Institute of Environmental Processes and Pollution Control, and School of Environmental and Civil Engineering, Jiangnan University, Wuxi 214122, China.
College of Environmental Science and Engineering, and Ministry of Education Key Laboratory of Marine Environment and Ecology, Ocean University of China, Qingdao 266100, China.
Sci Total Environ. 2019 Feb 25;653:675-683. doi: 10.1016/j.scitotenv.2018.10.320. Epub 2018 Oct 30.
The increasing occurrence of engineered nanoparticles (NPs) in soils may decrease water uptake in crops, followed by lower crop yield and quality. As one of the most common rare earth oxide NPs, lanthanum oxide (LaO) NPs may inhibit the relative expressions of aquaporin genes, thus reduce water uptake. In the present study, maize plants were exposed to different LaO NPs concentrations (0, 5, 50 mg L) for 72 h and 144 h right after the first leaf extended completely. Our results revealed that water uptake was reduced by LaO NPs through accelerating the development of apoplastic barriers in maize roots. The level of abscisic acid, determined by using ultra high performance liquid chromatography-tandem mass spectrometry, was increased upon LaO NPs exposure. Furthermore, ZmPAL, ZmCCR2 and ZmCAD6, the core genes specific for biosynthesis of lignin, were up-regulated by 3-13 fold in roots exposed to 50 mg L LaO NPs. However, ZmF5H was suppressed, indicating that lignin with S units could be excluded for the formed lignin in apoplastic barriers upon LaO NPs exposure. The level of essential component of apoplastic barriers - lignin was increased by 1.5-fold. The early development of apoplastic barriers was observed, and stomatal conductance and transpiration rate of LaO NPs-treated plants were significantly decreased by 63%-83% and 42%-86%, respectively, as compared to the control. The lignin enriched apoplastic barriers in juvenile maize thus led to the reduction of water uptake, subsequently causing significant growth inhibition. This is the first study to show early development of root apoplastic barriers upon LaO NPs exposure. This study will help us better understand the function of apoplastic barriers in roots in response to NPs, further providing fundamental knowledge to develop safer and more efficient agricultural nanotechnology.
越来越多的工程纳米颗粒（NPs）在土壤中的出现可能会降低作物的水分吸收，从而导致作物产量和质量下降。作为最常见的稀土氧化物 NPs 之一，氧化镧（LaO）NPs 可能会抑制水通道蛋白基因的相对表达，从而减少水分吸收。在本研究中，玉米植株在第一片叶子完全伸展后 72 小时和 144 小时分别暴露于不同浓度的 LaO NPs（0、5、50mg/L）下。我们的结果表明，LaO NPs 通过加速玉米根系质外体屏障的发育来减少水分吸收。通过超高效液相色谱-串联质谱法测定的脱落酸水平在 LaO NPs 暴露后增加。此外，在暴露于 50mg/L LaO NPs 的根中，ZmPAL、ZmCCR2 和 ZmCAD6（木质素生物合成的核心基因）的表达水平上调了 3-13 倍。然而，ZmF5H 受到抑制，表明在 LaO NPs 暴露时，木质素中 S 单位可能被排除在外，以形成质外体屏障中的木质素。质外体屏障的必需成分——木质素的水平增加了 1.5 倍。观察到质外体屏障的早期发育，暴露于 LaO NPs 的植物的气孔导度和蒸腾速率分别显著下降了 63%-83%和 42%-86%，与对照相比。幼年玉米中富含木质素的质外体屏障导致水分吸收减少，进而导致显著的生长抑制。这是第一项关于 LaO NPs 暴露后根质外体屏障早期发育的研究。这项研究将帮助我们更好地理解根中质外体屏障对 NPs 的反应功能，进一步为开发更安全、更有效的农业纳米技术提供基础知识。
