14CO2 Gas Research Articles

14C‐Partitioning and biomass allocation in common bean (Phaseolus vulgaris L.) under different moisture levels during pod filling

AbstractPlants modify their carbon allocation as a response to low water availability. The objective of this study was to evaluate, using a 14CO2 pulse‐chase analysis, the effect of moisture restriction on biomass production in common bean plants var. OTI. The plants were maintained with irrigation until the beginning of pods filling; then, three groups were formed, kept at 100%, 75% or 50% field capacity (FC). After 10 days, 14CO2 gas was supplied to the plants for 4 hr. The plants were harvested at 1, 3 and 7 days after applying the label. Ripe fruits imported more than 50% of the total 14C. Particularly, the label presented greater changes in pericarps of stage III of pod development. The fructose concentration doubled that of the glucose and decreased with the pod age; sucrose concentration increased in pericarps in stages III and IV of pod development in relation to those in stage II. The sucrose decrease only in stage II pericarps on day 7, as well as the starch concentration that decreased by half in the 50% FC condition. The latter coincided with the highest amylolytic activity as evaluated in native gels. These findings open new opportunities to research the carbon allocation mechanism under moisture restriction.

Allocation of photoassimilated carbon of radiata pine (Pinus radiata) seedlings as affected by soil water stress

ABSTRACT This study was carried out to determine the carbon (C) allocation of tree components following water stress in radiata pine (Pinus radiata) seedlings. The seedlings were exposed to various water contents (low, moderate and high soil water content) for 30 days and labelled with 14CO2 gas for six hours on the 31st day. Biomass in all seedling components (foliage, stems and roots) was significantly higher in the moderate soil water content treatment than in the low soil water content treatment, while seedling biomass did not significantly differ between the moderate soil water and high soil water content treatments. The shoot/root ratio of seedlings decreased when soil water content decreased. The C concentrations of radiata pine seedlings were not affected by the soil water content, whereas the soil water stress-induced difference in the C allocation of seedlings was attributed to differences in seedling biomass. The translocation of pulse-labelled 14C from the foliage to the roots was enhanced by low soil water content. The distribution of 14C was highest in foliage, followed by roots, stems and soil. The results indicate that soil water content was one of the primary factors influencing biomass allocation in the early growth of radiata pine seedlings.

Development and testing of a cryogenic system for radioactive 14CO2 gas separation for nuclear waste monitoring

A prototypal system for the separation of CO2 from air and concentration in small volume containers was developed and tested at ENEA in the frame of two European research projects (MetroRWM and MetroDECOM), funded by the European Metrology Research Programme (EMRP). The aim of the proposed system is to separate and concentrate in an effective way the CO2 content from radioactive air stream in nuclear installations or nuclear waste repositories during normal operation or decommissioning phase, by using a cryogenic process. This system is intended to be used as preparatory stage of the CO2 samples to be analysed by a radioactive gas-in-air monitor using a standardised 14CO2. Connecting the ENEA cryogenic system to the monitor will enable a sample of air to be processed and measured, and its 14CO2 activity concentration calculated, from knowledge of the volume of air sampled by the cryogenic system and the response of the monitor.Our work demonstrates the feasibility of a14C monitoring based on cryogenic method, according to which the components of a gaseous mixture can be separated on the basis of the differences between the phase transition properties of each gas components. The initial design was made considering the readily-available commercial instruments and devices and combining them in an optimum way. System testing showed almost 100% CO2 separation and recovery.

Visualization of 14CO2 gas fixation by plants

Using the real-time radioisotope imaging system (RRIS), we present the carbon dioxide gas fixation process of a soybean plant applying the 14C-labeled gas. When 14CO2 gas was supplied to the selected mature leaf, the fixed carbon, photosynthate, was transferred and accumulated to the younger leaves preferentially within 24 h. When 14CO2 gas was supplied to the younger leaves, fixed carbon was hardly moved. In the case of the pods, fixed 14CO2 gas in the leaf was preferentially transferred to the closest pod.

The complex character of photosynthesis in cucumber fruit.

