Santi Simonetta, Locci Geraldine, Monte Rossella, Pinton Roberto, Varanini Zeno
Dipartimento di Produzione Vegetale e Tecnologie Agrarie, University of Udine, Via delle Scienze 208, I-33100 Udine, Italy.
J Exp Bot. 2003 Aug;54(389):1851-64. doi: 10.1093/jxb/erg208.
An investigation was carried out to assess the effect of nitrate supply on the root plasma membrane (PM) H+-ATPase of etiolated maize (Zea mays L.) seedlings grown in hydroponics. The treatment induced higher uptake rates of the anion and the expression of a putative high-affinity nitrate transporter gene (ZmNRT2.1), the first to be identified in maize. Root PM H+-ATPase activity displayed a similar time-course pattern as that of net nitrate uptake and investigations were carried out to determine which of the two isoforms reported to date in maize, MHA1 and 2, responded to the treatment. MHA1 was not expressed under the conditions analysed. Genome analysis revealed that MHA2, described as the most abundant form in all maize tissues, was not present in the maize hybrid investigated, but a similar form was found instead and named MHA3. A second gene (named MHA4) was also identified and partially sequenced. Both genes, classified as members of the PM H+-ATPase subfamily II, responded to nitrate supply, although to different degrees: MHA4, in particular, proved more sensitive than MHA3, with a greater up- and down-regulation in response to the treatment. Increased expression of subfamily II genes resulted in higher steady-state levels of the enzyme in the root tissues and enhanced ATP-hydrolysing activity. The results support the idea that greater proton-pumping activity is required when nitrate inflow increases and suggest that nitrate may be the signal triggering the expression of the two members of PM H+-ATPase subfamily II.
开展了一项研究，以评估硝酸盐供应对水培生长的黄化玉米（Zea mays L.）幼苗根细胞质膜（PM）H⁺-ATP酶的影响。该处理诱导了阴离子更高的吸收速率以及一个推定的高亲和力硝酸盐转运蛋白基因（ZmNRT2.1）的表达，这是在玉米中首次鉴定出的此类基因。根PM H⁺-ATP酶活性呈现出与净硝酸盐吸收相似的时间进程模式，并开展了研究以确定玉米中迄今报道的两种同工型MHA1和MHA2中的哪一种对该处理有反应。在分析的条件下，MHA1未表达。基因组分析表明，被描述为在所有玉米组织中最丰富形式的MHA2在所研究的玉米杂交种中不存在，而是发现了一种类似的形式并将其命名为MHA3。还鉴定了第二个基因（命名为MHA4）并进行了部分测序。这两个基因均被归类为PM H⁺-ATP酶亚家族II的成员，对硝酸盐供应均有反应，尽管程度不同：特别是MHA4比MHA3更敏感，对该处理的上调和下调幅度更大。亚家族II基因表达的增加导致根组织中该酶的稳态水平更高，并增强了ATP水解活性。这些结果支持了以下观点，即当硝酸盐流入增加时需要更高的质子泵活性，并表明硝酸盐可能是触发PM H⁺-ATP酶亚家族II两个成员表达的信号。
