並列タイトル等Analysis of Nitrogen Fixation and Transport in Soybean (Glycine max (L.) Merr.) using Nitrogen Isotopes as Tracer
窒素同位体トレーサー法を用いたダイズの窒素固定と輸送の解析
一般注記The quantitative analysis of nitrogen fixation and the initial transport of fixed nitrogen in intact nodulated soybean plants (Glycine max [L.] Merr. cv. Williams) during relatively short time (8 h) was conducted at the vegetative stage (36 DAP) and pod-filling stage (91 DAP) by the 15N pulse-chase experiment. The nodulated roots of intact soybean plants were exposed to N2 gas labeled with a stable isotope 15N for 1 hour, followed by 0, 1, 3 and 7 hours of exposure with normal air. The results showed that young soybean plants at 36 DAP showed higher N2 fixation activity based on the dry weight (86μg/g DW) compared with pod filling soybean plants at 91 DAP (19μg/g DW). In both stages, approximately 90% of the fixed 15N was retained in the nodules and the 15N distribution in the basal nodules (78%) was higher than that of in the middle (12%) and distal nodules (0.1%) after 1 hour of stable isotope 15N2 exposure. The distribution of fixed 15N in the nodules decreased from 90% to 7% and increased in the roots (14%), stems (54%), leaves (12%), pods (10%), and seeds (4%) during the initial 7 hours of the chase-period at 91 DAP. The distribution of fixed 15N was negligible in the distal root segment, suggesting that the recycling of fixed N from the shoot to the roots was very low within 7 hours after fixation. The observation of fixed nitrogen transported in soybean plant by using 13N-labeled gas tracer and a positron-emitting tracer imaging system (PETIS) showed that the signals of N radioactivity could be observed in the stem at 20 minutes after feeding with 13N2 tracer gas. This is the first observation that the transport of fixed nitrogen in the stem could be observed at real-time in soybean plant. However, due to the short half-life of 13N (9.97 minutes) and short exposing time, the signal intensity of the fixed N translocation in the upper stem observed by PETIS was weak, but the autoradiography taken after PETIS experiment showed a clear picture of transport of fixed 13N in intact soybean plant. The result suggested that the fixed 13N translocation through the shoot may not move only in xylem system as the previous concept that the fixed N in nodule is transported through xylem by transpiration stream by mature leaves, but the fixed N may be transferred from xylem to phloem in the stem. This result indicates that the initial transport of fixed N was mainly in the stem and translocated to young leaves and buds via phloem system. The new finding in the initial transport of fixed nitrogen of soybean will become the basis for the future study of fixed-N transport with the whole legume plants. The effects of oxygen concentration in rhizosphere on the symbiotic nitrogen fixation in real-time was evaluated under various O2 partial pressure conditions. Soybean nodules were treated with mixed gas containing 13N-labeled N2 with various O2 concentrations, and the nitrogen fixation activity in the nodules was analyzed by PETIS. The results showed that under normal condition (20% O2) the nitrogen fixation activity of soybean plant was higher compared to that of under the other conditions (0% O2 and 10% O2). The nitrogen fixation activity of soybean nodules was strongly depressed with low O2 concentrations, although it was not inhibited completely even at 0%. On the other hand, the export rate of fixed nitrogen from nodules was not affected by the changes of oxygen conditions.
学位の種類: 博士（農学）. 報告番号: 甲第3931号. 学位記番号: 新大院博（農）甲第134号. 学位授与年月日: 平成26年3月24日
新大院博（農）甲第134号
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受理日（W3CDTF）2015-02-03T05:25:05+09:00
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