Wang R, Crawford N M
Department of Biology, University of California at San Diego, La Jolla 92093-0116, USA.
Proc Natl Acad Sci U S A. 1996 Aug 20;93(17):9297-301. doi: 10.1073/pnas.93.17.9297.
Two mutations have been found in a gene (NRT2) of Arabidopsis thaliana that specifically impair constitutive, high-affinity nitrate uptake. These mutants were selected for resistance to 0.1 mM chlorate in the absence of nitrate. Progency from one of the backcrossed mutants showed no constitutive uptake of nitrate below 0.5 mM at pH 7.0 in liquid culture (that is, within 30 min of initial exposure to nitrate). All other uptake activities measured (high-affinity phosphate and sulfate uptake, inducible high-affinity nitrate uptake, and constitutive low-affinity nitrate uptake) were present or nearly normal in the backcrossed mutant. Electrophysiological analysis of individual root cells showed that the nrt2 mutant showed little response to 0.25 mM of nitrate, whereas NRT2 wild-type cells showed an initial depolarization followed by recovery. At 10 mM of nitrate both the mutant and wild-type cells displayed similar, strong electrical responses. These results indicate that NRT2 is a critical and perhaps necessary gene for constitutive, high-affinity nitrate uptake in Arabidopsis, but not for inducible, high-affinity nor constitutive, low-affinity nitrate uptake. Thus, these systems are genetically distinct.
在拟南芥的一个基因（NRT2）中发现了两个突变，这些突变特异性地损害了组成型高亲和力硝酸盐吸收。这些突变体是在无硝酸盐的情况下筛选出对0.1 mM氯酸盐具有抗性的。回交突变体之一的后代在液体培养中（即最初接触硝酸盐后30分钟内），在pH 7.0时，对低于0.5 mM的硝酸盐没有组成型吸收。在回交突变体中，所测量的所有其他吸收活性（高亲和力磷酸盐和硫酸盐吸收、诱导型高亲和力硝酸盐吸收以及组成型低亲和力硝酸盐吸收）均存在或几乎正常。对单个根细胞的电生理分析表明，nrt2突变体对0.25 mM硝酸盐几乎没有反应，而NRT2野生型细胞则先出现去极化，随后恢复。在10 mM硝酸盐时，突变体细胞和野生型细胞都表现出相似的强烈电反应。这些结果表明，NRT2是拟南芥中组成型高亲和力硝酸盐吸收的关键基因，甚至可能是必需基因，但对于诱导型高亲和力硝酸盐吸收和组成型低亲和力硝酸盐吸收并非如此。因此，这些系统在遗传上是不同的。
