Positron-emitting Tracer Imaging System Research Articles

Transfer function analysis of positron-emitting tracer imaging system (PETIS) data

Quantitative analysis of the two-dimensional image data obtained with the positron-emitting tracer imaging system (PETIS) for plant physiology has been carried out using a transfer function analysis method. While a cut leaf base of Chinese chive ( Allium tuberosum Rottler) or a cut stem of soybean ( Glycine max L.) was immersed in an aqueous solution containing the [ 18F] F − ion or [ 13N]NO 3 − ion, tracer images of the leaf of Chinese chive and the trifoliate of soybean were recorded with PETIS. From the time sequence of images, the tracer transfer function was estimated from which the speed of tracer transport and the fraction moved between specified image positions were deduced.

Light activates H2 15O flow in rice: Detailed monitoring using a positron‐emitting tracer imaging system (PETIS)

Water (H2 15O) translocation from the roots to the top of rice plants (Oryza saliva L. cv. Nipponbare) was visualized over time by a positron-emitting tracer imaging system (PETIS). H2 15O flow was activated 8 min after plants were exposed to bright light (1 500 &mgr;mol m-2 s-1). When the light was subsequently removed, the flow gradually slowed and completely stopped after 12 min. In plants exposed to low light (500 &mgr;mol m-2 s-1), H2 15O flow was activated more slowly, and a higher translocation rate of H2 15O was observed in the same low light at the end of the next dark period. NaCl (80 mM) and methylmercury (1 mM) directly suppressed absorption of H2 15O by the roots, while methionine sulfoximine (1 mM), abscisic acid (10 &mgr;M) and carbonyl cyanide m-chlorophenylhydrazone (10 mM) were transported to the leaves and enhanced stomatal closure, reducing H2 15O translocation.

Real time visualization of 13N-translocation in rice under different environmental conditions using positron emitting Ttacer imaging system.

The ammonium ion is an indispensable nitrogen source for crops, especially paddy rice (Oryza sativa L. cv Nipponbare). Until now, it has been impossible to measure ammonium uptake and nitrogen movement in plants in real time. Using the new technologies of PETIS (positron emitting tracer imaging system) and PMPS (positron multi-probe system), we were able to visualize the real time translocation of nitrogen and water in rice plants. We used positron-emitting 13N-labeled ammonium (13NH4+) and 15O-water to monitor the movement. In plants cultured under normal conditions, 13NH4+ supplied to roots was taken up, and a 13N signal was detected at the discrimination center, the basal part of the shoots, within 2 minutes. This rapid translocation of (13)N was almost completely inhibited by a glutamine synthetase inhibitor, methionine sulfoximine. In general, nitrogen deficiency enhanced 13N translocation to the discrimination center. In the dark, 13N translocation to the discrimination center was suppressed to 40% of control levels, whereas 15O-water flow from the root to the discrimination center stopped completely in the dark. In abscisic acid-treated rice, 13N translocation to the discrimination center was doubled, whereas translocation to leaves decreased to 40% of control levels. Pretreatment with NO3- for 36 hours increased 13N translocation from the roots to the discrimination center to 5 times of control levels. These results suggest that ammonium assimilation (from the roots to the discrimination center) depends passively on water flow, but actively on NH4+-transporter(s) or glutamine synthetase(s).

Rapid N transport to pods and seeds in N-deficient soybean plants

Non-nodulated soybean (Glycine max (L.) Merr.) plants were cultivated hydroponically under N-sufficient (5 mM NaNO(3)) or N-deficient (0.5 mM NaNO(3)) conditions. (13)N- or (15)N- labelled nitrate was fed to the cut end of the stems, and the accumulation of nitrate-derived N in the pods, nodes and stems was compared. Real-time images of (13)N distribution in stems, petioles and pods were obtained using a Positron Emitting Tracer Imaging System for a period of 40 min. The results indicated that the radioactivity in the pods of N-deficient plants was about 10 times higher than that of N-sufficient plants, although radioactivity in the stems and nodes of N-deficient versus N-sufficient plants was not different. A similar result was obtained by supplying (15)NO(3) to cut soybean shoots for 1 h. The fact that the N translocation into the pods from NO(3) fed to the stem base was much faster in N-deficient plants may be due to the strong sink activity of the pods in N-deficient plants. Alternatively, the redistribution of N from the leaves to the pods via the phloem may be accelerated in N-deficient plants. The temporal accumulation of (13)NO(3) in nodes was suggested in both N-sufficient and N-deficient plants. In one (13)NO(3) pulse-chase experiment, radioactivity in the stem declined rapidly after transferring the shoot from the (13)NO(3) solution to non-labelled NO(3); in contrast, the radioactivity in the node declined minimally during the same time period.

