Attributes of the nitrogen uptake systems of maize (Zea mays L.): maximal suppression by exposure to both nitrate and ammonium
Attributes of the nitrogen uptake systems of maize (Zea mays L.): maximal suppression by exposure to both nitrate and ammonium
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DOI：
10.1111/j.1469-8137.1995.tb01827.x
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发表时间：
1995-07
期刊：
影响因子：
9.4
通讯作者：
W. Jackson;R. Volk
中科院分区：
文献类型：
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作者：
W. Jackson;R. Volk
高等植物通常暴露于其根环境中铵和硝酸盐的量和比例的快速变化。这种变化的一些潜在后果已经通过检查生长玉米（Zea mays L.）用高浓度（3 mM）的氮处理幼苗，随后从更稀（0.2 mM）的溶液中吸收氮。为了证明硝酸盐和铵供应在抑制中的相互作用，将生长溶液中这些离子的比例维持在3：0、2：1、1：2和0：3。硝酸盐和铵的吸收率，然后测量在初始（0-1小时）暴露于0.2 mM KNO 3或NH 4 NO3和每小时在随后的7小时的适应期的稀释溶液。只有当硝酸盐和铵存在（2：1和1：2）在以前的增长过程中，硝酸盐吸收的最大抑制发生。硝酸盐的吸收率增加了两到三倍，适应稀硝酸钾溶液的幼苗，但铵与硝酸盐在先前的生长溶液中的存在限制了从抑制中恢复的速度和程度。恢复进一步限制时，环境铵存在于适应期。无论是抑制的幅度，也不是恢复的速度和程度是很容易解释的（a）硝酸盐和铵的比例存在于以前的增长，（B）碳水化合物的浓度在根和地上部组织，（c）硝酸盐和铵的浓度在根组织中，或（d）铵对钾吸收的间接影响。总硝酸盐还原由整个植物在8小时的适应期下降的铵在先前的生长溶液中的比例增加。环境铵限制硝酸盐还原只有在以前生长的幼苗完全与铵。因此，环境铵对整个植物的硝酸盐还原的效果显着不同的硝酸盐吸收。由于几乎所有的铵吸收的根被同化，以及所产生的硝酸盐还原，看来，碳水化合物的供应并没有限制所观察到的吸收铵和硝酸盐。硝酸盐和特定的代谢产物的铵作为负的选举人在根中的积累可以解释大部分的观察。
summary Higher plants arc commonly exposed to rapid changes in the amounts and proportions of ammonium and nitrate in their root environment. Some of the potential consequences of such changes have been determined by examining the suppressive effects of growing maize (Zea mays L.) seedlings with a high concentration (3 mM) of nitrogen on the subsequent uptake of nitrogen from a more dilute (0.2 mM) solution. To document the interactive role of nitrate and ammonium supply in suppression, ratios of these ions in the growth solution were maintained at 3:0, 2:1, 1:2 and 0:3. Rates of nitrate and ammonium uptake were then measured during initial (0–1 h) exposure to 0.2 mM KNO3 or NH4NO3 and hourly during a subsequent 7 h period of adaptation to the dilute solutions. Maximal suppression of nitrate uptake occurred only when both nitrate and ammonium were present (2: 1 and 1:2) during prior growth. Nitrate uptake rates increased two- to three-fold as the seedlings adapted to the dilute KNO3 solution, but the presence of ammonium with nitrate in the prior growth solution restricted the rate and extent of recovery from suppression. Recovery was further restricted when ambient ammonium was present during the adaptation period. Neither the magnitude of suppression nor the rate and extent of recovery was readily explained by (a) the proportion of nitrate and ammonium present during prior growth, (b) carbohydrate concentrations in root and shoot tissues, (c) concentrations of nitrate and ammonium in the root tissue, or (d) indirect effects of ammonium on potassium uptake. Total nitrate reduction by the entire plant in the 8 h adaptation period decreased as the proportion of ammonium in the prior growth solution increased. Ambient ammonium restricted nitrate reduction only in seedlings previously grown entirely with ammonium. Thus the effect of ambient ammonium on nitrate reduction by the whole plant differed substantially from that on nitrate uptake. Since nearly all the ammonium taken up by the roots was assimilated, as well as that generated by nitrate reduction, it appears that carbohydrate supply did not limit the observed uptake of ammonium and nitrate. The accumulation in roots of both nitrate and specific metabolites of ammonium serving as negative electors could account for most of the observations.