Departamento de Bioquímica e Biologia Molecular and Instituto Nacional de Ciência e Tecnologia em Salinidade (INCTSal/CNPq), Universidade Federal do Ceará, Caixa Postal 6039, 60455-900 Fortaleza, Ceará, Brazil.
J Plant Physiol. 2011 Sep 15;168(14):1617-26. doi: 10.1016/j.jplph.2011.03.002. Epub 2011 Mar 31.
The effect of external inorganic nitrogen and K(+) content on K(+) uptake from low-K(+) solutions and plasma membrane (PM) H(+)-ATPase activity of sorghum roots was studied. Plants were grown for 15 days in full-nutrient solutions containing 0.2 or 1.4mM K(+) and inorganic nitrogen as NO(3)(-), NO(3)(-)/NH(4)(+) or NH(4)(+) and then starved of K(+) for 24, 48 and 72 h. NH(4)(+) in full nutrient solution significantly affected the uptake efficiency and accumulation of K(+), and this effect was less pronounced at the high K(+) concentration. In contrast, the translocation rate of K(+) to the shoot was not altered. Depletion assays showed that plants grown with NH(4)(+) more efficiently depleted the external K(+) and reached higher initial rates of low-K(+) uptake than plants grown with NO(3)(-). One possible influence of K(+) content of shoot, but not of roots, on K(+) uptake was evidenced. Enhanced K(+)-uptake capacity was correlated with the induction of H(+) extrusion by PM H(+)-ATPase. In plants grown in high K(+) solutions, the increase in the active H(+) gradient was associated with an increase of the PM H(+)-ATPase protein concentration. In contrast, in plants grown in solutions containing 0.2mM K(+), only the initial rate of H(+)-pumping and ATP hydrolysis were affected. Under these conditions, two specific isoforms of PM H(+)-ATPase were detected, independent of the nitrogen source and deficiency period. No change in enzyme activity was observed in NO(3)(-)-grown plants. The results suggest that K(+) homeostasis in NH(4)(+)-grown sorghum plants may be regulated by a high capacity for K(+) uptake, which is dependent upon the H(+)-pumping activity of PM H(+)-ATPase.
研究了外部无机氮和 K(+)含量对低钾溶液中 K(+)摄取和高粱根质膜（PM）H(+) - ATP 酶活性的影响。植物在含有 0.2 或 1.4mM K(+)和无机氮作为 NO(3)(-)、NO(3)(-)/NH(4)(+)或 NH(4)(+)的全营养溶液中生长 15 天，然后低钾饥饿 24、48 和 72 小时。全营养溶液中的 NH(4)(+)显著影响 K(+)的摄取效率和积累，而在高 K(+)浓度下，这种影响不太明显。相比之下，K(+)向地上部的转运速率没有改变。耗竭试验表明，与用 NO(3)(-)生长的植物相比，用 NH(4)(+)生长的植物更有效地耗尽了外部 K(+)，并达到了更高的初始低钾摄取率。证据表明，地上部 K(+)含量（而不是根部 K(+)含量）对 K(+)摄取有一定影响。增强的 K(+)摄取能力与 PM H(+) - ATP 酶诱导的 H(+)外排有关。在高 K(+)溶液中生长的植物中，活性 H(+)梯度的增加与 PM H(+) - ATP 酶蛋白浓度的增加有关。相比之下，在含有 0.2mM K(+)的溶液中生长的植物，只有 H(+)泵送和 ATP 水解的初始速率受到影响。在这些条件下，检测到 PM H(+) - ATP 酶的两种特定同工型，与氮源和缺乏期无关。在用 NO(3)(-)生长的植物中没有观察到酶活性的变化。结果表明，NH(4)(+)生长的高粱植物中的 K(+)稳态可能受到依赖于 PM H(+) - ATP 酶 H(+)泵送活性的高 K(+)摄取能力的调节。
