Vol. 75 No: 2

Title:
Ammonium and nitrate assimilation in Narcissus roots

Authors:
SAKCHAI RUAMRUNGSRI, SORAYA UAMRUNGSRI, TARO IKARASHI and TAKUJI OHYAMA

pp: 223-227

Abstract:
Narcissus cv. Garden Giant was cultivated in solution supplied with labelled-¹⁵NH₄⁺ or NO₃^-.The experiment was conducted with five treatments: T1: 1.0 mM¹⁵NH₄⁺-N, T2: 1.0 mM¹⁵NO₃^--N, T3: 0.5 mM¹⁵NH₄⁺-N plus 0.5 mM¹⁵ NO₃^--N, T4: 0.5 mM NH₄ ⁺-N plus 0.05 mM¹⁵NO₃ ^--N and T5: N free solution. Samples were harvested at 2, 4 and 7 d after feeding (DAF). Ammonium-N (T1) was more rapidly absorbed by roots 2 d after feeding (DAF) than nitrate-N (T2). However, at 4&plusm;7 DAF, the amounts of N absorbed from ammonium-N and nitrate-N were almost equal, suggesting that narcissus roots can absorb and assimilate both forms of N. When combined forms of ammonium and nitrate were supplied, roots absorbed ammonium in preference to nitrate. The presence of ammonium depressed nitrate absorption and assimilation. Asparagine was the major free amino acid in roots, with N-free solution (T5). When plants were supplied with ammonium, the concentration of glutamine dramatically increased. With the single supply of nitrate, asparagine and glutamine accumulated to the same levels. ¹⁵NH₄⁺ was very actively assimilated into glutamine, and the presence of NH₄⁺ depressed the assimilation of NO₃^- in the roots.

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