Plants absorb nitrogen mainly through their roots. Nitrogen sensing is required for the absorption and transport of different nitrogen nutrients. In this study, we constructed biosensors with immobilized Panax notoginseng root tip meristems based on a three-electrode system and successfully determined the kinetics of the interactions between the P. notoginseng root tip meristems and five important nitrogen nutrients, namely, urea, sodium nitrate, sodium glutamate, disodium inosinate, and disodium guanylate. We discovered that the biosensor’s sensing kinetics was similar to the enzyme–substrate kinetics, and the receptor–ligand interconnected allosteric interaction constant Ka (mol/L), analogous to the Michaelis constant, was calculated. The result showed that the root tip meristems of two- to four-year-old P. notoginseng plants had a higher capacity to sense inorganic nitrogen nutrients (sodium nitrate and urea) than the three organic nitrogen nutrients. The ability of the plants to sense inorganic nitrogen nutrients decreased with an increase in plant age. The sensing sensitivity of four-year-old P. notoginseng plants to disodium inosinate and disodium guanylate was 100- to 10,000-fold lower than that of the two- and three-year-old plants. Additionally, the capability to sense sodium glutamate decreased initially and then increased with an increase in plant age. The biosensors reached an ultra-sensitive level ( mol/L) in sensing the five nitrogen nutrients and exhibited advantages such as good stability and reproducibility, low cost, a simple structure, and a rapid response, providing a new approach for quantitative determination of the capability of plants to sense different nitrogen nutrients.

中文翻译：

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三七根尖分生组织生物传感器及其对五种重要氮营养素的传感动力学

植物主要通过根部吸收氮。不同氮养分的吸收和运输需要氮传感。在这项研究中，我们基于三电极系统构建了具有固定化三七根尖分生组织的生物传感器，并成功地确定了三七之间相互作用的动力学根尖分生组织和五种重要的氮营养素，即尿素、硝酸钠、谷氨酸钠、肌苷酸二钠和鸟苷酸二钠。我们发现生物传感器的传感动力学类似于酶-底物动力学，并且计算了受体-配体互连的变构相互作用常数 Ka (mol/L)，类似于 Michaelis 常数。结果表明，二至四年生三七植物的根尖分生组织对无机氮养分（硝酸钠和尿素）的感知能力高于三种有机氮养分。植物感知无机氮养分的能力随着植物年龄的增加而降低。四年生三七的感知灵敏度植物对肌苷酸二钠和鸟苷酸二钠的影响比两三年生植物低 100 到 10,000 倍。此外，感知谷氨酸钠的能力最初下降，然后随着植物年龄的增加而增加。生物传感器达到了超灵敏水平（ mol/L) 在感知五种氮养分方面表现出稳定性和重现性好、成本低、结构简单、响应速度快等优点，为定量测定植物感知不同氮养分的能力提供了一种新方法。