The surface area of a mature green cucumber (Cucumis sativa L.) fruit is comparable with that of a functional leaf, but the characteristics of fruit photosynthesis and its contribution to growth are poorly understood. Here, the photosynthetic properties of two genotypes of cucumber (dark green and light green fruits) were studied using a combination of electron microscopy, immunogold enzyme localization, chlorophyll fluorescence imaging, isotope tracer, and fruit darkening techniques. Chlorophyll content of the exocarp is similar to that of leaves, but there are no distinctive palisade and spongy tissues. The efficiency of PSII is similar to that in leaves, but with lower non-photochemical quenching (NPQ). Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is found mainly in the exocarp, while phosphoenolpyruvate carboxylase (PEPC) is primarily localized to vascular bundles and placenta tissue. Rubisco and PEPC expression at both transcriptional and translational levels increases concurrently during fruit growth. The contribution of fruit photosynthesis in exocarp to its own C accumulation is 9.4%, while ~88% of respiratory CO2 in fruit was captured and re-fixed. Photosynthesis by cucumber fruits, through direct fixation of atmospheric CO2 and recapture of respired CO2, as verified by 14CO2 uptake and gas exchange, makes an important contribution to fruit growth.

Application of a wet oxidation method for the quantification of 3H and 14C in low-level radwastes

Wet oxidation methods are utilized to separate and quantify 3H and 14C radionuclides in inorganic and organic radwastes generated at nuclear facilities. Because 3H and 14C are pure beta emitters with half-lives of 12.3 and 5,730 years, respectively, these radionuclides should be chemically separated from other radionuclides present in radwastes for accurate quantification. In particular, a collection technique for 14C radionuclide in radwastes is needed because it is converted into 14CO2 gas by an oxidation reaction.To confirm the recoveries of 3H and 14C, various standard radioactive sources were used to verify the proposed method. Because the majority of 3H radionuclides are distributed in tritiated water (HTO), only tritiated water was used as a standard for 3H radionuclides. Additionally, 14C-labeled methanol (14CH3OH), lauric acid (14CH3(CH2)10COOH), sodium bicarbonate (NaH14CO3), and toluene (C6H514CH3) were used as 14C standards. The compounds were oxidized with chemical oxidants and then separated. The individual species were mixed with a scintillation cocktail and counted using a liquid scintillation counter. The recoveries of 14C and 3H were 82–97% and 98%, respectively. The wet oxidation method will be applied to RI wastes for clearance.

ＴＲＵ廃棄物の地層処分を想定した放射性炭素の植物による経根吸収―酢酸を起源とする放射性炭素の植物への移行―

Hydroponic experiments were conducted to examine root-uptake of 14C in the form of acetic acid by 3 kinds of plants (marigold, tall fescue, and paddy rice) based on buried transuranic (TRU) waste disposal. Also, chamber experiment was conducted to examine loss of 14C as vaporized carbon dioxide (CO2) from the experimental tessera (spatially heterogeneous environment). The distribution of radioactivity in the plant, mediums, and carbon dioxide (14CO2) in the chamber were determined, and the distribution of 14C in the plant was visualized by the autoradiography. The plants absorbed and assimilated 14C through the roots. The amount of 14C in marigold and tall fescue were higher than that of paddy rice. However, the amounts of 14C-acetic acid absorbed by all the plants through their roots were considered to be very small. More so, 14CO2 gas was released from the culture solution to the atmosphere; however, it was not enough for the plant to perform photosyn-thesis. Assimilation of 14C in the plant shoots would be because of 14C movement of inorganic forms such as CO2 and HCO3-via the roots. Thus, the results indicated that the plants absorbed 14C through the roots and assimilated it into the shoots or edible parts not because of uptake of 14C-acetic acid but because of uptake of 14C in inorganic forms.

Responses of photosynthetic rates to genotypic differences in sink-to-source ratios in upland cotton (Gossypium hirsutum L.)

Photosynthesis is the process that cotton plants use to fix carbon from the atmosphere to generate new growth and ultimately, yield. Attempts to increase genetically the rate of photosynthesis requires a knowledge of the relationship between photosynthesis and growth stage, fruit load and environmental parameters. The purpose of this research was to determine if genetic differences in sink-to-source ratios influenced single-leaf photosynthetic rates. Five cotton (Gossypium hirsutum L.) genotypes differing in sink-to-source ratios were grown in a field environment. Photosynthetic rate was estimated at mid-morning and mid-afternoon with 14CO2 gas exchange on the uppermost fully expanded mainstem leaf. Seven measurements of photosynthetic rate were made at intervals commencing 52 days after planting (DAP) and terminating 104 DAP. At each sampling date solar irradiance, leaf and air temperature and leaf conductance were also measured. Correlations between these parameters and photosynthetic rate at each sampling date and over the entire season were generally not statistically significant. The occasional significant correlations were small. After photosynthetic rate was estimated, plants were harvested; leaf areas and dry weights were then measured. Photosynthetic rate, measured on single leaves, varied in response to light, leaf temperature, leaf conductance, growth traits and sink-to-source ratios (weight of fruit and stem per unit leaf area). Photosynthetic rate was low at the first sampling date and increased thereafter with significant differences being expressed among the five genotypes. Sink-to-source ratios increased at each sampling date with significant differences among genotypes. Single-leaf photosynthetic rate increased as the sink-to-source ratios increased.

