Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
Plant Physiol. 1992 Jun;99(2):456-63. doi: 10.1104/pp.99.2.456.
Transmembrane electrical potential differences (Deltapsi) of epidermal and cortical cells were measured in intact roots of barley (Hordeum vulgare L. cv Klondike). The effects of exogenous NO(3) (-) on Deltapsi (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 NO(3) (-) uptake. Both transport systems caused depolarization of Deltapsi, demonstrating that the LATS (like the HATS) for NO(3) (-) uptake is probably mediated by an electrogenic cation (H(+)?) cotransport system. Membrane depolarization by the HATS was "inducible" by NO(3) (-), and saturable with respect to exogenous [NO(3) (-)]. By contrast, depolarization by the LATS was constitutive, and first-order in response to external [NO(3) (-)]. H(+) fluxes, measured in 200 micromolar and in 5 millimolar Ca(NO(3))(2) solutions, failed to alkalinize external media as anticipated for a 2 H(+):1 NO(3) (-) symport. However, switching from K(2)SO(4) solutions (which were strongly acidifying) to KNO(3) solutions at the same K(+) concentration caused marked reductions in H(+) efflux. These observations are consistent with NO(3) (-) uptake by the HATS and the LATS via 2 H(+):1 NO(3) (-) 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 corn in their quantitative responses to external NO(3) (-).
在大麦（Hordeum vulgare L. cv Klondike）完整根系中测量了表皮和皮层细胞的跨膜电位差（Deltapsi）。研究了外源性硝酸盐（NO 3 - ）对 Deltapsi（浓度范围为 100 微摩尔至 20 毫摩尔）的影响，以探究硝酸盐通过高亲和力（HATS）和低亲和力（LATS）摄取系统摄取的机制。两种运输系统均导致 Deltapsi 去极化，表明 LATS（与 HATS 一样）摄取硝酸盐可能是由电生阳离子（H + ）共转运系统介导的。HATS 引起的膜去极化可被 NO 3 - 诱导，并且对外源[NO 3 - ]呈饱和关系。相比之下，LATS 引起的去极化是组成性的，并且对外界[NO 3 - ]呈一级反应。在 200 微摩尔和 5 毫摩尔 Ca（NO 3 ） 2 溶液中测量的 H + 通量未能如预期的那样使外部介质碱化，这是 2H + ：1NO 3 - 共转运的结果。然而，从 K 2 SO 4 溶液（强烈酸化）切换到相同 K + 浓度的 KNO 3 溶液会导致 H + 外流明显减少。这些观察结果与 HATS 和 LATS 通过 2H + ：1NO 3 - 共转运摄取硝酸盐的情况一致。这些观察结果表明，大麦根系硝酸盐摄取的 HATS 与早期研究人员在浮萍和玉米中报道的类似。然而，大麦和玉米在对外源 NO 3 - 的定量响应方面存在明显差异。
