Department of Agricultural Chemistry, Faculty of Agriculture, Kobe University, Rokko, 657, Kobe, Japan.
Planta. 1989 Oct;179(3):359-66. doi: 10.1007/BF00391081.
Nitrate reduction in roots and shoots and exchange of reduced N between organs were quantitatively estimated in intact 13-d-old seedlings of two-row barley (Hordeum vulgare L. cv. Daisengold) using the (15)N-incorporation model (A. Gojon et al. (1986) Plant Physiol. 82, 254-260), except that NH + (4) was replaced by NO - (2) . N-depleted seedlings were exposed to media containing both nitrate (1.8 mM) and nitrite (0.2 mM) under a light-dark cycle of 12:12 h at 20°C; the media contained different amounts of (15)N labeling. Experiments were started either immediately after the beginning (expt. 1) or immediately prior to the end (expt. 2) of the light period, and plants were sampled subsequently at each light-dark transition throughout 36 h. The plants effectively utilized (15)NO - (3) and accumulated it as reduced (15)N, predominantly in the shoots. Accumulation of reduced (15)N in both experiments was nearly the same at the end of the experiment but the accumulation pattern in roots and shoots during each 12-h period differed greatly depending on time and the light conditions. In expt. 1, the roots accounted for 31% (light), 58% (dark), and 9% (light) of nitrate reduction by the whole plants, while in expt. 2 the contributions of the root were 82% (dark), 20% (light), and 29% (dark), during each of the three 12-h periods. Xylem transport of nitrate drastically decreased in the dark, but that of reduced N rather increased. The downward translocation of reduced (15)N increased while nitrate reduction in the root decreased, whereas upward translocation decreased while nitrate reduction in the shoot increased. We conclude that the cycling of reduced N through the plant is important for N feeding of each organ, and that the transport system of reduced N by way of xylem and phloem, as well as nitrate reduction by root and shoot, can be modulated in response to the relative magnitude of reduced-N demands by the root and shoot, with the one or the other predominating under different circumstances.
在光照/黑暗周期为 12:12 小时、20°C 的条件下，使用 (15)N 掺入模型（A. Gojon 等人，(1986) Plant Physiol. 82, 254-260），定量估计了两排大麦（Hordeum vulgare L. cv. Daisengold）13 天大的完整幼苗中根部和地上部硝酸盐还原和器官间还原 N 的交换，除了 NH + (4) 被 NO - (2) 取代。缺氮的幼苗在含有硝酸盐（1.8 mM）和亚硝酸盐（0.2 mM）的培养基中暴露于光照/黑暗周期下；培养基中含有不同量的 (15)N 标记物。实验要么在光照周期开始时（实验 1）立即开始，要么在光照周期结束前（实验 2）立即开始，随后在整个 36 小时的每个光照/黑暗转换时对植物进行采样。植物有效地利用 (15)NO - (3) 并将其积累为还原的 (15)N，主要在地上部。在实验结束时，两个实验中还原的 (15)N 的积累几乎相同，但在每个 12 小时期间，根和地上部的积累模式因时间和光照条件而异。在实验 1 中，根部占整个植物硝酸盐还原的 31%（光照）、58%（黑暗）和 9%（光照），而在实验 2 中，根部在三个 12 小时期间的贡献分别为 82%（黑暗）、20%（光照）和 29%（黑暗）。黑暗中硝酸盐的木质部运输急剧减少，但还原 N 的运输反而增加。还原的 (15)N 的向下转运增加，而根部硝酸盐还原减少，而上行转运减少，而地上部硝酸盐还原增加。我们得出结论，还原 N 在植物中的循环对于每个器官的氮供应很重要，并且通过木质部和韧皮部的还原 N 运输系统以及根和地上部的硝酸盐还原可以根据根和地上部的还原-N 需求的相对大小进行调节，在不同情况下，一个或另一个占主导地位。
