STUDIES OF THE UPTAKE OF NITRATE IN BARLEY .4. ELECTROPHYSIOLOGY
STUDIES OF THE UPTAKE OF NITRATE IN BARLEY .4. ELECTROPHYSIOLOGY
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DOI：
10.1104/pp.99.2.456
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发表时间：
1992-06-01
期刊：
影响因子：
7.4
通讯作者：
KOCHIAN, LV
中科院分区：
文献类型：
--
作者：
GLASS, ADM;SHAFF, JE;KOCHIAN, LV
测定了大麦完整根的表皮细胞和皮层细胞的跨膜电位差。为了探讨高亲和力(HATS)和低亲和力(LATS)转运系统吸收硝酸盐的机制，研究了外源NO3-对Delta-psi(100微摩尔到20毫摩尔)的影响。这两种运输系统都引起了Delta-psi的去极化，表明LATS(与HATS一样)摄取N3-可能是由一个生电阳离子(H+？)联运系统。HATS的膜去极化是由NO3-“诱导”的，并且对于外源[NO3-]是饱和的。相反，LATS的去极化是结构性的，对外部[NO3-]的反应是一级的。在200微摩尔和5毫摩尔的Ca(NO3)2溶液中测量的H+通量，未能像预期的2H+：1NO3-符号那样使体外介质碱化。然而，从K2SO4切换。相同K+浓度的KNO3溶液(强酸化)使H+外流显著减少。这些观察结果与HATS和LATS通过2H+：1NO3-符号吸收NO3是一致的。这些观察结果表明，大麦根吸收硝酸盐的HAT基本上与早期工作者报告的Lemna和Zea Mays的HAT相似。然而，大麦和玉米对外源NO_3~-的数量反应存在明显差异。
Transmembrane electrical potential differences (DELTA-psi) of epidermal and cortical cells were measured in intact roots of barley (Hordeum vulgare L. cv Klondike). The effects of exogenous NO3-on DELTA-psi (in the concentration range from 100 micromolar to 20 millimolar) were investigated to probe the mechanisms of nitrate uptake by the high-affinity (HATS) and low-affinity (LATS) transport systems for NO3- uptake. Both transport systems caused depolarization of DELTA-psi, demonstrating that the LATS (like the HATS) for NO3- uptake is probably mediated by an electrogenic cation (H+?) cotransport system. Membrane depolarization by the HATS was "inducible" by NO3-, and saturable with respect to exogenous [NO3-]. By contrast, depolarization by the LATS was constitutive, and first-order in response to extemal [NO3-]. H+ fluxes, measured in 200 micromolar and in 5 millimolar Ca(NO3)2 solutions, failed to alkalinize extemal media as anticipated for a 2 H+:1 NO3- symport. However, switching from K2SO4. solutions (which were strongly acidifying) to KNO3 solutions at the same K+ concentration caused marked reductions in H+ efflux. These observations are consistent with NO3- uptake by the HATS and the LATS via 2 H+:1 NO3- symports. These observations establish that the HATS for nitrate uptake by barley roots is essentially similar to those reported for Lemna and Zea mays by earlier workers. There are, nevertheless, distinct differences between barley and com in their quantitative responses to extemal NO3-.