Abstract

NRT1.1 nitrate transporter acts as a nitrate sensor in some plant responses. We tried to check if it may be involved in the control of cytokinin level in the plants known to be involved in the growth responses to nitrate level. The experimental objects were Arabidopsis thaliana plants of the original ecotype Columbia (Col-0) and chl1-5 mutants. The effects of the NRT1.1 gene mutation in chl1-5 plants on hormonal and growth responses to nitrogen starvation were studied. Two types of growing conditions were used: (1) plants were placed on either standard Hoagland–Arnon or modified solution, where potassium and calcium nitrates were substituted with their chlorides; (2) plants were placed on Pryanishnikov medium, where ammonium nitrate serves as the source of nitrogen and nitrogen deficiency being modeled by its withdrawal from the medium. It has been first shown that mutation of the NRT1.1 resulted in a decline in cytokinin level in the roots of chl1-5 mutants, while roots of wild type plants were longer in accordance with lower cytokinin content in them; this hormone is known to inhibit root elongation. Cytokinin content decreased in A. thaliana, Columbia ecotype, paralleled by acceleration of root elongation in response to both variants of nitrogen starvation, while chl1-5 roots responded in this way only when nitrogen was withdrawn from Pryanishnikov solution. Substitution of nitrates by chlorides in the Hoagland–Arnon solution had no effects on either chl1-5 roots’ length or cytokinin content in them. The results suggested the involvement of NRT1.1 transceptor in the control of cytokinin level and root elongation rate in the nitrate but not in ammonium starved plants, confirming the specificity of response.

中文翻译：

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硝酸盐传感器NRT1.1在正常条件下和氮缺乏时参与细胞分裂素水平和根伸长的控制

摘要

NRT1.1硝酸盐转运蛋白在某些植物反应中充当硝酸盐传感器。我们试图检查它是否可能参与了已知参与对硝酸盐水平的生长反应的植物中细胞分裂素水平的控制。实验对象是原始生态型哥伦比亚（Col-0）和chl1-5突变体的拟南芥植物。NRT1.1基因突变在chl1-5中的作用研究了植物对氮饥饿的激素和生长反应。使用了两种类型的生长条件：（1）将植物放在标准的Hoagland-Arnon或改良的溶液中，用硝酸盐将硝酸钾和硝酸钙替换为氯化物；（2）将植物放在Pryanishnikov培养基上，其中硝酸铵是氮的来源，通过从培养基中抽出氮来模拟氮缺乏。首次显示，NRT1.1突变导致chl1-5突变体的根中细胞分裂素水平下降，而野生型植物的根因其中较低的细胞分裂素含量而变长。已知这种激素会抑制根的伸长。拟南芥中细胞分裂素含量降低哥伦比亚生态型，与氮饥饿的两种变体的根伸长加快相对应，而只有从Pryanishnikov溶液中抽出氮时，chl1-5根才以这种方式响应。Hoagland-Arnon溶液中的氯化物替代硝酸盐对chl1-5根的长度或其中的细胞分裂素含量均无影响。结果表明，NRT1.1受体参与了硝酸盐中细胞分裂素水平和根伸长率的控制，但在铵缺乏的植物中没有，这证实了反应的特异性。