State Key Laboratory of Agricultural Microbiology, College of Life Science and Technology and College of Science, Huazhong Agricultural University, Wuhan, 430070, PR China.
Nanoscale. 2017 Jul 20;9(28):9921-9937. doi: 10.1039/c7nr01948c.
The rhizobium-legume symbiosis system is critical for nitrogen-cycle balance in agriculture. However, the potential effects of carbon nanomaterials (CNMs) on this system remain largely unknown. Herein, we studied the effects of four carbon-based materials (activated carbon (AC), single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) and graphene oxide (GO)) on the rhizobium-legume symbiosis system consisting of Lotus japonicus and Mesorhizobium loti MAFF303099. Under non-symbiotic conditions, the bacterial growth and root development of plants were both clearly inhibited by SWCNTs and GO, while the elongation of plant stems was enhanced by MWCNTs to a certain degree. More importantly, only MWCNTs could increase the number of nodules and enhance the activity of nitrogenase in the rhizobium-plant interaction. Further analyses showed that the average number of nodules in plants treated with 100 μg mL MWCNTs was significantly increased by 39% at 14 days post inoculation (dpi) and by 41% at 28 dpi. Meanwhile, the biological nitrogen fixation of the nodules was promoted by more than 10% under 100 μg mL MWCNT treatment, which enhanced the above- and below-ground fresh biomass by 14% and 25% respectively at 28 dpi. Transmission electron microscopy images further indicated that MWCNTs penetrated the cell wall, and pierced through the cell membrane to be transmitted into the cytoplasm. In addition, gene expression analysis showed that the promotion of nodulation by MWCNTs was correlated with the up-regulation of certain genes involved in this signaling pathway. In particular, the expression of NIN, a crucial gene regulating the development of nodules, was significantly elevated 2-fold by MWCNTs at an early stage of nodulation. These findings are expected to facilitate the understanding and future utilization of MWCNTs in agriculture.
根瘤菌-豆科植物共生系统对农业氮循环平衡至关重要。然而，碳纳米材料（CNMs）对该系统的潜在影响在很大程度上尚不清楚。在此，我们研究了四种碳基材料（活性炭（AC）、单壁碳纳米管（SWCNTs）、多壁碳纳米管（MWCNTs）和氧化石墨烯（GO））对由百脉根（Lotus japonicus）和根瘤菌（Mesorhizobium loti MAFF303099）组成的根瘤菌-豆科植物共生系统的影响。在非共生条件下，SWCNTs 和 GO 明显抑制了细菌的生长和植物根系的发育，而 MWCNTs 在一定程度上促进了植物茎的伸长。更重要的是，只有 MWCNTs 可以增加根瘤的数量并增强根瘤菌-植物互作中的固氮酶活性。进一步分析表明，在接种后 14 天（dpi）和 28 dpi，用 100μg mL MWCNTs 处理的植物的根瘤数量分别显著增加了 39%和 41%。同时，在 100μg mL MWCNT 处理下，根瘤的生物固氮作用提高了 10%以上，这使得 28 dpi 时地上和地下鲜重分别提高了 14%和 25%。透射电子显微镜图像进一步表明，MWCNTs 穿透细胞壁，并刺穿细胞膜进入细胞质。此外，基因表达分析表明，MWCNTs 促进结瘤与调控该信号通路的某些基因的上调有关。特别是，在结瘤的早期阶段，MWCNTs 使调节根瘤发育的关键基因 NIN 的表达显著上调了 2 倍。这些发现有望促进对农业中 MWCNTs 的理解和未来利用。
