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首页> 外文期刊>Journal of Experimental Botany >Alleviation of rapid, futile ammonium cycling at the plasma membrane by potassium reveals K-sensitive and -insensitive components of NH transport.
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Alleviation of rapid, futile ammonium cycling at the plasma membrane by potassium reveals K-sensitive and -insensitive components of NH transport.

机译：钾在质膜上快速，无用的铵循环的减轻揭示了NH转运的钾敏感和不敏感成分。

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摘要

Futile plasma membrane cycling of ammonium (NH) is characteristic of low-affinity NH transport, and has been proposed to be a critical factor in NH toxicity. Using unidirectional flux analysis with the positron-emitting tracer p#pdN in intact seedlings of barley (Hordeum vulgare L.), it is shown that rapid, futile NH cycling is alleviated by elevated K supply, and that low-affinity NH transport is mediated by a K-sensitive component, and by a second component that is independent of K. At low external [K] (0.1 mM), NH influx (at an external [NH] of 10 mM) of 92 omol gp# hp# was observed, with an efflux:influx ratio of 0.75, indicative of rapid, futile NH cycling. Elevating K supply into the low-affinity K transport range (1.5-40 mM) reduced both influx and efflux of NH by as much as 75%, and substantially reduced the efflux:influx ratio. The reduction of NH fluxes was achieved rapidly upon exposure to elevated K, within 1 min for influx and within 5 min for efflux. The channel inhibitor Lapd decreased high-capacity NH influx only at low K concentrations, suggesting that the K-sensitive component of NH influx may be mediated by non-selective cation channels. Using respiratory measurements and current models of ion flux energetics, the energy cost of concomitant NH and K transport at the root plasma membrane, and its consequences for plant growth are discussed. The study presents the first demonstration of the parallel operation of K-sensitive and -insensitive NH flux mechanisms in plants.
机译：铵（NH）的无效质膜循环是低亲和力NH转运的特征，已被认为是NH毒性的关键因素。使用正电子发射示踪剂p＃pdN在大麦完整幼苗中进行单向通量分析，结果表明，钾供应的增加减轻了快速，徒劳的NH循环，并且介导了低亲和力的NH转运。在低外部[K]（0.1 mM）时，NH流入量（外部[NH]为10 mM）为92 omol gp＃hp＃。观察到，流出/流入比为0.75，表明快速，无效的NH循环。将钾的供应提高到低亲和力的K运移范围（1.5-40 mM），可使NH的流入量和流出量减少多达75％，并显着降低了流出量：流入量的比率。 NH流量的减少在暴露于升高的K时迅速实现，流入量在1分钟内，流出量在5分钟内。通道抑制剂Lapd仅在低K浓度下才降低高容量NH流入，这表明NH流入的K敏感成分可能是由非选择性阳离子通道介导的。使用呼吸测量和离子通量能量学的当前模型，讨论了在根质膜上伴随的NH和K迁移的能量成本及其对植物生长的影响。该研究首次证明了植物对钾敏感和不敏感的NH通量机制的并行运行。

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