Sayuri Tanabata

By Takuji Ohyama, Norikuni Ohtake, Kuni Sueyoshi, Yuki Ono, Kotaro Tsutsumi, Manabu Ueno, Sayuri Tanabata, Takashi Sato and Yoshihiko Takahashi

The ammonium produced by nitrogen fixation in the bacteroid is rapidly excreted to cytosol of infected cell of soybean nodules and then assimilated into glutamine and glutamic acid, by glutamine synthetase/glutamate synthase pathway. Most of the nitrogen is further assimilated into ureides, allantoin, and allantoic acid, via purine synthesis, and they are transported through xylem to the shoots. Nitrate absorbed in the roots is reduced by nitrate reductase and nitrite reductase to ammonia either in the roots or leaves. The ammonia is also assimilated by glutamine synthetase/glutamate synthase pathway, and mainly transported by asparagine, and not ureides. The nitrogen transported into leaves is readily utilized for protein synthesis, and then, some of them are decomposed and retransported to roots, apical shoots, and pods via phloem mainly in the form of asparagine.

Part of the book: Amino Acid

By Takuji Ohyama, Sayuri Tanabata, Norikuni Ohtake, Takashi Sato, Kuni Sueyoshi, Yoshihiko Takahashi, Shinji Ishikawa, Yuki Ono, Natsumi Yamashita and Akinori Saito

Soybean plants require a large amount of nitrogen either from nitrogen fixation in nodules or nitrogen absorption from roots. It is known that nitrate, a major inorganic nitrogen compound in upland soils, represses nodule growth and nitrogen fixation. Rapid and reversible inhibition of nodule growth and nitrogen fixation activity was found in the hydroponically cultivated soybeans after changing the nutrient solution with or without nitrate. Isotope tracer analysis revealed that the major cause of this inhibition depended on the changes in the partitioning of photo-assimilate between nodules and roots and was not directly related to the transported N compounds. Transcriptome and metabolome analyses supported that nitrate strongly promotes nitrogen and carbon metabolism in the roots but represses them in the nodules. The application of ammonium, glutamine, or urea also inhibited the nodule growth and nitrogen fixation like nitrate, although the inhibition was lower than that of nitrate. The degree of inhibition was related to the decrease in carbon isotope partitioning into the nodules, rather than the import of nitrogen isotope to nodules. Urea was detected in xylem sap and all parts of soybean, and some urea might be originated from ureide degradation.

Part of the book: Soybean