Rapid N transport to pods and seeds in N‐deficient soybean plants

Non‐nodulated soybean ( Glycine max (L.) Merr.) plants were cultivated hydroponically under N‐sufficient (5 mM NaNO 3 ) or N‐deficient (0.5 mM NaNO 3 ) conditions. 13 N‐ or 15 N‐ labelled nitrate was fed to the cut end of the stems, and the accumulation of nitrate‐derived N in the pods, nodes and stems was compared. Real‐time images of 13 N distribution in stems, petioles and pods were obtained using a Positron Emitting Tracer Imaging System for a period of 40 min. The results indicated that the radioactivity in the pods of N‐deficient plants was about 10 times higher than that of N‐sufficient plants, although radioactivity in the stems and nodes of N‐deficient versus N‐sufficient plants was not different. A similar result was obtained by supplying 15 \(NO_{3}^{{-}}\) to cut soybean shoots for 1 h. The fact that the N translocation into the pods from \(NO_{3}^{{-}}\) fed to the stem base was much faster in N‐deficient plants may be due to the strong sink activity of the pods in N‐deficient plants. Alternatively, the redistribution of N from the leaves to the pods via the phloem may be accelerated in N‐deficient plants. The temporal accumulation of 13 \(NO_{3}^{{-}}\) in nodes was suggested in both N‐sufficient and N‐deficient plants. In one 13 \(NO_{3}^{{-}}\) pulse‐chase experiment, radioactivity in the stem declined rapidly after transferring the shoot from the 13 \(NO_{3}^{{-}}\) solution to non‐labelled NO 3 ; in contrast, the radioactivity in the node declined minimally during the same time period.

Vanadium uptake and an effect of vanadium treatment on 18 F-labeled water movement in a cowpea plant by positron emitting tracer imaging system (PETIS)

We present real time vanadate (V5+ ) uptake imaging in acowpea plant by positron emitting tracer imaging system (PETIS). Vanadium-48was produced by bombarding a Sc foil target with 50 MeV α -particlesat Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) AVFcyclotron. Then 48 V was added to the culture solution to investigatethe V distribution in a cowpea plant. The real time uptake of the 48V was monitored by PETIS. We measured the distribution of 48Vin a whole plant after 3, 6 and 20 hours of V treatment by Bio-imaging AnalyzerSystem (BAS). After the 20 hour treatment, vanadate was detected at the up-groundpart of the plant. To know the effect of V uptake on plant activity, 18F-labeled water uptake was analyzed by PETIS. When a cowpea plantwas treated with V for 20 hours before 18 F-labeled water uptakeexperiment, the total amount of 18F-labeled water absorption wasdrastically decreased. Results suggest the inhibition of water uptake wasmainly caused by the vanadate already moved to the up-ground part of the plant.

Comparison of 15O-Labeled and 18F-Labeled Water Uptake in a Soybean Plant by PETIS (Positron Emitting Tracer Imaging System).

15O-Labeled and 18F-labeled water uptake manner in a soybean plant was compared by PETIS (Positron Emitting Tracer Imaging System) . 15O-Labeled water (half-life: 110 min) and 18F-labeled water (half-life: 2 min) was produced by a cyclotron by 14N (d, n) 15O and 16O (α, pn) 18F reactions, respectively. A root of a soybean plant was cut off and each labeled water was supplied from the basal part of the plant. The gamma-rays emitted from the sample was measured by a BGO counter with a detection area of 5 cm × 15 cm. The radioactivity from each stem was accumulated every 15 s till 20 min. It was found that 18F-labeled water was taken up much faster than 15O-labeled water, suggesting that in 18F-labeled water, fluorine was moved in the form of 18F-ion. When BAS image of 15O-labeled water in a plant after 5 min and 10 min of water supply was taken, it was found that the labeled water was observed only in the lowest internode, between a root and the first leaves.