Patterns of translocation of carbon in four common moss species in a black spruce (Piceamariana) dominated forest in interior Alaska

The patterns of translocation of carbon in different-age tissues of four common moss species in a black spruce (Piceamariana (Mill.) B.S.P.) dominated forest near Fairbanks, Alaska, were studied by 14C labelling and carbohydrate analysis. A simple, in-vial combustion technique was developed for combustion of small (< 10 mg) radioactively labelled samples of plant tissue. The method was used to measure specific activity of 14C in moss tissue 2 h and 5, 15, and 25 days after labelling with 14CO2 gas in sealed chambers. The procedure was repeated three times during the summer. Patterns of 14C translocation varied by species; Polytrichumcommune Hedw. retained the most label after 2 h and Sphagnumsubsecundum Nees. the least. Polytrichumcommune had the second-highest fraction of 14C in brown tissue after 35 days and S. subsecundum the highest. Hylocomiumsplendens (Hedw.) B.S.G. and Pleuroziumschreberi (Brid.) Mitt, did not show consistent patterns of translocation 2 h or 35 days after labelling. 14C was found to accumulate in the growing shoot tips and in the brown tissue of all four species. Loss of 14C because of respiration was high in all four species during the first labelling period indicating high rates of photosynthesis and growth during the peak summer season. The carbohydrate analysis indicated that the increase in 14C activity in brown tissue by the end of the season was due to translocation for storage. In all species there was a strong increase in the storage polysaccharide content by the end of the season after the growth was finished, especially in brown tissue.

Underestimation of metabolic rates owing to reincorporation of 14CO2 in the perfused rat liver.

(14)CO(2) production by perfused rat livers was simulated by infusing NaH(14)CO(3) into the perfusate. Recovery of label as (14)CO(2) gas + perfusate bicarbonate was 45-85%. Rates of (14)CO(2) exchange in the liver are 3-70 times greater than net rates of CO(2) production. Therefore (14)CO(2) reincorporation can lead to significant underestimations of rates of oxidation of (14)C-labelled substrates in liver.

Studies on Structure and Function of the Rice Ear : I. Fixation of <SUP>14</SUP>C by ear and shoot, and redistribution of <SUP>14</SUP>C-assimilates among organs

The main aims of the present investigations are (1) to determine the assimilation rates of 14CO2 of the organs consisting the rice ear, i.e. hulled grain, hull, abortive grain and rachis-branch (including rachis and pedicel), and then (2) to determine the redistribution of 14C-assimilates among those organs after a given time. Plants from 10 to 14 days after ear emergence were used through the present experiments. 14CO2 gas was applied to the materials in following two ways; one is to the ear, and another to the shoot. The materials were harvested immediately after one hour exposure to 14CO2 for (1) experiment and at one week after exposure to 14CO2 gas for (2) experiment. When 14CO2 gas was applied to the ear, assimilation rates of 14CO2, i.e. 14C/mg dry weight/hr and 14C/1OO spikelets/hr were high in the rachis-branch, while were very low and/or almost negligible in the hulled grain and the hull. The translocation rate of 14C-assimilates to the hulled grain was most rapid for one hour following one hour exposure to 14CO2 gas, and became slow thereafter. The translocation of 14C-assimilates to the hulled grain, however, seems to continue for five to seven hours after exposure to 14CO2 gas. For one week following exposure to 14CO2 gas, the hulled grain functioned as a greedy sink organ of 14C-assimilates, while the rachis-branch and the abortive grain as a rich and a poor source orga'n of 14C-assimilates, respectively. On the other hand, the hull worked as a source organ in some cases, but in others. Each of sink and source capacities of the hull, however, was very small compared to the hulled grain and the rachis-branch. The assimilation rate of 14CO2 of the rachis-branch, 14C/100 spikelets/hr tended to be higher in varieties which was heavier in dry weight of the rachis-branch per 100 spikelets. Tsuno, et al. (1975) showed that net ear photosynthesis correlated positively with chlorophyll content of the ear. Therefore, the basic benefit of heavy dry weight of the rachis-branch may be to associate with the dense thickness and the anatomy having relatively high proportion of photosynthetic components. It is interesting that the varieties showing high assimilation rate of 14C/ 100 spike1ets/hr tended to be also high in 14C/mg dry weight/hr. When 14CO2 gas was applied to the shoot, the assimilation rates of 14CO2 of leaf blade and sheath were the highest in flag leaf. The assimilation rate of 14CO2 of the rachis-branch, 14C/mg dry weight/hr was similar to it of the flag leaf sheath and from one-half to one fourth of the flag leaf blade. The rachis-branch worked as only one source organ of 14C-assimilates in the ear, while others as sink organs. The proportion fixed by the ear out of the total amount of 14C-assimilates, however, was 4%, and it fixed by the rachis-branch 3%.

