to the dose of radiation received following its ingestion by man, the biological mechanisms and kinetics of organically bound tritium (OBT) production are a major focus. Some predictive models of short-term or chronic exposure are described. Finally, the pending questions, concerning the fate of tritium in plants, are tackled.     

Incorporation of tritium from water into tissue components of the booklouse, Liposcelis bostrychophilus

Liposcelus bostrychophilus is one of the first insects and one of the few terrestrial arthropods for which the turnove of body water (³HOH) and the incorporation of the labelled hydrogen into other tissue components have been evaluated. Turnover of body water at 28°C in 85% r.h. proceeded at 60 to 80%/day, depending on the availability and palatibility of food. The amount of freely exchangeable tritium in a microgram of tissue solids was equal to the amount of tritium in 0.034 μg of the body water. The involvement of water in metabolic reactions is reflected in the more firmly bound tritium, which in the same units was 0.04 in adults that were fasting during exposure, 0.1 in others that were feeding, and 0.3 to 0.4 in those reared with ³HOH. Of the latter, 10% was not subject to turnover while other compartments were cleared at 5%/day and 12%/day. In regard to the radiation hazard of ³HOH, the total ³H per microgram of fresh weight did not exceed 0.8 of the concentration in ambient water; growth and reproduction were observed with a radiation dose rate of 100 rad/day.     

Movement of Water and Solutes in Sieve Tubes of Willow in Response to Puncture by Aphid Stylets. Evidence against a mass flow of solution

Experiments are described in which bark strips of willow were sealed to polythene tubes having two compartments. This allowed investigations to be made of the transport along the sieve tubes of tritiated water, ¹⁴C-labelled sugars, and ³²P-phosphates from one compartment, towards a stylet situated in the bark over the other compartment. Although activity from both ¹⁴C and ³²p was detected in the stylet exudate usually within 1 hour from isotope application, tritium activity was never detected even after a period of 8 hours in most experiments, though in certain cases, very low activities were detected after 4 hours. Subsequent experiments in which stylets were sited over both compartments showed that tritium activity moved laterally into the punctured sieve element more rapidly than either ¹⁴C or ³²P. Experiments using both live and dead bark in which stylets were not employed, showed that within 4 hours tritium activity had moved by diffusion along the whole length of a bark strip, therefore after this time tritium activity could have moved into the stylet exudate by a diffusional process. The lack of rapid longitudinal movement of tritiated water along the sieve tubes, indicates that the transport process is unlikely to be a mass flow of solution.     

Changes in apparent water permeability during the moulting cycle in the western rock lobster

The kinetics of water exchange, as measured by ³H₂O fluxes, were examined in the western rock lobster, Panulirus longipes (Milne Edwards) during stages C₄, D₃, D₄, D₄-E and B₁ of the moulting cycle. A series of samples of blood and external water was taken during each experiment and the inward and outward rate constants found using the SAAM 25 computer program, assuming a simple 2-compartment model with reversible exchange. Both inward and outward turnover rates remained constant up to the swelling prior to ecdysis when there was an increase of 203% inwards compared with 133% outwards. The latter increased in stage B₁, so that both rates were comparably high, probably due to the increased permeability of the soft integument.Further analysis showed that the rock lobster does not behave as a single compartment with respect to tritiated water. Two compartments were resolved by graphical analysis, one with fast and the other with slow exchange. It is suggested that blood and tissue ‘free’ water comprise one compartment and chemically ‘bound’ water the other, with fast exchange between the free and bound water and relatively slow exchange between free body water and the external medium.     