18F used as tracer to study water uptake and transport imaging of a cowpea plant

We present the water uptake ability of cowpea (Vigna unguliculata Walp)which has been regarded as one of the most drought resistant species amongthe pulse crops. It has been suggested that in the lower part of the stem,parenchymatous tissue for storing water has been developed for the functionof drought resistance. We confirmed that in this tissue, water amount washigh compared to the other stems by neutron radiography. Then the water uptakemanner was measured by positron emitting tracer imaging system (PETIS) using 18F labeled water produced by a cyclotron. Comparing the water uptakemanner of cowpea plant with that of common bean, cowpea plant was found tomaintain high water uptake activity after drying treatment, suggesting thehigh drought resistant character.

Circadian Rhythm in 15O-Labeled Water Uptake Manner of a Soybean Plant by PETIS(Position Emitting Tracer Imaging System).

We present a circadian rhythm of water uptake manner in a soybean plant through realtime imaging of water, labeled with 15O. Nitrogen gas was irradiated with deuterons accelerated by a cyclotron at Hamamatsu Photonics Co. to produce 15O-labeled water. Then the 15O-labeled water was supplied to a soybean plant from the root and the realtime water uptake amount was measured for 20 min by Positron Emitting Tracer Imaging System (PETIS) . All the targeting positions for the measurements were stems, two points at an internode between root and the first leaves, between the first leaves and the first trifoliates and between the first trifoliates and the second trifoliates. The water uptake amount was gradually increased and showed its maximum at around 13: 00, especially at the basal part of the stem. Then the water uptake activity was gradually decreased until 17: 00. The water amount taken up by a plant at 13: 00 was about 40% higher than that at 17: 00.

Visualization of 15O-water flow in tomato and rice in the light and dark using a positron-emitting tracer imaging system (PETIS)

15P-water flow from the roots to the top in tomato (Lycopersicon esculentum Mill.) and rice (Oryza sativa L.) plants was visualized with time using a positron-emitting tracer imaging system (PETIS). The 15O-water flow was switched on by light and completely stopped in the dark. The flow rate in the stem of tomato and the shoot of rice at a light intensity of 500 μmol·m−2·s−1 was 1.9 and 0.4 cm min−1, respectively.

13N-nitrate uptake sites and rhizobium-infectible region in a single root of common bean and soybean

The positron emitting tracer-imaging system (PETIS) was used to determine whether it was possible to obtain on image of 13N-distribution in common bean in which a single root was fed with a liquid medium containing nitrate at different concentrations with different 13N specific activities. The distribution of the images of the 13N atoms in the root could be obtained over a wide range of nitrate concentrations and 13N specific activities in the medium. As for nitrate stress on leguminous root nodulation, the positional relationship between the nitrate uptake sites and root hair just elongating area, where rhizobia capably initiate their infection, was studied in common bean and soybean. PETIS gave direct evidence that single roots of both common bean and soybean showed one or two dense 13N-distribution areas after 2 min pulse-feeding of 13N03 -. These areas remained stable over 30 min, and the first dense site, which was common in all the examined roots, extended over ca. 1 cm above the root apex. Microscopic observation revealed that this area covered both sites of rhizobium infection and of early nodule development in a common bean and soybean single root.

Visualizing real time [11C]methionine translocation in Fe-sufficient and Fe-deficient barley using a Positron Emitting Tracer Imaging System (PETIS)

[11C]methionine was supplied to Fe-deficient and Fe-sufficient barley plants through a single leaf, and real time 11C movement was monitored using a Positron Emitting Tracer Imaging System (PETIS). In Fe-deficient plants, [11C]methionine was translocated from the tip of the absorbing leaf to the ‘discrimination centre’ located at the base of the shoot, and then retranslocated to all the chlorotic leaves within 60 min, while a negligible amount was retranslocated to the roots. In Fe-sufficient plants, methionine was translocated to the discrimination centre and then only to the newest leaf on the main shoot within 60 min. A negligible amount was also retranslocated to the roots. In conclusion, methionine from the above-ground parts of a plant is not a precursor of mugineic acid under Fe-deficiency. The discrimination centre is suggested to play a vital role in the distribution of mineral elements and metabolites in graminaceous monocots.

