CHL1 is a dual-affinity nitrate transporter of arabidopsis involved in multiple phases of nitrate uptake
CHL1 is a dual-affinity nitrate transporter of arabidopsis involved in multiple phases of nitrate uptake
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DOI：
10.1105/tpc.11.5.865
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发表时间：
1999-05-01
期刊：
影响因子：
11.6
通讯作者：
Tsay, YF
中科院分区：
文献类型：
--
作者：
Liu, KH;Huang, CY;Tsay, YF
高等植物具有高亲和力和低亲和力的硝酸盐吸收系统。这些系统通常被认为是遗传上不同的。在这里，我们证明了一个众所周知的低亲和力的硝酸盐吸收突变体的拟南芥，chl 1，也有缺陷的高亲和力的硝酸盐吸收。硝酸盐诱导后2至3小时，在250 μ M硝酸盐（高亲和力浓度）的各种chl 1突变体的吸收活动只有野生型植物的18至30%。在这些突变体中，高亲和力硝酸盐吸收活性的诱导期和组成期都减少了，其中诱导期严重减少。在转基因chl 1植物中表达由花椰菜花叶病毒35 S启动子驱动的chl 1 cDNA有效地恢复了组成期但不恢复诱导期的高亲和力摄取缺陷，这与转基因植物中chl 1表达的组成性水平一致。CHL 1注射的爪蟾卵母细胞的硝酸盐摄取的动力学分析显示了一个双相模式与Michaelis-Menten K-m值类似于50 μ M的高亲和力相和类似于4 mM的低亲和力相。这些结果表明，除了作为一个低亲和力的硝酸盐转运蛋白，如前所述，CHL 1也参与了诱导和组成阶段的高亲和力的硝酸盐吸收在拟南芥。
Higher plants have both high- and low-affinity nitrate uptake systems. These systems are generally thought to be genetically distinct. Here, we demonstrate that a well-known low-affinity nitrate uptake mutant of Arabidopsis, chl1, is also defective in high-affinity nitrate uptake. Two to 3 hr after nitrate induction, uptake activities of various chl1 mutants at 250 mu M nitrate (a high-affinity concentration) were only 18 to 30% of those of wild-type plants. In these mutants, both the inducible phase and the constitutive phase of high-affinity nitrate uptake activities were reduced, with the inducible phase being severely reduced. Expressing a CHL1 cDNA driven by the cauliflower mosaic virus 35S promoter in a transgenic chl1 plant effectively recovered the defect in high-affinity uptake for the constitutive phase but not for the induced phase, which is consistent with the constitutive level of CHL1 expression in the transgenic plant. Kinetic analysis of nitrate uptake by CHL1-injected Xenopus oocytes displayed a biphasic pattern with a Michaelis-Menten K-m value of similar to 50 mu M for the high-affinity phase and similar to 4 mM for the low-affinity phase. These results indicate that in addition to being a low-affinity nitrate transporter, as previously recognized, CHL1 is also involved in both the inducible and constitutive phases of high-affinity nitrate uptake in Arabidopsis.