Use of positron-emitting tracer imaging system for measuring the effect of salinity on temporal and spatial distribution of C tracer and coupling between source and sink organs |
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Authors: | Ryuichi Suwa Shu Fujimaki Nobuo Suzui Naoki Kawachi Satomi Ishii Koichi Sakamoto Nguyen Tran Nguyen Hirofumi Saneoka Pravat K Mohapatra Reda E Moghaieb Shinpei Matsuhashi Kounosuke Fujita |
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Institution: | aGraduate School of Biosphere Science, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima 739-8528, Japan;bQuantum Beam Science Directorate, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan;cSchool of Life Science, Sambalpur University, Jyoti Vihar, Sambalpur 768019, India |
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Abstract: | Salinity stress affects photosynthate partitioning between sources and sinks of plants, but how it affects these systems is less well understood. Because sources and sinks are closely tied, any adverse effect under suboptimal conditions on one of these is often misinterpreted for an effect on the other. Carbon partitioning is indispensable for stress resistance and good plant growth. In the present study, carbon partitioning in tomato plants (Lycopersicon esculentum L. cv. Momotarou) in a saline (NaCl) environment was studied by feeding radioactive 11C and stable 13C isotopes. Pulse-chases were conducted to measure the spatial and temporal distribution of 13C. 13C was measured by a standard conventional technique, but 11C distribution was monitored using a positron-emitting tracer imaging system (PETIS). Salt stress resulted in reduced carbon translocation toward roots. The majority of the photosynthate accumulated in the leaf. We also observed that the reduction in translocation of carbon occurred well before the salt stress symptoms of reduced photosynthesis and reduced plant growth in salt-exposed plants. The effect on sink activity was also shown by a decrease in stem diameter. In addition, PETIS analysis of 11C translocation indicated that carbon translocation to roots was inhibited under salt conditions without a direct effect on leaf Na accumulation or osmotic stress. These results suggest that NaCl has direct effects on plants, inhibiting carbon partitioning within a few hours of salt exposure without inhibition of source activity. |
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Keywords: | NaCl PETIS Photosynthesis Source– sink Stem diameter Translocation |
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