Visualizing real time [11C]methionine translocation in Fe-sufficient and Fe-deficient barley using a Positron Emitting Tracer Imaging System (PETIS)

[ 11 C]methionine was supplied to Fe-deficient and Fe-sufficient barley plants through a single leaf, and real time 11 C movement was monitored using a Positron Emitting Tracer Imaging System (PETIS). In Fe-deficient plants, [ 11 C]methionine was translocated from the tip of the absorbing leaf to the 'discrimination centre' located at the base of the shoot, and then retranslocated to all the chlorotic leaves within 60 min, while a negligible amount was retranslocated to the roots. In Fe-sufficient plants, methionine was translocated to the discrimination centre and then only to the newest leaf on the main shoot within 60 min. A negligible amount was also retranslocated to the roots. In conclusion, methionine from the above-ground parts of a plant is not a precursor of mugineic acid under Fe-deficiency. The discrimination centre is suggested to play a vital role in the distribution of mineral elements and metabolites in gramin-aceous monocots.

Production of positron emitters and application of their labeled compounds to plant studies

The positron emitters11C,13N and18F and their labeled compounds have been produced for studies on plants using a newly developed positron emitting tracer imaging system. Although this system covers, at present, a limited area in a plant, the distribution of the positron emitter fed into the plant can be visualized dynamically. Further development of positron-emitter-labeled compounds is expected to elucidate the physiological function of plants in vivo.

根粒非着生と根粒着生ダイズにおける<SUP>13</SUP>NO<SUB>3</SUB><SUP>-</SUP>と<SUP>15</SUP>NO<SUB>3</SUB><SUP>-</SUP>を用いた硝酸吸収と移行の解析

ダイズにおける硝酸吸収と移行を調べるために, 同質遺伝子系統の根粒着生ダイズ (T202) と根粒非着生ダイズ (T201) を水耕栽培し, 13Nと15Nトレーサ実験を行った。TIARA AVFサイクロトロンで作製した13NO3-を水耕培地へ投与した。第一本葉における吸収された13Nの分布を, ポジトロンイメージング装置 (PETIS) とバイオイメージングアナライザ (BAS) を用いて観測した。また, 別の実験では15NO3-を1時間供給し, 各器官の15N増加量を発光分光法により定量した。放射能活性の二次元画像の経時的変化を, PETISにより観測でき, 植物全体における13Nの分布をBASにより観察できた。しかし, 13Nの実験では定量的なデータを得るのは困難であった。安定同位体の15Nによる分析は, 各々の器官における標識窒素の割合や量の定量的解析に有効であった。15Nと13Nトレーサ実験のデータを組み合わせることにより, 植物における窒素の吸収と移行がより明確になると期待される。

Uptake and transport of positron-emitting tracer ( 18F) in plants

The transport of a positron-emitting isotope introduced into a plant was dynamically followed by a special observation apparatus called ‘Positron-Emitting Tracer Imaging System’ to observe the damage and recovery functions of plants in vivo. In the system, annihilation γ-rays from the positron emitter are detected with two planar detectors (5 × 6 cm 2). The water containing ca. 5 MBq/ml of 18F was fed to the cut stem of soybean for 2 min and then the images of tracer activity were recorded for 30–50 min. When the midrib of a leaf near the petiole was cut just before measurement, the activity in the injured leaf was decreased but detected even at the apex. This result suggests that the damaged leaf recovered the uptake of water through the lamina. Maximum tracer activities in leaves of unirradiated plant were observed within 10 min, whereas those of irradiated plant at 100 Gy were observed after over 25 min. The final activity of irradiated plant after 30 min was lower than that of unirradiated plant. In case of beans, there was a difference in the absorption behavior of the 18F-labeled water between unirradiated and irradiated samples. These results show that the system is effective to observe the uptake and transportation of water containing positron emitting tracer for the study of damage and recovery functions of plants.