Effect of lifetime intake of organically bound tritium and tritiated water on the oocytes of rats

Summary Rats were continuously exposed to constant activity of tritium in drinking water (HTO group) or to tritium organically bound in food (T-food group) in the period from conception ofF ₁ generation through maturity. Female offspring were killed at the age of 21 and 71 days and the oocytes in their ovaries were counted. Mean dose rates absorbed in the ovaries were for the HTO groups 7.25 ± 0.37 and 14.73 ± 0.79 mGy/day and for the T-food group 4.84 ± 0.25 mGy/day.Reduction in the oocyte number in the ovaries of females exposed to tritiated food was bigger than in the ovaries of females exposed to tritiated water. The dependence of the survival of small oocytes on the dose rate and the corresponding total accumulated dose had an exponential character. The damaging effect of tritium was for the period from conception to 21 days of age bigger than from 21 to 71 days of age. Of all stages of oocyte development, the highest sensitivity to tritium irradiation was observed in small oocytes and oocytes with one complete layer of follicle cells. As a result, relative number of the growing and large oocytes increased.     

Energy metabolism used as a tool to model the transfer of 14C and 3H in animals

The transfer through the environment of ³H and ¹⁴C must be modelled differently than that of other radionuclides released from nuclear reactors because hydrogen and carbon enter straight into the life cycle. A solid understanding of the behaviour of ³H and ¹⁴C in the food chain is essential because ³H may be released in large quantities from future thermonuclear reactors, and ¹⁴C accumulates in the environment because of its long half-life. For the present study, the hypothesis that both ³H and ¹⁴C metabolism in mammals can be modelled based on the understanding of energy metabolism has been tested. Recently published results demonstrate that the loss rate of organically bound tritium and ¹⁴C from tissues of laboratory and farm animals can be assessed based upon their specific metabolic rates and enthalpy of combustion; the same is true for human beings. The improved model presented here relates the dynamics of organically bound tritium and ¹⁴C within organs to the whole body and has been expanded to account for the growth of ruminants. The improved model has been expanded and applied for ¹⁴C transfer in wild mammals and has been modified to apply to birds.     

Physical water compartments: a revised concept of perinatal body water physiology

This review presents experimental data on the perinatal significance of the recently developed concept of physical water compartments. This concept implies that in addition to the compartmentalization of body water into the intra- and extracellular spaces, motionally distinct water fractions - designated as physical water compartments - are also of importance in the neonatal body fluid redistribution. H(1)-NMR spectroscopy provides a quantitative estimate of tissue water fractions with different mobility as multicomponent analysis of the T(2) relaxation decay curves allows us to determine the fast and slow relaxing components of the curves corresponding to the bound and free fractions of tissue water. Using this method, free and bound water fractions were measured in fetal and neonatal rabbit tissues (skin, skeletal muscle, liver, brain, lung) at different stages of maturity and under conditions of various fluid intake. It has been demonstrated that water mobility in individual fetal/neonatal tissues varies greatly and there is a general tendency of increasing free water at the expense of bound water fraction with progressing maturation. This tendency appears to be accelerated in the immediate postnatal period when the tissue water content is markedly reduced. The importance of hyaluronan in this process has also been addressed as the hyaluronan content is markedly elevated in the fetal/neonatal tissues and due to its polyanionic, hydrophilic nature it has been claimed to play a prominent but not clearly defined role in the control of tissue hydration.     

A four compartment model to study the kinetics of strontium metabolism in man

Many drugs confer upon the body the characteristics of a four compartment model. This paper deals with the estimation of pharmacokinetic parameters of a four compartment model to study the distribution of strontium in the organism. The central compartment (where the introduction of the material takes place) is connected to two other compartments (which represent the organic fluids) and one of them is connected to the fourth compartment (which represents the fraction that can be exchanged in the bone). The elimination from the central compartment is through urine and the elimination from the third compartment is in the form of a non-exchangeable deposit. The method of solution involves an optimization method which provides the global minimum of δ, a single variable function. The model is tested for different sets of data and the results are compared with those obtained by the generalized leasr square method.     