Translocation of <SUP>14</SUP>C-Photosynthates from the Leaves at Different Stages of Development in Ipomoea Grafts.

The purpose of this study is to make clear the effects of sink on the translocation process of 14C-photosynthates from the leaves of several leaf plastochron indices (LPI) at different stages of development in Ipomoea grafts. 1. Two combination grafts were obtained by grafting the scion of improved variety (I. batatas POIRET var. Okinawa No. 100) on the stock of the wild type plant (I. trfida (H.B.K.) Don.·T-15) and the stock of Okinawa No. 100. 2. The leaves of LPI 4, 7, l2 and 19 in the respective grafts were exposed to 14CO2 gas for 30 minutes. The distinctions of leaves in each LPI were as follows: LPI 4, the leaves reached the beginning stage of rapid leaf expansion; LPI 7, the leaf areas were found about 65% of matured leaves; LPI 12 and 19, the leaves reached in full expansion stage. The plants were harvested in the lapse of 1 hour after the beginning of the exposure to 14CO2 gas. 3. In case where the leaves of LPI 4 were exposed to 14CO2 gas, 14C-photosynthates translocated slightly in upward and downward direction. In case of the leaves at LPI 7, downward translocation of 14C-photosynthates was more predominant in the grafts of Okinawa No. 100 stock than that in the grafts of T-15 stocks. On the other hand, the differences of upward translocation were not recognized between grafts. At LPI 12 leaves, downward translocation increased more than that of LPI 7 in the grafts of T-15 stocks. In case of the leaves at LPI 19, the differences of translocation pattern of 14C-photosynthates were not found between the grafts, and then the translocation of 14C-photosynthates was found predominantly in downward direction at both stock grafts. 4. From the above mentioned results, it may be considered that the translocations of 14C-photosynthatcs from the leaves of LPI 4 are not liable to be affected by the stock types, that those of the leaves at LPI 7 are apt to be affected remarkably in downward translocation by the stock type, and that those of the LPI 19 are not liable to be affected in upward and downward translocation by the stock types.

Effect of Foliar Fertilization on Photosynthesis, Leaf Nutrition, and Yield of Soybeans1

AbstractFoliar fertilization (FF) was reported to increase seed yields of soybean [Glycine max (L.) Merr.] in field experiments in Iowa, but yield increases were not consistent. The researchers hypothesized that FF should minimize nutrient depletion from leaves during seed development, and thereby delay the resulting decrease in leaf photosynthesis. To test this hypothesis, we conducted a field experiment in 1976 to determine the effect of FF on leaf element concentrations, gross leaf photosynthesis (Pg), and soybean seed yield. Five weekly foliar sprays were applied during the seed‐filling period of ‘Bragg’ soybean grown at Gainesville, Florida on Kendrick loamy sand (loamy, siliceous, hyperthermic grossarenic paleudult). At weekly intervals, we sampled upper leaves and total canopy leaves and analyzed them for N, P, and K, and measured Pg of upper leaves in mid‐day sun with a 14CO2 gas flow technique. Foliar applications of N, P, K, and S increased the N, P, and K concentration of total canopy leaves from 3.28, 0.24, and 0.92% to 3.48, 0.29, and 1.32%, respectively. FF significantly increased upper leaf Pg only at two late sample dates when seed growth was nearly complete and most leaves had already senesced and dropped. Even though nutrient concentrations were increased, FF did not significantly affect yields nor did it extend Pg duration or delay maturity. Treated soybeans yielded 3617 kg/ha compared to 3825 kg/ha for control soybeans. Leaf Pg and concentrations of N and P in leaves progressively decreased during seed‐filling until maturity but K did not decline. Leaf Pg was positively correlated with N (r = 0.87) and approached zero at approximately 1.75% N, a concentration similar to that of senesced, recently abscised leaves. Maximum Pg was predicted at 4.6 to 6.0% leaf N. Leaf Pg and percent P were also positively correlated. The relationship of Pg to leaf N during N removal from leaves can potentially be used to model photosynthetic decline during seed‐filling.

