Department of Biological Sciences, University of Toronto, 1265 Military Trail, Toronto, Ontario, Canada.
Plant Cell Environ. 2010 Jan;33(1):23-34. doi: 10.1111/j.1365-3040.2009.02046.x. Epub 2009 Sep 23.
ABSTRACT We present the first characterization of K(+) optimization of N uptake and metabolism in an NH(4)(+)-tolerant species, tropical lowland rice (cv. IR-72). (13)N radiotracing showed that increased K(+) supply reduces futile NH(4)(+) cycling at the plasma membrane, diminishing the excessive rates of both unidirectional influx and efflux. Pharmacological testing showed that low-affinity NH(4)(+) influx may be mediated by both K(+) and non-selective cation channels. Suppression of NH(4)(+) influx by K(+) occurred within minutes of increasing K(+) supply. Increased K(+) reduced free [NH(4)(+)] in roots and shoots by 50-75%. Plant biomass was maximized on 10 mm NH(4)(+) and 5 mm K(+), with growth 160% higher than 10 mm NO(3)(-)-grown plants, and 220% higher than plants grown at 10 mm NH(4)(+) and 0.1 mm K(+). Unlike in NH(4)(+)-sensitive barley, growth optimization was not attributed to a reduced energy cost of futile NH(4)(+) cycling at the plasma membrane. Activities of the key enzymes glutamine synthetase and phosphoenolpyruvate carboxylase (PEPC) were strongly stimulated by elevated K(+), mirroring plant growth and protein content. Improved plant performance through optimization of K(+) and NH(4)(+) is likely to be of substantial agronomic significance in the world's foremost crop species.
摘要 本研究首次描述了 K+对 NH4+耐受物种——热带低地水稻（IR-72 品种）吸收和代谢 N 的作用。13N 示踪表明，增加 K+供应可减少质膜上无效的 NH4+循环，降低单向流入和流出的速率。药理学测试表明，低亲和力的 NH4+流入可能由 K+和非选择性阳离子通道介导。增加 K+供应后几分钟内，NH4+流入就受到抑制。增加 K+供应使根和地上部的游离[NH4+]减少 50-75%。在 10 mM NH4+和 5 mM K+下，植物生物量达到最大值，比 10 mM NO3-培养的植物高 160%，比 10 mM NH4+和 0.1 mM K+培养的植物高 220%。与 NH4+敏感的大麦不同，生长的最优化不是由于质膜上无效的 NH4+循环的能量成本降低。高 K+强烈刺激谷氨酰胺合成酶和磷酸烯醇式丙酮酸羧化酶（PEPC）等关键酶的活性，与植物生长和蛋白质含量相吻合。通过优化 K+和 NH4+，提高植物性能可能对全球主要作物具有重要的农业意义。