The significance of immunity disorders in the development of tumorous effects during the long-term action of tritium in mice

In experiments with CBA mice it was shown that the long-term influence of tritium oxide administered with drinking water daily during 180 days (370 kBq.g-1 of body mass, cumulative dose 8.7 Gy, dose rate 4.5 cGy.day-1) causes the development of immunity deficiency 90 days after the onset of the administration that persists for up to 270 days. There is a 34% decrease in the average life of irradiated animals and an increase in the number of malignant neoplasms (postmortem examination was performed after natural death or killing on days 250, 350 and 450). There is a direct relationship between the occurrence of malignant neoplasms and the immunity deficiency.     

Endoplasmic reticulum-to-cytosol transport of free polymannose oligosaccharides in permeabilized HepG2 cells.

Free polymannose oligosaccharides have recently been localized to both the vesicular and cytosolic compartments of HepG2 cells. Here we investigated the possibility that free oligosaccharides originating in the lumen of the endoplasmic reticulum (ER) are transported directly into the cystosol. Incubation of permeabilized cells in the absence of ATP at 37 degrees C led to the intravesicular accumulation of free Man9GlcNAc2 which was generated from dolichol-linked oligosaccharide in the ER. This oligosaccharide remained stable within the permeabilized cells unless ATP was added to the incubations at which time the Man9GlcNac2 was partially converted to Man8GlcNAc2, and both these components were released from an intravesicular compartment into the cytosolic compartment of permeabilized cells. In contrast, when permeabilized cells, primed with either free triglucosyl-oligosaccharide or a glycotripeptide, were incubated with ATP both these structures remained associated with the intravesicular compartment. As the conditions in which free oligosaccharides were transported out of the intravesicular compartment into the cytosolic compartment did not permit vesicular transport of glycoproteins from the ER to the Golgi apparatus our data demonstrate the presence of a transport process for the delivery of free polymannose oligosaccharides from the ER to the cytosol.     

Effect of phosphorus application on transformation of zinc fraction in soil and on the zinc nutrition of lowland rice

We have studied in the laboratory the effect of different levels of P application on the transformation on native as well as of applied zinc in a rice-growing soil under two moisture regimes viz., flooded and nonflooded. Application of P caused a decrease in the water soluble plus exchangeable and organic complexed with a concomitant increase in the amorphous and crystalline sesquioxide bound forms of native soil zinc. Application of P also caused a decrease in the transformation of applied Zn into the water soluble plus exchangeable and organically complexed and an increase in the amorphous and crystalline sesquioxide bound forms of zinc. The above effects of P were more pronounced in soil under flooded than under nonflooded moisture regimes. The water soluble plus exchangeable and the organically complexed forms of Zn are considered to play an important role in Zn nutrition of lowland rice, while the role of the amorphous and crystalline sesquioxide bound forms are less important in this regard.The results of greenhouse experiments showed that P application caused a progressive decrease in the Zn concentration in shoot and root. This was attributed at least partly to the decrease in the water soluble plus exchangeable and organically complexed forms of Zn and an increase in the amorphous and crystalline sesquioxide bound forms in soil due to P application.     

Internalized proteins directed into accumulative compartments of mosquito oocytes by the specific ligand, vitellogenin

We have investigated the internalization pathways for a specific protein, vitellogenin, and a non-specific protein, horseradish peroxidase, in the mosquito oocyte in vivo. The internalized proteins were localized by electron microscopical immunocytochemistry or autoradiography; the relationship of their destination compartments with lysosomes was monitored by visualization of acid phosphatase. Proteins internalized by the oocyte follow either a specific accumulative route or a lysosomal degradative route. Via coated vesicles, both proteins enter the same compartment, the endosome, where they dissociate from membrane-binding sites. The route to their final destination depends on the presence of the specific ligand. In its absence, the degradative route is followed, and the endosome with non-specific protein fuses with lysosomes. In the presence of the specific ligand, the accumulative route is followed, and both specific and non-specific proteins are delivered into an accumulative compartment, the transitional yolk body. During the transformation of the transitional yolk body into the final storage compartment, a mature yolk body, vitellogenin undergoes crystallization, whereas the non-specific protein is concentrated in small vesicular extensions of the compartmental membrane. These vesicles are separated from the yolk bodies and apparently deliver the non-specific protein into the lysosomal system. We concluded that any protein bound to the membrane would be internalized by the oocyte, but only binding of the specific ligand to its receptor serves as a transmembrane signal stimulating the formation of accumulative compartments.     