An improved scintillation probe for continuous counting of expiratory 14CO 2-gas

The combination of an expiratory CO 2 flow system and a scintillation counting system is described for the continuous counting of respiratory 14CO 2 exhaled from a mouse. Respiratory H 2O is trapped by a cooling trap to eliminate quenching effects of water on the counting. Dried air with expiratory 14CO 2-gas is fed to a given volume of the hyamine scintillation fluid in the reservoir and is bubbled in the fluid to trap 14CO 2-gas. A portion of the radioactive scintillation fluid is fed into a scintillation probe and returned to the reservoir continuously by connecting the reservoir and the probe with fine teflon tube. In the probe, the tube is coiled and placed between opposing photomultiplier tubes. The probe is connected with 2 ratemeters following a recorder for continuous counting of radioactivity in the flow stream. This device is particularly suited for the continuous counting of expiratory 14CO 2 with high counting efficiency as well as that of a liquid scintillation counter. The expiratory 14CO 2 patterns did not vary with the date, if the same mouse was used during 10.00 a.m. – 1.00 p.m. The patterns of different mice also were almost concordant. Discussions are described in detail for the comparison of respiratory 14CO 2 patterns given by this device and the other counters.

Photosynthetic Activity of the Pods of Rape Plants (Brassica napus L.) and the Contribution of the Pods to the Ripening of Rape-seeds

The present study was conducted to clarify the photosynthetic activity of the pods of rape plants and the effect of the pods on the ripening of rape-seeds. In making the present study, the productive characters of the plants and the net photosynthetic rates of the pods were investigated. Furthermore, the processes of accumulation of 14C-photosynthates were also traced by means of a 14C-tracer method. The study results are summarized as follows: (1) At the early ripening stage, the surface areas of pods showed on about eight-fold areas, as compared with those of the leaf blades. Marked increases in the pod surface areas were observed during the period ranging from the early ripening stage to the late ripening stage, while the leaf blade areas showed decreases during the same period. (2) The dry weights of the pods or seeds were becoming heavier according as they have grown and the higher distribution ratios of dry matters were observed in the pods, as compared with those in other organs. The pods and leaf blades showed almost the same net photosynthetic activity at the early ripening stage, but at the late ripening stage, the pods came to show higher rate than that of leaf blades. (3) Chlorophyll-a and -b contents in the pods were low, as compared with those in leaf blades. Chlorophyll contents in the pods were equivalent to about one-fifth of those in the leaf blades. (4) From the results obtained through the 14C-tracer experiments in photosynthates, higher specific radioactivities were observed in the tissues of pods and peduncles, while lower ones were observed in the stems and roots. 14C-photosynthates in the seeds observed one hour after the 14CO2 gas exposure accounted for about sixty percent of those of the seeds observed seven days after the 14CO2 exposure. On the seventh day after 14CO2 feeding, a markedly rich accumulation of 14C-photosynthates was found only in the case of seeds, and the decreases in 14C-photosynthates were observed in the cases of other tissues. Therefore, it may safely be said that 14C-photosynthates in the pods may translocate mainly to the seeds. (5) Viewed from the histochemical point, the assimilating parenchyma and vascular bundles were developed in pods as well as the leaf blades. The starch granules were found far more abundantly in the palisade parenchyma of leaf blades than in the assimilating parenchyma of the pods. (6) From the above mentioned results, it might be concluded that the pods of rape plants have the photosynthetic function and contribute very actively to the accumulation of photosynthates in the rape-seeds.

An open gas-exchange system for the simultaneous measurement of the CO2 and 14CO2 fluxes from leaves

An open gas exchange system that uses an infrared gas analyzer and an ionization chamber to measure CO2 and 14CO2 is described. The system will continuously measure the CO2 and 14CO2 exchange from a leaf within 30 s after the 14CO2 gas mixture is supplied to the leaf. Measurements are obtained under steady rate conditions since the 14CO2 gas mixture is supplied at a constant composition from pressurized cylinders. Methods of determining true photosynthesis, apparent photosynthesis, CO2 evolution, and the specific activity of the 14CO2 evolved are clearly described. The rate of CO2 evolution in the light was not affected by the CO2 concentration and the evolved CO2 was derived from the early products of photosynthesis.