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CHL1 encodes a component of the low-affinity nitrate uptake system in Arabidopsis and shows cell type-specific expression in roots.

机译:CHL1编码拟南芥中低亲和力硝酸盐吸收系统的组成部分,并在根中显示细胞类型特异性表达。

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摘要

The Arabidopsis CHL1 (AtNRT1) gene confers sensitivity to the herbicide chlorate and encodes a nitrate-regulated nitrate transporter. However, how CHL1 participates in nitrate uptake in plants is not yet clear. In this study, we examined the in vivo function of CHL1 with in vivo uptake measurements and in situ hybridization experiments. Under most conditions tested, the amount of nitrate uptake by a chl1 deletion mutant was found to be significantly less than that of the wild type. This uptake deficiency was reversed when a CHL1 cDNA clone driven by the cauliflower mosaic virus 35S promoter was expressed in transgenic chl1 plants. Furthermore, tissue-specific expression patterns showed that near the root tip, CHL1 mRNA is found primarily in the epidermis, but further from the root tip, the mRNA is found in the cortex or endodermis. These results are consistent with the involvement of CHL1 in nitrate uptake at different stages of root cell development. A functional analysis in Xenopus oocytes indicated that CHL1 is a low-affinity nitrate transporter with a K(m) value of approximately 8.5 mM for nitrate. This finding is consistent with the chlorate resistance phenotype of chl1 mutants. However, these results do not fit the current model of a single, constitutive component for the low-affinity uptake system. To reconcile this discrepancy and the complex uptake behavior observed, we propose a "two-gene" model for the low-affinity nitrate uptake system of Arabidopsis.
机译:拟南芥CHL1(AtNRT1)基因赋予对除草剂氯酸盐敏感性,并编码硝酸盐调节的硝酸盐转运蛋白。但是,尚不清楚CHL1如何参与植物体内硝酸盐的吸收。在这项研究中,我们通过体内摄取测量和原位杂交实验检查了CHL1的体内功能。在大多数测试条件下,发现chl1缺失突变体吸收的硝酸盐量明显少于野生型。当由花椰菜花叶病毒35S启动子驱动的CHL1 cDNA克隆在转基因chl1植物中表达时,这种摄取不足被逆转。此外,组织特异性表达模式显示,在根尖附近,CHL1 mRNA主要在表皮中发现,但离根尖更远,mRNA在皮层或内胚层中发现。这些结果与CHL1参与根细胞发育不同阶段的硝酸盐吸收一致。在爪蟾卵母细胞中的功能分析表明,CHL1是一种低亲和力的硝酸盐转运蛋白,硝酸盐的K(m)值约为8.5 mM。此发现与chl1突变体的氯酸盐抗性表型一致。但是,这些结果不适合低亲和性摄取系统的单个组成成分的当前模型。为了调和这种差异和观察到的复杂的吸收行为,我们为拟南芥的低亲和力硝酸盐吸收系统提出了一个“双基因”模型。

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