PRIMARY ASSIMILATION PROCESS OF TRIPLY (^<15>N, ^<14>C and ^3H) LABELED ARGININE IN THE ROOTS OF ARGININE-FED BARLEY

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To clarify the mechanism of arginine utilization in barley roots, triply labeled (ureido-^<15>N, ureido-^<14>C and 5-^3H)arginine was applied to plants precultured with arginine (Arg-plants). (5-^3H)Arginine was incorporated mainly into ornithine, suggesting that arginase contributes in the first step of arginine metabolism. The arginase activity in the tissues was greatly enhanced by continuous supply of arginine, whereas urease activity was not by the same treatment. The amount of ^<14>CO_2 evolved form (ureido-^<14>C)arginine in the Arg-plants was several times higher than that in plants treated with NO_3-(NO_3-plants), and most ^<14> C-urea exogenously supplied to detached roots of Arg-plants was immediately decomposed to ^<14>CO_2. The urea released from arginine by arginase was cleaved to ^<15>NH_4^+ + ^<14>CO_2 by urease. Most of the ^<14>CO_2 was then lost from the root system. On the other hand, the released ^<15>NH_4^+ was reassimilated into amino acids probably through the pathway of ammonia assimilation. Released (5-^3H)ornithine was metabolized dominantly to proline.
社団法人日本土壌肥料学会の論文