Studies on mobilization of chromium with reference to its plant availability – Role of organic acids

Metal-organic acid interactions with special reference to their plant availability have been studied. The role of organic acids in the mobilization of Cr by converting it into labile organically bound form, enhancing its availability, is highlighted. Pot experiments are conducted to investigate the effect of various organic acids on the uptake and translocation of root absorbed trivalent and hexavalent chromium by maize (z. mays) plants grown in sand and soil culture. Statistically significant increases in chromium accumulation from CrIII-treated plants in the presence of increasing concentrations of organic acid suggest the existence of CrIII – organic acid interactions in the soil plant system. In order to support the above mentioned hypothesis of formation of organically bound CrIII in the presence of various organic acids (carboxylic and amino acids), separate experiments have been performed to synthesize and estimate its respective organically bound forms. Amendments with organic acids, however, do not appear to markedly affect chromium accumulation from CrVI treatment. The results are discussed on the basis of the potential of organic acids to form complexes with CrIII.     

Biosynthesis of membrane lipids in rat axons

Compartmented cultures of sympathetic neurons from newborn rats were employed to test the hypothesis that the lipids required for maintenance and growth of axonal membranes must be synthesized in the cell body and transported to the axons. In compartmented cultures the distal axons grow into a compartment separate from that containing the cell bodies and proximal axons, in an environment free from other contaminating cells such as glial cells and fibroblasts. There is virtually no bulk flow of culture medium or small molecules between the cell body and axonal compartments. When [methyl-3H]choline was added to the cell body-containing compartment the biosynthesis of [3H]-labeled phosphatidylcholine and sphingomyelin occurred in that compartment, with a gradual transfer of lipids (less than 5% after 16 h) into the axonal compartment. Surprisingly, addition of [methyl-3H]choline to the compartment containing only the distal axons resulted in the rapid incorporation of label into phosphatidylcholine and sphingomyelin in that compartment. Little retrograde transport of labeled phosphatidylcholine and sphingomyelin (less than 15%) into the cell body compartment occurred. Moreover, there was minimal transport of the aqueous precursors of these phospholipids (e.g., choline, phosphocholine and CDP-choline) between cell compartments. Similarly, when [3H]ethanolamine was used as a phospholipid precursor, the biosynthesis of phosphatidylethanolamine occurred in the pure axons, and approximately 10% of the phosphatidylethanolamine was converted into phosphatidylcholine. Experiments with [35S]methionine demonstrated that proteins were made in the cell bodies, but not in the axons. We conclude that axons of rat sympathetic neurons have the capacity to synthesize membrane phospholipids. Thus, a significant fraction of the phospholipids supplied to the membrane during axonal growth may be synthesized locally within the growing axon.     

A stochastic approach for the interpretation of single pulse experiments in morphological multicompartments of renewing and exponentially growing cell populations

A general approach for the interpretation of single pulse experiments in multicompartment systems is presented. It allows an extension of the classical single compartment Barret's methodology, and has been detailed in the pipeline model case to show its capabilities. FLM, FLC, grain count curves, labelling indices and compartment size ratios of each compartment, are fitted into a coherent scheme that fully describes the statistical aspects of the phase durations including possible losses. It is shown that if the compartments are identical, irrespective of the feedback coupling between them, the system may be treated as a single compartment. It is also shown that the FLC information is necessary to identify the existence of losses in the system, and how to correct the "apparent" transit times if losses are present. The pipeline model is treated and a suggestion is made to reconcile the "British" and "American" interpretations of the erythroid system. As a corollary, simple formulae are derived in the deterministic case through a coupling matrix describing the interaction between compartments. Computer codes are described and have been implemented in the J.E.N. Thermoecology Laboratory.