Kinetics of NH4+ influx in spruce
Kinetics of NH4+ influx in spruce
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DOI：
10.1104/pp.110.3.773
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发表时间：
1996-03-01
期刊：
影响因子：
7.4
通讯作者：
Glass, ADM
中科院分区：
文献类型：
--
作者：
Kronzucker, HJ;Siddiqi, MY;Glass, ADM
测定了（NH 4+）-N-13在云杉（Picea glauca（Moench）Voss）完整幼苗根质膜中的流入量。两个动力学不同的吸收系统NH 4+进行了鉴定。在N-剥夺植物中，Michaelis-Menten型高亲和力运输系统（HATS）在2.5至350 μ M的外部NH 4+浓度（[NH 4 +]（O））范围内运行。该HATS的V-max为1.9至2.4 μ mol g（-1）h（-1），K-m为20至40 μ M。在[NH 4 +]（o）从500 μ M到50 mM时，线性低亲和力系统（LATS）是明显的。净化海港计划和地方援助计划都是基本计划。对先前缺氮幼苗中NH 4+流入的时间依赖性研究表明，暴露于100 μ M [NH 4 +]（o）24 h后，NH 4+流入出现短暂的小幅增加。随后，4天后流入量下降至稳态值。在幼苗暴露于100 μ M的外部NO3-浓度为3天，V-max为NH 4+吸收HATS增加约30%相比，发现在N-剥夺幼苗，而LATS下调。本研究定义了高得多的吸收能力NH 4+比NO3-在幼苗的这个物种。
influxes of (NH4+)-N-13 across the root plasmalemma were measured in intact seedlings of Picea glauca (Moench) Voss. Two kinetically distinct uptake systems for NH4+ were identified. In N-deprived plants, a Michaelis-Menten-type high-affinity transport system (HATS) operated in a 2.5 to 350 mu M range of external NH4+ concentration ([NH4+](o)). The V-max of this HATS was 1.9 to 2.4 mu mol g(-1) h(-1), and the K-m was 20 to 40 mu M. At [NH4+](o) from 500 mu M to 50 mM, a linear low-affinity system (LATS) was apparent. Both HATS and LATS were constitutive. A time-dependence study of NH4+ influx in previously N-deprived seedlings revealed a small transient increase of NH4+ influx after 24 h of exposure to 100 mu M [NH4+](o). This was followed by a decline of influx to a steady-state value after 4 d. In seedlings exposed to 100 mu M external NO3- concentration for 3 d, the V-max for NH4+ uptake by HATS was increased approximately 30% compared to that found in N-deprived seedlings, whereas LATS was down-regulated. The present study defines the much higher uptake capacity for NH4+ than for NO3- in seedlings of this species.