Nitrogen Fixation and Metabolism in Soybean Plants by Takuji Ohyama, Norikuni Ohtake, Kuni Sueyoshi, Kaushal

By Takuji Ohyama, Norikuni Ohtake, Kuni Sueyoshi, Kaushal Tewari, Yoshihiko Takahashi, Sayuri Ito, Toshikazu Nishiwaki, Yoshifumi Nagumo, Satomi Ishii, Takashi Sato

Within the first half, the authors introduce the growth of researches on nitrogen metabolism of soybean nodules and roots. They examine the destiny of nitrogen fastened in soybean nodules through tracer scan with 15N2 gasoline. the implications point out that significant a part of fastened N in bacteroids (a symbiotic nation of rhizobia) is excreted speedily to cytosol of contaminated cells within the kind of ammonia, then the ammonia is assimilated into amino acids through GS/GOGAT pathway. Then the mounted nitrogen is assimilated into ureides, allantoin and allantoic acid, after which transported to the shoots through xylem. A small section of fastened N used to be assimilated within the bacteroids without delay into glutamate and alanine. nonetheless, nitrate absorbed from the roots are quite often assimilated into asparagine. The features of nitrate absorption and metabolism have been studied. it's renowned that nitrate is a effective inhibitor to nodulation and nitrogen fixation, even though the inhibitory mechanism isn't really absolutely understood. The authors lately came across that nitrate depresses person nodule progress and nitrogen fixation job quickly and reversibly whilst nodules have been in direct touch with nitrate. The oblique results of nitrate on nodule progress and nitrogen fixation task have been assorted between therapy focus and interval of provide. the continual provide of low degrees of nitrate from the decrease a part of roots promoted the nodulation and nitrogen fixation of the higher a part of the roots. Hypernodulation mutant traces of soybean have been remoted that have profuse nodulation in comparison with mom and dad. additionally they express partial-nitrate tolerant to nodulation. The features of hypernodulation mutant strains have been studied in terms of nitrate inhibition. the implications recommend that decrease nitrate absorption and assimilation job in hypernodulation mutants will be one cause to milder inhibition by means of nitrate on hypernodulation mutant strains.

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When 1 mM NO3- was added, the CO2 evolution increased by 18 times. The CO2 evolution associated with NO3reduction was inhibited by the addition of 1 mM DNP (2,4-dinitrophenol) or 1 mM HgCl2, but not by 1 mM KCN. 2 was severely depressed by 1 mM KCN and 1 mM HgCl2. Chapter 4 NITROGEN INHIBITION ON NODULE GROWTH AND NITROGEN FIXATION 1. NITRATE INHIBITION ON NODULE FORMATION AND NITROGEN FIXATION The inhibitory effects of externally supplied N especially NO3- have been reviewed (Streeter 1988, Harper 1987), however the nitrate inhibition is complex and we cannot explain by a single mechanism.

7 mM of 15NO3- was supplied to the solution for 1 day, an appreciable amount of NO3- and 15N was detected in nodule cortex, although a little was distributed in the infected region. In another experiment, 15NO3- solution was supplied to one large nodule through a cheese cloth wrapping the nodule. These results suggest that NO3- can be absorbed from nodule surface (epidermal cells or loosely packed lenticel cells), then it is transported from cell to cell into cortex via simplistic pathway. Arrese-Igor et al.

The decrease in starch concentration in nodules (Vessey et al. 1988, Gordon et al. 2002) and the down-regulation of sucrose synthase transcript within 1 day of nitrate treatment (Gordon et al. 2002) may imply that NO3- reduces photoassimilate flow into nodules and sucrose utilization in nodules. Nitrogen Inhibition on Nodule Growth and Nitrogen Fixation 53 Figure 47. Partitioning of 14C labeled photoassimilate in soybean plants supplied with 0 mM (-N) or 5 mM (+N) nitrate. From Fujikake et al. 2003 Figure 48.

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