Shabnam Nisha, Sharmila P, Kim Hyunook, Pardha-Saradhi P
Department of Energy and Environmental System Engineering, University of SeoulSeoul, South Korea.
Department of Chemistry, Indian Institute of Technology DelhiNew Delhi, India.
Front Plant Sci. 2017 Jun 21;8:1052. doi: 10.3389/fpls.2017.01052. eCollection 2017.
In this study, we have investigated variations in the potential of floating and submerged leaves of longleaf pondweed () to withstand silver ion (Ag)-toxicity. Both floating and submerged leaves changed clear colorless AgNO solutions to colloidal brown in the presence of light. Transmission electron microscopy revealed the presence of distinct crystalline Ag-nanoparticles (Ag-NPs) in these brown solutions. Powder X-ray diffraction pattern showed that Ag-NPs were composed of Ag and AgO. Photosystem (PS) II efficiency of leaves declined upon exposure to Ag with a significantly higher decline in the submerged leaves than in the floating leaves. Similarly, Ag treatment caused a significant reduction in the carboxylase activity of the ribulose bisphosphate carboxylase/oxygenase in leaves. The reduction in this carboxylase activity was significantly higher in the submerged than in the floating leaves. Ag treatment also resulted in a significant decline in the levels of non-enzymatic and enzymatic antioxidants; the decline was significantly lower in the floating than in submerged leaves. X-ray photoelectron spectroscopy revealed the presence of AgO in these leaves. Inductively coupled plasma mass spectrometry analysis revealed a three-fold higher Ag content in the submerged than in floating leaves. Our study demonstrates that floating leaves of longleaf pondweed have a superior potential to counter Ag-toxicity compared with submerged leaves, which could be due to superior potential of floating leaves to reduce Ag to less/non-toxic Ag/AgO-nanoparticles/nanocomplexes. We suggest that modulating the genotype of longleaf pondweed to bear higher proportion of floating leaves would help in cleaning fresh water bodies contaminated with ionic forms of heavy metals.
在本研究中，我们调查了长叶眼子菜（）漂浮叶和沉水叶耐受银离子（Ag）毒性的潜力差异。在光照条件下，漂浮叶和沉水叶均能将澄清无色的硝酸银溶液变为胶体棕色。透射电子显微镜显示这些棕色溶液中存在明显的结晶状银纳米颗粒（Ag-NPs）。粉末X射线衍射图谱表明Ag-NPs由银和氧化银组成。叶片暴露于银后，光系统（PS）II效率下降，沉水叶的下降幅度明显高于漂浮叶。同样，银处理导致叶片中核酮糖-1,5-二磷酸羧化酶/加氧酶的羧化酶活性显著降低。沉水叶中该羧化酶活性的降低幅度明显高于漂浮叶。银处理还导致非酶促和酶促抗氧化剂水平显著下降；漂浮叶中的下降幅度明显低于沉水叶。X射线光电子能谱显示这些叶片中存在氧化银。电感耦合等离子体质谱分析表明，沉水叶中的银含量比漂浮叶高两倍。我们的研究表明，与沉水叶相比，长叶眼子菜的漂浮叶具有更强的抵抗银毒性的潜力，这可能是因为漂浮叶具有更强的将银还原为毒性较小/无毒的银/氧化银纳米颗粒/纳米复合物的能力。我们建议，调控长叶眼子菜的基因型以使其长出更高比例的漂浮叶，将有助于净化被重金属离子形式污染的淡水水体。
