Plants take up water and nutrients through roots, and uptake efficiency depends on root behavior. Roots recognize the moisture gradient in the soil and grow toward the direction of high moisture. This phenomenon is called hydrotropism, and it contributes to efficient water uptake. As nutrients in soil are also unevenly distributed, it is beneficial for plants to grow their roots in the direction of increasing nutrient concentrations, but such a phenomenon has not been demonstrated. Here, we describe the directional growth of roots in response to a nutrient gradient. Using our assay system, the gradient of a nitrogen nutrient, NH4+, was sufficient to stimulate positive tropic responses of rice lateral roots. This phenomenon is a tropism of plant roots to nutrients; hence, we propose the name ‘nutritropism’. As well as other tropisms, differential cell elongation was observed before the elongation zone during nutritropism, but the pattern promoting cell elongation preferentially on the non-stimulated side was opposite to those in root hydrotropism and gravitropism. Our evaluation of the NH4+ gradient suggested that the root tips responded to a sub-micromolar difference in NH4+ concentration on both sides of the root. Hydrotropism, gravitropism and phototropism were described in plants as the ‘power of movement’ by Charles and Francis Darwin in 1880, and these three tropisms have attracted the attention of plant scientists for more than 130 years. Our discovery of nutritropism represents the fourth ‘power of movement’ in plants and provides a novel root behavioral property used by plants to acquire nutrients efficiently.

中文翻译：

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水稻根系向营养源的正向发展

植物通过根吸收水分和养分，吸收效率取决于根的行为。根系识别土壤中的水分梯度，并朝着高水分的方向生长。这种现象称为水溶现象，它有助于有效地吸收水分。由于土壤中的养分分布也不均匀，有利于植物在增加养分浓度的方向上生根，但这种现象尚未得到证实。在这里，我们描述了根对营养梯度的定向生长。使用我们的测定系统，氮营养素NH4 +的梯度足以刺激水稻侧根的正向性反应。这种现象是植物根系向养分的转化。因此，我们提出了“营养偏向”的名称。以及其他向性，在营养生长过程中，在伸长区之前观察到了不同的细胞伸长率，但在未受刺激的一侧优先促进细胞伸长的模式与根的水溶和重力运动相反。我们对NH4 +梯度的评估表明，根尖响应根两侧NH4 +浓度的亚微摩尔差异。在1880年，查尔斯和弗朗西斯·达尔文（Charles and Francis Darwin）在植物中将水溶，重力和光致同质性描述为“运动的力量”，这三种向性吸引了植物科学家130多年的关注。我们对营养的发现代表了植物的第四种“运动能力”，并为植物提供了一种新颖的根部行为特性，可有效地获取营养。