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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 NH4+ transport
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Alleviation of rapid, futile ammonium cycling at the plasma membrane by potassium reveals K+-sensitive and -insensitive components of NH4+ transport

机译：钾减轻质膜上快速，无效的铵循环，揭示了NH 4 + 转运的K + 敏感和-不敏感成分

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Futile plasma membrane cycling of ammonium (NH4+) is characteristic of low-affinity NH4+ transport, and has been proposed to be a critical factor in NH4+ toxicity. Using unidirectional flux analysis with the positron-emitting tracer 13N in intact seedlings of barley (Hordeum vulgare L.), it is shown that rapid, futile NH4+ cycling is alleviated by elevated K+ supply, and that low-affinity NH4+ 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), NH4+ influx (at an external [NH4+] of 10 mM) of 92 μmol g−1 h−1 was observed, with an efflux:influx ratio of 0.75, indicative of rapid, futile NH4+ cycling. Elevating K+ supply into the low-affinity K+ transport range (1.5–40 mM) reduced both influx and efflux of NH4+ by as much as 75%, and substantially reduced the efflux:influx ratio. The reduction of NH4+ fluxes was achieved rapidly upon exposure to elevated K+, within 1 min for influx and within 5 min for efflux. The channel inhibitor La3+ decreased high-capacity NH4+ influx only at low K+ concentrations, suggesting that the K+-sensitive component of NH4+ influx may be mediated by non-selective cation channels. Using respiratory measurements and current models of ion flux energetics, the energy cost of concomitant NH4+ 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 NH4+ flux mechanisms in plants.
机译：铵（NH 4 + ）的无效质膜循环是低亲和力NH 4 + 转运的特征，并被认为是NH 4 + 毒性的关键因素。使用正电子发射示踪剂 13 N在大麦完整幼苗中进行单向通量分析，结果表明快速，无用的NH 4 K + 的供给增加缓解了+ 循环，而K + + 的低亲和力NH 4转运被缓和。 sup> + 敏感组件，以及独立于K + 的第二个组件。在外部[K + ]低（0.1 mM）时，NH 4 + 流入（在外部[NH 4 观察到10 mM的> + ]为92μmolg -1 h -1 ，流出/流入比为0.75，表明快速徒劳的NH 4 + 循环。将K + 供应增加到低亲和力K + 传输范围（1.5–40 mM），可减少NH 4 + 多达75％，并显着降低了流出量：流入量比率。 NH 4 + 通量的减少在暴露于升高的K + 后迅速实现，流入量在1分钟内，流出量在5分钟内。通道抑制剂La 3 + 仅在低K + 浓度下才降低大容量NH 4 + 的涌入，表明NH 4 + 涌入的K + 敏感成分可能是由非选择性阳离子通道介导的。利用呼吸测量和离子通量能量学的当前模型，伴随着NH 4 + 和K + 在根质膜上运输的能量成本，讨论了其对植物生长的影响。该研究首次证明了植物对K + 敏感和不敏感的NH 4 + 通量机制的并行操作。

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